RU2575565C2 - Determination of heat flow released by heat-carrying fluid medium - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: method to determine a heat flow (dQ/dt) is proposed, where heat flow is released from heat-carrying fluid medium (12), which represents a mixture of at least two different fluid media, and which flows via a space (11) of the flow from the first position, where it has the first temperature (T1), to the second position, where it has due to this heat flow (dQ/dt) the second temperature (T2), which is lower than the specified first temperature (T1). Density and specific heat capacity of the specified heat-carrying fluid medium (12) is determined by measurement of sound speed (vs) in the specified fluid medium, and the specified density and specific heat capacity of the specified heat-carrying fluid medium (12) is used to determine heat flow (dQ/dt). Also the device is proposed for realisation of the specified method, including a facility for measurement of differential temperature, a facility for measurement of absolute temperature, a facility for measurement of sound speed in fluid medium, a facility for measurement of volume flow rate, and also a unit of assessment for determination of heat flow on the basis of produced data.

EFFECT: increased accuracy of determination of heat flow released from heat-carrying fluid medium.

20 cl, 2 dwg

Description

FIELD OF THE INVENTION

The present invention relates to a technology for measuring thermal quantities. It relates to a method for determining the heat flux emanating from a heat-carrying fluid according to the generic concept of claim 1.

BACKGROUND

Binary mixtures of two fluids are often used in terminal systems, mainly related to heating, cooling or air conditioning, etc. A well-known binary fluid is a mixture of water and a non-freezing fluid, mainly in the form of a mixture of water and glycol. When such a mixture or binary fluid transfers thermal energy and delivers this energy to the location of the fluid circulation system, it is necessary to know the actual mixing ratio of the heat-carrying fluid in cases where the delivered energy must be calculated based on certain measurements in the system.

Unfortunately, the mixing ratio of such a binary fluid or other fluid mixtures varies with time, because, for example, water can evaporate from the system or water can be added, while the mixing ratio changes.

DE102005043699 discloses a measurement unit for a vehicle in which a content of an anti-corrosion medium in a vehicle fluid system is determined. To determine the mixing ratio, the speed of sound in a fluid is measured.

In DE19533927, the results of measuring capacitance and measuring the speed of sound are combined to determine and control the concentration of detergent in a cleaning fluid.

DE3741577 discloses a method and system for measuring a mixing ratio of a binary fluid as a microwave signal passes through said liquid.

The above documents do not contain information regarding the determination of the heat flux emanating from a heat-carrying fluid, which is a mixture of various fluids.

SUMMARY OF THE INVENTION

The objective of the invention is to provide a method for determining the heat flux emanating from a heat-carrying fluid, which is a mixture of various fluids.

A further object of the invention is to provide a device for measuring a heat flux for implementing said method.

These and other problems are solved by the method according to p. 1 of the claims and the device for measuring the heat flux according to p. 13 of the claims.

The method according to the invention comprises the steps of:

a) measuring the differential temperature between said first temperature and said second temperature;

b) measuring the speed of sound in said heat transfer fluid in a predetermined portion of said flow space in the vicinity of said first and / or second position;

c) measuring the absolute temperature of the heat transfer fluid in said predetermined area;

d) measuring the volumetric flow rate in said predetermined area;

e) determining, based on said measured absolute temperature and said measured speed of sound, the mixing ratio of said heat-carrying fluid;

f) determining, based on said measured absolute temperature and said determined mixing ratio of said heat transfer fluid, the density and specific heat of said heat transfer fluid; and

g) determining, based on said measured differential temperature, said measured volumetric flow rate, said specific density and said specific specific heat capacity, a heat flux emanating from said heat-carrying fluid.

According to an embodiment of the method according to the invention, said heat transfer fluid is a binary mixture of two fluids.

In particular, said heat transfer fluid is a mixture of water and a freezing fluid.

More specifically, said heat transfer fluid is a mixture of water and glycol.

According to another embodiment of the method according to the invention, the mixing ratio of said heat transfer fluid is determined based on said measured absolute temperature and said measured sound velocity using a data table for the relationship between sound speed, absolute temperature and mixing ratio of a particular heat transfer fluid.

