CA1097521A - Ram pump flowmeter - Google Patents
Ram pump flowmeterInfo
- Publication number
- CA1097521A CA1097521A CA304,219A CA304219A CA1097521A CA 1097521 A CA1097521 A CA 1097521A CA 304219 A CA304219 A CA 304219A CA 1097521 A CA1097521 A CA 1097521A
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- liquid
- flow rate
- restrictors
- impeller
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Abstract
RAM PUMP FLOWMETER
ABSTRACT
A mass-rate flowmeter of the recirculation type wherein the recirculating flow is created by a ram type cen-trifugal pump having a substantially constant volume flow discharge rate over the operating pressure range of said mass-rate flowmeter.
ABSTRACT
A mass-rate flowmeter of the recirculation type wherein the recirculating flow is created by a ram type cen-trifugal pump having a substantially constant volume flow discharge rate over the operating pressure range of said mass-rate flowmeter.
Description
975Zl BACKGROUND OF THE .INVENTION
Mass-rate liquid flow meters of the recirculation type are disclosed in United States Patents 3~232,104; 3,2327105;
and 3,662,599. In these patents a gear pump is used to recir-culate a constant volume flow q. Use of a gear pump is satis-factory for liquids having some lubricating quality, sufficient to keep the gears of the pump fr~m wearing However, in many applications the liquids being measured ~ave either no lubricity 1~ or are chemically corrosive or both. A typical liquid without lubricity is water. Water has a corrosive effect on plain steel gears. Other liquids that have a much more co~rosive effect are the many acids and bases that are used in the petrochemical in-dustry. If one were to use a steel gear pump for such liquids, corrosion and wear-of the gears would reslllt. This would increas the leakage across the gears and -~hence c~cnge the value of q.
One could use gears made out of stainle~s steel. However, stain less gears present the problem of galling, i.e., the tendency of the gear surfaces to stick or bind when they contact during pump operation. Centrifugal pumps, which have no rubbing surfaces ex-posed to the liquid flowing through the pump, have previously been considered unsuitable for use in mass-rate flowmeters be-cause the pumping capacity of centrifugal pumps changes consid-erably with,changes in the pressure differential across the pump.
Thus, a centrifugal pump does not have a constant volu-metric flow when its pressure rise is varie~. Further, centri-fugal pump characteristics change with the v~scosity of the liquid. Therefore, centrifugal type pumps have not, prlor to the present invention, been used for creating t~e recirculating flow ~0 in mass-rate liquid flowmeters such as discl~sed in the prior art patents identified above.
Mass-rate liquid flow meters of the recirculation type are disclosed in United States Patents 3~232,104; 3,2327105;
and 3,662,599. In these patents a gear pump is used to recir-culate a constant volume flow q. Use of a gear pump is satis-factory for liquids having some lubricating quality, sufficient to keep the gears of the pump fr~m wearing However, in many applications the liquids being measured ~ave either no lubricity 1~ or are chemically corrosive or both. A typical liquid without lubricity is water. Water has a corrosive effect on plain steel gears. Other liquids that have a much more co~rosive effect are the many acids and bases that are used in the petrochemical in-dustry. If one were to use a steel gear pump for such liquids, corrosion and wear-of the gears would reslllt. This would increas the leakage across the gears and -~hence c~cnge the value of q.
One could use gears made out of stainle~s steel. However, stain less gears present the problem of galling, i.e., the tendency of the gear surfaces to stick or bind when they contact during pump operation. Centrifugal pumps, which have no rubbing surfaces ex-posed to the liquid flowing through the pump, have previously been considered unsuitable for use in mass-rate flowmeters be-cause the pumping capacity of centrifugal pumps changes consid-erably with,changes in the pressure differential across the pump.
Thus, a centrifugal pump does not have a constant volu-metric flow when its pressure rise is varie~. Further, centri-fugal pump characteristics change with the v~scosity of the liquid. Therefore, centrifugal type pumps have not, prlor to the present invention, been used for creating t~e recirculating flow ~0 in mass-rate liquid flowmeters such as discl~sed in the prior art patents identified above.
-2-10975Zl UMMARY OF THE INVENTION
According to the present invention, a new mass-rate flowmeter is provided which obviates the above mentioned problem encountered with a gear pump and which enables the advantages of a centrifugal type pump to be obtained. The centrifugal pump, as pointed out above, can be made of materials that will with- li stand corrosion, including corrosion by chemicals such as acids, bases and other corrosive liquids. Because centrifugal pumps }
lQ have rotating impellers with no rubbing parts as in the gear pump, there is no concern for wear.
