1、, I I- ? 3 NASA TECHNICAL NOTE NASA TN D-3952 N m OI cr) d z I- 4 v) 4 z I 21 i -323 I (PAOES) (CODE) d (CATEOORY) 2 (NASA CR OR TMX OR AD NUMBER) LOCAL HEAT-TRANSFER AND PRESSURE DISTRIBUTIONS FOR FLOW IN A VERTICAL TUBE FREON-113 CONDENSING IN DOWNWARD . by Jack H. Goodykoontz and Willzum F. Brown
2、 Lewis Reseurcb Center Cleveland, Ohio NATIONAL AERONAUTICS AND SPACE ADMINISTRATION WASHINGTON, D. C. MAY 1967 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-NASA TN D-3952 LOCAL HEAT-TRANSFER AND PRESSURE DISTRIBUTIONS FOR FREON- 113 CONDENSING IN
3、 DOWNWARD FLOW IN A VERTICAL TUBE By Jack H. Goodykoontz and William F. Brown Lewis Research Center Cleveland, Ohio NATIONAL AERONAUTICS AND SPACE ADMINISTRATION For sale by the Clearinghouse for Federal Scientific and Technical Information Springfield, Virginia 22151 - CFSTI price $3.00 Provided by
4、 IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-LOCAL HEAT- T R A N S FER AN D PRES S U R E D I S T R I BUT IO N S FOR FREON-113 CONDENSING IN DOWNWARD FLOW IN A VERTICAL TUBE by Jack H. Goodykoontz and William E Brown I Lewis Research Center SUMMARY Local heat
5、-transfer data and static-pressure distributions for Freon-1 13 condensing inside a vertical tube are presented. The test condenser was a 0.293-inch-inside- diameter by 8-foot-long7 water-cooled copper tube. Incomplete condensing occurred in the condenser with exit qualities ranging from 0.05 to 0.4
6、0. Local condensing heat- transfer coefficients varied from 3300 Btu per hour per square foot per OF at the vapor inlet end to 200 Btu per hour per square foot per OF at the discharge end. The local condensing heat-transfer coefficients for Freon-1 13 were satisfactorily correlated by using a Carpen
7、ter-Colburn type of relation for high-velocity condensing. Overall friction- pressure losses were computed and found to be a function of a group of variables used in single-phase pipe -friction problems. INTRODUCTION The research presented herein is a continuation of an experimental program initiate
8、d at the Lewis Research Center on inside-tube condensers. The program was designed to obtain local heat-transfer and static-pressure data for condensing with vapor velocities greater than 200 feet per second. References 1 and 2 present the results of previous work in which steam was used as the test
9、 fluid. The results of the steam work showed that local condensing heat-transfer coefficients were proportional to local vapor flow rates. The vapor velocity effect cor- roborated the analytical work of references 3 to 5. In addition, overall friction-pressure losses were correlated with a group of
10、variables that are commonly used in single-phase pipe-friction problems. The experimental results of references 1 and 2, however, left Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-open the question of the influence of various fluid properties on c
11、ondensing heat transfer. Therefore, the principal objective of the investigation described in this report was to study the fluid property effects. Local heat-transfer coefficients and friction-pressure losses were obtained for Freon-1 13 (trichlorotrifluoroethane) condensing inside a tube over a ran
12、ge of operating conditions. Freon-113 was selected because its fluid properties differ enough from water, used in the previous tests, to permit comparisons of their effects. properties of particular interest were the liquid Prandtl number and the li uid-to-vapor density ratio. The Prandtl number of
13、liquid Freon-113 is approximately 42 times that of water at saturation conditions and 1 atmosphere pressure. The liquid-to-vapor density ratio for Freon-113 is 195 at 1 atmosphere; the density ratio for water is 1600 at the same pressure. In addition to these considerations, the pressure, temperatur
14、e, and flow ranges for Freon-113 were compatible with the experimental apparatus used to ob- tain the steam data of references 1 and 2. The fluid 7 The test condenser was a 0.293-inch-inside-diameter by 8-foot-long water-cooled copper tube. The condenser was mounted vertically with the vapor enterin
15、g at the top and was cooled by water flowing countercurrently in an annulus around the tube. The range of variables covered was as follows: Test-fluid total flow rate, w, lb/hr Test-fluid total mass velocity, G, lb/(hr)(ft ). . 387 to 506 2 613 000 to 1 080 000 Inlet-vapor pressure, Psi, psia . 26.9
16、2 to 44.20 Inlet-vapor temperature, tvi, OF 193 to 229 Inlet-vapor superheat, Atsup, OF . 18 to 53 Coolant flow rate, Wk, lb/hr 434 to 1055 Coolant mass velocity, Gk, lb/(hr)(ft2) . 510 000 to 1 239 000 Coolant temperature, OF . 62 to 95 97 to 133 Inlet, tki, Exit, k0 APPARATUS AND PROCEDURE Descrip
17、tion of Facility The condenser facility is shown in figure 1. The test-fluid side of the apparatus was a once-through system using Freon-113. Demineralized water was continuously cir- culated in the coolant loop. Building supply steam at 100 pounds per square inch gage was used as the heat source an