Alternatively, the mixing ratio of said heat transfer fluid can be determined based on said measured absolute temperature and said measured speed of sound using the mathematical relationship between the speed of sound, absolute temperature and the mixing ratio of a specific heat transfer fluid.

According to another embodiment of the invention, the speed of sound in said heat transfer fluid is measured by an ultrasonic measuring device.

More specifically, the ultrasonic measuring device comprises a first ultrasonic transducer placed on the first side of said flow space and a second ultrasonic transducer placed on the second side of said flow space, so that an ultrasonic signal passing between said first and second ultrasonic transducers crosses the fluid into said space flow.

In particular, the first and second ultrasonic transducers are positioned relative to the fluid flow in said flow space so that an ultrasonic signal passing between said first and second ultrasonic transducers has a velocity component in the direction of said fluid flow, the speed of sound is measured in opposite directions between said the first and second ultrasonic transducers, and the volumetric flow rate is obtained on the basis of the measured various sound speeds in -mentioned opposite directions.

When a specialized device is used to measure the speed of sound, the fluid flow rate can be determined based on two different measurements of the speed of sound, namely in the direction of flow and against the direction of flow. In this case, the volumetric flow rate can be calculated based on the flow rate and the cross-sectional area of the flow space or pipe. However, according to another embodiment of the invention, said volumetric flow rate is measured with a separate flow meter.

According to another embodiment, the measurement of the speed of sound is based on measuring the transit time of an ultrasonic pulse passing between said first and second ultrasonic transducers.

More specifically, the measurement of the speed of sound is performed in accordance with the acoustic feedback method.

A device for measuring heat flux according to the invention comprises:

a) first means for measuring a differential temperature between said first temperature and said second temperature;

b) second means for measuring the speed of sound in said heat transfer fluid in a predetermined portion of said flow space in the vicinity of said first and / or second position;

c) third means for measuring the absolute temperature of the heat transfer fluid in said predetermined area;

d) a fourth means for measuring a volumetric flow rate in said predetermined section;

wherein said first, second, third and fourth means are connected to an evaluation unit for determining said heat flux based on data that it receives from said first, second, third and fourth means.

According to an embodiment of the heat flux measuring device according to the invention, said first differential temperature measuring means comprises a first temperature sensor located in said first position and a second temperature sensor placed in said second position located downstream of said first position.

More specifically, said second means for measuring the speed of sound in said heat-carrying fluid in a predetermined portion of said flow space comprises an ultrasonic measuring device that is connected to an ultrasound control unit.

In principle, the absolute temperature can be determined based on the measured first and second temperatures from the first and second temperature sensors. However, according to yet another embodiment of the invention, said third means for measuring the absolute temperature of the heat transfer fluid in said predetermined portion comprises a third temperature sensor which is interposed between said first and second temperature sensors in a flow direction.

According to yet another embodiment, said fourth means for measuring a volumetric flow rate in said predetermined section comprises a separate flowmeter.

According to yet another embodiment, a data table is provided for the relationship between the speed of sound, the absolute temperature and the mixing ratio of a particular heat transfer fluid, and the evaluation unit has access to said data table.

According to yet another embodiment of the invention, said ultrasonic measuring device comprises at least two ultrasonic transducers which are arranged such that an ultrasonic signal passing between said at least two ultrasonic transducers crosses said heat-carrying fluid.

More specifically, said at least two ultrasound transducers are positioned relative to the flow direction of said heat transfer fluid so that a measurement path between said at least two ultrasound transducers crosses said flow direction at an oblique angle.

BRIEF DESCRIPTION OF THE DRAWINGS

Now, the present invention will be explained in more detail in various embodiments and with reference to the accompanying drawings, in which:

FIG. 1 is a block diagram of a device for measuring heat flux according to an embodiment of the invention; and

FIG. 2 is a set of curves characterizing the dependence of the speed of sound on temperature for a binary mixture of water and glycol having a glycol fraction of 0, 20, 40, and 60%, which can be used to determine the mixing ratio when the speed of sound and absolute temperature are known.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1 shows a device 10 for measuring heat flux according to an embodiment of the present invention. The central part of the device is the space 11 of the flow, for example, a pipe. The fluid 12, in particular in the form of a binary fluid, more in particular in the form of a mixture of water and a non-freezing fluid, even more particularly in the form of a mixture of water and glycol, flows through said flow space 11, the flow having the direction indicated in FIG. . 1 set of arrows.

