CA1147574A - Method and a meter for measuring quantities of heat - Google Patents
Method and a meter for measuring quantities of heatInfo
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- CA1147574A CA1147574A CA000348879A CA348879A CA1147574A CA 1147574 A CA1147574 A CA 1147574A CA 000348879 A CA000348879 A CA 000348879A CA 348879 A CA348879 A CA 348879A CA 1147574 A CA1147574 A CA 1147574A
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- heat
- temperature
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Abstract
A B S T R A C T
A method and a meter for measuring the quantity of heat abstracted from a circulating flow of liquid by a consumption unit. Indirect measurement of the volume flow rate of the liquid is made, while maintaining a sub heat flow (? shunt) from or to the main heat flow transported by the flow of liquid and measuring the temperature at some points by means of temperature sensors (4). The volume flow rate of the flow of liquid is determined on the basis of the flow rate dependent heat transfer in the boundary layer (7) of the flow of liquid at the location, where the sub heat flow (? shunt) leaves or enters, by determi-ning the temperature differential ( .DELTA. Ti, b) across the boundary layer, and the sub heat flow (? shunt) passing through said boundary layer (7). At least one absolute temperature of the flow of liquid is measured for correcting the temperature depen-dency of the material constants of the liquid involved in said determination of the volume flow rate.
A method and a meter for measuring the quantity of heat abstracted from a circulating flow of liquid by a consumption unit. Indirect measurement of the volume flow rate of the liquid is made, while maintaining a sub heat flow (? shunt) from or to the main heat flow transported by the flow of liquid and measuring the temperature at some points by means of temperature sensors (4). The volume flow rate of the flow of liquid is determined on the basis of the flow rate dependent heat transfer in the boundary layer (7) of the flow of liquid at the location, where the sub heat flow (? shunt) leaves or enters, by determi-ning the temperature differential ( .DELTA. Ti, b) across the boundary layer, and the sub heat flow (? shunt) passing through said boundary layer (7). At least one absolute temperature of the flow of liquid is measured for correcting the temperature depen-dency of the material constants of the liquid involved in said determination of the volume flow rate.
Description
~1~7S74 - A method and a meter for measuring quantities of heat. -~ack~round of the Invention Field of the Invention The invention relates to a method and a meter for mea~uring the quantity of heat abstracted from a circulating flow of liquid by a consumption unit based upon the indirect measurement of the volume flow rate of the liquid, while maintaining a sub heat flow from or to the main heat flow transported by the flow of liquid and measuring the temperature at some points by means of tempera-ture sensors. Such a heat may for instance be provided in city wide heating networks for consumption on small æcale by the con-sumers.
Description of Prior Art .
In the future, city heating networks will be used in a progres-sively increasing number of towns and districts in which each house will obtain a connection to a public heating network instead of its own boiler for central heating. From this conneotion the con-sumer will obtain the hot water for his home heating system andtap water supply either directly or indirectly by means of a heat exchange.
It has become evident that consumption by individual consumers (and thus total consumption) in such city heating system decreases when the amount of heat consumed by the individual ccnsumer is measured. From the heat quantity meter the consumer will then have an idea of the cost of his heating. For this reason the installa-tion of heat quantity meters for consumption on small scale is considered to be useful.
Existing meters such as, for instance evaporation meters, often have the drawback that they are not accurate enough. With respect to others, such as meters including turbine parts, the initial cost and/or maintenance cost are too high.
Summar~ of the Invention ~0 The object of the invention is to provide a method and a heat quantity meter not exhibiting the above mentioned drawbacks among other things by the complete absence of moving parts or measuring .
119~7574 flanges in the flowing liquid so that there are no obstructions in the supply and return conduits. This will lead to a considerable decrease in maintainance of the meter.
In accordance with the invention this object is attained in that the volume flow rate of the liquid is determined on the basis of the flow rate dependent heat transfer in the boundary layer of the flow of liquid at the location where the sub heat flow leaves or enters. The temperature differential across the boundary layer and the sub heat flow passing through said boundary layer i8 determined, while measuring at least one absolute temperature of the flow of liquid for correcting the temperature dependency of the material constants of the liquid involved in the determination of the volume flow rate.
~rie~ Description of the Drawin~s The present invention will now be elucidated further with refe-rence to the annexed drawings in which like numerala denote like element :
Fig. 1a shows a basic sketch of the conduit sections including a thermal shunt connection of the heat quantity meter;
Fig. 1b shows a side elevation of a part of a conduit section having a bar shaped shunt connection according to fig. 1a fastened thereto by means of an angular junction;
Fig. 1c discloses a diagrammatioal view of the heat quantity me-ter including its temperature measuring points and the imaginary heat resistances R1 to R4, inclusive;
Fig. 1d discloses the relation between the measured volume flow rate and the measured temperatures;
Fig. 2 shows a side elevation of a production embodiment of the heat quantity meter;
Fig. 3a, b, c, and d shows a side elevation of four variants of the junction of the shunt connection to a conduit section; and Fig. 4 shows a side elevation of a variant of the location of a temperature sensor.
Description of a Preferred Exem~lar~ Embodiment The operation of the heat quantity meter in accordance with the present invention is based solely on the measurement of a number il~757~
of temperatures. Use is made of the fact that the heat transfer between the heat carrier or flowing liquid and a body, in which or along which this liquid i8 transported, is dependent among other things on the flow rate of the liquid at the relevant loca-tion. The more this flow rate increases the better the heat trans-fer will become. It is now aimed at measuring this coefficient of heat transfer.
When employing this method easily measurable temperature diffe-rentials occur without being accompanied by large (and consequent-ly unacceptable) heat losses in the main flow as in a thermal flow-meter. In a known flowmeter as i9 for instanoe known from the French Patent Specification 2,353,045 one tries to minimize the in-fluence of the laminar sub or boundary layer among others by a special shape of the wall surrounding the flow of liquid. In the present method and meter a measurement is made of the coefficient of heat transfer of the laminar sub layer of the flow of liquid considered to be turbulent.
Where this measurement can not be performed directly a sub or leakage heat flow is allowed to form which is dependent on the coefficient of heat transfer. For this purpose there is provided an energy connection or, in particular, a thermal connection be-tween the supply and drain or return conduit.
In the connection thus provided there will occur a heat flow de-pendent on the difference in temperature between the hot water in the supply conduit and the cooled water in the return conduit as well as on the total heat resistance. This total heat resistance consists of a fixed component determined by the thermal connec-tion possibly in combination with the walls of the conduits, and of a variable component mainly determined by the flow of the liquid in the thermal boundary layers. ~he magnitude of this branched heat flow may be measured by means of a temperature diffe-rential measurement. ~he magnitude of the temperature differential across one or both of the boundary layers together with the ma~-nitude of the heat flow through the connection determine the coef-ficient of heat transfer in situ.
In the general case of an energy connection, apart from the heatflow by conduction, radiation or convection, a heat transport due to thermo-electric effects may also occur if the connection is "~
~7574 electrically conductive. The electric current generated in this case (possibly by the Seebeck effect) will then be a measure for this form of energy or heat transport.
