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Ind. Eng. Chem. Res. 1998, 37, 636-642
Pressure Losses in Globe and Gate Valves during Two-Phase Oil/ Water Emulsion Flow Ching-Yi J. Hwang and Rajinder Pal* Department of Chemical Engineering, University of Waterloo, Waterloo, Ontario, N2L 3G1 Canada
The loss coefficients for fully-open and half-open globe and gate valves were determined experimentally during turbulent flow of two-phase oil/water mixtures. The oil concentration was varied from 0 to 97.3 vol %. The emulsions were of oil-in-water type up to an oil concentration of 64 vol %. Above 64 vol % oil, the emulsions were water-in-oil type. An in-line conductance cell was used to monitor the inversion point and the type of emulsion. The loss coefficients for the globe and gate valves during turbulent flow of emulsions are found to be comparable to the values reported for single-phase turbulent flow. The concentration and type of emulsions (oil-in-water or water-in-oil) flowing through the valves have negligible effect on the loss coefficients. Introduction In the recent years, several papers have been published on the flow of two-phase gas/liquid mixtures through valves and pipe fittings (Sookprasong et al., 1986; Friedel and Kissner, 1985; Simpson et al., 1985; Norstebo, 1985). However, little or no work has been reported on flow of two-phase liquid/liquid emulsions through valves and pipe fittings. Two-phase oil/water emulsions find application in a number of industries, such as petroleum, pharmaceutical, agriculture, and food industries, etc. (Pal, 1994). In many applications, pumping of emulsions through pipes and pipe fittings is required (Pal, 1993a). The determination of frictional energy loss in pipes, valves, and fittings is essential in order to specify the size of the pump required to pump the emulsions. In this paper, we report new results on frictional pressure loss in emulsion flow through globe valves and gate valves. Emulsions can generally be treated as pseudohomogeneous fluids with averaged properties as the dispersed droplets of emulsions are small and are well dispersed (Pal, 1993b). Consequently, one can apply the singlephase flow equation to correlate the pressure loss data for emulsion flow through globe and gate valves; that is
hf )
∆Pvalve V2 ) Kf F 2
Figure 1. Schematic pressure profile for a valve.
(1)
where hf is the frictional energy loss, ∆Pvalve is the pressure loss in the valve, F is the fluid density, Kf is the loss coefficient, and V is the average velocity in the pipe. If the flow is turbulent, Kf is generally constant independent of the Reynolds number. Figure 1 shows a schematic diagram of the pressure profile for flow through a valve. The frictional loss in the straight pipe section causes the decline in pressure. To eliminate the effect of the skin friction, the pressure loss due to a valve, ∆Pvalve, is determined from the measured pressure profile upstream and downstream * Author to whom all correspondence should be addressed. Telephone: (519)885-1211, ext. 2985. Fax: (519)746-4979. E-mail:
[email protected].
Figure 2. Schematic diagram of the flow loop.
of the valve (in the region of fully developed pipe flow) by extrapolating the pressure profiles as shown in Figure 1. Experimental Work A schematic diagram of the flow loop developed in the present work is shown in Figure 2. The emulsions were prepared in a large tank equipped with a variable speed mixer and a heating/cooling coil. A centrifugal pump
S0888-5885(97)00345-X CCC: $15.00 © 1998 American Chemical Society Published on Web 01/14/1998
Ind. Eng. Chem. Res., Vol. 37, No. 2, 1998 637
Figure 3. Conductance vs oil concentration plot.
enabled the fluid from the tank to be circulated in the flow loop. The temperature throughout the experiments was maintained constant at 25 °C with the help of a temperature controller. The globe and gate valves were installed in horizontal, stainless steel test sections of inside diameter 2.72 cm. The valves were supplied by Kitz Japan. Experiments were conducted with valves positioned at both fully-open
and half-open conditions. Six pressure taps were located at distances of 6, 11, and 25 diameters upstream and downstream from the center of the valve. The pressure differentials were measured with respect to the first pressure tap at a 25-diameter upstream position, using Validyne (variable-reluctance) differential pressure transducers. A Coriolis mass flowmeter (supplied by Micro Motion Inc.) was used to determine the emulsion flow rate in the flow loop. The Coriolis meter was first calibrated with water by diverting the flow into a weighing tank (see Figure 2). The output signals from the pressure transducers and the Coriolis meter were recorded by a microcomputer data-acquisition system. The oil used in the experiments was Bayol-35 supplied by Esso Petroleum Canada. This is a refined white mineral oil with a density of 780 kg/m3 and a viscosity of 2.72 mPa‚s at 25 °C. The emulsions were prepared by shearing the known amounts of oil and water in the mixing tank. Oil concentration in the emulsions was increased from 0 to 97.3 vol %. An in-line conductance cell was used to monitor the type of emulsion (oil-in-water or waterin-oil) flowing through the loop (Pal, 1993a). Figure 3 shows the conductance vs oil concentration data of
Figure 4. Pressure drop profiles for a fully-open globe valve during oil-in-water emulsion flow.
