Transient Calorimetric Technique Research Articles

Transient Calorimetric Measurement Method for Total Hemispherical Emissivity

The transient calorimetric technique was used to measure the total hemispherical emissivity of conductive materials. The emissivity was measured in a small central region of a thin strip heated electrically in a vacuum chamber. The axial heat transfer along the sample and the heat losses from the wires were considered in the transient heat transfer calculations. An appropriate time interval for the hot sample cooling rate is needed to improve the emissivity solution accuracy. Two ways were used to analyze the data, based on the known specific heat and the assumed functions of the emissivity and the specific heat. Comparisons with steady-state data showed that their results are very similar with a maximum difference of only 13% (944 K). Therefore, the transient method based on the function assumption is a good choice for measurements when there are inaccurate or insufficient specific heat data at the desired temperatures. Since ferromagnetic materials have Curie points at higher temperatures, this study also investigated the applicability of the transient calorimetric technique for high temperature emissivity measurements. For higher temperatures above the Curie point, the steady-state method is more accurate than the transient method. These analyses provide a comprehensive understanding of the transient method for measuring the total hemispherical emissivity.

503 非定常熱量法による固体の比熱の測定(GS-7 熱(1))

503 非定常熱量法による固体の比熱の測定(GS-7 熱(1))

Total hemispherical emissivity of glass sheets with different thicknesses measured by a transient calorimetric technique

Total emissivity of glass sheets varies with sheet thickness since glass is a semitransparent material. The total hemispherical emissivity, e h , of fused-silica and soda-lime glass sheets of different thicknesses was measured by a transient calorimetric technique previously proposed. The measured e h values are arranged together with those of borosilicate glass sheets reported in our previous work. The e h values obtained for various sheets are expressed as functions of sheet thickness and temperature. Further, the e h values are compared with other published data obtained by experiments and theory, and discussed. An edge effect caused by the temperature distribution on the specimen surface, is clarified and the error involved in the e h values measured by the transient calorimetric technique, is estimated. In addition, another edge effect caused by the distribution on the local total hemispherical emissivity on the specimen surface is made clear.

An Improved Transient Calorimetric Technique for Measuring the Total Hemispherical Emittance of Nonconducting Materials (Emittance Evaluation of Glass Sheets)

For measurements of the total hemispherical emittance e h of nonconducting materials, a problem of the thermal gradient produced in a sample specimen arises. An improved transient calorimetric technique to reduce the thermal gradient is proposed in this study. Glass sheets (borosilicate), semi-transparent for radiation, are selected as the nonconducting test material. The e h values of the glass sheets for various thicknesses are measured, and their results are presented as functions of thickness and temperature. The thermal gradients in the specimens are calculated by a three-dimensional analysis, and the corner effect due to them on the measured e h is estimated. It is shown that the proposed technique is useful for measuring the emittance e h of nonconducting materials.

Measurement of total hemispherical emittance of a nonconducting and semitransparent material by a transient calorimetric technique

An improved transient calorimetric technique was previously proposed for the measurement of the total hemispherical emittance, e h , of nonconducting materials and the results measured for Pyrex-glass sheets by the technique were reported. In this study, the e h values of a fused-silica glass sheet are measured by the same technique. A simple analytical way to evaluate the local total directional emittance, e*, of a glass sheet semitransparent to radiation is presented, and the e* values are computed on the surfaces of the specimen used. Further, values of the local total hemispherical emittance, e h *, on the specimen surfaces are obtained from e*. From the results for e* h , the edge effect of the specimen caused by the e* h distributions on the measured e h is clarified. The temperature distributions in the specimen are obtained by three-dimensional analysis, and then the edge effect caused by the distributions on e h is presented. It is found that the improved transient calorimetric technique is very suitable for measuring e h of nonconducting materials.

102 非定常熱量法による板ガラスの全半球放射率測定(熱工学)

By an improved transient calorimetric technique, total hemispherical emittance ε_h of glass sheets of borosilicate and fused silica has been measured. The temperature inside the glass-sheet specimen by the technique is analyzed, and it is confirmed that the effect of the temperature distribution inside the specimen on the measured ε_h is very little. Local total emittance ε_h on the specimen surface is also analytically obtained, and the effect of ε_h on the measured ε_h is examined.