The absolute temperatures of the flows of liquid at the location of the boundary layers are also of importance, because the relevant material constants, like the coefficient of heat conduction ~ , the specific heat c (weakly), and the viscosity ~ (strongly), are dependent on temperature.
The coefficient of heat transfer together with the several material constants fixedly determine the velocity gradient in the boundary layer. If the velocity profile in the conduit is also governed and reproduceable, then there will be an unambiguous relation between several tem-peratures and the volume flow rate of the liquid, and conse-quently between these temperatures and the net heat flowrate.
The signals supplied by the temperature sensors are processed in accordance with an empirically determined relation by an electronic unit into a quantity of heat per each unit Gf time or a time pulse per quantity o heat. By employing an integrating, summing or pulse counter circuit in the electronic unit, a total supplied quantity of heat per each chosen period of time can be accumulated, By having the meter constructed symmetrically both the volume flow rate in the hot supply conduit and in the colder drain conduit may be determined and compared with each other.
With reference now to Fig. la there is shown a basic sketch of a meter in accordance with the present invention, in which the reference numeral 1 indicates the supply conduit, the reference numeral 2 indicates the drain or return conduit and the reference numeral 3 indicates the ~75'74 - 4a -bar shaped thermal shunt connection. The temperatures Ti, Tb, To, T or temperature differentials may be measured by means of sensors 4, such as thermo~couples, to which a sensitive amplifier is connected. The thermo-couples mav be soldered onto or into the material.
With reference to Fig. lb there is shown a side elevation of a cross section of the angular junction of the thermal shunt connection 3 to one of the conduits 1 or 2. Likewise the laminar boundary layer 7 of the liquid at the tube wall of the conduits has .~
1~47S7 been indicated. ~he reference numeral 4 denotes the junction contact of the temperature differential sensor. This temperature differential sensor may be also consist of two separate absolute temperature sensors.
~or this type of heat transfer problems concerning the boundary layer one may apply a theory known in the theory of flows as the so called "film theory". In turbulent flowæ of liquid (as will occur in the supply and the drain conduits) one may consider the larger part of the velocity gradient and the entire tempe-rature gradient to be in the laminar sub layer at the wall. Ingeneral one may start from the empirical relation:
~' , , ~7574 Nu = 0~024 (1 + L) 0~66 ReO'8 PrO'33 (~vl ) '14 (1) in which:
Nu is the Nusselt number which is a measure for the coef-ficient of heat transfer of the boundary layer.
(1 + L) is a correction factor accounting for the inlet or starting area of the thermal boundary layer and in-cluding therein the ratio of the conduit or pipe di~-meter D and the distance L over which the heat trans-fer occurs.
10 Re is the Reynolds number relating the specific mass p , the rate of flow v and the conduit diameter D with the viscosity ~ of the liquid.
Pr is the Prandtl number indicating the ratio between impulse transport (friction) and heat transport. This is an zssembly of material constants, such as the spe-cific heat c, the viscosity ~ and the specific conduc-tivity A of the liquid. This therefore is a (tempera-ture dependent) material constant per se.
(~wl) is a correction term for the fact that the viscosity of the liquid in the turbulent center portion differs from that directly at the wall where a different tem-perature will prevail.
The relation (1) indicates that the coefficient of heat transfer a is about proportional to the output or volume flow rate to the power 0.8.
~ second relation, i.e. the generally known relation also applies to the meter of ~ig. 1a, b:
Qm = ¦ ~ c 0 ~ Ti Udt (2) in which 30 Q is the quantity of heat that the meter will have to indicate y is the specific mass of the liquid c is the specific heat capacity .~ .
75~7 0 is the output or the volume flow rate i,u the difference in temperature between supplied and discharged flow dt is the factor time to which the integration is per-formed.
When one takes the derivative ofrelation(2)(because thisprovides for a simple electronic analog), and combines both the rela-tions (1) and (2) the result will be Qm = f( A, ~ ~ ~W~ c, D, ~ '2.56 Ti u (3) in which Q is the first derivative of the quantity of heat, i.e.
the heat flow per each unit of time f(/~ ,c,D,~) is a function of the aforesaia meterial con-stants and of the dimensions of the meter. When used in practice f will be mainly a function of Ti and to a lesser degree of ~ ~i u i8 the expected actual coefficient of heat transfer.
~ i,u is the difference in temperature between the supplied and discharged flow.-Consequently relation (3) may also be written as follows ' 1,25 Qm f(~ i,u)~ i,u (4) ~ his makes it clear that for determining Qm it suffices to de-termine ~ and a Ti U- ~his may be performed by measuring four temperatures in the meter box.
~ ig. 1c diagrammatically shows the æupply and the return con-duit including the thermal shunt connection. In th~se parts there have been drawn the imaginary heat resistances R1 to R4 inclu-sive while it has been indicated diagrammatically at which points the four temperatures Ti, Tu~ Tb, ~O are mea9ured-~herein:
~1 is the heat resistance of the boundary layer at the hot side, R2 is the heat resistance of the tube raw material and ~1~7574 the composite body, R3 is the heat resistance of the thermal shunt connection, and R4 is the heat resistance of the boundary layer and the material resistance at the colder side.
~he first resistance R1, the boundary layer resistance, is formed by the coefficient of heat transfer a(which haa to be de-termined)and the surface area F across which the thermal shunt connection abstracts heat from the flow in the conduit. ~his surface area is substantially fixed by the dimensioning of the meter. ~he edges are subject to some di~placement beyond the original area, and the heat transfer by the pipe w~lls outside the composite body also will play a role upon decreasing flow of liquid. ~his increase of surface area will be indicated below as the border (line) effect.
The second indicated resistance R2 i9 formed by the intermedia-te material because a direct measurement of the wall temperature is difficult. The third resistance R3 i9 that of the shuntconnection between ~b and ~0, which resistance determines the heat trans-port by the first two resistances.
~he coefficient of heat transfer may be determined by measu-ring ~ ~i b and the heat transport in accordance with R1 (5) and R1 + R2 R~ (6) a ~i b ~ b,o which may be combined as follows 3 ~ = ( FR3 x ~ 2 ) (7) b,o ~y combining the relation (7) with the relation (4) the follo-wing i9 obtained ~, J~
1~47574 g ~ Ti b Qm = f1 (Ti- a Ti,u) f2 (~ Tb ) ~ Ti,U (8) ~ ased on this theory it appears to be possible indeed to deter-mine the heat consumption by measuring four temperatures.
~rom these temperatures the differential values a Ti U~ ~Ti b and ~ Tb O as well as the quotient of the latter two may be cal-culated. Subsequently these arguments are translated with the aid oi` tables and the two above mentioned function values, whereupon two multiplication operations provide the instantaneous heat consumption Qm.
