Radiative heat transfer in transient hot-wire measurements of thermal conductivity

1991 ◽  
Vol 12 (6) ◽  
pp. 985-997 ◽  
Author(s):  
C. A. Nieto de Castro ◽  
R. A. Perkins ◽  
H. M. Roder
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Transient Hot Wire ◽  
Hot Wire

scholarly journals Change in Conductive–Radiative Heat Transfer Mechanism Forced by Graphite Microfiller in Expanded Polystyrene Thermal Insulation—Experimental and Simulated Investigations

Materials ◽  
2020 ◽  
Vol 13 (11) ◽  
pp. 2626
Author(s):  
Aurelia Blazejczyk ◽  
Cezariusz Jastrzebski ◽  
Michał Wierzbicki
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Thermal Resistance ◽  
Thermal Insulation ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Expanded Polystyrene ◽  
Transfer Mechanism ◽  
Total Thermal Conductivity ◽  
Heat Transfer Mechanism

This article introduces an innovative approach to the investigation of the conductive–radiative heat transfer mechanism in expanded polystyrene (EPS) thermal insulation at negligible convection. Closed-cell EPS foam (bulk density 14–17 kg·m−3) in the form of panels (of thickness 0.02–0.18 m) was tested with 1–15 µm graphite microparticles (GMP) at two different industrial concentrations (up to 4.3% of the EPS mass). A heat flow meter (HFM) was found to be precise enough to observe all thermal effects under study: the dependence of the total thermal conductivity on thickness, density, and GMP content, as well as the thermal resistance relative gain. An alternative explanation of the total thermal conductivity “thickness effect” is proposed. The conductive–radiative components of the total thermal conductivity were separated, by comparing measured (with and without Al-foil) and simulated (i.e., calculated based on data reported in the literature) results. This helps to elucidate why a small addition of GMP (below 4.3%) forces such an evident drop in total thermal conductivity, down to 0.03 W·m−1·K−1. As proposed, a physical cause is related to the change in mechanism of the heat transfer by conduction and radiation. The main accomplishment is discovering that the change forced by GMP in the polymer matrix thermal conduction may dominate the radiation change. Hence, the matrix conduction component change is considered to be the major cause of the observed drop in total thermal conductivity of EPS insulation. At the microscopic level of the molecules or chains (e.g., in polymers), significant differences observed in the intensity of Raman spectra and in the glass transition temperature increase on differential scanning calorimetry(DSC) thermograms, when comparing EPS foam with and without GMP, complementarily support the above statement. An additional practical achievement is finding the maximum thickness at which one may reduce the “grey” EPS insulating layer, with respect to “dotted” EPS at a required level of thermal resistance. In the case of the thickest (0.30 m) panels for a passive building, above 18% of thickness reduction is found to be possible.

scholarly journals Experimental Methodology to Determine Thermal Conductivity of Nanofluids by Using a Commercial Transient Hot-Wire Device

2021 ◽  
Vol 12 (1) ◽  
pp. 329
Author(s):  
Jose I. Prado ◽  
Uxía Calviño ◽  
Luis Lugo
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Theoretical Model ◽  
Ethylene Glycol ◽  
Experimental Methodology ◽  
Transient Hot Wire ◽  
Hot Wire ◽  
Experimental Procedure ◽  
Transfer Processes ◽  
The Mean

The lack of a standard experimental procedure to determine thermal conductivity of fluids is noticeable in heat transfer processes from practical and fundamental perspectives. Since a wide variety of techniques have been used, reported literature data have huge discrepancies. A common practice is using manufactured thermal conductivity meters for nanofluids, which can standardize the measurements but are also somewhat inaccurate. In this study, a new methodology to perform reliable measurements with a recent commercial transient hot-wire device is introduced. Accordingly, some extensively studied fluids in the literature (water, ethylene glycol, ethylene glycol:water mixture 50:50 vol%, propylene glycol, and n-tetradecane) covering the range 0.100 to 0.700 W m−1 K−1 were used to check the device in the temperature range 283.15 to 333.15 K. Deviations between the collected data and the theoretical model, and repeatabilities and deviations between reported and literature values, were analyzed. Systematic deviations in raw data were found, and a correction factor depending on the mean thermal conductivity was proposed to operate with nanofluids. Considering all tested effects, the expanded (k = 2) uncertainty of the device was set as 5%. This proposed methodology was also checked with n-hexadecane and magnesium-oxide-based n-tetradecane nanofluids.

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