Measurement of Specific Heat Capacity from 150 to 310 K by Thermal Radiation Calorimetry

A novel method for measurement of the specific heat capacity in the temperature range from 150 to 310 K is described. In order to achieve good temperature homogeneity in a disk-shaped specimen, a cylindrical heater was used in an apparatus based on thermal radiation calorimetry. A mixture of Bi₂O₃ and MgO powders was used for blackening the surfaces of the specimen, the heater, and the inside wall of the chamber. The specific heat capacities of Ni, fused quartz glass, and BaTiO₃ ceramic were measured to test the performance of the calorimeter. Agreement to within 5% of the values published in the literature was obtained for these samples. Thermal hysteresis and anomalies associated with the first-order phase transition in BaTiO₃ were detected in the present experiment.     

An Apparatus for Specific Heat Capacity Measurement by Thermal Radiation Calorimetry

Specific heat capacity measurements of disk-shaped specimens have been performed with an apparatus based on thermal radiation calorimetry. The specimen surfaces were irradiated by two fiat heaters in a vacuum chamber so that homogeneous temperature distribution within an insulating specimen was achieved. Homogeneity was confirmed by computer simulation based on the control-volume method. The values of specific heat capacity were obtained by measurement of the specimen temperature, the time rate change of the specimen temperature, and the radiant power from the heater for heating and cooling modes. The specific heat capacities of Ni metal, A1₂O₃ ceramic, MgO ceramic, and A1N ceramic were measured in the temperature range from 220 to 500°C to confirm the validity of this calorimeter. The relative error involved in the measured values was estimated to be ±3%.     

Conventional Simultaneous Measurement of Specific Heat Capacity and Thermal Conductivity by Thermal Radiation Calorimetry

Thermal radiation calorimetry has been applied to measure the thermal conductivity and the specific heat capacity of an isolated solid specimen simultaneously. The system, in which a disk-shaped specimen and a flat heater are mounted in a vacuum chamber with the specimen heated on one face by irradiation, is presented. A theoretical formulation of the simultaneous measurement at quasi-steady state is described in detail. Noncontact temperature measurement of both specimen surfaces has been performed using pyrometers and a thermocouple set in the gap between the heater and the specimen. Pyroceram 9609 specimens, whose surfaces were blackened with colloidal graphite, were used in the measurement. The largest error involved in the noncontact temperature measurement is ±2°C in the range from 450 to 650°C. The resultant values of the specific heat capacity and the thermal conductivity deviate by about 10% from the recommended values for the Pyroceram specimen.     

A calorimeter for multilayer insulation (MLI) performance measurements at variable temperature

Here we describe a concentric cylindrical calorimeter with radiation guards developed to measure the thermal performance of multilayer insulation (MLI) for low temperature applications. One unique feature of this calorimeter is its ability to independently control the boundary temperatures between room temperature and about 15 K using two single-stage Gifford–McMahon cryocoolers. Also, unlike the existing calorimeters that use the evaporation rate of a liquid cryogen to measure the heat load, in the present system the total heat transfer through the MLI is measured by recording the temperature difference across a calibrated heat load support rod that connects the cold inner cylinder to the lower temperature cryocooler. This design allows the continuous mapping of MLI performance over a much wider temperature range with independently controlled boundary conditions. The calorimeter is also suitable for performing a variety of radiation heat transfer experiments including the determination of the temperature dependence of the total emissivity.     