The present invention also involves the provision of a new centrifugal pump, herein referred to as a "ram" pump-.''This new pump is characterize,d by the ability to operate, in the low-er aP range (the lower range of pressure differentials between the pump inlet and the pump outlet), with pumping characteristics that are substantially the same as those of the previously used gear pumps. ' There is another problem associated with the use of a 2~ centrifugal pump in mass-rate flowmeters as disclosed in the a-bove identified prior art patents. With centrifugal pumps, ther~
, are variations in output flow rate with changes in viscosity of the liquid being pumped. According to the present invention, this problem also can be solved. For example, a fifth restricto~
may be provided at the outlet of the ram pump, having flow char-acteristics which compensate for the pump output variations re-, sulting from viscosity changes. An alternate method is by de-signing the four restrictors in the branch conduits to provide such compensation.
30, ~` 10~75Zl In acco~dance with a broad aspect, the inYentiOn relates to a mass flowmeter adapted to ~eas:ure the mass flow rate of an effectively incompres:sible l;quid passing there-through comprising inlet and outlet conduits having a flow which is to be measured, first and second branch conduits connecting said inlet and outlet conduits, first and second flow restrictors in said first branch conduit, third and fourth flow restrictors in said second branch conduit, pumping means connecting said first and second branch conduits at points between the flow restrictors therein, said pumping means comprising a rotatable impeller for centrifugally pumping said liquid at a volumetric flow rate greater than the flow rate in said inlet and outlet conduits, said first and second restrictors having the same flow characteristics, said third and fourth flow restrictors having the same flow characteristics, the impeller of said pumping means producing an undesirable variation in volumetric flow rate with changes in liquid viscosity, and means for compensating for said undesirable variation comprising at least two of said restrictors dimensioned to have the same flow coefficient but whose flow coefficient changes with viscosity in the direction to compensate for said variation in volumetric flow rate produced by the impeller of said pumping means due to changes in said viscosity.
In accordance with another broad aspect, the invention relates to in a mass-rate liquid flowmeter of the recirculation type, the improvement which comprises a centrifugal pump for producing the recirculating liquid flow having a rotatable impeller ~ith at least one radially - 3a -~ ~097521 extending passage c~nnecting a pu~p inlet positioned adjacent the axis o~ rotation of the impellex with at least one chamber positioned adjacent the periphery of said impeller, said radially extending passage and said cham~er coacting upon rotation of said impeller to produce a pressure rise in the recirculati-ng liquid which is so high in relation to the rate of flow of the recirculating liquid over a selected range of operat;ng pressures that the volumetric flow rate of said recirculating liquid is substantially constant.
In accordance with a further broad aspect, the invention relates to apparatus for producing a signal which is a linear function of a mass-rate liquid flow to be measured, comprising, a pump having a substantially constant volumetric flow output over the pressure rise range at which the pump is to be operated, said pump comprising a rotatable impeller provided with radial flow passages ex-tending from an inlet adjacent the axis of rotation of said impeller respectively to a plurality of cavities spaced around the periphery of said impeller, and a casing surrounding said impeller provided with at least one outlet port for receiving liquid discharged under pressure from said cavities, means for adding and subtracting the liquid flow produced by said pump to and from the flow of the liquid to be measured, creating pressure differentials in said added flows and in said subtracted flows, and producing a signal from said pressure differentials which is a linear function of the mass-flow rate of the liquid to be measured.
-- 3b -10"75;~1 ~
BRIEF D~SCRIPTION OF THE DRAWINGS
- Figure 1 is a graph showing the relationship between flow rate and pressure rise of the ram pump of the present inven- ;
tion as compared to the prior art centrifugal pumps and gear pumps.
Figure 2 is a schematic flow diagram of the ram pump ', mass-rate flowmeter system of the present invention, wherein the constant volumetric recirculating flow q is less than the input volumetric flow Q.
Figure 3 is a schematic diagram of the ram pump mass-rate flowmeter system of the present invention wherein the con-stant volumetric recirculating flow q is greater than the input volumetric flow Q.
- Figure 4 is a graph of the relationship between orifice coefficient C for a sharp edge orifice and the Reynolds number.
Figure 5 is a graph of the relationship between the pressure rise aP and the flow rates q, for a centrifugal pump (including-the ram pump of the present invention), for liquids having different viscosities.