On the left side of the space 11 of the flow fluid 12 has a first temperature T1, on the right side of the space 11 of the flow has a second temperature T2, which is lower than T1. The temperature difference or differential temperature ΔT = T1-T2 is a consequence of the heat flux dQ / dt that comes from the fluid 12 and leaves the space 11 of the flow (see the wide arrow in Fig. 1). The heat flux dQ / dt may be generated by a heating radiator or heat exchanger, or the like.

In accordance with basic physical principles (see, for example, US4440507), the heat flux dQ / dt can be determined using the following equation:

,(one) $$dQ/dt=\dot{Q}=\rho ·C·\dot{V}(T\mathrm{one}-T2)=\rho ·C\frac{dV}{dt}\Delta T$$

,

является объемным расходом текучей среды и С является теплоемкостью. Дифференциальную температуру ΔТ можно легко определять путем измерения температур Т1 и Т2 в положениях, показанных выше. Объемный расход dV/dt можно легко определять по скорости потока текучей среды 12 и площади поперечного сечения пространства 11 потока. Однако ситуация является иной для плотности ρ и теплоемкости С. Когда текучая среда 12 представляет собой смесь по меньшей мере двух различных текучих сред, особенно смесь воды и незамерзающей текучей среды, подобной гликолю, что является частым случаем в области нагрева и кондиционирования воздуха, оба коэффициента зависят не только от абсолютной температуры, но также и от отношения смешения текучей среды 12. Если вид незамерзающей текучей среды и отношение смешения известны, то можно довольно просто ввести точные (зависящие от Т) коэффициенты ρ и С в уравнение (1), приведенное выше.where ρ is the density of the fluid, $$\dot{V}=dV/dt$$

is the volumetric flow rate of the fluid and C is the heat capacity. The differential temperature ΔT can be easily determined by measuring the temperatures T1 and T2 in the positions shown above. The volumetric flow rate dV / dt can be easily determined by the flow rate of the fluid 12 and the cross-sectional area of the flow space 11. However, the situation is different for density ρ and heat capacity C. When the fluid 12 is a mixture of at least two different fluids, especially a mixture of water and a non-freezing fluid like glycol, which is a common case in the field of heating and air conditioning, both factors It depends not only on the absolute temperature, but also on the ratio of mixing of the fluid 12. If the type of anti-freeze fluid and mixing ratio are known, it can be quite easy to enter accurate (depending on T) and s cients ρ and C in equation (1) above.

However, it often happens that the mixing ratio of the fluid 12 changes over time, for example, when water evaporates from the fluid circulation system or water is added to it, as a result of which the coefficients ρ and C change and, as a result, the heat flux dQ / dt is determined using the equation (1) becomes unlawful. Accordingly, the mixing ratio should be determined at least from time to time to ensure that the results of calculating the heat flux are correct.

Further, it is known from the prior art (see, for example, DE 10 2005 043 699, specifically [0024]) that the mixing ratio of a fluid mixture can be determined based on the speed of sound that is measured in said mixture. After the speed of sound is measured in such a fluid, calibration measurements or mathematical relationships between parameters (algorithms) can be used to determine the actual mixing ratio. In FIG. Figure 2 shows a set of curves that characterize the dependence of sound velocity v _s on temperature T for a binary mixture of water and glycol having a glycol fraction of 0, 20, 40, and 60%. Although only four exemplary curves are shown, it is clear that in order to accurately determine the mixing ratio, it is necessary to have much more curves with very small distances between adjacent curves.

Using the graph of FIG. 2, the mixing ratio can be determined by finding the intersection point on the graph for a given absolute temperature T and a given sound speed v _s . This intersection point lies on one of these curves, and it denotes the corresponding mixing ratio associated with the curve. It is clear that such a graph can be converted into a data table containing discrete values of the included parameters. Such a data table can be easily accessed by a computer to find the exact value of the mixing ratio in the case when the corresponding values of the absolute temperature T and sound speed v _s are known.