The above notedfunction curves(f1, ~)have beendetermined empiri-cally.In orderto explain thismeasurement,relation (2) should~ be compared with relation (8). It then appears that it will be ne-cessary to investigate the relation between on the one hand ~ c0 and on the other hand ~ ~i b ~ Tb ' Ti and ~ Ti u .
Fig. 1d shows the relation between the measured volume flow rate and the measured temperatures when performing this type of test . Along the ordinate the normalized value of thte product ~ c 0 has been plotted and along theabscissa the ~ quotient of the measured temperature differentialsh Ti b and ~Tb O~ while the temperature Ti occurs as parameter. These measurements have been performed at a fixed value of ~ Ti u ~ased on a number of tests (in which first of all special attention was paid to the repro-ducability)it was concluded that it is possible to record the course of the function of ~ c 0 andd ~i.b in one table b,o and that simple corrections of arithmetic nature could be intro-duced in the table values to compensate for the influences of . and ~ T
l , U
~y correctly shaping the shunt connection as regards length 3 and cross section inconjunction with the choice of mate-rials for the connection and the tube,together with the asso-ciated coefficients of heat conductivity,itTappears to be pos-sible to keep the course of the quotient ~ , as the functionb,o ;' ~ .
.
, of the volume flow rate(over a C 0 measuring range of 1 to 40), between the limits of 1/8 to 8. ~his provides acceptable mea-surable temperature differentials ~ Ti b or a Tb at a given minimum temperature differential between supplied and drained flow (~ ~i u)f 10C.
~ he calculation of the differences, quotients, products and the handling of the table including the introduction of arith-metical corrections of the results is performed in this instance by a micro computer in IC-format.
With reference to Fig. 2 there has been shown a possible embo-diment of the heat quantity meter ac¢ording to the invenion. In this figure the reference numerals 1 and 2 indicate the supply and drain conduits, respectively, the reference numeral 10 the housing of the meter, the reference numeral 8 the electronic processing unit, the reference numeral 9 the electric power unit and the reference numeral 11 the reading panel (display).
An electronic signal processing unit capable of computing the total heat flow from four absolute temperatures on the basis of relation (8) has been realized by means of micro elect~nics as already used in pocket computers. In view of the micro electro-nics already present this meter will possess additional posssi-bilities such as telemetric reading, control of system functio-ning, day/night/season tariff, etc.
Also within the scope of the invention the meter may be applied solely for the determination of volume flow rates of liquids.
Some important aspects with regard to the measurement princi-ple of the present heat quantity meter are among others:
a. The dimensions of tne heat transferring surface area within the conduits and the dimensions or nature of the thermal shu~t conneftion.
a sence o a b. ~e~requirement of a shunt connection for creating a partial or sub heat flow. Even a (measurable) heat exchangeAfrom the surroundings offers the possibility to determine the proper-ties of the boundary layer and consequently the volume flow rate via temperatures.
c. The influence of foreign components in the water circulation that might deposit on the wall and might consequently influ-.. ~ , .: .
11~7574 ence the heat resistance of the boundary layer.
d. ~he flow profile of the flows of liquid and the contacting of the heat transferring surfaces;
e. The choice of the temperature measurement points in or on the thermal shunt'connection and the choice of the shape by means of which the shunt connection is coupled to one or both of the conduits.
With respect to item a above, the surface in which the thermal connection i9 joined to the conduit, is limited. The heat transport by this connection is continued not only at the location of this junction but also in the surrounding conduit walls. The influence of this border ef-fect is dependent on the'wall thickness of the conduit, the co-efficient of heat conductivity of the materials used and the co-efficient of heat transfer of the flowing liquid to the'conduit wall and consequently on the volume flow rate.
The border line effect tends to cause a deterioration of the non-linear relation between the temperatures to be measured and the heat flux to be determined. The influence of this border ef-fect may be restricted by thinning the conduit wall at the lo-cation of the edges with the thermal connection or by providinga piece of insulating material ~5 in Fig. 4).
With reference to Figs. 3a and b there are shown two examplas of a conduit section including a shunt connection fas-tened thereto by means of a point junction~gand3a)conduit section including a s~uFnt co3n~ection 3 fastened thereto by means of an annular junctlon~ In both the embodiments the border effects will act differently. The ratio of edge length to transfer area is larger for the point junction than for the annular junction. Moreover,the point junction possesses edges in the longitudinal direction of the flow whereas the annular junc-tion possesses only edges in the transverse direction.
With reference to Fig. 3c there is shown a further vari-ant of the annular juncticn in which the block shaped shunt con-nection is brought in contact with the flows over a greater length than width. The participation of the edges is thereby re-r~ ;` latively small. ~ile junction pieces 14 consist of a good 757~
heat conductive material, such as coppper, whereas the fixed re-sistance part 3 between the junction pieces 14 is made however of aless heat conductive material, such as stainless steel, so that within a small volume efficient heat resistance is provided.
The highly conductive junction pieces 14 lessen the critical character of mounting the temperature sensors for measurement of To and ~b.
With reference to Fig. 3d there has been shown a side eleva-tion of a coupling body 6 arranged coaxially within a conduit section 1, 2 at the end of the thermal connection 3. ~he coaxial arrangement has the advantage that the flow rate in the center of the conduit contributes most to the output. Moreover the flow contacting form of the coupling body may be chosen in such a manner that there will be a simple relation between the heat transport through the conduit and the temperature differential measured across the thermal connection. It has therein clearly been indicated that a thermal insulationring 5 may be provided between the thermal connection 3 and the wall of the conduit 1,
Description of Prior Art .
In the future, city heating networks will be used in a progres-sively increasing number of towns and districts in which each house will obtain a connection to a public heating network instead of its own boiler for central heating. From this conneotion the con-sumer will obtain the hot water for his home heating system andtap water supply either directly or indirectly by means of a heat exchange.
It has become evident that consumption by individual consumers (and thus total consumption) in such city heating system decreases when the amount of heat consumed by the individual ccnsumer is measured. From the heat quantity meter the consumer will then have an idea of the cost of his heating. For this reason the installa-tion of heat quantity meters for consumption on small scale is considered to be useful.
Existing meters such as, for instance evaporation meters, often have the drawback that they are not accurate enough. With respect to others, such as meters including turbine parts, the initial cost and/or maintenance cost are too high.
Summar~ of the Invention ~0 The object of the invention is to provide a method and a heat quantity meter not exhibiting the above mentioned drawbacks among other things by the complete absence of moving parts or measuring .
119~7574 flanges in the flowing liquid so that there are no obstructions in the supply and return conduits. This will lead to a considerable decrease in maintainance of the meter.
In accordance with the invention this object is attained in that the volume flow rate of the liquid is determined on the basis of the flow rate dependent heat transfer in the boundary layer of the flow of liquid at the location where the sub heat flow leaves or enters. The temperature differential across the boundary layer and the sub heat flow passing through said boundary layer i8 determined, while measuring at least one absolute temperature of the flow of liquid for correcting the temperature dependency of the material constants of the liquid involved in the determination of the volume flow rate.
