1、Designation: D 2766 95 (Reapproved 2005)An American National StandardStandard Test Method forSpecific Heat of Liquids and Solids1This standard is issued under the fixed designation D 2766; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revi
2、sion, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defense.1. Scope1.1 This test method c
3、overs the determination of the heatcapacity of liquids and solids. It is applicable to liquids andsolids that are chemically compatible with stainless steel, thathave a vapor pressure less than 13.3 kPa (100 torr), and that donot undergo phase transformation throughout the range of testtemperatures.
4、 The specific heat of materials with higher vaporpressures can be determined if their vapor pressures are knownthroughout the range of test temperatures.1.2 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.1.3 This standard does
5、 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-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Stand
6、ards:2D 1217 Test Method for Density and Relative Density(Specific Gravity) of Liquids by Bingham Pycnometer3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 specific heatthe ratio of the amount of heat neededto raise the temperature of a mass of the substance by aspecified amou
7、nt to that required to raise the temperature of anequal mass of water by the same amount, assuming no phasechange in either case.3.2 Symbols:Tf= temperature of hot zone, C,Tc= initial temperature of calorimeter, C,T8 = Tf Tc= temperature differential, C,R1= resistance of nominal 1-V standard resisto
8、r,R100= resistance of nominal 100-V standard resistor,R10 000= resistance of nominal 10 000-V standard resis-tor,E1= emf across nominal 1-V standard resistor,E100= emf across nominal 100-V standard resistor,E10 000= emf across nominal 10 000-V standard resis-tor,tc= time of application of calibratio
9、n heater current,s,q = total heat developed by calibration heater, cal,DEc= total heat effect for container, mV,DEs= total heat effect for sample + container, mV,Dec= total heat effect for calibration of calorimetersystem during container run, mV,Des= total heat effect for calibration of calorimeter
10、system during sample run, mV,DHc= total enthalpy change for container changingfrom Tfto Tc,DHT= total enthalpy change for sample plus containerchanging from Tfto Tc,DHs= total enthalpy change for sample changing fromTfto Tc,F = calorimeter factor,W = weight of sample corrected for air buoyancydf= de
11、nsity of sample at Tf,dc= density of sample at Tc,VT= total volume of sample container,Vf= volume of sample vapor at Tf,Vc= volume of sample vapor at Tc,Pf= vapor pressure of sample at Tf,Pc= vapor pressure of sample at Tc,Nf= moles sample vapor at Tf,Nc= moles sample vapor at Tc,N = moles sample va
12、por condensed,DHv= heat of vaporization of sample,R = gas constant, andK = heat of vaporization correction.3.3 Units:1This test method is under jurisdiction of ASTM Committee D02 on PetroleumProducts and Lubricants and is the direct responsibility of Subcommittee D02.11 onEngineering Sciences of Hig
13、h Performance Fluids and Solids.Current edition approved June 1, 2005. Published September 2005. Originallyapproved in 1968. Last previous edition approved in 2000 as D 276695(2000).2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.o
14、rg. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.3.1 The energy and thermal (heat) capacity units used inthis m
15、ethod are defined as follows:1 cal (International Table) = 4.1868 J1 Btu (British thermal unit, International Table) =1055.06 J1 Btu/lb F = 1 cal/g C1 Btu/lb F = 4.1868 J/g K3.3.2 For all but the most precise measurements made withthis method the rounded-off value of 4.19 J/cal can be used asthis is
16、 adequate for the precision of the test and avoids thedifficulty caused by the dual definition of the calorie.4. Summary of Test Method4.1 The enthalpy change, DHc, that occurs when an emptysample container is transferred from a hot zone of constanttemperature to an adiabatic calorimeter at a fixed
17、initialtemperature is measured for selected hot zone temperaturesevenly spread over the temperature range of interest.4.2 The enthalpy change, DHT, that occurs when a containerfilled with the test specimen is transferred from a hot zone ofconstant temperature, Tc, to an adiabatic calorimeter at a fi
18、xedinitial temperature is measured for selected hot-zone tempera-tures evenly spread over the temperature range of interest.4.3 The net enthalpy change per gram of sample is thenexpressed as an analytical power function of the temperaturedifferential T8. The first derivative of this function with re
