Experimental investigation of energy and exergy efficiency of a pulsating heat pipe for chimney heat recovery

A prototype heat exchanger is proposed for exhaust heat recovery by means of pulsating heat pipe. The device is made up of an exhaust channel, an air channel, and a row of pulsating heat pipes with the filling ratio of 40% and ethanol and silver nano-fluid as working fluids. The exhaust hot gas from the combustion of natural gas feeds the device. For exergy analysis of the device, the inlet and outlet temperatures of the hot gas and cold air were measured with appropriate devices. Having the exergy of each flow, the exergetic efficiency of the system was calculated at different inlet temperatures. The calculations were carried out for two distinct working fluids within the heat pipes. The energy analysis results show that ethanol, at an inlet smoke temperature of 120 °C, has the best functionality. Exergy analysis also demonstrated the better performance of silver nano-fluid compared to ethanol. The use of silver nano-fluid instead of ethanol increases exergy efficiency as much as 1–3% and decreases exergy losses as much as 8–14%.