~rie~ Description of the Drawin~s The present invention will now be elucidated further with refe-rence to the annexed drawings in which like numerala denote like element :
Fig. 1a shows a basic sketch of the conduit sections including a thermal shunt connection of the heat quantity meter;
Fig. 1b shows a side elevation of a part of a conduit section having a bar shaped shunt connection according to fig. 1a fastened thereto by means of an angular junction;
Fig. 1c discloses a diagrammatioal view of the heat quantity me-ter including its temperature measuring points and the imaginary heat resistances R1 to R4, inclusive;
Fig. 1d discloses the relation between the measured volume flow rate and the measured temperatures;
Fig. 2 shows a side elevation of a production embodiment of the heat quantity meter;
Fig. 3a, b, c, and d shows a side elevation of four variants of the junction of the shunt connection to a conduit section; and Fig. 4 shows a side elevation of a variant of the location of a temperature sensor.
Description of a Preferred Exem~lar~ Embodiment The operation of the heat quantity meter in accordance with the present invention is based solely on the measurement of a number il~757~
of temperatures. Use is made of the fact that the heat transfer between the heat carrier or flowing liquid and a body, in which or along which this liquid i8 transported, is dependent among other things on the flow rate of the liquid at the relevant loca-tion. The more this flow rate increases the better the heat trans-fer will become. It is now aimed at measuring this coefficient of heat transfer.
When employing this method easily measurable temperature diffe-rentials occur without being accompanied by large (and consequent-ly unacceptable) heat losses in the main flow as in a thermal flow-meter. In a known flowmeter as i9 for instanoe known from the French Patent Specification 2,353,045 one tries to minimize the in-fluence of the laminar sub or boundary layer among others by a special shape of the wall surrounding the flow of liquid. In the present method and meter a measurement is made of the coefficient of heat transfer of the laminar sub layer of the flow of liquid considered to be turbulent.
Where this measurement can not be performed directly a sub or leakage heat flow is allowed to form which is dependent on the coefficient of heat transfer. For this purpose there is provided an energy connection or, in particular, a thermal connection be-tween the supply and drain or return conduit.
In the connection thus provided there will occur a heat flow de-pendent on the difference in temperature between the hot water in the supply conduit and the cooled water in the return conduit as well as on the total heat resistance. This total heat resistance consists of a fixed component determined by the thermal connec-tion possibly in combination with the walls of the conduits, and of a variable component mainly determined by the flow of the liquid in the thermal boundary layers. ~he magnitude of this branched heat flow may be measured by means of a temperature diffe-rential measurement. ~he magnitude of the temperature differential across one or both of the boundary layers together with the ma~-nitude of the heat flow through the connection determine the coef-ficient of heat transfer in situ.
In the general case of an energy connection, apart from the heatflow by conduction, radiation or convection, a heat transport due to thermo-electric effects may also occur if the connection is "~
~7574 electrically conductive. The electric current generated in this case (possibly by the Seebeck effect) will then be a measure for this form of energy or heat transport.
The absolute temperatures of the flows of liquid at the location of the boundary layers are also of importance, because the relevant material constants, like the coefficient of heat conduction ~ , the specific heat c (weakly), and the viscosity ~ (strongly), are dependent on temperature.
The coefficient of heat transfer together with the several material constants fixedly determine the velocity gradient in the boundary layer. If the velocity profile in the conduit is also governed and reproduceable, then there will be an unambiguous relation between several tem-peratures and the volume flow rate of the liquid, and conse-quently between these temperatures and the net heat flowrate.
The signals supplied by the temperature sensors are processed in accordance with an empirically determined relation by an electronic unit into a quantity of heat per each unit Gf time or a time pulse per quantity o heat. By employing an integrating, summing or pulse counter circuit in the electronic unit, a total supplied quantity of heat per each chosen period of time can be accumulated, By having the meter constructed symmetrically both the volume flow rate in the hot supply conduit and in the colder drain conduit may be determined and compared with each other.
With reference now to Fig. la there is shown a basic sketch of a meter in accordance with the present invention, in which the reference numeral 1 indicates the supply conduit, the reference numeral 2 indicates the drain or return conduit and the reference numeral 3 indicates the ~75'74 - 4a -bar shaped thermal shunt connection. The temperatures Ti, Tb, To, T or temperature differentials may be measured by means of sensors 4, such as thermo~couples, to which a sensitive amplifier is connected. The thermo-couples mav be soldered onto or into the material.
With reference to Fig. lb there is shown a side elevation of a cross section of the angular junction of the thermal shunt connection 3 to one of the conduits 1 or 2. Likewise the laminar boundary layer 7 of the liquid at the tube wall of the conduits has .~
1~47S7 been indicated. ~he reference numeral 4 denotes the junction contact of the temperature differential sensor. This temperature differential sensor may be also consist of two separate absolute temperature sensors.
~or this type of heat transfer problems concerning the boundary layer one may apply a theory known in the theory of flows as the so called "film theory". In turbulent flowæ of liquid (as will occur in the supply and the drain conduits) one may consider the larger part of the velocity gradient and the entire tempe-rature gradient to be in the laminar sub layer at the wall. Ingeneral one may start from the empirical relation:
~' , , ~7574 Nu = 0~024 (1 + L) 0~66 ReO'8 PrO'33 (~vl ) '14 (1) in which:
Nu is the Nusselt number which is a measure for the coef-ficient of heat transfer of the boundary layer.
(1 + L) is a correction factor accounting for the inlet or starting area of the thermal boundary layer and in-cluding therein the ratio of the conduit or pipe di~-meter D and the distance L over which the heat trans-fer occurs.
10 Re is the Reynolds number relating the specific mass p , the rate of flow v and the conduit diameter D with the viscosity ~ of the liquid.
Pr is the Prandtl number indicating the ratio between impulse transport (friction) and heat transport. This is an zssembly of material constants, such as the spe-cific heat c, the viscosity ~ and the specific conduc-tivity A of the liquid. This therefore is a (tempera-ture dependent) material constant per se.
(~wl) is a correction term for the fact that the viscosity of the liquid in the turbulent center portion differs from that directly at the wall where a different tem-perature will prevail.
The relation (1) indicates that the coefficient of heat transfer a is about proportional to the output or volume flow rate to the power 0.8.
~ second relation, i.e. the generally known relation also applies to the meter of ~ig. 1a, b:
Qm = ¦ ~ c 0 ~ Ti Udt (2) in which 30 Q is the quantity of heat that the meter will have to indicate y is the specific mass of the liquid c is the specific heat capacity .~ .
75~7 0 is the output or the volume flow rate i,u the difference in temperature between supplied and discharged flow dt is the factor time to which the integration is per-formed.
When one takes the derivative ofrelation(2)(because thisprovides for a simple electronic analog), and combines both the rela-tions (1) and (2) the result will be Qm = f( A, ~ ~ ~W~ c, D, ~ '2.56 Ti u (3) in which Q is the first derivative of the quantity of heat, i.e.
the heat flow per each unit of time f(/~ ,c,D,~) is a function of the aforesaia meterial con-stants and of the dimensions of the meter. When used in practice f will be mainly a function of Ti and to a lesser degree of ~ ~i u i8 the expected actual coefficient of heat transfer.
