1、Designation: D7863 13Standard Guide forEvaluation of Convective Heat Transfer Coefficient ofLiquids1This standard is issued under the fixed designation D7863; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revisio
2、n. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This guide covers general information, without specificlimits, for selecting methods for evaluating the heating andcooling perform
3、ance of liquids used to transfer heat whereforced convection is the primary mode for heat transfer.Further, methods of comparison are presented to effectivelyand easily distinguish performance characteristics of the heattransfer fluids.1.2 The values stated in SI units are to be regarded asstandard.
4、 No other units of measurement are included in thisstandard.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-b
5、ility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D445 Test Method for Kinematic Viscosity of Transparentand Opaque Liquids (and Calculation of Dynamic Viscos-ity)D1298 Test Method for Density, Relative Density, or APIGravity of Crude Petroleum and Liquid Petrol
6、eum Prod-ucts by Hydrometer MethodD2270 Practice for Calculating Viscosity Index from Kine-matic Viscosity at 40 and 100CD2717 Test Method for Thermal Conductivity of LiquidsD2766 Test Method for Specific Heat of Liquids and SolidsD2887 Test Method for Boiling Range Distribution of Pe-troleum Fracti
7、ons by Gas ChromatographyD2879 Test Method for Vapor Pressure-Temperature Rela-tionship and Initial Decomposition Temperature of Liq-uids by IsoteniscopeD4530 Test Method for Determination of Carbon Residue(Micro Method)D6743 Test Method for Thermal Stability of Organic HeatTransfer FluidsE659 Test
8、Method for Autoignition Temperature of LiquidChemicals3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 heat transfer fluid, na fluid which remains essen-tially a liquid while transferring heat to or from an apparatus orprocess, although this guide does not preclude the evaluati
9、on ofa heat transfer fluid that may be used in its vapor state.3.1.1.1 DiscussionHeat transfer fluids may be hydrocar-bon or petroleum based such as polyglycols, esters, hydroge-nated terphenyls, alkylated aromatics, diphenyl-oxide/biphenylblends, mixtures of di- and triaryl-ethers. Small percentage
10、s offunctional components such as antioxidants, anti-wear andanti-corrosion agents, TBN, acid scavengers, or dispersants, ora combination thereof, can be present.3.1.2 heat transfer coeffcient, na term, h, used to relatethe amount of heat transfer per unit area at a given temperaturedifference betwe
11、en two media and for purposes of this guide,the temperature difference is between a flow media and itssurrounding conduit.3.1.2.1 DiscussionThe heat transfer coefficient for condi-tions applicable to fluids flowing in circular conduits underturbulent flow is referred to as the convective heat transf
12、ercoefficient.4. Summary of Guide4.1 The convective heat transfer coefficient for flow in acircular conduit depends in a complicated way on manyvariables including fluid properties (thermal conductivity, k,fluid viscosity, , fluid density, , specific heat capacity, cp),system geometry, the flow velo
13、city, the value of the character-istic temperature difference between the wall and bulk fluid,and surface temperature distribution. It is because of thiscomplicated interaction of variables, test results can be biasedbecause of the inherent characteristics of the heat transferapparatus, measurement
14、methods, and the working definition1This guide is under the jurisdiction of ASTM Committee D02 on PetroleumProducts and Lubricants and is the direct responsibility of Subcommittee D02.L0.06on Non-Lubricating Process Fluids.Current edition approved May 1, 2013. Published July 2013. DOI: 10.1520/D7863
15、-13.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO B
16、ox C700, West Conshohocken, PA 19428-2959. United States1for the heat transfer coefficient. Direct measurement of theconvective heat flow in circular conduits is emphasized in thisguide.4.2 This guide provides information for assembling a heattransfer apparatus and stresses the importance of providi
17、ngreporting information regarding the use and operation of theapparatus.5. Significance and Use5.1 The reported values of convective heat transfer coeffi-cients are somewhat dependent upon measurement techniqueand it is therefore the purpose of this guide to focus on methodsto provide accurate measu
18、res of heat transfer and precisemethods of reporting. The benefit of developing such a guide isto provide a well understood basis by which heat transferperformance of fluids may be accurately compared and re-ported.5.2 For comparison of heat transfer performance of heattransfer fluids, measurement m
