Experimental study on a pulsating heat pipe heat exchanger for energy saving in air-conditioning system in summer

Abstract A new-type pulsating heat pipes heat exchanger (PHP-HE) was made to recover energy from exhausted air in air-conditioning system. It consisted of 40 pulsating heat pipes, which each had length of 21.6 m, the inner diameter of 2.0 mm, and bent into 40 turns. The working fluid used in the heat pipe was R134a with a filling rate of 50%. In order to simulate the summer operation condition, the outdoor air temperature was controlled in the range of 30 °C to 45 °C, while the indoor air temperature was kept constant at 26 °C. The wind speed was controlled in the range of 1.0 to 3.5 m/s, and the installation angle varied from 0 to 90° Results of this study show that the PHP-HE operated well both in the horizontal and bottom heated modes, and started up under a small temperature difference (less than 4.0 °C) between the fresh and exhaust air. The overall effectiveness of this PHP-HE was in the range of about 30% and 50%, depending on operation conditions such as the installation angle, fresh air temperature, and the wind speed. In general, this PHP-HE with R134a showed a good start-up and operating performance, which is beneficial to its application in air conditioning system.