19、spectto the actual temperature, Tf, yields the specific heat of thesample as a function of temperature. Actual values of thespecific heat may be obtained from solutions of this equationwhich is valid over the same range of temperatures over whichthe total enthalpy changes, DHT, were measured.5. Sign
20、ificance and Use5.1 The specific heat or heat capacity of a substance is athermodynamic property that is a measure of the amount ofenergy required to produce a given temperature change withina unit quantity of that substance. It is used in engineeringcalculations that relate to the manner in which a
21、 given systemmay react to thermal stresses.6. Apparatus6.1 Drop-Method-of-Mixtures Calorimeter, consisting es-sentially of a vertically mounted, thermostatically controlled,tube furnace and a water-filled adiabatic calorimeter. Thefurnace is mounted with respect to the calorimeter in such away that
22、it may be swung from a remote position to a locationdirectly over the calorimeter and returned rapidly to the remoteposition. The sample container may thus be dropped directlyinto the calorimeter with a minimum transfer of radiation fromfurnace to calorimeter. Details of construction are shown inFig
23、. 1.6.2 Sample ContainerA stainless steel sample containerwith a polytetrafluoroethylene seal suitable for use at tempera-tures up to 533 K (500F) is shown in Fig. 2.6.3 Potential Measuring Devices (two required), potentialmeasuring device capable of measurement of up to 1 V with aprecision of 106V
24、or a potentiometer assembly with sensitiv-ity of at least 1 V or a digital multimeter with equivalentsensitivity, range, and a minimum of six digit resolution isacceptable. A direct reading digital temperature indicatingdevice may be substituted for the potential measuring devicefor the purpose of m
25、easuring the temperature of the capsulewhile in the tube furnace. See Fig. 3.6.4 Resistor,1-V precision type.3,46.5 Resistor, 100-V precision type.3,46.6 Resistor, 10 000-V precision type.3,46.7 Amplifier, zero centered range, linear response withpreset ranges to include 625 nV, 6100 V, 6200 V,6500V
26、, 61000 V, and 62000 V; with error not to exceed60.04 % of output; with zero drift after warm-up not to exceed3If you are aware of alternative suppliers, please provide this information toASTM International Headquarters. Your comments will receive careful consider-ation at a meeting of the responsib
27、le technical committee,1which you may attend.4The sole source of supply of the apparatus known to the committee at this timeis Models 9330/1, 9330/100, 9330/10K, Guildline Instruments, Inc., 103 CommerceSt., Ste 160, Lake Mary, FL 32795-2590.FIG. 1 Specific Heat ApparatusD 2766 95 (2005)260.5 V offs
28、et within which drift will not exceed 60.2V/min. Equivalent instrumentation with different fixed poten-tial ranges is acceptable provided the same overall potentialranges are covered.6.8 Strip Chart Recorder, with nominal 25 cm chart, 65mV, zero center.6.9 Binding Posts, low thermal emf-type, with p
29、rovision forguard circuit.6.10 Rotary Switch, low thermal emf-type, with provisionfor guard circuit.6.11 Thermistor Bridge.3,56.12 Thermistor.3,56.13 Thermocouple, copper-constantan, stainless steelsheath, 3.2 mm (18 in.) in outside diameter.3,66.14 Power Supply, 24 V dc.NOTE 1Two 12 V automobile ba
30、tteries in series have proved satis-factory as a power supply. They should be new and fully charged.6.15 Power Supply, constant-voltage, for potentiometer.3,76.16 Standard Cell, unsaturated cadmium type, for potenti-ometer.3,87. Calibration7.1 The enthalpy change, DHc, that occurs when an emptysampl
31、e container is transferred from the tube furnace at a fixedtemperature into the adiabatic calorimeter is not a function onlyof the composition of the container and the temperaturedifference between the furnace and the calorimeter. Becauseheat losses occur as the results of both conduction and radiat
32、ionfrom the container during the transfer process, some heat isalso transferred by radiation to the calorimeter at the sametime. The measured value of DHcas a function of temperatureserves a dual purpose: (1) it provides the value of containerenthalpy change that must be deducted from DHTto determin
33、eDHS;(2) simultaneously it affords a correction term thatcancels out the effect of conduction and radiation that occurduring sample transfer.7.2 The following procedure is used to determine DHcateach selected temperature for each sample container over thetemperature range of interest (Note 3): Bring
34、 the empty samplecontainer to a constant temperature in the vertical tube furnace.Monitor its temperature with the copper-constantan thermo-couple that is fitted into the center well of the container. Whilethe container is equilibrating, adjust the temperature of thecalorimeter by cooling or warming
