Investigation of the effect of using phase change material in cold side heat exchanger on output parameters of a three-layer thermoelectric generator designed for exhaust waste heat recovery

In this thesis study, a three-layer thermoelectric generator (TEG) previously manufactured from aluminum material was experimentally investigated for the use of phase change material (PCM) in cold-side heat exchangers mounted on both surfaces of a central exhaust heat exchanger designed to recover exhaust waste heat in a two-cylinder propane-fueled spark-ignition engine. For this purpose, a central exhaust heat exchanger was designed to consist of cold-side heat exchangers mounted on both surfaces of a two-cylinder propane-fueled spark-ignition engine for exhaust waste heat recovery. (PCM) in the cold-side heat exchangers. For this purpose, the engine coolant (EC) heat exchangers placed on both sides of the central exhaust heat exchanger were filled with FDM (paraffin) with a melting temperature of 53°C and a fusion heat of 170 kJ/kg, and the EC was passed through serpentine copper pipes inside the paraffin. Three groups of experimental studies were conducted by adding 10% by weight of Al2O3 and graphite nanoparticles to the PCM to increase its heat transfer efficiency. The experiments were conducted at five different engine speeds in the range of 2000–4000 rpm under the engine's normal operating (regime) temperature and Wide-open thottle (100% WOT). According to experimental findings, as the engine speed increased, the ΔT on the TEG increased, and consequently, the electrical output parameters of the system increased regularly. In the system using pure paraffin, the total output power was 40.06 W at 2000 rpm and reached 80.16 W at 4000 rpm. Under the same conditions, the 90% paraffin + 10% Al2O3 mixture produced a total output power of 82.33 W, while the 90% paraffin + 10% graphite mixture produced 85.12 W. The recovered fuel energy ratio was determined to be 0.215% for pure paraffin, 0.221% for the Al2O3-added system, and 0.229% for the graphite-added system at 4000 rpm. TEG efficiency followed the same trend, reaching values of 2.298%, 2.364%, and 2.456%, respectively. The results show that nano-doped phase change materials significantly increase the TEG performance, and especially the graphite doping maximizes the system stability both thermally and electrically.