~ i,u is the difference in temperature between the supplied and discharged flow.-Consequently relation (3) may also be written as follows ' 1,25 Qm f(~ i,u)~ i,u (4) ~ his makes it clear that for determining Qm it suffices to de-termine ~ and a Ti U- ~his may be performed by measuring four temperatures in the meter box.
~ ig. 1c diagrammatically shows the æupply and the return con-duit including the thermal shunt connection. In th~se parts there have been drawn the imaginary heat resistances R1 to R4 inclu-sive while it has been indicated diagrammatically at which points the four temperatures Ti, Tu~ Tb, ~O are mea9ured-~herein:
~1 is the heat resistance of the boundary layer at the hot side, R2 is the heat resistance of the tube raw material and ~1~7574 the composite body, R3 is the heat resistance of the thermal shunt connection, and R4 is the heat resistance of the boundary layer and the material resistance at the colder side.
~he first resistance R1, the boundary layer resistance, is formed by the coefficient of heat transfer a(which haa to be de-termined)and the surface area F across which the thermal shunt connection abstracts heat from the flow in the conduit. ~his surface area is substantially fixed by the dimensioning of the meter. ~he edges are subject to some di~placement beyond the original area, and the heat transfer by the pipe w~lls outside the composite body also will play a role upon decreasing flow of liquid. ~his increase of surface area will be indicated below as the border (line) effect.
The second indicated resistance R2 i9 formed by the intermedia-te material because a direct measurement of the wall temperature is difficult. The third resistance R3 i9 that of the shuntconnection between ~b and ~0, which resistance determines the heat trans-port by the first two resistances.
~he coefficient of heat transfer may be determined by measu-ring ~ ~i b and the heat transport in accordance with R1 (5) and R1 + R2 R~ (6) a ~i b ~ b,o which may be combined as follows 3 ~ = ( FR3 x ~ 2 ) (7) b,o ~y combining the relation (7) with the relation (4) the follo-wing i9 obtained ~, J~
1~47574 g ~ Ti b Qm = f1 (Ti- a Ti,u) f2 (~ Tb ) ~ Ti,U (8) ~ ased on this theory it appears to be possible indeed to deter-mine the heat consumption by measuring four temperatures.
~rom these temperatures the differential values a Ti U~ ~Ti b and ~ Tb O as well as the quotient of the latter two may be cal-culated. Subsequently these arguments are translated with the aid oi` tables and the two above mentioned function values, whereupon two multiplication operations provide the instantaneous heat consumption Qm.
The above notedfunction curves(f1, ~)have beendetermined empiri-cally.In orderto explain thismeasurement,relation (2) should~ be compared with relation (8). It then appears that it will be ne-cessary to investigate the relation between on the one hand ~ c0 and on the other hand ~ ~i b ~ Tb ' Ti and ~ Ti u .
Fig. 1d shows the relation between the measured volume flow rate and the measured temperatures when performing this type of test . Along the ordinate the normalized value of thte product ~ c 0 has been plotted and along theabscissa the ~ quotient of the measured temperature differentialsh Ti b and ~Tb O~ while the temperature Ti occurs as parameter. These measurements have been performed at a fixed value of ~ Ti u ~ased on a number of tests (in which first of all special attention was paid to the repro-ducability)it was concluded that it is possible to record the course of the function of ~ c 0 andd ~i.b in one table b,o and that simple corrections of arithmetic nature could be intro-duced in the table values to compensate for the influences of . and ~ T
l , U
~y correctly shaping the shunt connection as regards length 3 and cross section inconjunction with the choice of mate-rials for the connection and the tube,together with the asso-ciated coefficients of heat conductivity,itTappears to be pos-sible to keep the course of the quotient ~ , as the functionb,o ;' ~ .
.
, of the volume flow rate(over a C 0 measuring range of 1 to 40), between the limits of 1/8 to 8. ~his provides acceptable mea-surable temperature differentials ~ Ti b or a Tb at a given minimum temperature differential between supplied and drained flow (~ ~i u)f 10C.
~ he calculation of the differences, quotients, products and the handling of the table including the introduction of arith-metical corrections of the results is performed in this instance by a micro computer in IC-format.
With reference to Fig. 2 there has been shown a possible embo-diment of the heat quantity meter ac¢ording to the invenion. In this figure the reference numerals 1 and 2 indicate the supply and drain conduits, respectively, the reference numeral 10 the housing of the meter, the reference numeral 8 the electronic processing unit, the reference numeral 9 the electric power unit and the reference numeral 11 the reading panel (display).
An electronic signal processing unit capable of computing the total heat flow from four absolute temperatures on the basis of relation (8) has been realized by means of micro elect~nics as already used in pocket computers. In view of the micro electro-nics already present this meter will possess additional posssi-bilities such as telemetric reading, control of system functio-ning, day/night/season tariff, etc.
Also within the scope of the invention the meter may be applied solely for the determination of volume flow rates of liquids.
Some important aspects with regard to the measurement princi-ple of the present heat quantity meter are among others:
a. The dimensions of tne heat transferring surface area within the conduits and the dimensions or nature of the thermal shu~t conneftion.
a sence o a b. ~e~requirement of a shunt connection for creating a partial or sub heat flow. Even a (measurable) heat exchangeAfrom the surroundings offers the possibility to determine the proper-ties of the boundary layer and consequently the volume flow rate via temperatures.
c. The influence of foreign components in the water circulation that might deposit on the wall and might consequently influ-.. ~ , .: .
11~7574 ence the heat resistance of the boundary layer.
d. ~he flow profile of the flows of liquid and the contacting of the heat transferring surfaces;
e. The choice of the temperature measurement points in or on the thermal shunt'connection and the choice of the shape by means of which the shunt connection is coupled to one or both of the conduits.
With respect to item a above, the surface in which the thermal connection i9 joined to the conduit, is limited. The heat transport by this connection is continued not only at the location of this junction but also in the surrounding conduit walls. The influence of this border ef-fect is dependent on the'wall thickness of the conduit, the co-efficient of heat conductivity of the materials used and the co-efficient of heat transfer of the flowing liquid to the'conduit wall and consequently on the volume flow rate.
The border line effect tends to cause a deterioration of the non-linear relation between the temperatures to be measured and the heat flux to be determined. The influence of this border ef-fect may be restricted by thinning the conduit wall at the lo-cation of the edges with the thermal connection or by providinga piece of insulating material ~5 in Fig. 4).
With reference to Figs. 3a and b there are shown two examplas of a conduit section including a shunt connection fas-tened thereto by means of a point junction~gand3a)conduit section including a s~uFnt co3n~ection 3 fastened thereto by means of an annular junctlon~ In both the embodiments the border effects will act differently. The ratio of edge length to transfer area is larger for the point junction than for the annular junction. Moreover,the point junction possesses edges in the longitudinal direction of the flow whereas the annular junc-tion possesses only edges in the transverse direction.