19、ethods and test apparatus shouldbe identical, but in reality heat transfer rigs show differencesfrom rig to rig. Therefore, methods discussed in the guide aregenerally restricted to the use of heated tubes that have walltemperatures higher than the bulk fluid temperature and withturbulent flow condi
20、tions.5.3 Similar test methods are found in the technicalliterature, however it is generally left to the user to reportresults in a format of their choosing and therefore directcomparisons of results can be challenging.6. Test Apparatus and Supporting Equipment6.1 BackgroundConvective heat transfer
21、may be free(buoyant) or forced. Forced convection is associated with theforced movement of the fluid and heat transfer of this type isemphasized herein. To greatly minimize to the buoyantcontribution, the Reynolds Number should be sufficiently highto eliminate thermal stratification and provide a fu
22、lly devel-oped turbulent velocity profile. The use of a vertical heatedsection also helps in this regard due to less likelihood offorming voids near the walls. To minimize the contribution ofradiation heat transfer, which is proportional to the forth powerof temperature, high wall temperatures (350C
23、 +) should beavoided. However, for those cases where high wall tempera-tures are present, corrections for the radiant heat contributionare necessary. Conduction (heat flow through materials) willalways be present to some extent and the design of any testapparatus must account for all conduction path
24、s, some ofwhich contribute to heat losses. Energy balance, that is,accounting for all heat flows in and out of the system, isimportant for accurate determination of heat transfer coeffi-cients.6.1.1 A conventional convective heat transfer apparatuspumps the fluid of interest through a heated tube wh
25、ere theamount of energy absorbed by the fluid from the hot wall ismeasured. By allowing the walls to be cooler that the fluid,then cooling transfer coefficients could be derived, but fluidheating is the focus of this guide. The heat transfer coefficient,h (W/cm2C) may be derived through appropriate
26、calculations.Two types of wall boundary conditions are generally em-ployed; a constant wall temperature or a constant heat fluxwhere heat is distributed over a given area such as W/m2.Itisimportant to define the wall conditions because the temperaturedistributions in the axial flow direction, dT/dz,
27、 for the wall andbulk fluid differ depending on wall condition. Measurement ofthe wall temperature distribution may be used to verifyboundary conditions and to obtain estimates of experimentalerror.6.1.2 A reliable method for setting up a constant heat fluxcondition is to utilize resistive heating o
28、f the conduit (theconduit acts as a resistor when connected to the terminals of anelectrical power supply). One advantage of this method is therelative ease for measuring the electrical power input (Watts)and inferring the wall temperature from the temperaturecoefficient of resistance () for the wal
29、l material. Constant walltemperature boundary conditions are established by surround-ing the heat transfer conduit with a medium at constanttemperature (such as a thermal bath). A suggested setup for aconstant flux heat transfer apparatus is shown in Fig. 1.6.1.3 The apparatus shown in Fig. 1 exhibi
30、ts a free surfaceat atmospheric pressure within the reservoir and therefore thesystem is open and non-pressurized. For fluids with low vaporpressure, it may be necessary to run a closed and pressurizedsystem. Desired bulk fluid temperature and wall temperatureswill significantly impact the design an
31、d operation of the loop.Select seals within the pump to be compatible with the fluidand withstand the operating pressure and temperature. For theloop shown, a constant speed pump with external bypasscontrol is employed. Variable speed pumps with no bypass maybe used; however, a pump speed control un
32、it will be necessary.The installation of a safety relief valve to prevent pressurebuildup is recommended.6.1.4 The electrically heated test section is shown in avertical position. This arrangement generally prevents hotspots on the walls from forming mainly due to fluid voids orthe development of “c
33、onvection cells” and stratified flows. Theelectrical resistance of a steel or copper tube will be quite low,and therefore extremely high electrical currents are necessaryto produce the desired heat flux. For 0.5-in. diameter tubes ofa few feet in length, it is not uncommon to see currents in the1000
34、 amp range. Employ large copper buss bars to carrycurrent to the heated tube. Accurate measurement of voltageand current will provide an accurate measure of power deliv-ered. Because of the presence of high currents, adequate safetysystems should be employed.6.1.5 Due to the high electrical currents
