1、Designation: D7863 13D7863 17Standard 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
2、 revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope Scope*1.1 This guide covers general information, without specific limits, for selecting methods for evaluating the heating an
3、d coolingperformance of liquids used to transfer heat where forced convection is the primary mode for heat transfer. Further, methods ofcomparison are presented to effectively and easily distinguish performance characteristics of the heat transfer fluids.1.2 The values stated in SI units are to be r
4、egarded as standard. No other units of measurement are included in this standard.1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety safety, health and healthen
5、vironmental practices and determine theapplicability of regulatory limitations prior to use.1.4 This international standard was developed in accordance with internationally recognized principles on standardizationestablished in the Decision on Principles for the Development of International Standard
6、s, Guides and Recommendations issuedby the World Trade Organization Technical Barriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2D445 Test Method for Kinematic Viscosity of Transparent and Opaque Liquids (and Calculation of Dynamic Viscosity)D1298 Test Method for Density, R
7、elative Density, or API Gravity of Crude Petroleum and Liquid Petroleum Products byHydrometer MethodD2270 Practice for Calculating Viscosity Index from Kinematic Viscosity at 40 C and 100 CD2717 Test Method for Thermal Conductivity of LiquidsD2766 Test Method for Specific Heat of Liquids and SolidsD
8、2879 Test Method for Vapor Pressure-Temperature Relationship and Initial Decomposition Temperature of Liquids byIsoteniscopeD2887 Test Method for Boiling Range Distribution of Petroleum Fractions by Gas ChromatographyD2879D4052 Test Method for Vapor Pressure-Temperature Relationship and Initial Deco
9、mposition Temperature Density,Relative Density, and API Gravity of Liquids by IsoteniscopeDigital Density MeterD4530 Test Method for Determination of Carbon Residue (Micro Method)D6743 Test Method for Thermal Stability of Organic Heat Transfer FluidsD7042 Test Method for Dynamic Viscosity and Densit
10、y of Liquids by Stabinger Viscometer (and the Calculation of KinematicViscosity)E659 Test Method for Autoignition Temperature of Chemicals3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 heat transfer fluid, na fluid which remains essentially a liquid while transferring heat to
11、 or from an apparatus or process,although this guide does not preclude the evaluation of a heat transfer fluid that may be used in its vapor state.1 This guide is under the jurisdiction of ASTM Committee D02 on Petroleum Products Products, Liquid Fuels, and Lubricants and is the direct responsibilit
12、y ofSubcommittee D02.L0.06 on Non-Lubricating Process Fluids.Current edition approved May 1, 2013Aug. 1, 2017. Published July 2013August 2017. Originally approved in 2013. Last previous edition approved in 2013 as D7863 13.DOI: 10.1520/D7863-13.10.1520/D7863-17.2 For referencedASTM standards, visit
13、theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard
14、an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is
15、to be considered the official document.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.1.1.1 DiscussionHeat transfer fluids may be hydrocarbon or petroleum based such
16、as polyglycols, esters, hydrogenated terphenyls, alkylatedaromatics, diphenyl-oxide/biphenyl blends, and mixtures of di- and triaryl-ethers. Small percentages of functional componentssuch as antioxidants, anti-wear and anti-corrosion agents, TBN, acid scavengers, or dispersants, or a combination the
17、reof, can bepresent.3.1.2 heat transfer coeffcient, na term, h, used to relate the amount of heat transfer per unit area at a given temperaturedifference between two media and for purposes of this guide, the temperature difference is between a flow media and itssurrounding conduit.3.1.2.1 Discussion
18、The heat transfer coefficient for conditions applicable to fluids flowing in circular conduits under turbulent flow is referred to asthe convective heat transfer coefficient.4. Summary of Guide4.1 The convective heat transfer coefficient for flow in a circular conduit depends in a complicated way on
19、 many variablesincluding fluid properties (thermal conductivity, k, fluid viscosity, , fluid density, , specific heat capacity, cp), system geometry,the flow velocity, the value of the characteristic temperature difference between the wall and bulk fluid, and surface temperaturedistribution. It is b