With reference to Fig. 3c there is shown a further vari-ant of the annular juncticn in which the block shaped shunt con-nection is brought in contact with the flows over a greater length than width. The participation of the edges is thereby re-r~ ;` latively small. ~ile junction pieces 14 consist of a good 757~
heat conductive material, such as coppper, whereas the fixed re-sistance part 3 between the junction pieces 14 is made however of aless heat conductive material, such as stainless steel, so that within a small volume efficient heat resistance is provided.
The highly conductive junction pieces 14 lessen the critical character of mounting the temperature sensors for measurement of To and ~b.
With reference to Fig. 3d there has been shown a side eleva-tion of a coupling body 6 arranged coaxially within a conduit section 1, 2 at the end of the thermal connection 3. ~he coaxial arrangement has the advantage that the flow rate in the center of the conduit contributes most to the output. Moreover the flow contacting form of the coupling body may be chosen in such a manner that there will be a simple relation between the heat transport through the conduit and the temperature differential measured across the thermal connection. It has therein clearly been indicated that a thermal insulationring 5 may be provided between the thermal connection 3 and the wall of the conduit 1,
2 in order to suppress an optional heat transfer from or to the wall of the conduit.
With respect to the foregoing item ~, i~ those systems in which the supply and the drain are not near enough to each other and the heat transport for the sub flow by means of Peltier effects is impossible or i9 hampered by practical considerations, it it possible to make the desired heat transportoccur from thesu~ply conduit to the surroundingsor ~iceversa or heatlng by means of a cooling~body. In that case the drain conduit isno longer necessary for determining the volume flow rate of the liquid and/or the heat output. However, the sub heat flow or from to~the surroundings will have to be measured because this flow keeps playing a roll in the electronic signal processin&.
~ he same may be performed with the drain conduit, however, in that case the temperature differential with respect to the surroundings will be much smaller and the direction Or the sub heat flow will also run from the inside to the outside.
With respect to item c above, substances for preventing corrosion are often added to the circulating water of the city heating net-work. In the future, presum--13~
~ly yet other substances may be added in order to operate at a lower stowing force of the pumps (drag reduction). It may be possible that some substances will influence the heat transfer properties of the liquid boundery layer to the walls. No indi-cations of this sort, however, have yet been found bytests including oxide particles, salt solutions and suspensions.
Accordingly the fear of such effects is greatly lessened.
With respect to item d above, the relation between the water output or volume flow rate of the water and the variable heat resistance is determined by physical effects in the boundery layer. In a turbulent flow of liquid ~s is the case in the present heat mete~ one may presume that substantially the main part of the flow rate gradient and the entire temperature gradient is to be found in the laminar boundary layer. This boundary layer has a thickness in ths mag-nitude of some tenths of micrometers.
The profile of the flow determines the relation between the output and the flow rate gradient at the location of the boun-dary layer. The profile of the flow should therefore be control-ledinorder to maintain the relation between temperatures and heat flux.~ends, valves, couplings, etc have their own influence on the profile of the flow, BO that the length of the conduit of the heat meter is bound to a minimum, presently ten times its own diameter. The interfering influences of the above mentioned accessories may be suppressed by correctly shaping the inlet opening so that a shorter length of the conduit of the heat me-ter may suffice.
With respect to item e above, in a connection constructed like represented in Fig. 4 the field of isotherms,by means of which the heat flow via the boundary layer manifests itself ln the materia~ of the conduit wall and shunt connection,is notradially symmetric.~ symmetricalfield is, of course,impossible because the heat ultimatelyhas to flow in one direction, for instance towards the other conduit. The heat flow occurring in the head side of the connection (at 4 in Fig.
4) will have to flow via the sides to the central middle por-~1~L757~
tion. Consequently an additional decrease in temperature will occur in the sides. This additional decrease in temperature appears to be dependent on the flow. ~his is because increa-sing volume flow rate of the liquid~the boundary layer resis-tanceto becomesmaller so that the material resistances will beco-me of greater influence on the heat flow lines in the side~. As a result thereof there will occur a different temperature dis-tribution.
Empirically it has been found possible to give the junction according to ~ig. 4 such dimensions that the change in the Ti b signal, by measuring at the head side (point 4), causes such a change in the quotient ~ ~i b/ ~b O that the relation between this quotient and the volume flow rate or output of liquid may be straigtrened within acceptable limits over the entire measu-ring range from 1 to 40. ~he term "acceptable" should thereby beunderstood as 1% within the final answer.
With respect to the foregoing item ~, i~ those systems in which the supply and the drain are not near enough to each other and the heat transport for the sub flow by means of Peltier effects is impossible or i9 hampered by practical considerations, it it possible to make the desired heat transportoccur from thesu~ply conduit to the surroundingsor ~iceversa or heatlng by means of a cooling~body. In that case the drain conduit isno longer necessary for determining the volume flow rate of the liquid and/or the heat output. However, the sub heat flow or from to~the surroundings will have to be measured because this flow keeps playing a roll in the electronic signal processin&.
~ he same may be performed with the drain conduit, however, in that case the temperature differential with respect to the surroundings will be much smaller and the direction Or the sub heat flow will also run from the inside to the outside.
With respect to item c above, substances for preventing corrosion are often added to the circulating water of the city heating net-work. In the future, presum--13~
~ly yet other substances may be added in order to operate at a lower stowing force of the pumps (drag reduction). It may be possible that some substances will influence the heat transfer properties of the liquid boundery layer to the walls. No indi-cations of this sort, however, have yet been found bytests including oxide particles, salt solutions and suspensions.
Accordingly the fear of such effects is greatly lessened.
With respect to item d above, the relation between the water output or volume flow rate of the water and the variable heat resistance is determined by physical effects in the boundery layer. In a turbulent flow of liquid ~s is the case in the present heat mete~ one may presume that substantially the main part of the flow rate gradient and the entire temperature gradient is to be found in the laminar boundary layer. This boundary layer has a thickness in ths mag-nitude of some tenths of micrometers.
The profile of the flow determines the relation between the output and the flow rate gradient at the location of the boun-dary layer. The profile of the flow should therefore be control-ledinorder to maintain the relation between temperatures and heat flux.~ends, valves, couplings, etc have their own influence on the profile of the flow, BO that the length of the conduit of the heat meter is bound to a minimum, presently ten times its own diameter. The interfering influences of the above mentioned accessories may be suppressed by correctly shaping the inlet opening so that a shorter length of the conduit of the heat me-ter may suffice.
With respect to item e above, in a connection constructed like represented in Fig. 4 the field of isotherms,by means of which the heat flow via the boundary layer manifests itself ln the materia~ of the conduit wall and shunt connection,is notradially symmetric.~ symmetricalfield is, of course,impossible because the heat ultimatelyhas to flow in one direction, for instance towards the other conduit. The heat flow occurring in the head side of the connection (at 4 in Fig.
