Thermal performance evaluation of thin vapor chamber

Abstract

Present study proposes a semi-empirical method to measure the effective thermal conductivities (keff) of a thin vapor chamber (VC). With the liquid-vapor phase change processes as the dominant heat transfer mechanisms in a VC, the keff measurements are expressed as the functions of heat flux and VC orientation. Thermal performance tests measuring the thermal resistances and keff at horizontal and vertical orientations are carried out using three thin VCs of the identical capillary structure with the total thickness of 0.3 mm, 0.4 mm, and 0.5 mm. With the augmented counteracting vapor-liquid flows in these thin VCs, the thermal resistances are raised from a conventional VC. But the thermal spreading performances indexed by keff over the evaporator region remain compatible with the conventional VCs. The sub-cooling effect significantly undermines the thermal spreading performance over the condenser region. When the interior copper pillars are immerged within the excess liquid in condenser, the condenser keff can be less than the thermal conductivity of copper, which phenomenon requires design precautions. While the VC thickness exhibits the noticeable impacts on the thermal performances of the thin VCs, their thermal resistances and evaporator keff are less affected by VC orientation to confirm the anti-gravity properties. A set of empirical correlations evaluating the thermal resistance of these thin VCs are devised for design applications.