Figure 6 is a graph of the relationship be-tween orifice coefficient C and the Reynolds number for a round edge orifice.
Figure 7 is a schematic diagram of the ram pump mass-rate flowmeter system of the present invention, showing the lo-cation of the ram pump and the fifth restrictor relative to the branch conduits.
Figure 8 is a sectional view of the new ram pump of the present invention with the ram impeller in the pump housing.
_4~
. . " -.
1(~t9752~
Figure 9 is an elevational View of the impeller shown in Figure ~.
Figure 10 is an elevational view of the impeller along the line 10-10 of Figure 9.
Figure 11 is a cross-sectional view~ along the line 11-11, of the middle portion of the impeller shown in Figure 9.
According to the present invention, a new mass-rate flowmeter is provided which obviates the above mentioned problem encountered with a gear pump and which enables the advantages of a centrifugal type pump to be obtained. The centrifugal pump, as pointed out above, can be made of materials that will with- li stand corrosion, including corrosion by chemicals such as acids, bases and other corrosive liquids. Because centrifugal pumps }
lQ have rotating impellers with no rubbing parts as in the gear pump, there is no concern for wear.
The present invention also involves the provision of a new centrifugal pump, herein referred to as a "ram" pump-.''This new pump is characterize,d by the ability to operate, in the low-er aP range (the lower range of pressure differentials between the pump inlet and the pump outlet), with pumping characteristics that are substantially the same as those of the previously used gear pumps. ' There is another problem associated with the use of a 2~ centrifugal pump in mass-rate flowmeters as disclosed in the a-bove identified prior art patents. With centrifugal pumps, ther~
, are variations in output flow rate with changes in viscosity of the liquid being pumped. According to the present invention, this problem also can be solved. For example, a fifth restricto~
may be provided at the outlet of the ram pump, having flow char-acteristics which compensate for the pump output variations re-, sulting from viscosity changes. An alternate method is by de-signing the four restrictors in the branch conduits to provide such compensation.
30, ~` 10~75Zl In acco~dance with a broad aspect, the inYentiOn relates to a mass flowmeter adapted to ~eas:ure the mass flow rate of an effectively incompres:sible l;quid passing there-through comprising inlet and outlet conduits having a flow which is to be measured, first and second branch conduits connecting said inlet and outlet conduits, first and second flow restrictors in said first branch conduit, third and fourth flow restrictors in said second branch conduit, pumping means connecting said first and second branch conduits at points between the flow restrictors therein, said pumping means comprising a rotatable impeller for centrifugally pumping said liquid at a volumetric flow rate greater than the flow rate in said inlet and outlet conduits, said first and second restrictors having the same flow characteristics, said third and fourth flow restrictors having the same flow characteristics, the impeller of said pumping means producing an undesirable variation in volumetric flow rate with changes in liquid viscosity, and means for compensating for said undesirable variation comprising at least two of said restrictors dimensioned to have the same flow coefficient but whose flow coefficient changes with viscosity in the direction to compensate for said variation in volumetric flow rate produced by the impeller of said pumping means due to changes in said viscosity.
In accordance with another broad aspect, the invention relates to in a mass-rate liquid flowmeter of the recirculation type, the improvement which comprises a centrifugal pump for producing the recirculating liquid flow having a rotatable impeller ~ith at least one radially - 3a -~ ~097521 extending passage c~nnecting a pu~p inlet positioned adjacent the axis o~ rotation of the impellex with at least one chamber positioned adjacent the periphery of said impeller, said radially extending passage and said cham~er coacting upon rotation of said impeller to produce a pressure rise in the recirculati-ng liquid which is so high in relation to the rate of flow of the recirculating liquid over a selected range of operat;ng pressures that the volumetric flow rate of said recirculating liquid is substantially constant.
In accordance with a further broad aspect, the invention relates to apparatus for producing a signal which is a linear function of a mass-rate liquid flow to be measured, comprising, a pump having a substantially constant volumetric flow output over the pressure rise range at which the pump is to be operated, said pump comprising a rotatable impeller provided with radial flow passages ex-tending from an inlet adjacent the axis of rotation of said impeller respectively to a plurality of cavities spaced around the periphery of said impeller, and a casing surrounding said impeller provided with at least one outlet port for receiving liquid discharged under pressure from said cavities, means for adding and subtracting the liquid flow produced by said pump to and from the flow of the liquid to be measured, creating pressure differentials in said added flows and in said subtracted flows, and producing a signal from said pressure differentials which is a linear function of the mass-flow rate of the liquid to be measured.
