1、REPORT 1020MEASUREMENTS OF AVERAGE HEAT-TRANSFER AND FRICTION COEFFICIENTSAn iniwtigationa880ciated pressureFOR SUBSONIC FLOW OF AIR IN SMOOTH TUBES AT HIGHSURFACE AND FLUID TEMPERATURES 1By LEROY V. HUMBLE,WARRENH. LOWDEWIIX. and LELnm C. DESMOXSUMMARYoj forced-emuvctiim heat transfer anddrop8 was
2、conducted with. air flom”nathrough emothtubefOT-an imi-all range of eurjace ta few re8ult8are includedfor cooling of the air. The mer-allrange of aurfaee-to-airtemperaiurt?rai% wa8fio?n 046 to 3.6.Correlationof the measuredawrage heat-tranejerandfrictioncoej%iente with heat addi$hn by conzxmtionatlm
3、ethods whereinthe physical prapertie8 of the air were t?wduutedat the aoerageair temperature rewlted in considerable decrea8e8in both tlw.Vu88el#number and thefrtktian coej%ieti at mn.etantReynoldinumber in the turbulent re”on, as the ratio of eqface npera-ture to air temperature wa8 increoxed. The
4、eect of 8urfa4e-to-air temperature ratio wag eliminated by ewduating thephysical properties of air, includ,.-.-.evaluated athe ti temperature Tf. The daa of figure 15 (a) .-are replotted in this manner in figure 15 (b). The trendswith T,/To are ebi.nated for ReynoMs numbers above20,000 and the data
5、can be represented with reasonableaccuracy by the Ez belhnouthentmmx; Inlet-air temp?mture, S35R.Effect of Iength-diameter ratio and hdet-air tempera-ture,-Friction data. obtained with heat addition to the airfor length-diameter ratios of 30 and 120 and for idebairtempmaturea from 535 to 1460 R arc
6、shown in figure 16 (b).The data of figure 16 (b), which are for a belhnouthentrance, fall above the h“6rmfm line, whereas the belllnout,lldata in figure 15 (b), which correspond to a length-diameterratio of 60, fall on the line, ATOparticular significance can beat t.achml to these differences, howev
7、er, and it is fdt that t-hedata for the range of length-diamotm ratio and inlet-airtemperature considered can be represented with sufficientaccuracy by equation (19).COMMITTEE FOR AERONAUTICS,t , r , r r I r1 I I+-# Entronce TP/Tb :)o Long opprooch 53 -1750 1.O-2.3R Rqh t-orqleedge 535-/960 lUk.7.Of
8、1 1 t 1“ “ /f length-dlamdcrratio, 13Jinlet-ah tamwature, S35R.(b) Efket of kngthdiameter ret!o and Ink-t4r temperature wfth heat 8ddItIon, Inconcl(a) Effeet ofheatexfraetkm.hwm%itube;lerrgth-dbimctor mtlo, WFmuBr ltl.-VarlatIon of modLlledhaU.frfetkm merncknt with modblcd Reynohls number,Effect of
9、heat extraction, -Friction coefficimts obtuinwsimultaneously with thv data of figure 11 for hctit ust ractionfrom the air are shown in figurr 16 (c). Dttta for no h(altransfer arc included. Tlw coordinates and th refermcrIinc are the same as in figures 15 (b) to 16 (b). hc data POT1be rcprcscmtcd wi
10、th reasonable accuracy by thr rvfcrencc linrfor turbulent flow.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-SUMMARY OF IMWJL!I!SThe results of this investigation of heat transfer andassociated pressure drops conducted with air flowing throughsmoot
11、h tubes for a range of surface-to-air temperature ratiohorn 0.46 to 3.5, surface temperature bm 535 to 3050 R,inlet-air temperature horn 535 to 1500 R, Reynolds num-ber up to 500,000, exit Mach number up to 1.0, length-diameter ratio from 30 to 120, and for three entrsnce con-figurations may be summ
12、arized as follows:1. onventional methods of correlating average heat-h-ansfer coefficients, wherein specific -heat, viscosity, andthermal conductivity are evaluated at the average airtemperature, resulted in a considerable and progressiveseparation of the data with increed surface-to-air tempera-tur
13、e ratio for heat addition to the air. Evaluation of thephysical properties at the ti or surface temperature, insteadof the bulk temperature, aggravated the sepmation.Z. Satisfactory correlation of heating data obtained withinlet-air temperatures near 535 R was obtained for the rangeof surface temper
14、ature considered when the Reynolds numberwas modified by substituting the product of air density evalu-ated at the surface tempwature and velocit y evahmte,d at theaverage total air temperature for the conventiomd mass flowper unit cross-sectional area, and the properties of the airwere evaluated at