The heat flow measuring device 10 of FIG. 1 comprises an ultrasonic measuring device 13, which can be used not only to measure the sound velocity v _s in the fluid 12 of the flow space 11, but also to measure or determine the volumetric flow rate dV / dt of the fluid 12 flowing through the flow space 11. The ultrasonic measuring device 13 comprises a first ultrasonic transducer 14 and a second ultrasonic transducer 15. Both transducers 14, 15 indicate a measuring path in the flow space 11, which is throughout the entire length in the fluid 12. The measuring path intersects the flow direction of the fluid 12 at an oblique angle .

Ultrasonic transducers 14 and 15 can emit and receive ultrasonic pulses that pass along the measuring track. When the first transducer 14 emits an ultrasonic pulse that is received by the second transducer 15, the transit time of this pulse downstream between these transducers is t 1, and it can be expressed as

,(2) $$t\mathrm{one}=\frac{L}{v_s+a·v_f}$$

,

where L is the length of the measuring track and (a · v _f ) is a component of the velocity v _f of the fluid flow 12 parallel to the direction of the measuring track.

When the second transducer 15 emits an ultrasonic pulse that is received by the first transducer 14, the travel time of this pulse towards the flow between these transducers is t2, and it can be expressed as:

(3) $$t2=\frac{L}{v_s-a·v_f}$$

By subtractively combining equations (2) and (3), the sound velocity v _s can be eliminated, so that the velocity v _f of the fluid stream 12 will be:

,(four) $$v_f=k\frac{L}{2}\left(\frac{\mathrm{one}}{t\mathrm{one}}-\frac{\mathrm{one}}{t2}\right)$$

,

where the experimentally determined calibration coefficient k includes not only the coefficient a given above, but also the effects associated with the non-ideal measurement situation (due to the flow profile, side effects, etc.).

Based on the flow velocity v _f and the known cross-sectional area A of the flow space or pipe 11, the volumetric flow rate dV / dt can be determined from the following expression:

.(5) $$\dot{V}=dV/dt=A·v_f=A·k\frac{L}{2}\left(\frac{\mathrm{one}}{t\mathrm{one}}-\frac{\mathrm{one}}{t2}\right)$$

.

By additively combining equations (2) and (3), the flow velocity v _f can be eliminated in order to obtain the sound velocity v _s :

,(6) $$v_s=k\text{'}\text{'}·\frac{L}{2}\left(\frac{\mathrm{one}}{t\mathrm{one}}+\frac{\mathrm{one}}{t2}\right)$$

,

which contains another calibration coefficient k 'of the previously described form.

The accuracy of determining the speed of sound can be improved by using the so-called acoustic feedback method (see, for example, JP2003302270). In the device 10 for measuring heat flux from FIG. 1, an acoustic feedback loop is created when an ultrasonic pulse is sent from the transducer 14 to the transducer 15. The pulse is received and fed through the feedback channel to the ultrasound control unit 19, which then excites the transducer 14 with a new ultrasonic pulse. This circuit functions several times, and in block 19 Ultrasound control measures the total time spent on these several acoustic feedback cycles. After that, the time spent by the pulse on a single passage along the measuring track is determined by dividing the total time by the number of completed cycles.

Thus, the ultrasonic measuring device 13, together with the transducers 14 and 15 and the ultrasound control unit 19 for controlling the transducers 14 and 15, is able to measure and determine the sound velocity v _s in the fluid 12, as well as the volumetric flow rate dV / dt in space (11) flow. However, it is also possible to measure the volumetric flow rate dV / dt directly using a separate flow meter 24, which may be of the kind well known in the art. The results of these measurements and determinations are transmitted to the central evaluation unit 20, which has the processing power necessary to calculate and / or determine the actual mixing ratio of the fluid 12.

Using data table 21, which is the numerical equivalent of a graph similar to that shown in FIG. 2, the estimator 20 obtains the actual values of the sound velocity v _s and the absolute temperature T and reads the corresponding mixing ratio value from the data table 21. The absolute temperature T is measured by a temperature sensor 17 located close to the measuring track of the ultrasonic measuring device 13. Instead of using table 21 of the data, the mixing ratio can be estimated using a suitable algorithm. Alternatively, the absolute temperature T can be defined as the average temperature T1 and T2.

