1、3NATIONAL,.ADVISORY COMMITTEE FOR AERONAUllCSWABTIME lumolw”ORIGfNALLY ISSUEDAugust 1945 asAdvance Restricted Report E5F07HEAT-TRANSFER TESTS OF AQUEOUS ETHYLENE GLYCOLSOLUTIONS IN AN ELECTRICALLY HEATED TUBEBy Everett Bernardo and Carroll S. EianAircraft Engine Research LaboratoryCleveland, Ohioti”
2、 D is inside diameter of -tube; k Is thermal conductivityof liquid; o is specifio heatof liquld; v is absolute viscosity of liquld; and G Is masrate of liqtia flow. In the evaluation of this equation, the phys-Ioal properties used fortho aqueous ethylene glyool solutionsandwater were those compiled
3、by C. S. Cragoe (NationalBureau ofStandards) for the CoordinatingResearch Council.niTRoDucrIoNA satisfactoryanalyels of liquid-coolodengino cooling dataroqulres a lmowledgo of the heat-transfer propmtlos of the coolantsused. Heat-transfer characteristicsof liquids may generellybopredictedfrom tholr
4、phyeloal properties by means of the Nussoltrelation, which has been exporlmentallyverified for a variety ofliquids (rofmxmco 1, p. 181). The physical propm?tlos of ethyleneglyool and othylone glycol-watermixtures have boon eerlmentallydetermlnod ovor llmltod tempe=turo rangoa and havo boon oxtra-pol
5、atadbJyondthoso ranges (rofmoncu 2). Few heat-transfer data,howover, havo bom previously obtainod for AN-E-2 ethylene glycoland other ethylene glyool-watcrmixtures; hence, the applioabllltyof tho physical proportloe of thoau coolants for a range of trmnpera-tures to the correlation Ccol-water mixtur
6、es for a rango of avmage liqulrltemperatures, llquld-flow rates, and heat fluxes. Heat-transfer coofflclentswero alsodeterminedfor wntor and commrcial butanol (p-butylalcohol) forchock pursos inasmuoh as heat-transferdata for theso liquidsaro avallablo (rof%rence 1, pp. 180 and ll).Tho toets wore co
7、nducted ina modified version of the single-tubo ht oxchangor described In roforanco 3. The tubo was olQc-trlcally honted by the wmago of current through the tube, whichrsulted.In huat fluxes of tho samo ordor of magnltudo as thosoWOvailing h rnodGrnliquld-coolodmglno cylinders.-. _lProvided by IHSNo
8、t for ResaleNo reproduction or networking permitted without license from IHS-,-,-3A schematicdiagram of tho olootrloallyheated alnglo-tubo.,.heat oxohangerand the amociated oqulpment used In.tho tests Is%.shown in figuro 1.Hoator TubuThe details of tho heater-tube suction,which consisted of anI-8:8s
9、tainless-stesltuba witha l/2-3noh outddo dlamotor and al/32-inchwall thickness,aro shown in figuro 2. Copper adapterswore allver-soldoredto each end of the tmbo, resulting In aneffective tubo lunh of 22.75 inohos. Each adaptor was connmtodto a 9-inch Unh of l/2-inch standurd plpo (0.62 in. I.D.) and
10、 a6-lnoh electric-insulati coupling of the samo Internal tiamotar(fig. 1).Tube-wall tempomtures weromoasuredat 25 looatlons (fig. 2)bymeana of Iron-constantanthermocouploa (24-gagofloxlblo-glassinsulatedwlru) and a callbratodsulf-bnlanclngIndioatlng-typopotontiomuter. Thu thormocouplcmworo syot-wold
11、odto thn outsiduof tho tubo WU1l and prmaution wna tnlconthat thu last point ofcontact butwom tho wlros was at tbo tubo mrfuco. Tho tubo WSthermally Insulatmdbya wrap ing of floxiblo-ass taps, a l-inch7layer of glaas wool, and a 1 4-inch lnyor of asbestos.Electrical SemPowur was supplied to tho tubo
12、 from a 20!3-voltaltmnating-curront supply lino throughan autotmnsformor, 1voltage ragulatorof tbo saturablo-corureactor typu, ,nnd a 20:1 power transfonwr(fig. 1). Tho olectrloal connectionsat the tube wuro mude throughclamp-typo coppor connectors. The tubo was oluotricallyInsulatedfrom thu rest of