4) will have to flow via the sides to the central middle por-~1~L757~
tion. Consequently an additional decrease in temperature will occur in the sides. This additional decrease in temperature appears to be dependent on the flow. ~his is because increa-sing volume flow rate of the liquid~the boundary layer resis-tanceto becomesmaller so that the material resistances will beco-me of greater influence on the heat flow lines in the side~. As a result thereof there will occur a different temperature dis-tribution.
Empirically it has been found possible to give the junction according to ~ig. 4 such dimensions that the change in the Ti b signal, by measuring at the head side (point 4), causes such a change in the quotient ~ ~i b/ ~b O that the relation between this quotient and the volume flow rate or output of liquid may be straigtrened within acceptable limits over the entire measu-ring range from 1 to 40. ~he term "acceptable" should thereby beunderstood as 1% within the final answer.
Claims (26)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method for measuring the quantity of heat abstracted from a circulating flow of liquid by a consumption unit based upon the indirect measurement of the volume flow rate of the liquid, while maintaining a sub heat flow with respect to the main heat flow transported by the flow of liquid and measur-ing the temperature at some points by means of temperature sensors, characterized in that the volume flow rate of the flow liquid is determined on the basis of the flow rate de-pendent heat transfer in the boundary layer of the flow of liquid at the location of the sub heat flow by determining the temperature differential across the boundary layer, and the sub heat flow passing through said boundary layer, while measuring at least one absolute temperature of the flow of liquid for correcting the temperature dependency of the material constants of the liquid involved in said determin-ation of the volume flow rate,
2. The method of claim 1, characterized in that the sub heat flow passing through the boundary layer is determined by measuring the temperature differential across a fixed heat resistance in a part of the path of the sub heat flow outside said boundary layer.
3. The method of claim 1, characterized in that the quotient of the temperature differential across the fixed heat nests-tance and the temperature differential across the boundary layer is determined by means of an electronic computation circuit as a measure for the flow rate dependent heat trans-fer in the boundary layer.
4. The method of claim 2, characterized in that the quotient of the temperature differential across the fixed heat resis-tance and the temperature differential across the boundary layer is determined by means of an electronic computation cir-cuit as a measure for the flow rate dependent heat transfer in the boundary layer.
5. The method of claim 3, characterized in that said quotient is used in the electronic computation circuit for determining the volume flow rate while employing a relation also deter-mined by the shape of a heat quantity meter to be used and the material constants of the liquid,
6. The method of claim 5 wherein the flow of liquid is sup-plied to and drained from the consumption unit via a supply conduit and drain conduit respectively, characterized in that said volume flow rate is multiplied in the electronic compu-tation circuit with the difference in temperature of the flow of liquid in the supply conduit and in the drain conduit, respectively to obtain the instantaneous heat consumption.
7. Apparatus for determining the flow rate of a liquid through a conduit, said liquid including a laminar boundary layer ad-jacent to the walls of said conduit, and said liquid having various material constants associated therewith, said apparatus comprising:
- means for generating a signal indicative of heat transfer through the boundary layer of said conduit, said heat transfer being indicative of said flow rate;
- means for generating a signal indicative of the temperature of the liquid in said conduit, said temperature being indicative of said liquid material constants; and - electronic processing means responsive to said signals, for determining said flow rate from said heat transfer and said material constants.
- means for generating a signal indicative of heat transfer through the boundary layer of said conduit, said heat transfer being indicative of said flow rate;
- means for generating a signal indicative of the temperature of the liquid in said conduit, said temperature being indicative of said liquid material constants; and - electronic processing means responsive to said signals, for determining said flow rate from said heat transfer and said material constants.
8. The apparatus of claim 7 wherein said means for generating a signal indicative of heat transfer through said boundary layer includes:
- means for inducing a leakage heat flow with respect to said conduit.
- means for inducing a leakage heat flow with respect to said conduit.
9. The apparatus of claim 8 wherein said means for inducing a leakage heat flow comprises:
- a thermal shunt member of predetermined thermal resistance thermally coupled at one end to said conduit, the other end thereof being maintained at temperatures different from the temperature of said one end; and - said means for generating a signal indicative of said heat transfer comprises first and second temperature sensors, said first sensor disposed in said shunt member at said one end, and said second sensor being disposed at said other end.
- a thermal shunt member of predetermined thermal resistance thermally coupled at one end to said conduit, the other end thereof being maintained at temperatures different from the temperature of said one end; and - said means for generating a signal indicative of said heat transfer comprises first and second temperature sensors, said first sensor disposed in said shunt member at said one end, and said second sensor being disposed at said other end.
10. Apparatus for measuring the liquid flow to a consuming unit in a system wherein said liquid flow is provided to said con-suming unit through a supply conduit and removed from said unit by a return conduit, said liquid flow including a laminar boun-dary layer in proximity to the walls of said conduit, said apparatus comprising:
- a shunt member, of predetermined fixed thermal resistance, thermally connecting said supply and return conduits;
- first temperature sensor means for generating a signal indicative of the temperature (Ti) of the liquid in said supply conduit;
- a second temperature sensor means for generating a signal indicative of the temperature (Tu) of the liquid in said return conduit;
- third temperature sensor means for generating a signal indicative of the temperature (Tb) of said shunt member in the proximity of said supply conduit;
- fourth temperature sensor means for generating a signal indicative of the temperature (To) of said shunt member in the proximity of said return conduit; and - electronic processing means, responsive to said signals, for determining the heat transfer in the boundary layer of the liquid in one of said supply and return conduits, said boundary layer heat transfer being indicative of flow rate through said one conduit.
- a shunt member, of predetermined fixed thermal resistance, thermally connecting said supply and return conduits;
- first temperature sensor means for generating a signal indicative of the temperature (Ti) of the liquid in said supply conduit;
- a second temperature sensor means for generating a signal indicative of the temperature (Tu) of the liquid in said return conduit;
- third temperature sensor means for generating a signal indicative of the temperature (Tb) of said shunt member in the proximity of said supply conduit;
- fourth temperature sensor means for generating a signal indicative of the temperature (To) of said shunt member in the proximity of said return conduit; and - electronic processing means, responsive to said signals, for determining the heat transfer in the boundary layer of the liquid in one of said supply and return conduits, said boundary layer heat transfer being indicative of flow rate through said one conduit.
11. The apparatus of claim 10 adapted for measuring the quantity of heat drawn from said liquid by said unit wherein said elec-tronic processing means includes means for generating indicia of a quantity equal to volume flow rate multiplied by the difference in temperature between the liquid in the supply conduit and liquid in the return conduit.
12. The apparatus of claim 10 wherein said electronic pro-cessing means includes means for generating indicia of a quantity equal to the temperature differential across said shunt member fixed heat resistance, divided by the difference in temperature between the liquid in said one conduit and said shunt member in the proximity of said one conduit.