The mixing ratio defined in this way can be used in various ways. First of all, a signal can be emitted using an optical or acoustic signal unit 22, which is connected to and activated by the evaluation unit 20 when the mixing ratio crosses a predetermined limit. In the case where a minimum content of non-freezing fluid is necessary to prevent freezing of the system, for example, on cold winter days, a signal may be issued when the content of non-freezing fluid becomes less than a predetermined lower limit.

In addition, a determined or estimated mixing ratio can be used in conjunction with the measured absolute temperature T and information about the type and parameters of the considered non-freezing fluid to determine the actual density ρ and specific heat C of the binary fluid 12. In this case, using equation (1) and the result measuring the differential temperature ΔТ (temperature sensors 16 and 18), the actual heat flux dQ / dt can be estimated.

On the one hand, the estimated heat flow dQ / d t can be integrated over time to accurately determine the amount of thermal energy transferred from the fluid circulation system for heating cost accounting. On the other hand, the estimated heat flux dQ / dt can be used to control the fluid circulation system and transfer heat energy through the heat flux control unit 23, which is connected to the evaluation unit 20.

LIST OF REFERENCE POSITIONS

10 - device for measuring heat flux

11 - flow space (e.g. pipe)

12 - fluid (mainly binary)

13 - ultrasonic measuring device

14, 15 - transducer (ultrasonic)

16, 17, 18 - temperature sensor

19 - control unit ultrasound

20 - evaluation unit

21 - data table

22 - signal block

23 - heat flow control unit

24 - flow meter

T , T 1, T 2 - temperature

Δ T - differential temperature

dQ / dt - heat flux

dV / dt - volumetric flow rate

v _f - flow rate

v _s is the speed of sound

Claims (20)

