Investigations on effect of evaporator length on heat transport of axially grooved ammonia heat pipe

Abstract

Axially grooved ammonia heat pipes are widely used in spacecraft for thermal management of electronic packages, which are of various dimensions and heat dissipation levels. In order to study the effect of evaporator length on the maximum heat transport of heat pipes, two nominally charged dual channel axially grooved heat pipes (one for operating at a nominal temperature of 20 °C and the other for operating at a nominal temperature of 60 °C) were fabricated and tested using heaters of various lengths. In order to avoid flooding of the grooves/impact of puddle on the heat transport capability due to uncertainty in the charge quantity, all the tests were carried out at some adverse tilt. Experimental results reveal that at a given operating temperature, with decrease in the evaporator length, the evaporator heat flux increases and the maximum heat transport decreases. Analysis of the test results shows that decrease in the maximum heat transport with decrease in the evaporator length is mainly due to decrease in the available capillary pressure. Decrease in the capillary pressure with increase in the heat flux is postulated to be due to increase in the apparent contact angle between the working fluid and the wick surface.