Figure 5. hf vs V2/2 data for oil-in-water emulsions flowing through a fully-open globe valve.
638 Ind. Eng. Chem. Res., Vol. 37, No. 2, 1998 Table 1. Range of Reynolds Number Covered in Emulsion Flow through a Globe Valve Reynolds number range
emulsion type
dispersed-phase concentration (φ)
viscositya (mPa‚s)
fully-open
half-open
O/W O/W O/W O/W O/W W/O W/O W/O W/O
0 0.2144 0.3886 0.5043 0.6035 0.3543 0.3050 0.1958 0.0272
0.90 2.39 5.25 8.87 13.90 6.00 5.37 4.21 2.89
54163-110873 13820-39292 8098-16712 4595-9415 4123-5655 9278-14028 9884-15539 12859-19006 16511-25405
53717-96919 22838-33407 9599-15004 5209-8506 3900-5131 9725-12649 11160-13990 13078-17229 13121-22454
a The viscosity data for the emulsions were taken from the work of Pal (1993a), who measured the viscosity of the same emulsions using pipeline viscometers.
Figure 6. Loss coefficient for a globe valve (fully-open) as a function of oil concentration.
emulsions. The emulsions were oil-in-water (O/W) type up to an oil concentration of 62 vol %. With further increase in oil concentration, an inversion of phases occurred at 64 vol % oil; the conductance of emulsion dropped sharply to almost zero value. Above 64 vol % oil, the emulsions were water-in-oil (W/O) type. The pressure-drop data were collected for oil-in-water type emulsions as well as water-in-oil type emulsions obtained after inversion. Results and Discussion Globe Valve. Fully-Open. For a fully-open globe valve, the experimental pressure drop (∆P) profiles obtained for oil-in-water (O/W) emulsions at different
fluid velocities are presented in Figure 4. The pressure drop (∆P) is measured with respect to the first pressure tap at a 25-diameter upstream position. Each of the graphs shown in Figure 4 differs in the volume fraction of the dispersed phase (oil) in the emulsion, represented by the symbol φ. The pressure profiles are nearly linear up to 6 pipe diameters, both upstream and downstream from the valve. Because there is no change in the pipe cross section and hence no change in mean velocity, the slopes of the pressure profiles before and after the valve are nearly the same. The pressure drop profiles obtained for water-in-oil (W/O) emulsions after an inversion of oil-in-water emulsion were similar to those of the oil-in-water emulsions shown here. Figure 5 shows the frictional energy loss (∆Pvalve/F) versus velocity head (V2/2) data for various differently concentrated oil-in-water emulsions. Clearly, hf vs V2/2 data exhibit a linear relationship. The water-in-oil emulsions (obtained after an inversion of O/W emulsion) exhibited a similar behavior. The loss coefficient for a fully-open globe value (Kf) was determined from the slope of these plots. Note that the flow regime was turbulent (see Table 1); consequently, Kf is independent of the Reynolds number. The Kf values for different emulsions are plotted as a function of oil concentration in Figure 6; clearly, the loss coefficient is independent of the type and concentration of emulsion and has an average value of 8.3. The measured Kf values for emulsions are compared with the literature values. As shown in Figure 6, the experimental values agree quite well with the value
Figure 7. Pressure drop profiles for a half-open globe valve during oil-in-water emulsion flow.
Ind. Eng. Chem. Res., Vol. 37, No. 2, 1998 639
Figure 8. hf vs V2/2 data for oil-in-water emulsions flowing through a half-open globe valve.