15、- the average surface temperature.3. orrelation of the heating data obtained at inlet-airtemperatures above 535 R by the modified method resuhedin a decrease in Nusselt number for an increase in averageair temperature, -which was eliminated by the assumptionthat the t,hermil conductivity of air vari
16、es as the square rootof temperature and by the evacuation of the physical prop-,ert.ies of air including density at a temperature midwaybetween air and surface temperatures instead of at thesurface temperature.4. TIM the assumption that thermal conductivity variesas the square root of temperature, d
17、ata obtained for cooIingof t-he air indicated that the effect of surface-to-air temper-ature ratio was the sane as for heat addition, so thah bothheat and” cooling data can be represented by the sameequation.5. The use of diflerent entrmces to the test section (that is,a long-approach; a right_ngle-
18、edge, or a bellmouth entmmce)had negligible effect on average heat-tiansfer coticimts, atIeast for Iength-diameter ratios of 60 or greater.6. Variation in tube Iength-ckneter ratio had a rektivelysmall effect on average heat-trader coefficients, which wassatisfactorily accounted for by including a p
19、arameter forlength-diameter ratio in the correlation equation.7. Friction coefficients for no heat transfer, calculatedfrom a dynamic pressure based on an average air density,were in good agreement with those obtained by other inves-tigators. The cmrespond friction coefficients obtainedwith heat add
20、ition to the air showed a considerable effect- ofsurface-to-ak tempemture ratio for the ReynoIds numbers inthe turbulent region.8. MI the friction data cmdd be represented with reason- “-able accuracy by the Ktirmhu-Mlmradse reIat.ion for incom-preseibIe turbulent flow by usiq a friction coefficient
21、 cal-. _culated from a dynamic pressure based on a density evalu-ated at the fi temperature and the modified ReynoIds _number in which the density and viscosity were evaluated at .-a temperature midway between the air and surface tern- -peiaturw.LEWIS FLIGHT PROPUMION LABOMTOHY . hrATIOXL fhmcsorm C
22、O-WE FOB AEBoxT.4umcscLEvEkm, OHIO, ecernber S1, 1960.-1.2.3.4.5.6.7.8.9.10.11.12.13.REFERENCESh-usselt, Wilhelm: Der Elniluss der Gastemperat ur auf den lt%rmeiibergang im Rohr. Techn. Mechan. u. Thermodynamic,BcLI, Nr. 8, Aug. 1930, S. 277290.MoAns, YiiUiamH.: Heat !lkansmicsson. McGraw-HUl Book -
23、Co., blC., 2d cd., 1942.Humble, Leroy V., Lovidermillr, arren H., sad Grele, likon: -Heat Transfer from High-Temperature Surfaces to Fluids. .-IPreliminary Investigation with Air in Inconel Tube withRounded Entrance, inside Diameter of 0.4 In and lkngth of _24 Inches. XACA RM E7L31, 1948.LowdermiIk,
24、 =en H., and Grele, MUton D.: Heat Transfer -from High-Temperature Surfaces to F1uick 11-Correlation ofHeat-Tramfer and Friction Data for Air Flowing in InconeI .=Tube with Rounded Entrance. NACA RM E8L03, 1949.Lewder Warren H., and Grele, Milton D.: Influence of Tube-Entrance Configuration on Avera
25、ge Heat-Transfer Coefficients -and Friction Faotors fr Air FIoviing in an Inconel Tube.NACA RM E50EX+ 1950.IXamo% LeIand G., and Sams, EIdon W.: Correlation of Forced- “Convection HeaGTransfer Data for Air FIowing in SmoothPlatinum Tube viith Long-Approach Entrance at High Surfaceand Inlet-Air Tempe
26、ratuw. NACA RM E50H23, 1950.Triius, Iyronl and Boelter, L. M. K.: An Investigation of Air-craft Heaters. II-properties of Gases. NACA ARR, Oct.1942.BoeIter, L- M. K., tmd Sharp, W. H.: An Instigation of AircraftHeaters. XXXI-Wasurement of Thermal (%nduct.ivity of-Air and of Ezhaust Gases Between 50
27、and 900 F. NACATX 1912, 1949.Keenan, Joseph H., and Ksye, Joseph: Thermodynamic Properties of _Air. John WiIey & Sons, Inc., 1945.Grtieber, H., .und Erk, S.: Die Grundgesetze der R%ermeileber- -g- Jfius Springer (BerIin), 1933.Bernardo, Everett, and Eian, CarroIJ S.: Heat-Transfr Tests of “” “Aqueou
28、s Ethylene Glycol Solutions in an ElectricaIIy HeatedTube. ,ACA R E57, 1945.Deiasler, Robert G.: haIyticaI Investigation of Turbulent J?IOWinSmooth Tubes with Heat Transfer with Variable FIuid Proper-ties for PrandtI Number of 1. N.*CA TN 2242, 1950.Choletta, Albert: Heat Transfer-Local and Av&rt&e Coefficients _”for Air FIowing Inside Tubas. Chem. Eng. Prog., VOLM, no. 1,Jan. 1948, pp. 81-88.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
