1、NASA TECHNICAL NOTE NONCAVITATING AND CAVITATING PERFORMANCE OF TWO LOW-AREA-RATIO WATER JET PUMPS WITH THROAT LENGTHS OF 5.66 DIAMETERS by Nelson L, Sanger Lewis Reseurch Center CleveZund, Ohio NATIONAL AERONAUTICS AND SPACE ADMINISTRATION WASHINGTON, D. C. AUGUST 1968 I3 Provided by IHSNot for Res
2、aleNo reproduction or networking permitted without license from IHS-,-,-NONCAVITATING AND CAVITATING PERFORMANCE OF TWO LOW-AREA-RATIO WATER JET PUMPS WITH THROAT LENGTHS OF 5.66 DIAMETERS By Nelson L. Sanger Lewis Research Center Cleveland, Ohio NATIONAL AERONAUTICS AND SPACE ADMINISTRATION For sal
3、e by the Clearinghouse for Federal Scientific and Technical Information Springfield, Virginia 22151 - CFSTI price $3.00 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-ABSTRACT Performance of two jet pumps was determined over a range of spacings of t
4、he nozzle exit from the throat entrance of 0 to 2.9 throat diameters. Maximum measured efficien cies of 31.3 and 37.6 percent were achieved for nozzle- to throat-area ratios of 0.066 and 0.197, respectively. These efficiencies were improvements over those obtained for previously investigated jet pum
5、ps with throat lengths of 7.25 diameters. A simple one-dimensional analysis predicted noncavitating performance within 2 percent at the best-efficiency conditions. The point of total headrise deterioration due to cavitation was predicted with reasonable accuracy by each of two related parameters. ii
6、 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-CONTENTS Page SUMMARY 1 INTRODUCTION . 2 PERFORMANCE ANALYSES 3 Principle of Operation 3 Analyses 4 Assumptions 4 Basic parameters . 4 Noncavitation analysis . 5 Cavitation analysis . 5 APPARATUS AND P
7、ROCEDURE Test Pump . Apparatus . Test facility . Instrumentation . Experimental Procedure . Testing method . Cavitation criteria . Air content Incipience . 6 6 a a a 9 9 10 11 11 RESULTS AND DISCUSSION . 11 Noncavitation Performance 11 Overall performance 11 Efficiency and headrise . 12 Best-efficie
8、ncy nozzle position . 13 Comparison of theory to experiment . 14 Mixing characteristics . 15 Effect of flow ratio 15 Effect of nozzle spacing . 17 Effect of area ratio 20 Effect of throat length 21 Cavitation Performance 21 Overall performance 21 Effect of flow ratio 21 Effect of nozzle spacing . 24
9、 iii . Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Prediction parameters . 25 Cavitation prediction parameter. w . 25 Cavitation prediction parameter. CY . 26 SUMMARY OF RESULTS 28 CONCLUDING REMARKS 29 APPENDIXES A.SYMBOLS . 30 B .DETERMINATION
10、OF FRICTION LOSS COEFFICIENTS 32 REFERENCES 34 iv -_ . Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-NONCAVITATING AND CAVITATING PERFORMANCE OF TWO LOW-AREA-RATIO WATER JET PUMPS WITH THROAT LENGTHS OF 5.66 DIAMETERS by Nelson L. Sanger Lewis Rese
11、arch Center SUMMARY The noncavitating and cavitating performance of two jet pumps with nozzle- to throat-area ratios of 0.066 and 0.197 was evaluated in a water facility. Both pumps evaluated had throat lengths of 5.66 diameters and diffuser included angles of 6. The investigation was conducted to e
12、xperimentally determine overall noncavitating and cavi tating performance; to study the mixing characteristics over a wide range of geometrical and flow conditions; to compare the experimental results to those obtained for a previ ously investigated configuration with a throat length of 7.25 diamete
13、rs and a diffuser in cluded angle of 86; and to compare the overall experimental performance to noncavi tating theoretically predicted performance. Experimental performance was obtained by operating two nozzles separately in a single test section. Spacing of the nozzle exit from the throat entrance
14、was varied from 0 to 2.9 throat diameters. Deaerated, room-temperature, tap water was used as the test fluid . Maximum measured efficiencies of 31.3 and 37.6 percent were achieved at area ratios of 0.066 and 0.197, respectively. These efficiencies constitute an improvement over those recorded for th
15、e pumps with throat lengths of 7.25 diameters and a diffuser included angle of 86. Outlet static pressures were also improved by the reduction in throat length. Noncavitating performance predicted at the fully inserted nozzle position by a one-dimensional analysis was within 5 percent for the 0.066-
16、area-ratio pump, and within 10 percent for the 0.197-area-ratio pump, both at the best-efficiency flow conditions. At best-efficiency nozzle positions the same analysis predicted performance to within 2 percent for both area-ratio pumps. The point of total headrise deterioration due to cavitation wa
17、s predicted within reasonable accuracy by each of two related parameters. The jet pump configuration evaluated in this investigation represents a good compromise between optimum noncavi tation and cavitation operation. Provided by IHSNot for ResaleNo reproduction or networking permitted without lice
18、nse from IHS-,-,-INTRODUCTION The requirements of cavitation resistance, long-term dependability, and simplicity have resulted in the selection of the jet pump for several possible applications in liquid-metal Rankine-cycle electric power generation systems (refs. 1 and 2). One of the prin cipal jet