13、 tho systum by *ho nonconduotlng couplings.mu autotrzmaformcra71nd voltage-regulatorunit pmmittodad$zsting and mintalnlng a constantvoltagtJand tho power trans-fozmmr provided largo currentsthrough tho tUbiJc A oallbratedammuter in conjunctionwith a 240:1 Instrument current transformerwas used to mu
14、asure tho currunt throu tho tubo and a hl-reslstanm+ calibratedvoltmotor conmotod ncross the tubo at thecoppor adapters wa9 used to measuro tho voltago drop. The vollmmtorleads were nude of Ho. 8 solid coppor who and were malntalnod asshort as possiblu In ordur to obvlatcivoltmeter corrections.L_ _
15、.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-4Llquld SystamHACAARR no. mThe llquld was circulatedby a centrlfu pump through a heat-ing snd oooling blendlng unit and then through a plate-t fIlterto the tube (fig. 1). 3hwm the tube the liquid flowe
16、d throu arotametor and baok to the pump with a small amount of the liquidbeing shunted to a tank that was located above the hlghast point Inthe system. The tank pruvlded for llquld erpansicm,makeup liquld,and the Introductionof oompresaedair for oonductIng tests at liq-uld pressures above atmospheri
17、c. A bleed line from the tank wasused to relieve tho compressedair when tests were conducted atatmosphsrlc pressure.Thb liqtia-flOw rate thmzgh the tubo was regulated by athrottle valve located at either end of the tube (fig. 1). The flowrate was measured with the rotamter, Which had been calibrated
18、fora range of tenqxmatureswith the various liqulde used. m liqtiateupnmture into the Wbe was controlledtith the heathg and ooolingblending unit, which conslstod of an electric hsater, a cooler, anda miring-valve-typetemperaturerugulator. Liquid temperaturesweremeasured at the entrance and the exit o
19、f tha tubo with slnglo therm-ocouplesIn conunctionwith thu self-bnlancl indicating-typepotentIcmoter.Mre accmte msaaurements than those obtained with the singlethermocoupleswere efforded by two thmmopilos In comblnatlcawitha portable potentIonnter. Tho themopila constructionand the methodof Installa
20、tionIs illustratedIn figuzw 3. Eaoh of the two thormo-plles consisted of four single thermocouplescozumctod In serlos anddistributedacross the PIW diameter. Thu themopllos wore alsoconmcted dlfferentlally in ordur to measuro directly tho temyraturerise of the llqwld In flowing through tho tubo. The
21、hot Junctionof all tho liquid thw?mocouplGswas c.ontodwith an insulatingvarnishin order to reduco tho possibility of error In tho indicated tapo-turos resulting from elootrolfiicaotion.Liquids and CorrosionInhibitorsThe liqulds used in the tests WUIWAN-E-2 othyleno glycol(spoolfIcd on a weight basis
22、 as 94.5 porcont othylono GIYOO1, 2.5 per-oent tr.lethanolamincphosphate,and 3 porcmt watc3r),water, nominal(by volume) 70-30 and 30-70 glycol-watermixtures and commercialbutanol (n-butylalcohol). The ycol ccmwntration lnJ4N-E-2 ethyl-ono glycol and the moro aqueous glycol mixtures was dotomuhod frc
23、mtho specificg?xnlty of samplus taken at Inturvalsthroughout thetl)sta.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-NACA ARE No. E5Fcq 5A corrosian Inhlbltor,sodium chromte, was used In prellmi-inary tests oonducted with water. This p.%ctice was d
24、iscontinuedbefore the fInal tests, however, because the sodium chromatewasbelieved.to be affeutlng the llquld thermocouple calibrations. Inpreliminarytests conductedwith the glycol-water solutIons, lnoon-sistenclesappeared in the results eftervery short periods ofope=tion. These Inoonslstencleswere
