GB1604332A - Centrifugal ram pump flowmeter - Google Patents

Description

(54) CENTRIFUGAL RAM PUMP FLOWMETER (71)1, WALTER MASNIK, a citizen of the United States of America, of 9, Penbroke Drive, Mendham, New Jersey 07945, United States of America, do hereby declare the invention, for which I pray that a patent be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement:- Mass-rate liquid flow meters of the recirculation type are disclosed in United States Patents 3,232,104; 3,232,105; and 3,662,599. In these patents a gear pump is used to recirculate a constant volume now q. Use of a gear pump is satisfactory for liquid having some lubricating quality, sufficient to keep the gears of the pump from wearing.However, in many applications the liquids being measured have either no lubricity or are chernicaTry 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 corrosive effect are the many acids and bases that are used in the petrochemical industry. If one were to use a steel gear pump for such liquids, corrosion and wear of the gears would result. This would increase the leakage across the gears and hence change the value of q. One could use gears made out of stainless steel.

However, stainless 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 exposed to the liquid flowing through the pump, have previously been considered unsuitable for use in mass-rate flowmeters because the pumping capacity of centrifugal pumps changes considerably with changes in the pressure differential across the pump.

Thus, a centrifugal pump does not have a constant volumetric flow when its pressure rise is varied. Further, centrifugal pump characteristics change with the viscosity of the liquid. Therefore, centrifugal type pumps have not, prior to the present invention, been used for creating the recirculating flow in mass-rate liquid flowmeters such as disclosed in the prior art patents identified above.

According to the present invention there is a mass flowmeter adaPted to measure the mass flow rate of an effective incompressible liquid passing there-throug comprising inlet arid 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 restrictions in said first branch conduit, third and fourth flow restrictors in said second branch conduit, a centrifugal pump adapted to operate in a region of low AP so as to closely approximate the constant flow characteristics of a gear pump, said ram pump connecting said first and second branch conduits at points between the flow restrictors therein and comprising a rotatable impeller for centrifugally pumping said liquid at an approximately constant volumetric flow rate either greater or less than the flow rate in said inlet and outlet conduits, 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 ram pump means for changes in flow due to changes in viscosity of the fluid flowing through the flow meter.

Preferably the pumping means has a characteristic which provides decreasing flow with increasing viscosity in which case the fifth orifice is a rounded edge orifice.

Alternatively, the pumping means may have a characteristic which provides increasing flow with increasing viscosity in which case the fifth orifice is a sharp-edged orifice.

In the accompanying drawings: Fig. 1 is a graph comparing the relationship between flow rate and pressure rise of the centrifugal ram pump, which may be used as part of the pumping means of the present invention, with prior art centrifugal pumps and gear pumps; Fig. 2 is a schematic flow diagram of a centrifugal ram pump mass-rate flowmeter system embodying 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 centrifugal ram pump mass-rate flowmeter system of the present invention wherein the constant 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 centrifugal ram pump employed in the present invention), for liquids having different viscosities; Figure 6 is a graph of the relationship between orifice coefficient C and the Reynolds number for a round edge orifice; Figure 7 is a schematic diagram of the mass-rate flowmeter system of the present invention, showing the location of the ram pump and the fifth restrictor relative to the branch conduits; Figure 8 is a sectional view of the centrifugal ram pump with the ram impeller in the pump housing.

Figure 9 is an elevational view of the impeller shown in Figure 8; Figure 10 is an elevational view of the impeller along the line 10-10 of Figure 9; and Figure 11 is a cross-sectional view, along the line 11-11, of the middle portion of the impeller shown in Figure 9.

It will be seen that a ram pump suitable for use in the flowmeter of the present invention, when operating in the region of low AP as shown in Figure 1, very closely approximates the constant volume flow characteristics of the gear pump. This low AP 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 invention 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 a multiplicity of flow passages 3, respectively connecting the Impeller inlet 4 tp 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 inlet 4 to flow radially outward through 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 Figure 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 rear wall of the cavity.

Thus, although the pump is a centrifugal pump in that centrifugal force causes the outward flow of liquid through passages 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 housing. 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 a ump suitable for use with this invention wil be seen to be substantially the same in constant flow 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 very steep between points A and B of the region in which the ram pump would be operating 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 viscosity of the liquid being pumped. This is also true, to some extent, of the ram pump. This is shown in Figure 5, where the curves 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 åPt 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 coefficient.

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 Figure 6. One can see that the orifice flow coefficient decreases with decreasing Reynolds number. Reynolds number, which relates liquid viscosity to liquid flow, is a dimensionless parameter whose equation is: sVD Reynolds No.