Figure 9. Loss coefficient for a globe valve (half-open) as a function of oil concentration.
obtained from the Hydraulic Institute Standards (Hydraulic Institute, 1961) for the valve of the same dimension. Sookprasong et al. (1986) report a value of 7.8 for a 5.08-cm-diameter valve. As a smaller valve of 2.72 diameter was used in this study, the loss coefficient is expected to be larger than the value reported by
Sookprasong et al. (1986). The Kf value obtained from McCabe et al. (1993) is 10 and from Perry et al. (1984) is 6. Half-Open. The half-open position of the valve was determined by placing the stem halfway between fullyopen and fully-closed positions. Figure 7 presents the experimental pressure drop profiles for oil-in-water emulsions at different fluid velocities. The pressure profiles for a half-open valve are nearly linear up to 6 pipe diameters, both upstream and downstream from the valve. The slopes of the pressure profiles before and after the valve are nearly the same, as expected. The water-in-oil emulsions behaved in a manner similar to the oil-in-water emulsions shown in Figure 7. Figure 8 shows the frictional loss (∆Pvalve/F) vs velocity head (V2/2) data for various differently concentrated oilin-water emulsions. Since the flow regime is turbulent (see Table 1), hf vs V2/2 data exhibit a linear relationship. The slope of these plots gives the loss coefficient for a half-open globe valve. The Kf values for different emulsions (O/W and W/O) are plotted as a function of oil concentration in Figure 9; clearly, the loss coefficient is independent of the type
Figure 10. Pressure drop profiles for a fully-open gate valve during oil-in-water emulsion flow.
640 Ind. Eng. Chem. Res., Vol. 37, No. 2, 1998
Figure 11. hf vs V2/2 data for oil-in-water emulsions flowing through a fully-open gate valve. Table 2. Range of Reynolds Number Covered in Emulsion Flow through a Gate Valve Reynolds number range
emulsion type
dispersed-phase concentration (φ)
viscositya (mPa‚s)
fully-open
half-open
O/W O/W O/W O/W O/W W/O W/O W/O W/O
0 0.2144 0.3886 0.5043 0.6035 0.3543 0.3050 0.1958 0.0272
0.90 2.39 5.25 8.87 13.90 6.00 5.37 4.21 2.89
54452-116159 23471-41041 10440-17321 6137-9724 4235-5828 9753-14746 10483-16217 13879-19587 18830-26105
78308-122371 20212-43306 9862-18212 6180-18104 4150-6081 9475-15515 10203-17102 13764-20570 15858-27320
a The viscosity data for the emulsions were taken from the work of Pal (1993a), who measured the viscosity of the same emulsions using pipeline viscometers.
and concentration of emulsion and has an average value of 15.2. Perry et al. (1984) report a Kf value of 9.5 Gate Valve. Fully-Open. The measured pressure profiles for a gate valve during oil-in-water emulsion flow are presented in Figure 10. Each of the graphs shown in Figure 10 differs in the volume fraction of the dispersed phase (φ). The pressure drop profiles for the water-in-oil emulsions were similar to these oil-in-water emulsions. The pressure at 6 pipe diameters upstream and downstream from the center of the valve deviates slightly from the linear pressure profile. Therefore, the pressure losses for a fully-open gate valve were obtained by taking the difference between the linear pressure profiles extrapolated from 25 and 11 diameters to the center of the valve. Figure 11 shows the frictional loss (∆Pvalve/F) vs the velocity head (V2/2) data for various differently concentrated oil-in-water emulsions. Since the flow regime is turbulent (see Table 2), hf vs V2/2 data are expected to exhibit a linear relationship. While the experimental data for a fully-open gate valve can be described by a linear relationship passing through the origin, the data exhibit a large scatter as can be seen from Figure 11. A similar behavior was exhibited by the water-in-oil emulsions obtained after an inversion of the oil-in-water emulsion. The scatter in the data is probably due to the relatively small magnitude of the pressure losses for the gate valve. The precise measurement of small pressure drops is difficult. The plot of the loss coefficient (Kf) as a function of oil concentration is shown in Figure 12. In the low-
Figure 12. Loss coefficient for a gate valve (fully-open) as a function of oil concentration.