微乳化乙醇柴油热物性计算与分析

车用清洁型微乳化油是内燃机的理想代用燃料之一．微乳化油热物性参数难以计算,从而影响在内燃机上对它的定量计算研究．以微乳化乙醇柴油为例,用经验公式计算其蒸发焓、生成焓、液体比热容、导热率和微乳化油蒸气的扩散系数,分析了温度和压力以及不同溶醇量对热物性参数的影响规律,为微乳化油热物性参数的计算提供一种工程方法．结果表明：随着温度的增加,微乳化乙醇柴油蒸发焓、导热率降低,定压比热容和微乳化油蒸气扩散系数增加;随着压力增加,微乳化油蒸气扩散系数降低;随着混合燃料中乙醇含量的增加,定压比热容和混合气扩散系数均增大,蒸发焓减小;乙醇含量对混合燃料导热率的影响与燃料温度有关,在一定温度下乙醇含量效应发生逆转;微乳化乙醇柴油中乙醇含量增加有利于燃料蒸发．     

Measurement of thermophysical properties of molten salts: Mixtures of alkaline carbonate salts

The purpose of this study is to develop measuring methods for the thermal diffusivity, the specific heat capacity, and the density of molten salts, as well as to measure these properties of mixtures of alkaline carbonate salts. The thermal diffusivity is measured by the stepwise heating method. The sample salt is poured into a thin container, and as a result, a three-layered cell is formed. The thermal diffusivity is obtained from the ratio of temperature rises at different times measured at the rear surface of the cell when the front surface is heated by the stepwise energy from an iodine lamp. The specific heat capacity is measured using an adiabatic scanning calorimeter. The density is measured by Archimedes' principle. Thermal conductivity is determined from the above properties. Measured samples are Li₂CO₃-K₂CO₃ (42.7–57.3, 50.0-50.0, and 62.0-38.0 mol%).Invited paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

Measurements of thermophysical properties by a stepwise heating method

An outline of the stepwise heating method for measuring thermal diffusivity and specific heat capacity of samples in both solid and liquid phases is described. The method is based on the measurement of temperature response at the surface of a solid sample when the other surface is heated in step-function. By making the best use of the characteristic points of this method, applications to samples in the liquid state, especially to high temperature melts such as molten salts, have been tried. As examples of measurement results, the thermal diffusivity, specific heat capacity, and thermal conductivity of zirconia brick and the thermal diffusivity of molten salts are shown in graphic form.Presented at the Japan-United States Joint Seminar on Thermophysical Properties, October 24–26, 1983, Tokyo, Japan.     

Thermophysical properties of MPG-6 graphite

The thermal diffusivity and heat capacity of four MPG-6 graphite samples (density from 1664 up to 1825 kg/m³) are measured within the temperature range from 293 K up to 1650 K by the following methods: the laser flash, the differential scanning calorimetry, and the adiabatic calorimeter of linear heating. The uncertainties of the data on the thermal diffusivity, heat capacity, and density were (2–4)%, (3–5)%, and 0.5%, respectively. On the basis of the measurement results, the temperature dependence of the MPG-6 thermal conductivity is calculated and a generalizing dependence is obtained which allows one to estimate the thermal conductivity of graphite of various porosity for a wide temperature range using only the data on the macroscopic density of the samples. Reference data tables have been developed for the thermal conductivity of MPG-6 graphite of various densities.     

Evaluation of Hemispherical Total Emissivity for Thermal Radiation Calorimetry

An attempt to derive the hemispherical total emissivity from the normal emission spectrum is proposed for Vycor and fused silica glasses. The normal emission spectrum from a clear surface has been measured at steady state in the temperature range from 400 to 750 K. The sample is heated on one metal-backed face by thermal radiation from a heater. Temperatures inside the sample were monitored by thermocouples at two points near the surfaces. Evaluation of the hemispherical total emissivity from the normal emission spectrum is determined by means of Kramers–Krönig analysis and virtual mode equations. Assuming a linear temperature distribution within the sample, the thermal conductivities of silicate glasses were obtained at elevated temperatures. The results are comparable with those obtained by previous investigators. The effect of radiation heat transfer in a sample is also discussed.     