25、probably due to foullng ofthe Inside tube-wall surface even thou the tube was thoroughlycleanedwith a fine-grade steel wool before every test series. Asa oorrective measure, 0.2 percent by volume of lWIBT (sodiummerc8ptobenzothiazole)was added to the AN-E-2 ethyleneglycol Wthe other glycol-watermixt
26、ures In the final tests. A corrosioninhibitorwas not used In the tests ccmductedwith butanol.Various preliminary tests were conducted In order to check theaccuracy of the heater-tube instrumentation. A detailed discussionof these tests Is presented In appendix A. The results of the pre-liminary inve
27、stigationIndicatedthat: (a) the electric currentsand mgnetic fields in and around the tube did not introduceanynoticeable error in the tube-wall thermocouple readings; (b) andlosses Mfected the tube-wall temperature distributionat the endsectionsbut had little effect on the temperature distributiono
28、fthe central 12 inches; and (c) the electricalresistance of thetube per inch lenh as calculated from the ammeter and the volt-meter readings and the length of tho tube could be used for powm-input computations.FINAL TISTSAND CALCULATIONSFinal TestsFinal tests were oonductedto obtain forced-convectio
29、nheat-transfer coefficientsfor tha various liquids over the followlngmnges of oondltlmns:. . Average llquldtemperature, %? . . . . . . . . . . . 100t0250Llquld.-flowrate, pounds per second . . . . . . . . . 0.17 to 2.50Reynolds number . . . . . . . , . . . . . . . . . 5,000t0300,000Heat flux, Btu pe
30、r second per square foot . . . . . . . . 4 to 36. . .Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Eaoh factor was independentlyvaried while maintaining theother faotors approximately oonstant. The tests were repeated atseveral clifferent values of
31、 the constant factors. Moat of the teatswere conducted at approximately oonstant absolute liquid pressuresof 53 to 70 pounds per square Inch. In a few of the tests, however,each run was made at two different pressures In order to determinethe effeot Ethat is, the test seotion of thetube was consider
32、edto consist of the central 12 Inohes ti order toreduoe the possibility of introducingerrors h the final results1 . . . Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-0OWIM to the effect of end losses on the tube-wall temperature dis-tribution at th
33、e end sections. (See appendix A.) Average insiile-tube-waU temperatures t were calculatedusing the followlngrelation, which is derived In aendix B:=-!n (%-%)x 0.5where + IS equal to 0.123 oquare foot and k6 la obtained frfigure 4, prepared fram references 4 and 5, at the valecf theaverage outside-tu
34、be-walltemperature to.Power Input and heat-transfer coefficients,- The power Inputto the tube q wae calculated ushg the 1% law where the totalelectricalresistmce R is equal to the prodctof tho resistanceof the tube per inch length r and the length of the test sectionconsidered (12 In.). Fgure 5 show
35、s r as a function of teWQra-ture as deterralnedIn the check tests. Val.uosof r were obtainedat the value of the average outside-tuke-wal-ltemperature to.Heat-transfer coefficier:tsh were calculated as follows:h= qAi (ti - t)where Al is equal to 0.115 square foot.Heat rejections and phyGlcal properti
36、es. - The total heatreJected to the liquld based on the full-lenh tube was calculatedas follows:qr =WcAtwhere At, the temperature rise of the llqvld, was obtained franthe differentiallyconmcted thermopiles.The specific heat cm, the the,nualconductivity k, and theaksolu+e scmlty p of the liquids were
37、 determined at the valueof the average liquid temperature t. Fjgures 6 and 7 (data fromreference 2) and figure 8 (data from references 6, 7, and 8) showthe physical property values of water, aqueo!s ethylene glycolsolutions,and butanol, respectively,as a function of temperature.The physical properti