concentration range, the loss coefficient tends to increase somewhat with an increase in the oil concentration. However, the loss coefficient is independent of the type of emulsion and oil concentration at oil concentrations above 40% by volume. The experimental values of the loss coefficient are comparable to the value reported by the Hydraulic Institute (1961) for singlephase turbulent flows. The observed scatter of the loss coefficient data for a fully-open gate valve is likely due to errors in the measurement of low-pressure drops. Half-Open. For a half-open gate valve, Figure 13 presents the experimental pressure drop profiles obtained for oil-in-water emulsions at different fluid velocities. The pressure profiles are nearly linear up
Ind. Eng. Chem. Res., Vol. 37, No. 2, 1998 641
Figure 13. Pressure drop profiles for a half-open gate valve during oil-in-water emulsion flow.
Figure 14. hf vs V2/2 data for oil-in-water emulsions flowing through a half-open gate valve.
Figure 15. Loss coefficient for a gate valve (half-open) as a function of oil concentration.
to 6 pipe diameters, both upstream and downstream from the center of the valve.
Figure 14 shows the frictional loss (∆Pvalve/F) vs velocity head (V2/2) data for various differently concen-
642 Ind. Eng. Chem. Res., Vol. 37, No. 2, 1998
trated oil-in-water emulsions. The hf vs V2/2 data exhibit a linear relationship, as expected for turbulent flow. The water-in-oil emulsions behaved in a manner similar to these oil-in-water emulsions. The Kf values for different emulsions are plotted as a function of oil concentration in Figure 15; clearly, the loss coefficient is independent of the type of emulsion and oil concentration and has an average value of 2.8. Perry et al. (1984) give a Kf value of 4.5 for a half-open gate valve whereas McCabe et al. (1993) report a value of 5.6. Conclusions The main conclusions of this study are as follows: Single-phase Newtonian equations can be used to calculate pressure loss during turbulent flow of twophase oil/water mixtures through globe and gate valves. The loss coefficients for the globe and gate valves investigated in the present work are found to be comparable to the values reported in the published literature for single-phase turbulent flow. The loss coefficients are not significantly influenced by the type and concentration of emulsions flowing through the globe and gate valves. Acknowledgment The financial support for this project was provided by the Natural Sciences and Engineering Research Council (NSERC) of Canada. The assistance provided by Mr. Frank Wassmer in constructing the flow loop is greatly appreciated.
Literature Cited Friedel, L.; Kissner, H. M. Pressure loss in safety valves during two-phase gas/vapour-liquid flow. Proceedings of the 2nd International Conference on Multi-phase Flow, London, England; BHRA, The Fluid Engineering Centre: Cranfield, Bedford, England, 1985; pp 39-65. Hydraulic Institute Standards, 3rd ed.; Hydraulic Institute: New York, 1961. McCabe, W. L.; Smith, J. C.; Harriott, P. Unit Operations of Chemical Engineering; McGraw-Hill: New York, 1993. Norstebo, A. Pressure drop in bends and valves in two-phase refrigerant flow. Proceedings of the 2nd International Conference on Multi-phase Flow, London, England; BHRA, The Fluid Engineering Centre: Cranfield, Bedford, England, 1985; pp 8192. Pal, R. Pipeline flow of unstable and surfactant-stabilized emulsions. AIChE J. 1993a, 39 (11), 1754-1764. Pal, R. Flow of oil-in-water emulsions through orifice and venturi meters. Ind. Eng. Chem. Res. 1993b, 32 (6), 1212-1217. Pal, R. Metering of two-phase liquid-liquid emulsions. Ind. Eng. Chem. Res. 1994, 33 (6), 1413-1435. Perry, R. H.; Green, D. W.; Maloney, J. O. Perry’s Chemical Engineers’ Handbook; McGraw-Hill: New York, 1984. Simpson, H. C.; Rooney, D. H.; Callander, T. M. S. Pressure loss through gate valves with liquid-vapour flows. Proceedings of the 2nd International Conference on Multi-phase Flow, London, England; BHRA, The Fluid Engineering Centre: Cranfield, Bedford, England, 1985; pp 67-80. Sookprasong, P.; Brill, J. P.; Schmidt, Z. Two-phase flow in piping components. J. Energy Res. Technol. 1986, 108, 197-201.
Received for review May 14, 1997 Revised manuscript received November 14, 1997 Accepted November 20, 1997 IE970345Z