Freezing-Induced Strains and Pressures in Wet Porous Materials and Especially in Concrete Mortars

A theory based on thermodynamics will be presented by which the pressure in the pore structure of wet porous materials can be deduced during freezing. The pore structure is partly filled with liquid and inert gases such as air. The theory is based solely on thermodynamic relationships; no knowledge of the real geometry of the pore system or the degree of liquid filling in the void space is needed. The only inputs needed in the theory are relative humidity and temperature measured in the sample chamber during the freezing. The validity of the theory will be compared with the test results of mortar samples frozen and thawed in a low temperature calorimeter. During the cooling from 20 to −70°C and subsequent heating of the sample, the strains, heat capacity, and ice evolution of the samples were measured simultaneously in the calorimeter. Two of the three mortar samples were produced using an air-entraining admixture.     

R32风冷冷（热）水机组低温制热性能探讨

普通热泵空调系统在超低温环境下制热衰量减大,难以满足中国北方冬季取暖需求,在一套普通R410A风冷冷（热）水机组上分别对喷液技术和EVI技术进行超低温环境测试对比。结果表明,喷液系统和EVI系统在低温和超低温下具有较好的制热量及制热能效的提升,并且可以解决普通热泵在超低温环境下的应用问题,同时R32的热物理性质与R410A基本相同,提出在低温风冷冷（热）水机组上使用R32替代R410A的设想。     

Simultaneous Measurement of Specific Heat Capacity, Thermal Conductivity, and Thermal Diffusivity by Thermal Radiation Calorimetry

Thermal radiation calorimetry has been applied to measure the thermal diffusivity of a solid specimen, along with simultaneous measurements of specific heat capacity and thermal conductivity. In this calorimeter, a disk-shaped solid specimen whose surfaces are blackened is heated and cooled slowly on one face by irradiation in a vacuum chamber. A quasi-steady-state approximation in which a linear temperature gradient within the specimen was assumed is considered in the analysis. The validity of this approximation was confirmed by the results of computer simulation based on the control-volume method. Measurements of Pyroceram 9606 and Pyrex 7740 by use of thermocouples in the temperature range between 250 and 400°C gave values consistent with those obtained by previous authors, within experimental error, for all three thermophysical properties.     

Specific heat capacity and emissivity measurements of ribbon-shaped graphite using pulse current heating

A measurement method for specific heat capacity and hemispherical total emissivity of electrically conductive materials with pulse current heating is investigated, in which a ribbon-shaped sample is heated up to 3000K in a subsecond-duration experiment. Specific heat capacity and hemispherical total emissivity of the sample are calculated from the time variations of heat generations and surtace temperature of the sample measured during heating and cooling phases. The true surface temperature of the rihhon-shaped samples is obtained with a radiation thermometer: the directional spectral emissivity of the sample surface is measured using a hemisplicrical mirror centered at the sample surface. Measurements are performed for POCO AXM-5Ql graphite in the temperature range from 1500 to 3000 K.Paper presented at the Twelfth Symposium on Thermophysical Properties. June 19–34, 1994 Boulder, Colorado, U.S.A.     

Thermal Conductivity Measurement of Liquids by Using a Suspended Microheater

In this paper, the traditional \(3\omega \) method is modified in order to measure the thermal conductivity of a droplet of liquid. The \(3\omega \) sensor is microfabricated using bulk silicon etching on a silicon wafer to form a microheater on a suspended bridge structure. The Si substrate of over 400 \(\upmu \hbox {m}\) thickness beneath the microheater is etched away so that the sample liquid can fill the gap created between the heater and the bottom boundary of the sensor. The frequency of the sinusoidal heating pulses that are generated from the heater is controlled such that the thermal penetration depth is much smaller than the thickness of the liquid layer. The temperature oscillation of the sample fluid is measured at the thin-film heater to calculate the thermal conductivity of the surrounding fluid. The thermal conductivity and measured values of the de-ionized water and ethanol show a good agreement with the theoretical values at room temperature.     