19、 pump applications in Rankine-cycle systems is as an auxiliary boost pump for the radiator condensate pump. For such applications jet pumps with low ratios of nozzle exit to throat area (area ratio, R) are required. This requirement results from the com bination of high boiler temperatures and press
20、ures, low radiator temperatures and pres sures, and a requirement for low jet pump power absorption. There has been relatively little detailed investigation of low-area-ratio ( 0 3.0 o 3.8 n 4.8 A 4.9 )Visual incjpient cavitatior Net positive suction head of secondary fluid, Hsv, ft of water I I I I
21、 I I Net positive suction head of secondary fluid, Hsv, m of water (c) Nozzle spacing, 1.54. (d) Nozzle spacing, 2 58. Figure 14. - Effect of inlet pressure and flow ratio on jet pump cavitation performance. Area ratio, 0.066; primary flow rate, 33. o gallons per minute (208x10-3 m3lsec). 22 Provide
22、d by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-I- . Flow ratio. 0 1 0 2 0 3 0 4 0 5 0 1 0 2 0 3 0 4 0 5 0 Net positive suction head of secondary fluid, H, ft of water -uu 0 2 4 6 8101214 4 6 8 10 12 14 0 2 4 6 8 101214 Net positive suction head of secondar
23、y fluid, H, m of water (a) Nozzle spacing, 0. (b) Nozzle spacing, 1.36. (c) Nozzle spacing, 2 66 Figure 15. - Effect of inla pressure and flow ratio on jet pump cavitation performance. Area ratio, 0.197; primary flow rate, 75.0 gallons per minute (474x10-3 m3lsec). Provided by IHSNot for ResaleNo re
24、production or networking permitted without license from IHS-,-,-1 I I I I I I I Nozzle Area Primary flow rate spacing, ratio, Q , s/dt R gallmin tm3/sec);j0.066 33 (2.0810-1 2.58 0 1.36) 0.197 75 (4.7410-) 2.661 11 I/I dI ZII */r 4I II 5 l o w I 1 1 2 3 5 Flow ratio, M Figure 16. - Effect of flow ra
25、tio on required net positive suction head. At a fixed nozzle position, higher secondary-f luid-inlet pressure was required as flow ratio was increased. As flow ratio is increased, cavitation becomes a greater problem because a higher flow ratio produces lower levels of static pressure in the inlet r
26、egion of the pump (due to higher velocities) and a lower axial pressure gradient in the throat (fig. 9). Both effects act to sustain cavitation. The best-efficiency flow conditions occurred near a point midway in the flow range of each pump (figs. 6(a) and (b). The net positive suction head required
27、 at headrise breakdown for these conditions was only 12 to 15 feet (3.7 to 4.6 m) of water (fig. 16). Effect of nozzle spacing: Figures 14 and 15 also show that required Hsv decreased as the nozzle spacing was increased at constant flow ratio. The effect is summarized in figure 17. Except for a port
28、ion of one curve (M = 3.8) and perhaps only one point on the curve, the trends indicated by figure 17 suggest that to improve cavitation performance the noz 1zle spacings should be greater than 1to 1%throat diameters. The same trend was ob served in reference 4. Determination of an optimum operating
29、 nozzle position must take into account both cavitating and noncavitating operation (fig. 7). Comparison of cavita tion and noncavitation data leads to the conclusion that if high efficiency and good cavita tion performance were both design objectives, they could be achieved by operating the nozzle
30、at a spacing of about 1 throat diameter for an area ratio of 0.066, and at about 113 throat diameters for an area ratio of 0.197. 24 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-e Are; Priimary flow ;ate, R Q 1,ratio, ga/min(msec)I I I I al = 10 5
31、 0 Nozzle spacing, s/dt Figure 17. - Effect of nozzle spacing on required net positive suction head of secondary fluid. Cavitation performance changes with nozzle spacing because retraction of the nozzle affects the static pressure distribution in the pump (fig. 10). For a constant flow ratio, as th
32、e nozzle was retracted the static pressure level in the throat increased. The re traction of the nozzle corresponds to an increase in the secondary annular area. For a fixed flow rate, an increase in area results in a decrease in velocity and an increase in static pressure. A secondary factor which
33、contributes to an increased susceptibility to cavitation at small nozzle spacings is the wake produced by the nozzle wall. This wake increases the turbulence in the mixing layer where cavitation occurs and has a greater influence at small nozzle spacings because the static pressure in the throat is
34、low. Prediction parameters. - Two related cavitation prediction parameters may be used to predict conditions at the jet pump headrise dropoff point. Cavitation prediction parameter, w: The parameter presented earlier (eq. (2) was used to correlate the points of cavitation-induced total headrise drop
35、off for performance runs conducted at three primary flow rates at each area ratio. No effect of primary flow rate was observed. Typical results are presented in figure 18 for several nozzle positions at each area ratio. The parameter w is plotted as a function of the ratio of secondary to primary fluid velocity at throat entrance V3/Vn for various values of 25 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