-- 3b -10"75;~1 ~
BRIEF D~SCRIPTION OF THE DRAWINGS
- Figure 1 is a graph showing the relationship between flow rate and pressure rise of the ram pump of the present inven- ;
tion as compared to the prior art centrifugal pumps and gear pumps.
Figure 2 is a schematic flow diagram of the ram pump ', mass-rate flowmeter system of the present invention, wherein the constant volumetric recirculating flow q is less than the input volumetric flow Q.
Figure 3 is a schematic diagram of the ram pump mass-rate flowmeter system of the present invention wherein the con-stant volumetric recirculating flow q is greater than the input volumetric flow Q.
- Figure 4 is a graph of the relationship between orifice coefficient C for a sharp edge orifice and the Reynolds number.
Figure 5 is a graph of the relationship between the pressure rise aP and the flow rates q, for a centrifugal pump (including-the ram pump of the present invention), for liquids having different viscosities.
Figure 6 is a graph of the relationship be-tween orifice coefficient C and the Reynolds number for a round edge orifice.
Figure 7 is a schematic diagram of the ram pump mass-rate flowmeter system of the present invention, showing the lo-cation of the ram pump and the fifth restrictor relative to the branch conduits.
Figure 8 is a sectional view of the new ram pump of the present invention with the ram impeller in the pump housing.
_4~
. . " -.
1(~t9752~
Figure 9 is an elevational View of the impeller shown in Figure ~.
Figure 10 is an elevational view of the impeller along the line 10-10 of Figure 9.
Figure 11 is a cross-sectional view~ along the line 11-11, of the middle portion of the impeller shown in Figure 9.
3 10975Zl DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
Consider the flow equation of a Flo-Tron meter, such as disclosed in United States Patents 3,232,104, 3,232,105; and 3,662,599, and for the case shown in Figure 3:
~ Pl-4 c2 A2 Equation (1) where ~ is normally a constant and;
I0 ~ Pl 4 = differential pressure output signal q = volumetric recirculating flow W = measured mass flow passing through the meter c2 = orifice coefficient of meter A = area of orifice k = constant From this equation it can be seen that if recirculating flow q were to vary then ~Pl 4 would vary not only with mass flow rate W, but also with recirculating flow q.
A centrifugal pump does not have a constant volumetric flow when its pressure rise is varied. Figure 1 shows the varia-tion of flow rate q versus pressure rise a P for a gear pump, a conventional centrifugal pump and the novel centrifugal pump of the present invention, herein referred to as a ram pump. The gear pump is a positive displacement pump and, therefore, meets the requirements of delivering a constant volume flow, regardless of pressure rise. On the other hand, a conventional centrifugal pump has a changing (decreasing) flow with increasing pressure rise across the pump.
3o ~3"752~
It will be seen that the ram pump of the present inven-tion~ when operating in the region of low ~P aS ~shown in Figure 1 very closely approximates the constant volume flow characteristic of the gear pumpl This low a P region is the selected region in which the ram pump operates in the mass-rate flowmeter of the present inVention, The construction of the ram pump of the present inven-tion is shown in Figures 8, 9, 10 and 11. It comprises a housing 1 enclosing the impeller 2. The impeller is a solid disc having 1~ a multiplicity of flow passages 3 ? respectively connecting the impe]ler inlet 4 to a multiplicity of cavities 6 spaced around the periphery 5 of the impeller.
.~ . . When the impeller rotates a pressure determined by the . centrifugal force on the liquid in passages 3 is generated in transversely extending discharge cavities 6, formed by scalloped portions in the periphery of the impeller. The impeller has a close fit between its periphery 5 and the housing 6 to prevent leakage and dissipation of the pressure of trapped liquid in the cavities 6.
. Rotation of the impeller causes liquid entering the in-let 4 to flow radially outward thrQugh the passages 3 and into the transversely or tangentially extending cavities 6~ These cavities are thus filled, as the impeller rotates? and when each cavity, in turn, arriVes at the rotational position wherein it-connects with the outlet 7, as shown in ~igure 8, the liquid in that cavity is positively displaced through the pump outlet port 7 by the piston-like effect of the impeller face 8 forming the 3P rear wall the ca-ity.
lOg75Zl Thus, although the pump is a centrifugal pump in that centrifugal force causes the outward flow of liquid through pass-ages 3, and thereby pressurizes the liquid in the cavities 6, it additionally creates a "ram" pressure by the piston-like effect created by the movement of cavity 6, and its rear wall 8, past the discharge port 7 of the pump h~using, The resultant pressure head in the outlet 7 is herein referred to as the ram pressure.