低温アルミニウムの全半球ふく射率の高精度測定法

To measure total hemispherical emissivities eTH(T) of metals at low temperatures, a new transient calorimetric technique is developed to improve its accuracy. The accuracy of this technique mainly depends upon heat loss Qt through a thermocouple (TC) which suspends a specimen and measures its temperature. To reduce Qt, an Iron. Constantan TC with diameter of about 20μm is used, and the temperature profile of TC is controlled by a guard heater attached to the other sides of TC. eTH(T) of aluminum specimens which shaped wire (99.9994% purity) and plate (99.988%) are measured in the temperature range from 125 to 350K. The specimens are mechanically polished. The roughness of the plate surface is measured. Qt, evaluated by a combined radiation and conduction heat transfer analysis, is less than 1% of the total power loss of the specimen. eTH(T) for wire and annealed plate are in good agreement with each other, and close to the values extrapolated from the date obtained above room temperature. An increase in eTH(T) of the plate without annealing may be due to the Beilby/damaged surfaces formed by mechanical polishing.

Simultaneous measurements of specific heat and total hemispherical emissivity of chromel and alumel by a transient calorimetric technique

Using a transient calorimetric technique, the specific heat and total hemispherical emissivity of chromel and alumel were measured simultaneously in the temperature range 360–760 K. Two types of specimens for each material were prepared. To obtain reliable experimental values of specific heat and total hemispherical emissivity, an expression for the time history of the temperature of the specimens was developed; this expression is accurate over the whole temperature range. An error analysis is made and the uncertainty (the total error) in the values of specific heat and total hemispherical emissivity is estimated to be 3.1% for the well-designed specimens.

Simultaneous Measurement of Specific Heat and Total Hemispherical Emissivity of Metals by the Transient Calorimetric Technique. 2nd Report, Experimental Verification with Cylindrical Compound Specimens.

The specific heat c and total hemispherical emissivity εh of iron and constantan have been measured using the simultaneous-measurement method proposed in our previous report to verify the accuracy in the measurement. Cylindrical specimens, whose geometrical shape is presumed to be more appropriate than those in the previous report, are used as the compound specimens necessary for the method. To obtain more accurate results, an expression for the temperature versus time curve has been developed ; this expression is highly accurate over the entire temperature range. For iron, the measured c- and εh-values are compared with c-values recommended in CINDAS Data Series and with εh-values previously measured by H. Masuda and M. Higano, respectively. For constantan, empirical relations between c and T (temperature) and εh and T are obtained. Errors in the present results are analyzed and the total errors in the results are estimated.

Validity of transient calorimetric technique for measuring the total hemispherical emissivity of metals

Validity of transient calorimetric technique for measuring the total hemispherical emissivity of metals

A method for the simultaneous measurement of total hemispherical emissivity and specific heat of metals by the transient calorimetric technique

A resistive self-heating technique by which an electric current is passed through a specimen has been applied to multiple measurements of the thermophysical properties of metals. An alternative approach is proposed for the simultaneous measurement of the total hemispherical emissivity ϵ h and specific heat c of metals. The measuring method used here is the transient calorimetric technique, which has been used in the past only for measuring ϵ h of metals. In the proposed approach, it is necessary to prepare two types of specimens, one made of a metallic material to be measured, and the other a compound specimen constructed of both the material to be measured and a standard reference metallic material whose emissivity and specific heat are well known. The ϵ h and c values of the measured material can be simultaneously determined from the experimental results obtained for the two specimens, that is, the two temperature-versus-time curves. Constantan and copper were selected as the material to be measured and the standard reference material, respectively, and were used for the two types of specimens. The measurements were performed in the temperature range of 380–720 K, and the ϵ h and c values were obtained. From the results, it was verified that the proposed approach is applicable to the simultaneous measurement of the total hemispherical emissivity and specific heat of metals.

Simultaneous measurement of specific heat and total hemispherical emissivity of metals by the transient calorimetric technique.

A new principle for performing a simultaneous measurement of the specific heat, c, and the total hemispherical emissivity, εh, of metals is proposed. The measuring technique used is not the resistive self-heating method by electric current, but essentially the transient calorimetric method which is usually used only for measuring the εh. On this principle, two kinds of specimens need to be prepared; one is a specimen made of the material to be measured, and another is a compound specimen made of the above-mentioned material and a standard one. From the experimental results for these two specimens, the c and the εh values can be determined simultaneously. Constantan and copper were selected, respectively, as the test material and the standard, and measurements were performed in the range of 380-720K. The method appears suitable for performing a simultaneous measurement of c and εh of metals, particularly for measuring εh of alloys of which the specific heat data are lacking.