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 thw flow coefficient C.

For compensating the decreasing pump flow with increasing liquid viscosity in accordance with the resent invention a fifth orifice is placed 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 orifice is designed to have a flow coefficient that will increase with increasing viscosity of the liquid.

An increasing flow coefficient means there is less resistance to flow with increasing viscosity. Therefore, by proper matching of the flow coefficient of the fifth orifice with the ram pump characteristic it is possible to maintain a constant recirculating flow through the flowmeter regardless of viscosity variation of the liquid. Figure 4 illustrates a sharp edge orifice flow coefficient that can be used for pump viscosity compensation.

The flow equation for an orifice is

where q=volume flow C=orifice flow coefficient A=orifice area AP=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 AP.

When referring to "sharp edge" or "rounded edge" orifices, 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 increasing viscosity. In the event the pump should have the opposite effect, that is, increasing flow with increasing viscosity, similar compensation techniques can still be used but with the fifth orifice having a rounded edge.

Measurement of the signal indicative of mass flow, in the apparatus of the present invention, is described in the above referred to prior art patents and is illustrated in Figures 2 and 3 hereof.

The flow capacity of the passages 3 can be so proportioned (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 of 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 cavity is initially opened to the pump discharge port.

A related mass flow meter is described and claimed in my Application No. 21371/78 Ser. No. 1604331 out of which the Application was divided.

WHAT I CLAIM IS: 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 inelt and outlet conduits, first and second flow restrictors in said first branch conduit, third and fourth flow restrictors in said second branch conduit, a centrifugal ram pump adapted to operate in a region of low AP so as to closely approximate the constant flow characteristics of a gear pump, said ram pump connecting said first and second branch conduits at points between the flow restrictors therein and comprising a rotatable impeller for centrifugally pumping said liquid at an approximately constant volumetric flow rate either greater or less than the flow rate in said inlet and outlet conduits, 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 ram pump means for changes in flow due to changes in viscosity of the fluid flowing through the flow meter.

2. A mass flow meter according to claim 1 and in which theumping means has a characteristic which provides decreasing flow with increasing viscosity and in which the fifth orifice is a round-edged orifice.

3. A mass flow meter according to claim 1 and in which the pumping means has a characteristic which provides increasing flow with increasing viscosity and in which the fifth orifice is a sharp-edged orifice.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. 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 thw flow coefficient C. For compensating the decreasing pump flow with increasing liquid viscosity in accordance with the resent invention a fifth orifice is placed 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 orifice is designed to have a flow coefficient that will increase with increasing viscosity of the liquid. An increasing flow coefficient means there is less resistance to flow with increasing viscosity. Therefore, by proper matching of the flow coefficient of the fifth orifice with the ram pump characteristic it is possible to maintain a constant recirculating flow through the flowmeter regardless of viscosity variation of the liquid. Figure 4 illustrates a sharp edge orifice flow coefficient that can be used for pump viscosity compensation. The flow equation for an orifice is where q=volume flow C=orifice flow coefficient A=orifice area AP=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 AP. When referring to "sharp edge" or "rounded edge" orifices, 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 increasing viscosity. In the event the pump should have the opposite effect, that is, increasing flow with increasing viscosity, similar compensation techniques can still be used but with the fifth orifice having a rounded edge. Measurement of the signal indicative of mass flow, in the apparatus of the present invention, is described in the above referred to prior art patents and is illustrated in Figures 2 and 3 hereof. The flow capacity of the passages 3 can be so proportioned (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 of 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 cavity is initially opened to the pump discharge port. A related mass flow meter is described and claimed in my Application No. 21371/78 Ser. No. 1604331 out of which the Application was divided. WHAT I CLAIM IS:

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 inelt and outlet conduits, first and second flow restrictors in said first branch conduit, third and fourth flow restrictors in said second branch conduit, a centrifugal ram pump adapted to operate in a region of low AP so as to closely approximate the constant flow characteristics of a gear pump, said ram pump connecting said first and second branch conduits at points between the flow restrictors therein and comprising a rotatable impeller for centrifugally pumping said liquid at an approximately constant volumetric flow rate either greater or less than the flow rate in said inlet and outlet conduits, 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 ram pump means for changes in flow due to changes in viscosity of the fluid flowing through the flow meter.

2. A mass flow meter according to claim 1 and in which theumping means has a characteristic which provides decreasing flow with increasing viscosity and in which the fifth orifice is a round-edged orifice.

3. A mass flow meter according to claim 1 and in which the pumping means has a characteristic which provides increasing flow with increasing viscosity and in which the fifth orifice is a sharp-edged orifice.