Referring to Figure 1~ the ram pressure created by the novel pump of this invention will be seen to be substantially the 1 same in constant Ilow characteristics as that of the conventional gear pump in the lower range of pressure rise across the pump.
Because the ram pump Pressure rise curve is yery steep between points A and B of the region in which the ram pump would be oper-ating in the mass~rate flowmeter of the present invention~ it .
can successfully be utilized in the mass-rate flowmeter of the present invention.
Centrifugal pump characteristics change with the visco-sity of the liquid being pumped. This is also true, to some ex-2 ¦ tent, of the ram pump. This is shown in Figure 5, where thecurves A, B, C are for liquids of different viscosities with C
being the highest viscosity liquid. As shown on the curves, for a constant pressure rise ~ Pl different q's result with different viscosities - that is, the recirculating flow q decreases with increasing viscosity. This decrease in q, however, can be offset by having orifices in the meter bridge with a decreasing coeffi-cient.
Referring to Equation 1, if q and c2 both change in the same proportion then their ratio q/C2 remains a constant. Round edge orifices have such a characteristic as shown in ~igure 6.
One can see that the orifice fIow coefficient decreases with de-creasing Reynolds number. Reynolds number, which relates liquid viscosity to liquid flow, is a dimensionless parameter whose e-: quation is:
Reynolds No. = sVD
u where s = liquid density V = liquid velocity D = diameter of flow opening u = viscosity Thus, for increasing viscosity the Reynolds number decreases and, ~as shown in Figure 6, this increasing viscosity brings about a : decrease in the flow coefficient C. Therefore, by suitably matc~ _ : . ing the rounded orifice coefficients with the pump characteris-tics, a mass flow meter can be provided capable of operating over .
a very wide viscosity range with the output signal linear and proportional to mass flow.
Another approach for compensating the decreasing pump flow with increasing liquid viscosity is to place a fifth orifice in the flow line connecting the discharge port of the pump to a branch conduit at a point intermediate the restrictors in the branch conduit, as shown in Figures 2, 3 and 7. The fifth ori-fice is designed to have a flow coefficient that will increase with increasing viscosity of the liquid.
An increasing flow coefficient means there is less re-sistance to flow with increasing viscosity. Therefore, by pro-per matching of the flow coefficient of the fifth orifice with the ram pump characteristic it is possible to maintain a constant .
recirculatine flow through t~e flowmeter reg~rdless of viscosity ~ 752:~
variation of the liquid. Figure 4 illustrates a sharp edge ori-fice flow coefficient that can be used for pump viscosity com-pensation.
The flow equation for an orifice is q = CQ
where q = volume flow C = orifice flow coefficient A = orifice area ~0 ~P = pressure drop across the orifice s = liquid density From this equation one can readily see that raising or lowering the value of C will raise or lower the value of q for a given ~P.
When referring to "sharp edge" or "rounded edge" ori-fices, the edges referred to are those on the side of the orifice from where the liquid flows into the orifice.
The viscosity compensation techniques just described are for the case of the pump having decreasing flow with increas-ing viscosity. In the event the pump should have the opposite effect, that is, increasing flow with increasing viscosity, simi-lar compensation techniques can still be used but with the use of sharp edge and round edge orifices reversed. In other words, in the case of the fifth orifice the orifice would be a rounded edge orifice and in the case where the bridge orifices are used for compensation they would be sharp edged orifices.
It is also possible to use a combination Or both tech-niques for v~scosity compensation of the pump. That is, a fifth 3o orifice, as well as compensation type bridge orifices.
1(~1475Zl Further, in the case of the bridge orifices either a pair of the or~fices could be used having the identical correct compensating flow coefficient~ or all four orifices may have i-: dentical flow coefficients for compensation.
Measurement of the signal indicative of mass flow~ inthe apparatus of the present invention, is described in the a-bove referred to prior art patents and is illustrated in Figures 2 and 3 hereof.
The flow capacity of the passages 3 can be so proportion ~ 10 ed (in cross-sectional area) relative to the volume of cavities .
