Evaporation heat transfer characteristics of composite porous wick with spherical-dendritic powders

Highlights: • A composite porous wick with spherical-dendritic powders is proposed. • Two evaporation heat transfer modes have been observed. • The spherical-dendritic copper composite porous wick has large critical heat flux. • No dry out occurs in composite porous wick. • The temperature fluctuation may not affect the evaporator wall temperature. -- Abstract: A composite porous wick with spherical-dendritic powders is proposed in this paper. Both the small pores between the dendritic powders and the pores between the spherical and dendritic powders are formed. Moreover, the inhomogeneous local thermal conductivity may increase the tortuosity of the evaporating interface and provide more evaporating area. Two kinds of materials (copper and nickel) and two kinds of structures (spherical and dendritic powders) are chosen to prepare four composite porous wicks, and the evaporation heat transfer characteristics are studied experimentally. Two evaporation heat transfer modes have been observed. The composite porous wick with spherical-dendritic copper powders has the largest critical heat flux of 15.1 W/cm². At high heat load, the upper surface temperature of composite porous wick may be equal to or even lower than the vapor temperature. The temperature fluctuation may occur, but not affect the evaporator wall temperature. According to the distribution of the evaporating meniscus in porous wick, the critical heat flux may be predicted. The reasonable design of the pore size distribution and large evaporating rate in small pores can increase the critical heat flux.