20、ecause of this complicated interaction of variables, test results can be biased because of the inherentcharacteristics of the heat transfer apparatus, measurement methods, and the working definition for the heat transfer coefficient.Direct measurement of the convective heat flow in circular conduits
21、 is emphasized in this guide.4.2 This guide provides information for assembling a heat transfer apparatus and stresses the importance of providing reportinginformation regarding the use and operation of the apparatus.5. Significance and Use5.1 The reported values of convective heat transfer coeffici
22、ents are somewhat dependent upon measurement technique and it istherefore the purpose of this guide to focus on methods to provide accurate measures of heat transfer and precise methods ofreporting. The benefit of developing such a guide is to provide a well understood well-understood basis by which
23、 heat transferperformance of fluids may be accurately compared and reported.5.2 For comparison of heat transfer performance of heat transfer fluids, measurement methods and test apparatus should beidentical, but in reality heat transfer rigs show differences from rig to rig. Therefore, methods discu
24、ssed in the guide are generallyrestricted to the use of heated tubes that have wall temperatures higher than the bulk fluid temperature and with turbulent flowconditions.5.3 Similar test methods are found in the technical literature, however it is generally left to the user to report results in a fo
25、rmatof their choosing and therefore direct comparisons of results can be challenging.6. Test Apparatus and Supporting Equipment6.1 BackgroundConvective heat transfer may be free (buoyant) or forced. Forced convection is associated with the forcedmovement of the fluid and heat transfer of this type i
26、s emphasized herein. To greatly minimize to the buoyant contribution, theReynolds Numbernumber should be sufficiently high to eliminate thermal stratification and provide a fully developed turbulentvelocity profile. The use of a vertical heated section also helps in this regard due to less likelihoo
27、d of forming voids near the walls.To minimize the contribution of radiation heat transfer, which is proportional to the forthfourth power of temperature, high walltemperatures (350C(350 C +) should be avoided. However, for those cases where high wall temperatures are present, correctionsfor the radi
28、ant heat contribution are necessary. Conduction (heat flow through materials) will always be present to some extent andthe design of any test apparatus must account for all conduction paths, some of which contribute to heat losses. Energy balance,that is, accounting for all heat flows in and out of
29、the system, is important for accurate determination of heat transfer coefficients.6.1.1 A conventional convective heat transfer apparatus pumps the fluid of interest through a heated tube where the amount ofenergy absorbed by the fluid from the hot wall is measured. By allowing the walls to be coole
30、r that the fluid, then cooling transfercoefficients could be derived, but fluid heating is the focus of this guide. The heat transfer coefficient, h (W/cm2 C) may be derivedthrough appropriate calculations. Two types of wall boundary conditions are generally employed;employed: a constant walltempera
31、ture or a constant heat flux where heat is distributed over a given area such as W/m2. It is important to define the wallconditions because the temperature distributions in the axial flow direction, dT/dz, for the wall and bulk fluid differ depending onwall condition. Measurement of the wall tempera
32、ture distribution may be used to verify boundary conditions and to obtainestimates of experimental error.6.1.2 A reliable method for setting up a constant heat flux condition is to utilize resistive heating of the conduit (the conduitacts as a resistor when connected to the terminals of an electrica
33、l power supply). One advantage of this method is the relative easeD7863 172for measuring the electrical power input (Watts) and inferring the wall temperature from the temperature coefficient of resistance() for the wall material. Constant wall temperature boundary conditions are established by surr
34、ounding the heat transfer conduitwith a medium at constant temperature (such as a thermal bath). A suggested setup for a constant flux heat transfer apparatus isshown in Fig. 1.6.1.3 The apparatus shown in Fig. 1 exhibits a free surface at atmospheric pressure within the reservoir and therefore the
