Thermal analysis with contact resistance of packed bed by a homogenization method

• The proposed method is a useful tool for modeling heat transfer with contact resistance.
• Thermal radiation was dominant at high temperature and for large particle.
• It is not necessary for high Biot number to consider thermal contact resistance.

Effective thermal conductivity with contact resistance is analyzed by a homogenization method that can precisely represent the microstructure of a packed bed. The homogenization used in this study explains the heat transfer due to conduction through the solid, the fluid phase, and the contact area between particles, and radiation between solid surfaces. In particular, the effects of parameters, such as the hardness, contact pressure, roughness, temperature, and particle size of the packed bed, on conductivity are estimated in order to clarify the thermal conduction mechanism for the complex packed structure. Heat transfer with thermal contact resistance does not dominate if the Biot number is near 100. In case of larger particle size and no convective heat transfer, the micro-hardness, contact pressure, surface roughness are important factor for effective thermal conductivity. Moreover, thermal radiation in the bed becomes more important for larger particles (> 1 mm) and contact resistance can be neglected. However, effective thermal conductivity of pebble bed is dependent on the void fraction.

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