Experimental study on the heat transfer performance of vapor chamber with uniform/gradient wicks

The balance of the combined effect of wick permeability and capillary pressure is very important to improve the heat transfer capability of the vapor chamber (VC). In this paper, a series of VCs were designed and fabricated, in which the wick was a gradient structure with composite particle shape and composite particle size, and their heat transfer effects were studied experimentally and compared with VCs with uniform-structure wick. The difference in characteristics and mechanisms of heat transfer for various types of VCs at five filling ratios were analyzed. The results indicated that the average temperature on the evaporator side of VC with the gradient-structure wick was 4.45–15 °C lower than that of VC with the uniform-structure wick, indicating that the gradient structure wick significantly improved the VC's heat transfer capability. Moreover, the VC with a composite particle-shape gradient wick (sintered using 75 μm irregular copper powder particles in the hotspot area and 110 μm spherical copper powder particles in the peripheral area) demonstrated the highest heat transfer performance. Its thermal resistance was less than 0.1 °C/W, and the maximum heating power reached 55 W at the optimal filling ratio.