18、d cooling tower water as the final heat sink. 2 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-The equipment in the Freon-113 circuit consisted of a pot boiler, superheater, flow straightener, test section, condensate cooler, condensate flow measuri
19、ng station, and receiver tank. The boiler was a 94-gallon tank with coiled tubes at the bottom of the tank, through which building supply steam flowed. A wire mesh screen and a baffle separator were located at the boiler exit to impede liquid droplet carryover. The super- heater was a shell-and-tube
20、 heat exchanger with building supply steam on the shell side and Freon-113 vapor in the tubes. Wall heaters were installed around the vapor line between the superheater and the test-section inlet to reduce heat losses in this region. The wall heater consisted of 0.25-inch tubing spirally wrapped aro
21、und the vapor line and soldered in place. Supply steam, flowing inside the 0.25-inch tubing, served as the heat source. The single-tube condenser (fig. 2) was a shell and tube heat exchanger; the vapor condensed inside the inner tube and water flowed in the annulus between the inner and outer tubes.
22、 The test section was mounted vertically; the vapor entered at the top and the coolant flowed countercurrently in the annulus. The inner tube was a copper tube with an outside diameter of 0.541 inch and an inside diameter of 0.293 inch. The outer jacket was a copper tube with a 0.750-inch outside di
23、ameter and a 0.670-inch inside diameter. The space between the inner and outer tubes was 0.0645 inch. Spacer pins were placed in the annulus to maintain concentricity between the inner and outer tubes. The total length of the heat-exchange region was 8 feet. The inner diameter of the inlet- vapor li
24、ne changed from 1.049 to 0.293 inch at a distance of 18.5 inches upstream of the test section. A bell-shaped fitting at this location accommodated the change in cross section. A stainless steel ring (inset in fig. 2) was placed between the inlet-vapor line and the beginning of the heat-exchange regi
25、on of the test condenser to reduce axial heat conduction in the thick-wall tube. The lower end of the test section was equipped with a stainless steel bellows between the inner tube and the outer jacket to allow for thermal expansion. All vapor lines were insulated with molded magnesia, and the test
26、-section shell was lagged with blanket insulation. The condensate cooler was a shell-and-tube heat exchanger that condensed the ex- cess vapor and/or subcooled the fluid flowing from the test section. Coolant-loop com- ponents included a variable-speed pump, a turbine-type flowmeter, a heat exchange
27、r, and an expansion tank. I nst r urne ntation The locations of the pressure and temperature measuring stations on the single-tube test condenser are shown in figure 3. Pressures were measured with U-tube manometers that used mercury as the manometer fluid and a hydrostatic liquid of known height, 3
28、 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-namely Freon-113, between the pressure tap and the manometer fluid. A horizontal run of bare metal tubing 12 inches long was installed between the pressure tap in the test sec- tion and the vertical li
29、ne to the manometer for assurance of an all-liquid hydrostatic head. Ambient pressure existed on the reference leg of the manometer. All temper- atures were measured with iron-constantan thermocouples that were insulated with mag- nesium oxide and swaged inside a 1/16-inch-diameter sheath. The therm
30、ocouple wires were 0.005 inch in diameter. The coolant thermocouples were placed at the midpoint of the annular gap between the inner and outer tubes with the leads projecting radially out- ward. The inner-tube-wall thermocouple leads, as well as the static-pressure tubes, passed radially outward th
31、rough the coolant stream, and bellows compensated for rela- tive motion between the inner and outer tubes. The construction and installation of the wall thermocouples and the pressure taps are shown in the insets in figure 3. a position 2.16 feet upstream of the heat-exchange region of the test sect
32、ion. In addition, vapor temperatures were measured at three axial positions in the small-diameter tube (0.293-in. inner diam) between the transition section and the beginning of the test section All temperatures were recorded on a self-balancing potentiometer. Total condensate flow rate was measured
33、 volumetrically. The system consisted of a quick-shutoff valve located downstream of a 3-foot-long section of 2-inch tubing. The tube was equipped with a sight glass that allowed visual observation and timing of the liquid-level rise when the valve was closed. The temperature of the condensate at th