35、 and potentiallyextremely high tube temperature, both electrical and thermalisolation are needed at each end of the heated section. Useceramics that can be machined to manufacture isolators ofdesired characteristics. Many ceramic materials can handle1500F in an untreated condition, whereas simple he
36、at treatingof these materials will allow for operation above 2500F. ToD7863 132further reduce heat losses, the heated tube will require substan-tial insulation. Ceramic blankets work very well, especially forhigh temperature applications.6.1.6 Document wall roughness of the heated section. Com-merci
37、ally drawn stainless steel tubing is preferred, but tubewall roughness shall approach hydraulically smooth conditionswith Darcy-Weisbach relative roughness values approaching0.00001 or better.6.1.7 The heated test section shall be easily removed forinspection and for possibly changing tube sizes. It
38、 is especiallyadvantageous to accommodate sectioning of the tube upon thecompletion of a test sequence for the purpose of examiningdeposits on the tube wall via carbon burn off methods (TestMethod D4530) or Auger electron spectroscopy. The lattermethod is a widely used analytical technique for obtai
39、ningchemical composition of solid surfaces.36.1.8 Do not exceed temperature limitations set by pumpseals and other seals. For many installations, this means thatextremely hot fluids going through the loop (and heatedsection) will need to be cooled before they enter the pump. Thiscooling will set up
40、thermal cycling of the fluid by heating andcooling the fluid every time the fluid circulates through theloop.6.2 Required MeasurementsMeasure temperature (walland fluid) and flow rate to obtain sufficient information forcalculating the heat transfer coefficient. However, when com-paring test results
41、 to observations of others, it is necessary toobtain fluid property data and dimensions of the test sections.The reason, convective heat transfer predictions are usuallycast in terms of non-dimensional groups of Nusselt number,Reynolds number, and Prandtl number. Other non-dimensionalgroups may also
42、 be applicable. Therefore values of fluidviscosity (Test Method D445, Practice D2270), thermal con-ductivity (Test Method D2717), fluid density (Test MethodD1298) and heat capacity (Test Method D2766) all as afunction of temperature are necessary for various heat transfercorrelations.6.2.1 Other pro
43、perties of fluids are required for completedocumentation and safety of operation. These include boilingrange distributions (Test Method D2887), vapor pressure-temperature relationship (Test Method D2879) and autoigni-tion temperature (Test Method E659).6.2.2 Suggested test section temperature measur
44、ements areshow in Fig. 2. This figure shows a constant heat flux boundarycondition. A constant wall temperature condition may also beimposed by surrounding the tube within an isothermal bath.6.2.3 The subscript “b” denotes a bulk fluid temperature(sometimes referred to as the bulk mixing cup tempera
45、ture) andthe subscript “w” denotes a wall temperature. It is suggested3Chourasia, A. R., and Chopra, D. R., Handbook of Instrumental Techniques forAnalytical Chemistry, Chapter 42, 1997.FIG. 1 Apparatus for Measuring the Convective Heat Transfer CoefficientD7863 133that five or more wall temperature
46、s be obtained over the testsection length. For a constant heat flux condition, dTw/dz isconstant and the value of Twincreases form inlet to outlet andin the case of a constant temperature wall, Twis a constant overthe entire length. These temperature distributions should bereported along with the te
47、st results to ensure reasonablecomparisons of results from other sources.6.2.4 If the wall thickness is large (more than 10 % of thediameter), the inside wall temperature may be significantlydifferent than the measured outside wall temperature, espe-cially for conditions of high heat flux. For these
48、 situations, theinside wall temperature shall be estimated or measured. Wallthickness, wall material, and heat rate (W or Btu/h) informationis needed for estimating the inside wall temperature. The insidewall temperatures (measured or estimated) are used in the heattransfer coefficient equations cit
49、ed in 6.3.6.3 Calculations:6.3.1 Definitions of the Convective Heat Transfer Coeff-cient (for Flow in a Conduit)Where a solid surface is warmerthan the fluid (heat being transferred from the solid to thefluid), the rate of heat flow across the solid-fluid interfacedepends upon the area of the interface and the temperature dropfrom the solid wall to the fluid as indicated in Eq 1.Q 5 hAT (1)where:Q = heat flow into the fluid (W),A = characteristic area,T = characteristic temperaturedifference, andproportionality factor h = heat transfer coefficient.6.3.1.1 Note tha
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