; 6 that a particular cavity will fill completely with liquid pumped thereunto by the passage 3 during rotation Or the impeller . from the position wherein the rear wall 8 of a particular cavity has just passed the pump discharge port to the position wherein the cavlty is initially opened to the pump discharge port.
Consider the flow equation of a Flo-Tron meter, such as disclosed in United States Patents 3,232,104, 3,232,105; and 3,662,599, and for the case shown in Figure 3:
~ Pl-4 c2 A2 Equation (1) where ~ is normally a constant and;
I0 ~ Pl 4 = differential pressure output signal q = volumetric recirculating flow W = measured mass flow passing through the meter c2 = orifice coefficient of meter A = area of orifice k = constant From this equation it can be seen that if recirculating flow q were to vary then ~Pl 4 would vary not only with mass flow rate W, but also with recirculating flow q.
A centrifugal pump does not have a constant volumetric flow when its pressure rise is varied. Figure 1 shows the varia-tion of flow rate q versus pressure rise a P for a gear pump, a conventional centrifugal pump and the novel centrifugal pump of the present invention, herein referred to as a ram pump. The gear pump is a positive displacement pump and, therefore, meets the requirements of delivering a constant volume flow, regardless of pressure rise. On the other hand, a conventional centrifugal pump has a changing (decreasing) flow with increasing pressure rise across the pump.
3o ~3"752~
It will be seen that the ram pump of the present inven-tion~ when operating in the region of low ~P aS ~shown in Figure 1 very closely approximates the constant volume flow characteristic of the gear pumpl This low a P region is the selected region in which the ram pump operates in the mass-rate flowmeter of the present inVention, The construction of the ram pump of the present inven-tion is shown in Figures 8, 9, 10 and 11. It comprises a housing 1 enclosing the impeller 2. The impeller is a solid disc having 1~ a multiplicity of flow passages 3 ? respectively connecting the impe]ler inlet 4 to a multiplicity of cavities 6 spaced around the periphery 5 of the impeller.
.~ . . When the impeller rotates a pressure determined by the . centrifugal force on the liquid in passages 3 is generated in transversely extending discharge cavities 6, formed by scalloped portions in the periphery of the impeller. The impeller has a close fit between its periphery 5 and the housing 6 to prevent leakage and dissipation of the pressure of trapped liquid in the cavities 6.
. Rotation of the impeller causes liquid entering the in-let 4 to flow radially outward thrQugh the passages 3 and into the transversely or tangentially extending cavities 6~ These cavities are thus filled, as the impeller rotates? and when each cavity, in turn, arriVes at the rotational position wherein it-connects with the outlet 7, as shown in ~igure 8, the liquid in that cavity is positively displaced through the pump outlet port 7 by the piston-like effect of the impeller face 8 forming the 3P rear wall the ca-ity.
lOg75Zl Thus, although the pump is a centrifugal pump in that centrifugal force causes the outward flow of liquid through pass-ages 3, and thereby pressurizes the liquid in the cavities 6, it additionally creates a "ram" pressure by the piston-like effect created by the movement of cavity 6, and its rear wall 8, past the discharge port 7 of the pump h~using, The resultant pressure head in the outlet 7 is herein referred to as the ram pressure.
Referring to Figure 1~ the ram pressure created by the novel pump of this invention will be seen to be substantially the 1 same in constant Ilow characteristics as that of the conventional gear pump in the lower range of pressure rise across the pump.
Because the ram pump Pressure rise curve is yery steep between points A and B of the region in which the ram pump would be oper-ating in the mass~rate flowmeter of the present invention~ it .
can successfully be utilized in the mass-rate flowmeter of the present invention.
Centrifugal pump characteristics change with the visco-sity of the liquid being pumped. This is also true, to some ex-2 ¦ tent, of the ram pump. This is shown in Figure 5, where thecurves A, B, C are for liquids of different viscosities with C
being the highest viscosity liquid. As shown on the curves, for a constant pressure rise ~ Pl different q's result with different viscosities - that is, the recirculating flow q decreases with increasing viscosity. This decrease in q, however, can be offset by having orifices in the meter bridge with a decreasing coeffi-cient.
Referring to Equation 1, if q and c2 both change in the same proportion then their ratio q/C2 remains a constant. Round edge orifices have such a characteristic as shown in ~igure 6.