1. A method for determining the heat flux (dQ / dt) emanating from a heat-carrying fluid (12), which is a mixture of at least two different fluids and which flows through the space (11) of the flow from a first position, where it has a first temperature (T1) to the second position, where, due to this heat flux (dQ / dt), it has a second temperature (T2) that is lower than the first temperature (T1), said method comprising the steps of:
a) measuring a differential temperature (ΔT) between said first temperature (T1) and said second temperature (T2);
b) measuring the speed (v _s ) of sound in said heat transfer fluid (12) in a predetermined portion of said flow space (11) in the vicinity of said first and / or second position;
c) measuring the absolute temperature (T) of the heat transfer fluid (12) in said predetermined area;
d) measuring the volumetric flow rate (dV / dt) in said predetermined area;
e) determining, based on said measured absolute temperature (T) and said measured sound speed (v _s ), the mixing ratio of said heat-carrying fluid (12);
f) determining, based on said measured absolute temperature (T) and said determined mixing ratio of said heat transfer fluid (12), the density and specific heat of said heat transfer fluid (12); and
g) determining, based on said measured differential temperature (ΔT), said measured volumetric flow rate (dV / dt), said specific density and said specific specific heat, a heat flux (dQ / dt) emanating from said heat-carrying fluid (12). 2. The method according to p. 1, characterized in that said heat transfer fluid (12) is a binary mixture of two fluids. 3. The method according to p. 2, characterized in that the said heat-carrying fluid (12) is a mixture of water and antifreeze fluid. 4. The method according to p. 3, characterized in that the said heat-carrying fluid (12) is a mixture of water / glycol. 5. The method according to one of paragraphs. 1-4, characterized in that the mixing ratio of said heat-carrying fluid (12) is determined based on said measured absolute temperature (T) and said measured velocity (v _s) of sound using a table (21) data for the ratio between the velocity (v _s ) sound, absolute temperature (T) and mixing ratio of a specific heat-carrying fluid (12). 6. The method according to one of paragraphs. 1-4, characterized in that the mixing ratio of said heat transfer fluid (12) is determined based on said measured absolute temperature (T) and said measured speed (v _s ) of sound using the mathematical relationship between the speed (v _s ) of sound and absolute temperature (T) and the mixing ratio of a specific heat transfer fluid (12). 7. The method according to p. 1, characterized in that the speed (v _s ) of sound in said heat-carrying fluid (12) is measured by an ultrasonic measuring device (13). 8. The method according to claim 7, characterized in that the ultrasonic measuring device (13) comprises a first ultrasonic transducer (14) placed on the first side of said flow space (11) and a second ultrasonic transducer (15) placed on the second side of said the space (11) of the flow in such a way that an ultrasonic signal passing between the first and second ultrasonic transducers (14, 15) crosses the fluid (12) in the said space (11) of the flow. 9. The method according to p. 8, characterized in that the first and second ultrasonic transducers (14, 15) are positioned relative to the fluid flow in said flow space (11) so that the ultrasonic signal passing between the first and second ultrasonic transducers (14 , 15) has a velocity component in the direction of said fluid flow velocity (v _s) of sound is measured in opposite directions between said first and second ultrasonic transducers (14, 15), and the volumetric flow rate (dV / dt) is obtained on the axles Hovhan various measured velocity (v _s) of sound in said opposite directions. 10. The method according to p. 1, characterized in that the said volumetric flow rate (dV / dt) is measured by a separate flow meter (24). 11. The method according to p. 8 or 9, characterized in that the measurement of sound velocity (v _s ) is based on measuring the transit time of an ultrasonic pulse passing between the first and second ultrasonic transducers (14, 15). 12. The method according to p. 11, characterized in that the measurement of the speed (v _s ) of sound is performed in accordance with the method of acoustic feedback. 13. Device (10) for measuring heat flux for implementing the method according to one of claims. 1-12, while the said device (10) for measuring heat flux contains:
a) the first means (16, 18) for measuring the differential temperature (ΔT) between said first temperature (T1) and said second temperature (T2);
b) second means (13, 19) for measuring the speed (v _s ) of sound in said heat-carrying fluid (12) in a given section of said flow space (11) in the vicinity of said first and / or second position;
c) third means (17) for measuring the absolute temperature (T) of the heat-carrying fluid (12) in said predetermined area;
d) fourth means (13, 24) for measuring volumetric flow (dV / dt) in said predetermined area;
wherein said first, second, third and fourth means (13, 16, 17, 18, 19, 24) are connected to the evaluation unit (20)
to determine said heat flux (dQ / dt) based on the data that it receives from said first, second, third and fourth means (13, 16, 17, 18, 19, 24). 14. A device for measuring heat flux according to claim 13, characterized in that said first means for measuring differential temperature (ΔT) comprises a first temperature sensor (16) placed in said first position and a second temperature sensor (18) placed in said second position downstream of said first position. 15. A device for measuring heat flux according to claim 14, characterized in that said second means for measuring sound velocity (v _s ) in said heat-carrying fluid at a predetermined portion of said flow space (11) comprises an ultrasonic measuring device (13), which connected to the ultrasound control unit (19). 16. A device for measuring heat flux according to claim 15, characterized in that said third means for measuring the absolute temperature (T) of the heat-carrying fluid (12) in said predetermined section comprises a third temperature sensor (17) which is placed between the first and second temperature sensors (16, 18) in the direction of flow. 17. A device for measuring heat flux according to claim 15 or 16, characterized in that said fourth means for measuring volumetric flow (dV / dt) in said predetermined section comprises a separate flow meter (24). 18. Device for measuring heat flux according to one of paragraphs. 13-16, characterized in that a data table (21) is provided for the relationship between the speed (v _s ) of sound, the absolute temperature (T) and the mixing ratio of a particular heat-carrying fluid (12), and the evaluation unit (20) has access to the aforementioned data table (21). 19. A device for measuring heat flux according to claim 15, characterized in that said ultrasonic measuring device (13) comprises at least two ultrasonic transducers (14, 15), which are located in such a way that an ultrasonic signal passing between said at least with two ultrasonic transducers (14, 15), crosses said heat-carrying fluid (12). 20. A device for measuring heat flux according to claim 19, characterized in that said at least two ultrasonic transducers (14, 15) are located relative to the flow direction of said heat-carrying fluid (12) so that the measuring path between said at least two ultrasonic transducers (14, 15) crosses the mentioned flow direction at an oblique angle.

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