EXPERIMENTAL STUDY ON THERMAL PERFORMANCE OF PULSATING HEAT PIPE WITH Al_2O_3-DEIONIZED WATER NANOFLUID AT DIFFERENT ORIENTATIONS

摘要

Thermal resistance as a function of heat load and start-up temperature with respect to time have been investigated for a pulsating heat pipe (PHP) at different inclination angles. PHP was made of 1.45 mm inner diameter copper tubes having 6 turns. Al_2O_3 nanofluid (concentration 0.25%, 0.5,1.0,1.25,1.5, and 2.5% by wt.) with particle size 45 nm at an optimum filling ratio of 50% was used. It is found that as the concentration increases from 0.25% to 1.0% there is considerable decrease in thermal resistance as compared to that of the base fluid but as the concentration increases from 1.25% to 2.5% the thermal performance deteriorates. Optimum concentration of nanoparticles was 1.0% by wt. in base fluid with respect to start-up and thermal resistance for PHP in vertical orientation and 45° inclination, while in horizontal orientation 0.5% by wt. concentration showed the best results. Maximum decrease in thermal resistance with respect to deionized (DI) water was observed at 50 W for 1.0% nanofluid concentration by wt. at 45° inclination, which was 33.6%. Heat transfer coefficients at evaporator and condenser are also investigated at vertical mode of operation.