One can see that the orifice fIow coefficient decreases with de-creasing Reynolds number. Reynolds number, which relates liquid viscosity to liquid flow, is a dimensionless parameter whose e-: quation is:
Reynolds No. = sVD
u where s = liquid density V = liquid velocity D = diameter of flow opening u = viscosity Thus, for increasing viscosity the Reynolds number decreases and, ~as shown in Figure 6, this increasing viscosity brings about a : decrease in the flow coefficient C. Therefore, by suitably matc~ _ : . ing the rounded orifice coefficients with the pump characteris-tics, a mass flow meter can be provided capable of operating over .
a very wide viscosity range with the output signal linear and proportional to mass flow.
Another approach for compensating the decreasing pump flow with increasing liquid viscosity is to place a fifth orifice in the flow line connecting the discharge port of the pump to a branch conduit at a point intermediate the restrictors in the branch conduit, as shown in Figures 2, 3 and 7. The fifth ori-fice is designed to have a flow coefficient that will increase with increasing viscosity of the liquid.
An increasing flow coefficient means there is less re-sistance to flow with increasing viscosity. Therefore, by pro-per matching of the flow coefficient of the fifth orifice with the ram pump characteristic it is possible to maintain a constant .
recirculatine flow through t~e flowmeter reg~rdless of viscosity ~ 752:~
variation of the liquid. Figure 4 illustrates a sharp edge ori-fice flow coefficient that can be used for pump viscosity com-pensation.
The flow equation for an orifice is q = CQ
where q = volume flow C = orifice flow coefficient A = orifice area ~0 ~P = pressure drop across the orifice s = liquid density From this equation one can readily see that raising or lowering the value of C will raise or lower the value of q for a given ~P.
When referring to "sharp edge" or "rounded edge" ori-fices, the edges referred to are those on the side of the orifice from where the liquid flows into the orifice.
The viscosity compensation techniques just described are for the case of the pump having decreasing flow with increas-ing viscosity. In the event the pump should have the opposite effect, that is, increasing flow with increasing viscosity, simi-lar compensation techniques can still be used but with the use of sharp edge and round edge orifices reversed. In other words, in the case of the fifth orifice the orifice would be a rounded edge orifice and in the case where the bridge orifices are used for compensation they would be sharp edged orifices.
It is also possible to use a combination Or both tech-niques for v~scosity compensation of the pump. That is, a fifth 3o orifice, as well as compensation type bridge orifices.
1(~1475Zl Further, in the case of the bridge orifices either a pair of the or~fices could be used having the identical correct compensating flow coefficient~ or all four orifices may have i-: dentical flow coefficients for compensation.
Measurement of the signal indicative of mass flow~ inthe apparatus of the present invention, is described in the a-bove referred to prior art patents and is illustrated in Figures 2 and 3 hereof.
The flow capacity of the passages 3 can be so proportion ~ 10 ed (in cross-sectional area) relative to the volume of cavities .
; 6 that a particular cavity will fill completely with liquid pumped thereunto by the passage 3 during rotation Or the impeller . from the position wherein the rear wall 8 of a particular cavity has just passed the pump discharge port to the position wherein the cavlty is initially opened to the pump discharge port.
Claims (6)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A mass flowmeter adapted to measure the mass flow rate of an effectively incompressible liquid passing there-through comprising inlet and outlet conduits having a flow which is to be measured, first and second branch conduits connecting said inlet and outlet conduits, first and second flow restrictors in said first branch conduit, third and fourth flow restrictors in said second branch conduit, pumping means connecting said first and second branch conduits at points between the flow restrictors therein, said pumping means comprising a rotatable impeller for centrifugally pumping said liquid at a volumetric flow rate greater than the flow rate in said inlet and outlet conduits, said first and second restrictors having the same flow characteristics, said third and fourth flow restrictors having the same flow characteristics, the impeller of said pumping means producing an undesirable variation in volumetric flow rate with changes in liquid viscosity, and means for compensating for said undesirable variation comprising at least two of said restrictors dimensioned to have the same flow coefficient but whose flow coefficient changes with viscosity in the direction to compensate for said variation in volumetric flow rate produced by the impeller of said pumping means due to changes in said viscosity.
