Mathematical and experimental analysis of an internally finned double pipe heat exchanger for coupling of solid oxide fuel cell cathode exhaust heat and vapor absorption refrigeration system on refrigerated trucks

Solid oxide fuel cells (SOFCs) generate electricity with high quality waste heat which if harnessed and used as energy source for vapor absorption refrigeration systems (VARS) will address the emission issues related to refrigerated transport infrastructure. The temperature range of the heat source required at the desorber of the VARS is between 120 °C and 200 °C, while SOFCs cathode exhaust heat temperatures are 600 °C and above. Therefore, an internally finned double pipe heat exchanger (DPHX) was used in this study with thermal oil as the coupling fluid to experimentally couple the SOFC cathode exhaust heat with the VARS indirectly. The experimental setup mimics a 5 kWe SOFC stack. Results showed that 1.84 kW of heat was recovered at a cathode exhaust flowrate of 24.64 L s^-1 resulting in a heat exchanger effectiveness of 12.22% and overall heat transfer coefficient of 60.15 W m^-2 K^-1. The recovered 1.84 kW of heat are able to power a single effect VARS on board a small, refrigerated truck to supply 1 kW of cooling load. Results also revealed an exchanger effectiveness and overall heat transfer coefficient increase by 70.2% and 19.4%, respectively, at a reduced exhaust flowrate of 7.347 L s^-1. Further improvement of 81.1% and 39.22%, respectively, of exchanger effectiveness and overall heat transfer coefficient was achieved at 4.653 L s^-1 exhaust flowrate.