Total hemispherical emissivities of cobalt and nickel in the range 350–1000 K

The transient calorimetric technique was used to measure the total hemispherical emissivities of single-crystal cobalt and nickel over the temperature range 350–1000 K. Anomalous emissivities and cooling rates of these samples were observed in the critical region. It was found that the temperature dependence of the thermal coefficient of the dc resistivities is very similar to that of the emissivities. It is reasonable to use this similarity to explain the anomalous emissivities of cobalt and nickel in their respective critical regions. Outside those regions the experimental results are in reasonable agreement with those calculated using the Drude theory.

Measurement of Total Hemispherical Emissivities of Metal Wires by Using Transient Calorimetric Technique

An application of the transient calorimetric technique was studied for measuring total hemispherical emissivities of metal wires. A unique idea of using guard wires, which have a function similar to usual guard heaters, was incorporated into the emissivity apparatus to reduce conduction heat losses through thermocouple leads suspending a specimen. Emissivity measurements were performed by using a copper wire as a specimen. The heat losses through the leads were analyzed in considering radiation heat transfer from the leads, and the effect of the guard wires on the heat losses was clarified. Temperature distributions in the specimen were also obtained analytically. From these results, it was found that an improved transient calorimetric technique in this work is applicable to the emissivity measurement on metal wires, and that the accuracy in the measurements is adequate.

New Transient Calorimetric Technique for Determining the Total Hemispherical Emissivity of Metals — An Application of Laser Flash Method

Article New Transient Calorimetric Technique for Determining the Total Hemispherical Emissivity of Metals — An Application of Laser Flash Method was published on July 1, 1986 in the journal High Temperature Materials and Processes (volume 7, issue 2-3).

Transient calorimetric technique for measuring total hemispherical emissivities of metals with rigorous evaluation of heat loss through thermocouple leads

An apparatus for the transient calorimetric technique used for measuring the total hemispherical emissivities of metals has been developed. Measurements have been made on specimens of copper and aluminum in the temperature range of 330–630 K. An exact analysis is given of the conduction heat loss through thermocouple leads suspending the specimen. From the numerical results of the lead-wire heat loss, the significant effect of a guard heater employed in the apparatus is illustrated. By taking account of the heat loss, the emissivities of the specimens are accurately evaluated and are compared with the data of previous investigators.

Chart for estimation of conduction heat leak from specimens used in the measurements of properties by the transient calorimetric technique

In measuring thermophysical properties using the transient calorimetric method, conduction heat leak from test specimens can be a source of error if not properly accounted for. An analysis method is presented in this paper for determining the magnitude of this leak. The analysis consists of deriving the temperature profiles in the specimen support. These temperatures are then used to determine the heat leak using two different approaches. In the first approach, the heat penetration depth in the support is derived and used to obtain an added thermal capacitance to the specimen. In the second approach, the heat leak was considered to reduce the net heat input. Both small and large heat-leak cases were analyzed, with the latter estimated by means of two recurrence relations. A chart was also developed for a rapid estimation of this leak. In the absence of a reliable experiment to measure the heat leak, this paper provides a viable alternative for accurate leak determination.

Adsorbate-induced change in the total hemispherical emissivity of W(100)

A variation on the transient calorimetric technique is used to measure the change in the total hemispherical emissivity of the clean (100) surface of tungsten induced by adsorption of oxygen, carbon monoxide, and carbon. In each case, monolayer quantities of adsorbate cause a fractional decrease in the emissivity of about 1% over the temperature range 450–1000 K. An explanation of this behavior is proposed that involves the change in conduction electron scattering at the surface caused by quenching of the W(100) surface resonance at 0.3 eV.

Total hemispherical emissivity of W(100)

The transient calorimetric technique is used to measure the total hemispherical emissivity of the clean (100) surface of single crystal tungsten over the temperature range 340 to 1260 °K. The emissivity is found to be only slightly sensitive to adsorption of monolayer quantities of oxygen on the surface. Results are fit to a free-electron Drude model with a correction term for interband absorption.

The total hemispherical emissivity of copper

The transient calorimetric technique is used to measure the temperature dependence of the total hemispherical emissivity of polished copper. Our experimental results do not agree with the emissivity predicted by Parker and Abbott. With no adjustable parameters good agreement is obtained between experimental results and a model in which electron-phonon and electron-surface scattering are included in the Drude approximation.