13. Apparatus for determining the flow rate of a liquid through a conduit, said liquid having a laminar layer adjacent to the walls of said conduit, said apparatus comprising:
- a thermal shunt member, thermally coupled at one end to said conduit; and having a fixed thermal resistance between said one end and the second end thereof, a leakage heat flow being maintained through said shunt member;
- a first temperature sensor for generating a signal indica-tive of the temperature (Ti) of the liquid in said conduit;
- a second temperature sensor for generating a signal indica-tive of the temperature (Tb) of said shunt member one end in proximity to said conduit;
- a third temperature sensor for generating a signal indica-tive of the temperature (To) at said shunt member second end;
and - electronic processing means, responsive to said temperature signals, for generating indicia of the quantity (Ti - Tb)/
(Tb - To), said quantity being indicative of said flow rate.
- a thermal shunt member, thermally coupled at one end to said conduit; and having a fixed thermal resistance between said one end and the second end thereof, a leakage heat flow being maintained through said shunt member;
- a first temperature sensor for generating a signal indica-tive of the temperature (Ti) of the liquid in said conduit;
- a second temperature sensor for generating a signal indica-tive of the temperature (Tb) of said shunt member one end in proximity to said conduit;
- a third temperature sensor for generating a signal indica-tive of the temperature (To) at said shunt member second end;
and - electronic processing means, responsive to said temperature signals, for generating indicia of the quantity (Ti - Tb)/
(Tb - To), said quantity being indicative of said flow rate.
14. The apparatus of claims 9 or 13, wherein said shunt member one end includes first and second portions, said first portion being generally annular shaped portion surrounding a portion of said conduit, said second temperature sensor being disposed in said second portion.
15. The apparatus of claim 10 wherein said shunt member comprises a first portion having relatively low heat resistance in thermal connection with said supply conduit, said second temperature sensor being disposed in said shunt member first portion in proximity to said supply conduit;
- a second portion having relatively low heat resistance in thermal connection with said return conduit, said fourth tem-perature sensor being disposed in said shunt member second portion in proximity to said return conduit; and - a third portion having relatively high heat resistance thermally coupling said first and second portion.
- a second portion having relatively low heat resistance in thermal connection with said return conduit, said fourth tem-perature sensor being disposed in said shunt member second portion in proximity to said return conduit; and - a third portion having relatively high heat resistance thermally coupling said first and second portion.
16. The apparatus of claim 15 wherein said shunt member first and second portions are in part annular shaped and surround a portion of said conduits.
17. Apparatus for determining the flow rate of a liquid through a conduit according to claim 7 wherein the apparatus is addi-tionally adapted to function as a heat quantity meter for measuring heat abstracted from a circulating flow by a con-sumption unit by further comprising a conduit section for the flow of liquid to be supplied, a conduit section for the flow of liquid to be drained, a shunt connection between both said conduit sections to obtain a sub heat flow with respect to the main heat flow of said liquid, said shunt connection having a fixed heat resistance associated therewith and a number of temperature sensors, one of which on the supply conduit section and a second one on the drain conduit section, characterized in that two additional temperature sensors are provided, dis-posed on the shunt connection on respective sides of the heat resistance thereof, and further characterized in that the shunt connection is arranged to have such a length, cross section and junction surface area at least at the supply conduit section and the material of the shunt connection and of at least the supply conduit section at the location of the junction with the shunt connection possesses such a coefficient of heat conductivity, that the quotient of the temperature differential across the fixed heat resistance of the shunt connection and the temperature differential across the boundary layer of the flow of liquid at the location of the junction with the shunt connection lies between 8 and 1/8 for the entire operative measurement range of volume flow rates of the liquid thus warranting reasonably measurable temperature differentials.
18. The heat quantity meter of claim 17, characterized in that said shunt connection comprises a fixed resistance disposed in the middle portion thereof, and at least the supply con-duit section is coupled to the shunt connection by means of an annular junction, the shape of the end of said junction turned away from the middle portion of the shunt connection comprising the fixed heat resistance, being such that for higher volume flow rates of the liquid the transferred sub heat flow leads to an additional temperature difference in said end, one of the two temperature sensors for measuring the temperature differential across the heat resistance being disposed on said end, so that this additonal temperature difference will contribute in compensating a possible non-linear relation between the quotient and the volume flow rate of the liquid.
19. The heat quantity meter of claim 17, characterized in that the conduction of heat through the wall at least of the supply conduit section outside the annular junction with the shunt connection is restricted by the selection of the material of the supply conduit section outside the annular junction so that the sub heat flow in the shunt connection is governed by the heat transfer of the boundary layer at the location of the annular junction.
20. The heat quantity meter of claim 17, further including an electronic computation circuit for determining the temper-ature differentials, for determining the said quotient, for deriving the volume flow rate of the liquid form the quotient in accordance with a predetermined relation, for correcting the temperature dependency of the material constants, and for multiplying the volume flow rate thus obtained with the temperature differential between the flow of liquid in the supply conduit and the drain conduit.
21. The heat quantity of claim 10, characterized in that the electronic computation circuit includes an integrating cir-cuit for determining the quantity of heat transferred per each time unit to the consumption unit.
22. The heat quantity meter of claim 17 or 18, characterized in that the electronic computation circuit is provided with further circuits for telemetric reading, control of the functioning of the meter, for recording casu quo indicating day/night/season tariff, etc.
23. The heat quantity meter of claim 19, further including an electronic computation circuit for determining the temperature differentials, for determining the said quotient, for deriving the volume flow rate of the liquid from the quotient in accor-dance with a predetermined relation, for correcting the tem-perature dependency of the material constants, and for multi-plying the volume flow rate thus obtained with the temperature differential between the flow of liquid in the supply conduit and in the drain conduit.
24. The heat quantity meter of claim 19, characterized in that the electronic computation circuit is provided with further circuits for telemetric reading, control of the functioning of the meter, for recording casu quo indicating day/night/season tariff, etc.
25. The heat quantity meter of claim 20, characterized in that the electronic computation circuit is provided with further circuits for telemetric reading, control of the functioning of the meter, for recording casu quo indicating day/night/season tariff, etc.
26. The heat quantity meter of claim 21, characterized in that the electronic computation circuit is provided with further circuits for telemetric reading, control of the functioning of the meter, for recording casu quo indicating day/night/season tariff etc.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000348879A CA1147574A (en) | 1980-03-31 | 1980-03-31 | Method and a meter for measuring quantities of heat |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000348879A CA1147574A (en) | 1980-03-31 | 1980-03-31 | Method and a meter for measuring quantities of heat |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1147574A true CA1147574A (en) | 1983-06-07 |
Family
ID=4116603
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000348879A Expired CA1147574A (en) | 1980-03-31 | 1980-03-31 | Method and a meter for measuring quantities of heat |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1147574A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5026171A (en) * | 1989-06-07 | 1991-06-25 | Feller Murray F | Apparatus for flow rate and energy transfer measurements |
-
1980
- 1980-03-31 CA CA000348879A patent/CA1147574A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5026171A (en) * | 1989-06-07 | 1991-06-25 | Feller Murray F | Apparatus for flow rate and energy transfer measurements |
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