Effects of sintered structural parameters on reducing the superheat level in heat pipe evaporators

Abstract

For applications involving high heat density and low heat load, this study investigates the correlation among superheat, evaporative heat transfer, and the sintered structural parameters of heat pipe evaporators. In the experiments, structural parameters, such as powder size, powder shape, and structural thickness, all influence evaporative heat transfer performance. To measure the evaporative heat flux at low superheat levels, this study developed an advanced facility integrated with a temperature data acquisition system, a low heat loss chamber, a directly sintered design, and a pressure controllable environment. Among the combinations of the structural parameters, evaporation could occur stably at the superheat of only 1.90 K when the structural parameters are composed of 45-μm dendritic powder and 751-μm thickness, moreover, the evaporative heat flux could still achieve 8.91 W/cm2 at this superheat level. To enhance evaporative heat transfer and lower corresponding superheat, this study suggests that an improved result can be attained by having a powder shape of inter-pores, smaller powder size, and thinner structural thickness. However, these parameters are constrained by practical applications, such as the effects of permeability, capillary effect, and dry-out prevention. In conclusion, the total amount of thin film, working fluid level in structure, and effective thermal conductivity may be the factors affecting evaporative heat transfer and corresponding superheat in evaporators.