35、systemis open and non-pressurized. For fluids with low vapor pressure, it may be necessary to run a closed and pressurized system.Desired bulk fluid temperature and wall temperatures will significantly impact the design and operation of the loop. Select sealswithin the pump to be compatible with the
36、 fluid and withstand the operating pressure and temperature. For the loop shown, aconstant speed pump with external bypass control is employed. Variable speed pumps with no bypass may be used; however, apump speed control unit will be necessary. The installation of a safety relief valve to prevent p
37、ressure buildup is recommended.6.1.4 The electrically heated test section is shown in a vertical position. This arrangement generally prevents hot spots on thewalls from forming mainly due to fluid voids or the development of “convection cells” and stratified flows.The electrical resistanceof a stee
38、l or copper tube will be quite low, and therefore extremely high electrical currents are necessary to produce the desiredheat flux. For 0.5-in. 0.5 in. diameter tubes of a few feet in length, it is not uncommon to see currents in the 1000 amp range.Employ large copper buss bars to carry current to t
39、he heated tube. Accurate measurement of voltage and current will provide anaccurate measure of power delivered. Because of the presence of high currents, adequate safety systems should be employed.6.1.5 Due to the high electrical currents and potentially extremely high tube temperature, both electri
40、cal and thermal isolationare needed at each end of the heated section. Use ceramics that can be machined to manufacture isolators of desired characteristics.Many ceramic materials can handle 1500F1500 F in an untreated condition, whereas simple heat treating of these materials willallow for operatio
41、n above 2500F.2500 F. To further reduce heat losses, the heated tube will require substantial insulation.Ceramic blankets work very well, especially for high temperature applications.6.1.6 Document wall roughness of the heated section. Commercially drawn stainless steel tubing is preferred, but tube
42、 wallroughness shall approach hydraulically smooth conditions with Darcy-Weisbach relative roughness values approaching 0.00001or better.6.1.7 The heated test section shall be easily removed for inspection and for possibly changing tube sizes. It is especiallyadvantageous to accommodate sectioning o
43、f the tube upon the completion of a test sequence for the purpose of examining depositsFIG. 1 Apparatus for Measuring the Convective Heat Transfer CoefficientD7863 173on the tube wall via carbon burn off methods (Test Method D4530) or Auger electron spectroscopy. The latter method is a widelyused an
44、alytical technique for obtaining chemical composition of solid surfaces.36.1.8 Do not exceed temperature limitations set by pump seals and other seals. For many installations, this means that extremelyhot fluids going through the loop (and heated section) will need to be cooled before they enter the
45、 pump. This cooling will set upthermal cycling of the fluid by heating and cooling the fluid every time the fluid circulates through the loop.6.2 Required MeasurementsMeasure temperature (wall and fluid) and flow rate to obtain sufficient information for calculatingthe heat transfer coefficient. How
46、ever, when comparing test results to observations of others, it is necessary to obtain fluid propertydata and dimensions of the test sections. The reason, convective heat transfer predictions are usually cast in terms ofnon-dimensional groups of Nusselt number, Reynolds number, and Prandtl number. O
47、ther non-dimensional groups may also beapplicable. Therefore values of fluid viscosity (Test Method D445 or D7042, Practice D2270), thermal conductivity (Test MethodD2717), fluid density (Test Method D1298) or D4052), and heat capacity (Test Method D2766) all as a function of temperatureare necessar
48、y for various heat transfer correlations.6.2.1 Other properties of fluids are required for complete documentation and safety of operation. These include boiling rangedistributions (Test Method D2887), vapor pressure-temperature relationship (Test Method D2879), and autoignition temperature(Test Meth
49、od E659).6.2.2 Suggested test section temperature measurements are show in Fig. 2. This figure shows a constant heat flux boundarycondition. A constant wall temperature condition may also be imposed 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 temperature) and thesubscript “w” denotes a wall temperature. It is suggested that five or more wall temperatures be obtained over the test sectionlength. For a constant heat flux condition, dTw/dz is constant and
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