Transient Calorimetric Measurement Method for Total Hemispherical Emissivity

2012 ◽  
Vol 134 (11) ◽  
Author(s):  
Tairan Fu ◽  
Peng Tan
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Specific Heat ◽  
Good Choice ◽  
Thin Strip ◽  
Time Interval ◽  
Transient Method ◽  
Steady State Method ◽  
Calorimetric Technique ◽  
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.

Measurement of Total Hemispherical Emittance and Specific Heat of Aluminum and Inconel 718 by a Calorimetric Technique

2005 ◽  
Vol 128 (3) ◽  
pp. 302-306 ◽  
Author(s):  
Giovanni Tanda ◽  
Mario Misale
Keyword(s):  
Heat Transfer ◽  
Specific Heat ◽  
Radiative Heat Transfer ◽  
Inconel 718 ◽  
Radiative Heat ◽  
Time History ◽  
Inconel 718 Alloy ◽  
Joule Effect ◽  
Calorimetric Technique ◽  
Total Hemispherical Emittance

An apparatus for the measurement of the total hemispherical emittance and specific heat of metals has been developed. The measurement principle is based on the calorimetric technique: the sample, heated by Joule effect and placed in a vacuum chamber, exchanges radiative heat transfer with the walls of the container, kept at a relatively low temperature. Emittance is deduced from the radiative heat transfer laws at the steady state. When the heating power is switched off, the specific heat of the sample can be recovered from the time history of the sample temperature during the cooling transient. Measurements have been performed on samples of aluminum Anticorodal alloy and Inconel 718 alloy under different surface conditions in the 350-635K range.

scholarly journals Heat Transfer in a Concrete Composite Cross-Section

2016 ◽  
Vol 16 (2) ◽  
pp. 61-66
Author(s):  
Maroš Klabník ◽  
Juraj Králik
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Capacity ◽  
Boundary Conditions ◽  
Specific Heat ◽  
Cross Section ◽  
Specific Heat Capacity ◽  
Time Interval ◽  
Capacity Coefficient ◽  
Material Characteristics

Abstract The work is concerned with the spread of heat in 2D coupled cross section with respect to the material characteristics and boundary conditions of calculation. Heat transfer was simulated in the program ANSYS in time interval up to 180 minutes. Nine various models were created to investigate the rate of influence of the changes in thermal material characteristics such as the specific heat capacity coefficient and thermal conductivity, upon the course and difference of temperature in the concrete cross-section. The comparison of results obtained using non-linear and constant values of the variables in simulation was made, too.

scholarly journals Interstitial condensation in Chinese residential buildings: cliché or challenge?

2021 ◽  
Vol 2069 (1) ◽  
pp. 012206
Author(s):  
Hanyu Yang ◽  
Xing Zheng ◽  
Mingfang Tang ◽  
Chi Feng
Keyword(s):  
Steady State ◽  
Residential Buildings ◽  
Transient Method ◽  
Climate Conditions ◽  
Steady State Method ◽  
Hygrothermal Simulation ◽  
State Method

Abstract In this paper, we compare the predictions of interstitial condensation by the steady-state method and the transient method under different climate conditions in China. Simulations reveal significant differences between the two methods, and the wind-driven rain also plays an important role. As a result, the transient hygrothermal simulation considering wind-driven rain should be recommended instead of the steady-state method for predicting interstitial condensation under complicated climate conditions.

Simultaneous Retrieval of Total Hemispherical Emissivity and Specific Heat From Transient Multimode Heat Transfer Experiments

2008 ◽  
Vol 130 (6) ◽  
Author(s):  
G. Venugopal ◽  
M. Deiveegan ◽  
C. Balaji ◽  
S. P. Venkateshan
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Specific Heat ◽  
Transient Response ◽  
Convection Heat Transfer ◽  
Simultaneous Estimation ◽  
Transfer Coefficients ◽  
Transient Heating ◽  
Number Range ◽  
Total Hemispherical Emissivity

Transient cooling experiments of a heated vertical aluminum plate with an embedded heater, in quiescent air, were conducted for the simultaneous estimation of total hemispherical emissivity and specific heat of the plate material. During cooling, the heat loss from the hot plate by natural convection and radiation was taken into account. During the experiments, plate temperatures were recorded at several locations using a data acquisition system. A numerically computed transient response of the plate is then compared with the experimentally known transient response to estimate the residual, the minimization of which using Levenberg–Marquardt’s iterative procedure retrieves the parameters pertinent to the problem. The experiments were conducted for three different surface emissivities of the plate obtained by using suitable surface treatment. A consistency test for the present approach was also done by conducting transient heating experiments using the retrieved values of parameters and a comparison of simulated and calculated natural convection heat transfer coefficients as a function of temperature. The experiments have been performed over a temperature range of 320–430K and a Rayleigh number range of 2×106–2×107. The emissivity values are in good agreement with previous reported results.

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