35、 it as required to bring it toa temperature just below the selected initial starting point (Note4). Adjust the thermistor bridge so that it will have zero outputat the selected initial temperature. Any changes of this bridgesetting will require recalibration of the system. The amplifiedoutput of the
36、 thermistor bridge is displayed on the recorder(Note 5). As the calorimeter approaches the selected startingtemperature, the output of the bridge becomes less negativeand approaches zero (the starting temperature). Just before theoutput reaches zero, determine the temperature of the capsuleby readin
37、g the output of the copper-constantan thermocouple tothe nearest 1 V (Note 6). At the moment the calorimetertemperature passes through the selected starting temperature,swing the vertical furnace over the calorimeter and drop thesample container into the calorimeter. Return the furnaceimmediately to
38、 its rest position. As the calorimeter warms,adjust the potentiometer bias to bring the recorded temperaturetrace on scale. Record the temperature until it resumes a nearlylinear drift. Then determine the total heat effect, measured inmillivolts, by taking the algebraic sum of the initial and finalp
39、otentiometer biases and the extrapolated differences in thetemperature traces (Note 7). In order to determine the exactenergy equivalent of the millivolt change measured during thedrop of the container, it is necessary to perform a heater run.This run is made after every drop as the calibration of t
40、hesystem is a function of the size of the heat effect as well as ofthe water content of the calorimeter. Since the rate of energyinput from the electrical heater is of necessity much smallerthan that encountered in the drop itself, it is not possible toduplicate the heat effect of the drop exactly.
41、Instead, adjust thetemperature of the calorimeter so that the bias of the potenti-ometer is such that an electrical heat effect of known size willoccur over a range intermediate between the initial and finalpoints of the drop (Note 8). During the heater run, measure thecurrent through the heater and
42、 the potential drop across theheater by monitoring the potentials across standard resistors R1and R10 0. Measure the time interval of application of heat tothe nearest 0.1 s, and determine the change in potential due tothe electrical heat effect by taking the algebraic sum of theinitial and final po
43、tentiometer biases and the extrapolatedinitial and final temperatures.NOTE 2If organic materials are to be studied, it is suggested thatfifteen determinations of DHcmade at roughly equal intervals over thetemperature range from 311 to 533 K (100 to 500F) will suffice in mostinstances.5The sole sourc
44、e of supply of the apparatus known to the committee at this timeis VWR, Welch Div., Chicago, IL, under the following catalog number: ThermistorBridgeNo. S-81601; ThermistorNo. S-81620.6The sole source of supply of the apparatus known to the committee at this timeis Thermocouple Products Co., Inc., V
45、illa Park, IL.7The sole source of supply of the apparatus known to the committee at this timeis No. 245G-NW-19, Instrulab, Inc., Dayton, OH.8The sole source of supply of the apparatus known to the committee at this timeis Eppley Laboratory, Inc., Newport, RI.FIG. 2 Specific Heat Sample CellD 2766 95
46、 (2005)3NOTE 3The initial temperature is usually selected to be slightly lowerthan average room temperature so that calorimeter drift due to stirring anddeviations from complete adiabaticity will result in a slow, almost lineardrift through the selected starting temperature.NOTE 4Normally a 50 V ful
47、l-scale setting of the amplifier is usedand initial potentiometer bias is set at zero.NOTE 5Provided that an accurate calibration of the thermocouple ismade prior to its use, it should be possible to determine the temperature tothe nearest 0.1C with accuracy.NOTE 6To compensate for differences in th
48、e initial and final rates ofdrift, it is good practice to extrapolate both initial and final rates to thatpoint in time at which one half of the total heat effect has occurred. For theheat effect occurring after a drop, it has been found that one half of thetotal heat effect occurs so rapidly that n
49、o significant error occurs inextrapolating the final drift back to the initial time. For heater runs, it isnecessary to make an empirical determination of the point at which onehalf of the heat effect has occurred in order to perform a properextrapolation.NOTE 7Thus, if the total heat effect of the drop is found to be 8 mVand a heater run will cause a change of 2 mV, the initial bias of the heaterrun should be set at 3 mV so the final point will be 5 mV. This procedurecompensates almost completely for the non-linearity of the thermistor.Theerror inc