Calorimetric Measurement of Pulsed Laser Output Energy

There are several methods by which one may measure the energy output of the pulsed laser. However, the technique which seems to be most promising as far as accuracy and precision are concerned is the calorimetric method. We have designed, built, and calibrated calorimeters for measuring the output energy of the pulsed ruby laser (6943?). The heart of the calorimeter is a small absorption cell containing an aqueous solution of CuSO4. The temperature of the absorption cell, as measured by a thermocouple, indicates the energy absorbed by the calorimeter. The calorimeter was calibrated in two different ways: 1) the known heat capacity of the absorption cell and the thermocouple sensitivity calibration gives a calorimeter calibration, which agrees within 0.3 percent of 2) an electrical energy substitution calibration which is obtained via a heater wire contained in the absorption cell solution. A method has been devised by which two calorimeters may be intercompared. Calorimeters which we have built and calibrated agree with each other to about 0.7 percent. This specific calorimeter has been designed to measure energies up to 30 J and will take peak powers of up to 200 MW/cm2.     

Variable temperature FIR-optical cryostat with unique features

This paper describes a convenient cryostat for optical and far infrared transmission and photoconductivity studies at temperatures in the range 5 K to 300 K. Up to four samples can be loaded in a cell and inserted into the cryostat from above without disturbing large metal seals or optical tails. Thermal contact between the heat sink and the cell is made automatically during the cooling process. The thermal link between the heat sink and liquid cryogen reservoir is varied by means of a modified thermosyphon. Even samples which are poor thermal conductors can be controlled in temperature within ± 10 mK by an exchange gas in the sample cell.     

Fibre mortar composites under fire conditions: effects of ageing and moisture content of specimens

Two small scale test series were performed using the cone calorimeter heating method to detect any differences in the way various fibres affect the thermal properties of a standard mortar. The cone shaped heater of the cone calorimeter produces a uniform heat flux on the sample surface over an area of 100×100 mm². The heat flux was adjusted to 50 kW m^?2, which corresponds to the early stage of a fully developed fire. The total exposure also corresponds roughly to the ISO 834 time-temperature curve during the first 30 minutes. Short ageing of the specimens gave very clear differences in thermal properties between fibre mortars. However, no such differences were observed with oven dried samples. This shows the importance of carrying out tests in conditions as close as possible to the end use conditions of the material or product.     

纳米晶体铁的低温热容和热稳定性

用等离子体法制备的纳米晶体铁由XRD和SEM等方法测定其晶粒尺寸的平均值为87nm，用绝热量热方法在79－371K温区精确测定了其低温热容，测量结果比大晶粒Fe的热容值有明显的增强，在80－300K温区之间增强热容为8％－14％，差示扫描量热（DSC）在温区的研究结果则表明，纳米晶体Fe在400－700K温区有一个宽的放热峰，对应于非平衡晶格缺陷所引起的焓释放，850K观察到一个放热峰，是纳米晶体铁从α相向α＋γ相转变所引起的。     

Combined DSC and Pulse-Heating Measurements of Electrical Resistivity and Enthalpy of Tungsten,Niobium, and Titanium

Measurements of thermophysical properties such as enthalpy, electrical resistivity, and specific heat capacity as a function of temperature starting from the solid state into the liquid phase for W, Nb, and Ti are presented in this work. An ohmic pulse-heating technique allows measurements of enthalpy and electrical resistivity from room temperature to the end of the stable liquid phase within 60 μ s. The simultaneous optical measurement of temperature is limited by the fast pyrometers with an onset temperature of T_min = 1200–1500 K; below these temperatures, the fast pyrometers are not sensitive. A differential scanning calorimeter (DSC) is used for determination of the specific heat capacity, and also to obtain enthalpy values in the temperature range of 600–1700 K. Combining the two methods entends the range of values of electrical resistivity and enthalpy versus temperature down to 600 K. Results on the metals W, Nb, and Ti are reported and compared to literature values. This paper is a continuation of earlier work. Paper presented at the Seventh International Workshop on Subsecond Thermophysics, October 6–8, 2004, Orléans, France.