Experimental study on serpentine-looped minichannel pulsating heat pipe heat exchanger with horizontal installation for full-year efficient heat recovery in air conditioning.

The heat recovery technology is considered to be one of the effective energy-saving means for buildings. The heat pipe, as a simple passive device with high thermal conductivity, has been widely used in heat recovery applications. Due to the opposite positions of cold and heat sources in winter and summer, vertical or inclined heat
pipe heat exchangers can be difficult to operate in a certain seasonal condition. The horizontal heat pipe heat exchanger can solve this problem, but suffers from low heat transfer efficiency. The horizontal air-to-air finned heat exchanger is proposed based on the serpentine-looped minichannel pulsating heat pipe (SLMPHP) for efficient heat recovery in air conditioning. The SLMPHP heat exchanger is experimentally studied including the effects of the filling ratio, air flowrate and indoor and outdoor temperatures. The internal oscillation behaviors are also explored using Power Spectrum Density (PSD) method. Results show that the optimal range of the filling ratio for the SLMPHP is 45–65 % with greater oscillation intensity, and the maximum temperature effectiveness can reach 83.8 % in summer and 84.5 % in winter under horizontal installation, respectively. A thermal resistance map of SLMPHP heat exchanger is also presented for analysis and further prediction of its heat transfer performance to provide a guideline for the SLMPHP application in building heat recovery.