Abstract
Foam materials are widely used in heat exchange because of their high porosity and large specific surface area. Correctly characterizing heat transfer characteristics is the key to ensuring efficient heat transfer. In this paper, single-blow transient test technology is used to experimentally measure the temperature. Silicon carbide ceramics with various thicknesses ranging from 30 to 105 mm and different pore structures were used in the experiments. The test was carried out at the velocity ranging from 0.5 to 1.8 m/s. The air temperature distributions of the inlet and outlet were obtained by processing the experimental data, and the regularity of the average volumetric heat transfer coefficient was obtained and analyzed. Subsequently, the simplified tetrakaidecahedron models with a porosity of 0.85 and 0.75 were used to analyze the heat transfer characteristics. The local thermal equilibrium and local thermal non-equilibrium at the pore scale were analyzed. By comparing the simulation with the experiment, it shows that the larger thickness affects local thermal equilibrium and leads to a decrease in the volumetric heat transfer coefficient. The conclusion can be used to guide the optimization of the design of foam material-mediated heat exchange equipment.
Highlights
IntroductionFoam material is a type of porous, lightweight, high-strength, low-density media [1], which has high heat transfer characteristics and strong flow mixing characteristics due to its inherent properties such as high porosity, large specific surface area, disordered pore distribution, tortuous flow path [2]
Studying heat transfer characteristics of foam should be taken into should accountbe astaken an important influencing factor, which can avoid the overestimation of materials, thickness into account as an important influencing factor, which can avoid the overestimation volumetric heatof transfer coefficient due to local thermal equilibrium caused by larger thickness
The experiment with different geometries of silicon carbide and numerical simulation with simplified tetrakaidecahedron have been presented to understand the effects of key factors such as thickness and pore structure on local thermal equilibrium and heat transfer characteristics
Summary
Foam material is a type of porous, lightweight, high-strength, low-density media [1], which has high heat transfer characteristics and strong flow mixing characteristics due to its inherent properties such as high porosity, large specific surface area, disordered pore distribution, tortuous flow path [2]. For the single-blow method, the temperature of the channel section can be ensured to be uniform by processing the experimental test section, and it becomes a mainstream scheme [22,23] In this method, the volumetric heat transfer coefficient correlations are determined on foam materials with different geometric structures, such as those described by Dietrich [18] and Xia [19]. The phenomenon of local thermal equilibrium (LTE) occurs inside the foam due to the complex structure and the high volumetric heat transfer coefficient At this time, the temperature of the fluid-solid phase is equal, which means that the local convective heat transfer is equal to zero. The results show that the phenomenon of LTE and LTNE change along the thickness direction
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