34、e flow-measuring station was recorded so that the flow rate could be evaluated in mass units. Coolant flow rate was measured with a turbine-type flowmeter. . Vapor temperature at the midpoint of the stream was measured in the l-inch line at Test P roced u re Prior to the acquisition of the experimen
35、tal data, noncondensable gases were re- moved from the test fluid and the test facility. The air content of the Freon-113 as delivered was 20 parts per million on a weight basis. The air content of the liquid in the boiler during the tests remained at this value, as indicated by samples withdrawn fr
36、om the boiler. The boiler was isolated from the remaining portion of the loop and was filled under vacuum with 80 gallons of the liquid. The test-section side of the U-tube manom- eter system was purged with Freon-113 to ensure an all-liquid hydrostatic head between the pressure tap and the manomete
37、r fluid. The manometer valves were closed, and the test loop was evacuated to approximately 50 microns of mercury. The vacuum pump was then turned off. The boiler was opened to the test loop, and 10 to 15 percent of the boiler inventory (8.0 to 12.0 gal) was boiled off. This procedure allowed any re
38、sidual noncon- densable gases to collect in the receiver tank, which was the low-pressure region of the 4 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-system. The pressure in the receiver tank rose to the saturation pressure correspond- ing to the
39、 temperature of the liquid (4.5 to 5.5 psia) and remained constant during a run. Early in the program, the vapor flow rate was found constant, regardless of the liquid level in the boiler. Therefore, obtaining a data point consisted in adjusting the flow rate of the test fluid (by adjusting steam pr
40、essure to the boiler) at a given coolant flow rate and monitoring the pressures, temperatures, and flow rates. All data were taken after the facility reached a steady-state condition where the vapor-inlet and coolant- exit temperatures had not changed for a period of at least 15 minutes. Approximate
41、ly 10 minutes were required to record all data. The most time consuming were the pres- sure readings from the manometers. Measuring the condensate flow rate required less than 1 minute. System pressures did not change when the quick shutoff valve of the condensate-flow-rate measuring station was clo
42、sed; therefore, it was assumed that the flow remained constant throughout the flow-measuring operation. When the boiler inventory was reduced to approximately 20 gallons, the tests were terminated. The liquid in the receiver tank was transferred to the boiler, and the process of loop evacuation and
43、boiloff was repeated. It was felt that this mode of opera- tion always kept the noncondensable gases away from the heat-transfer test region. * METHOD OF DATA ANALYSIS The experimental data obtained in the tests are presented in table I. The experimen- tal measurements (pressures, temperatures, and
44、flow rates) were used to calculate local heat flux, local condensing heat-transfer coefficients, mean condensing heat-transfer coefficients, and overall friction-pressure losses. These computed values are also given in table I. relation (see appendix B): The local condensing heat-transfer coefficien
45、t hcl was calculated from the following qi tvs - tiw hcl = (Symbols are defined in appendix A, and the methods used to obtain the heat flux and tem- peratures in equation (B2) are given in appendix B. ) defines the static-pressure change in the condenser: The overall friction-pressure loss was obtai
46、ned from the following relation, which g APs = APf + APm + AP 5 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-The momentum-pressure change APm was obtained from The exit vapor velocity Vvo was calculated from the equation of continuity by assuming
47、that vapor alone occupied the cross section of the tube. Table I shows that, for all runs, the vapor 0.02 foot upstream of the condenser inlet was in a superheated state. In addition, the first wall thermocouple (0.14 ft downstream of the condenser inlet) measured a temperature higher than the vapor
48、 saturation temper - ature. To locate the position in the condenser where condensation began, it was assumed that the inner-wall temperature had to be lower than the local vapor saturation temper- ature. The difference between the inner-wall temperature and the measured wall tem- perature, however,
49、was very small (1.3 F maximum). Therefore, the location where the measured-wall, axial-temperature profile intersected the axial saturated-vapor- temperature profile was taken as the start of the condensing portion of the test section. ment of length (0.25 ft), as outlined in detail in appendix B. No correction was needed for heat loss from the outer jacket of the test section in calculatin
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