Heat transport limitations and performance enhancement of anodized grooved heat pipes charged with ammonia under gravity and anti-gravity condition

• First-time ammonia charged anodized grooved heat pipes tested under anti-gravity. • Semi spherical shape pores formed through anodization in a grooved heat pipe. • Heat transport limitations of anodized grooved heat pipes were modelled. • Anodization reduced 51.1% resistance and enhanced 36.6% heat transfer coefficient. • Anodized grooved heat pipes transferred maximum of 35 W under anti-gravity condition. Grooved Heat Pipes (GHPs) are the essential heat transfer devices for space applications, as they can effectively work with and without the aid of gravity. In the present study, the heat transport limitations of anodized grooved heat pipes were modelled by incorporating an anodised surface coating parameters under gravity and anti-gravity conditions. Variations in the heat transport limitations such as capillary limit, boiling limit, and entrainment limits due to the anodization over non-anodized grooved heat pipes are presented. The heat transfer performance of an internally anodized and non-anodized grooved heat pipe charged with ammonia as a coolant is experimentally investigated and compared. Two sets of grooved heat pipes are fabricated with 40 numbers of rectangular grooves. Semi-spherical pores are formed by carefully adjusting the voltage and current supply between the electrodes during the anodization process. Experiments in grooved heat pipes are conducted at different inclinations (0-90°) under gravity and anti-gravity for various heat inputs of both heat pipes. Due to the anodization, thermal resistance reduction of 51.1% and enhancement in heat transfer coefficient of 36.6% was obtained at an optimum inclination of 45° for the grooved heat pipes with 0.4 mm groove width. Also, a maximum of 35 W heat input was transferred due to the anodization under anti-gravity with an inclination of 30°. Results suggest that the grooved heat pipes with semi-spherical pores charged with ammonia as a coolant was the best combination for enhanced heat transfer, preferably for space applications.