2. A mass flowmeter adapted to measure the mass flow rate of an effectively incompressible liquid passing therethrough comprising inlet and outlet conduits having a flow which is to be measured, first and second branch conduits connecting said inlet and outlet conduits, first and second flow restrictors in said first branch conduit, third and fourth flow restrictors in said second branch conduit, pumping means connecting said first and second branch conduits at points between the flow restrictors therein, said pumping means comprising a rotatable impeller for centrifugally pumping said liquid at a volumetric flow rate less than the flow rate in said inlet and outlet conduits, said first and fourth restrictors having the same flow characteristics, said second and third flow restrictors having the same flow characteristics, the impeller of said pumping means producing an undesirable variation in volumetric flow rate with changes in liquid viscosity, and means for compensating for said undesirable variation comprising at least two of said restrictors dimensioned to have the same flow coefficient but whose flow coefficient changes with viscosity in the direction to compensate for said variation in volumetric flow rate produced by the impeller of said pumping means due to changes in said viscosity.
3. A mass flowmeter adapted to measure the mass flow rate of an effectively incompressible liquid passing therethrough comprising inlet and outlet conduits having a flow which is to be measured, first and second branch conduits connecting said inlet and outlet conduits, first and second flow restrictors in said first branch conduit, third and fourth flow restrictors in said second branch conduit, a constant volumetric pumping means for pumping a given constant volumetric flow rate independently of changes in density of said liquid connecting said first and second branch conduits at points between the flow restrictors therein, said pumping means comprising rotatable impeller for centrifugally pumping liquid at a constant volumetric flow rate greater than the flow rate in said inlet and outlet conduits, said pumping means connecting said branch conduits at points between the flow restrictors therein; and a fifth orifice in the connection between one of said branch lines and the discharge outlet of said pumping means for compensating the volumetric flow rate of said centrifugal pump means for changes in flow due to changes in viscosity of the fluid flowing through the flowmeter.
4. A mass flowmeter adapted to measure the mass flow rate of an effectively incompressible liquid passing therethrough comprising inlet and outlet conduits having a flow which is to be measured, first and second branch conduits connecting said inlet and outlet conduits, first and second flow restrictors in said first branch conduit, third and fourth flow restrictors in said second branch conduit, a constant volumetric pumping means for pumping a given constant volumetric flow rate independently of changes in density of said liquid connecting said first and second branch conduits at points between the flow restrictors therein, said pumping means comprising a rotatable impeller for centrifugally pumping said liquid at a constant volumetric flow rate less than the flow rate in said inlet and outlet conduits, said pumping means connecting said branch conduits at points between the flow restrictors therein; and a fifth orifice in the connection between one of said branch lines and the discharge outlet of said pumping means for compensating the volumetric flow rate of said centrifugal pump means for changes in flow due to changes in viscosity of the fluid flowing through the flowmeter.
5. In a mass-rate liquid flowmeter of the recirculation type, the improvement which comprises a centrifugal pump for producing the recirculating liquid flow having a rotatable impeller with at least one radially extending passage connecting a pump inlet positioned adjacent the axis of rotation of the impeller with at least one chamber positioned adjacent the periphery of said impeller, said radially extending passage and said chamber coacting upon rotation of said impeller to produce a pressure rise in the recirculating liquid which is so high in relation to the rate of flow of the recirculating liquid over a selected range of operating pressures that the volumetric flow rate of said recirculating liquid is substantially constant.
6. Apparatus for producing a signal which is a linear function of a mass-rate liquid flow to be measured, comprising, a pump having a substantially constant volumetric flow output over the pressure rise range at which the pump is to be operated, said pump comprising a rotatable impeller provided with radial flow passages extending from an inlet adjacent the axis of rotation of said impeller respectively to a plurality of cavities spaced around the periphery of said impeller, and a casing surrounding said impeller provided with at least one outlet port for receiving liquid discharged under pressure from said cavities, means for adding and subtracting the liquid flow produced by said pump to and from the flow of the liquid to be measured, creating pressure differentials in said added flows and in said subtracted flows, and producing a signal from said pressure differentials which is a linear function of the mass-flow rate of the liquid to be measured.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA304,219A CA1097521A (en) | 1978-05-26 | 1978-05-26 | Ram pump flowmeter |
| CA367,279A CA1114646A (en) | 1978-05-26 | 1980-12-19 | Ram pump flowmeter |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA304,219A CA1097521A (en) | 1978-05-26 | 1978-05-26 | Ram pump flowmeter |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1097521A true CA1097521A (en) | 1981-03-17 |
Family
ID=4111559
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA304,219A Expired CA1097521A (en) | 1978-05-26 | 1978-05-26 | Ram pump flowmeter |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1097521A (en) |
-
1978
- 1978-05-26 CA CA304,219A patent/CA1097521A/en not_active Expired
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |