Experimental Analysis on the Evaporator Startup Behaviors in a Trapezoidally Grooved Heat Pipe

The startup behaviors of evaporation heat transfer in a trapezoidal groove are experimentally studied by using an axial heat pipe with trapezoidal grooves. The effects of heat load and inclined angles on the evaporation startup behaviors are analyzed and discussed. The startup regime diagram is provided to quantitatively describe the behaviors of evaporation heat transfer based on the Weber number and Bond number. The results indicate that, only the gradual startup is observed for the evaporation heat transfer in trapezoidal grooves, however the gradual startup and overshoot startup is experienced in sequence in the tilt condition as the heat load increases. The appearance of evaporation startup regime transition from the gradual startup to overshoot startup is induced by the evaporation regime transition from the fin-film evaporation to the corner-film evaporation inside the evaporator section. The gradual startup occurs for a small Weber number and the overshoot startup occurs for a large Weber number. Increase in Bond number introduces a larger transition Weber number for the startup regime variation of evaporation heat transfer in a trapezoidal groove. Interestingly, the occurrence of the temperature overshoot of few Celsius degrees can be observed to verify whether the grooved heat pipe is in a horizontal position.