38、es of the glycol-watermixtures wereevaluatedby assuming that the corrosion inhibitors in the solutionswere qproxlmately equal to an equivalentamount of ethylene glycoloProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-lwclk ARRNo. E5F07 9For example, t
39、he properties of AN-E-2 ethylene glyool were evaluatedas for anominal (by volume) 97-3 glyool-watermlxkmre; henoe,correotlone were not made for the small effeots of the mrrosioninhlbitoreon the Individual physioal-propertyvalues. The errorsIntroduced in the final results by making this assumption we
40、re rela-tively small.mmL!J?s ANDmscuasIoN. of DataA sumary of data and restits for all of the tests exoeptpreliminary and cheek tests IS presented In table I. The valuespresented for the heat reeoted to the liquid represents the totalheat rejeoted on the basfs of the full-length tube (22.75 in.).The
41、 total heat reJeoted to the liquids 1S usually lower than thetotal eleotrioalheat input. The maximum devlatim ie less than10 percent In most oases. The heat loss through the themal insula-tion m the tube WSS estt to be lees 1 pomt of the heatInput and the rlfi portion of the total heat loss Is attri
42、butedto end losses through the copper adapters and busses. At theoentral 12-i.n test seotionj however, heat-inputmessurementsould be acowate mgases of heat transfer inasmuch as the effeotof end loss on this portion of the tubedlx A.)Individual Heat-TransferThe variation of the heat-transferis neglig
43、ible. (See appen-Coeffiolentscoefficientwith rate ofheat Input is shown in figure 9 from the results of tests conduoedwith water at an average ilquid temperature of approximatelyMO” F,at a liquid pressure of 65 pounds per equare inch absolute, and ata liquid-flowrate of 0.20 pound per seoond. The he
44、at-transfercoefflolentsremained approximately constant for variati in thepower supplied to the tube. Thls mndtant relation 1s, in effect,a preolelon oheok of the entire setup lnasmuoh as a oonetant llquid-flow rate and average liquid ta?.uperature(henoe physloal properties)pr D ie Inside diameter of
45、tube; k is thermal conductivity of liquid; c Ie speoificheatof liquid; p 1s abeoluto viscosity of liquid; and G is mass rateof liquid fluw. W the evaluation and (b) the heat flow Is In onlyone dlrectlon (towardthe llquld),for a section of unit lenh theheat generated from the cuter radius y. to any o
46、ther radius yIs as follows:and the heat conductedq= p fipE2(yoz- ;)1s:q=2fiyka WCombinationof equations (2) and (3) results In the follcwlng:P-#(Y02- #)=2fiyk8 Qor separatingthe variables and rewriting:(2)(3)Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IH
47、S-,-,- I16 N.ACA HO. E5F07Integratln$between the limits of 71 and 70 ad ti and to:YtE2 y. ()21*; “ x E2 (Y02 - Yi2)to .t=p -B (4)2YCPk 4% p ksBut the total heat produoed can be expressed as=fi$ (Y02 - Y2)and substitutingfrom this expression into equation (4) results Inthe followlng:()Yg7023fj to - t
48、 = q.2YCks (Y02 - Y12) 4Z ksor rewriting2tiks (t. - ti)q.c)oyo2loge 1COkMITTEE FOR AERONAUTICS Run Tube Heat. rate, Btu/sec Llquld- Liquid Liquid Average tube-wall Heat-transfer Prandtl Reynolds Nusselt St ant oncurrent Input Rejected flow rate temperature pressure temperature Of coefficient nwaber
49、number number number(:P) Test section w(OF) c #k E Ml/k h/c GFull sectiOn to ;C (lb/see) -AveFa8e e ( lb%q center 12 inchegof test section (Btu)( sec )(cent% 12 in. ) (22.7in. ) t At in. abao-(OF) (sq ft)(OF)lute ) Outside Insideto tTest with variable heat input; liquid, water323 331 0.7s 1.41 1.13 0
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