Özet:

Approximately 40% of the heat energy of the fuel in internal combustion engines is emitted to the atmosphere as waste heat along with exhaust gases. Recovery of some of the exhaust waste heat energy could remarkably increase the fuel conversion efficiency. In this study, to optimize the hot side (exhaust) heat exchanger surface temperature and distribution in the thermoelectric generator where electrical energy is generated from the exhaust waste heat energy of the spark-ignition engine, the heat exchangers having different fin number and arrangement were analyzed by computational fluid dynamics method. In the study, the internal volume of the exhaust heat exchanger, whose main dimensions were determined by designing in the previous study, was divided into two equal parts with the using a separator plate, and heat exchanger arrangements were created by three different fins ranking types using in the literature (i.e. accordion, fishbone, and serial plate). Different from the fin geometries (i.e. square, rectangular, triangular, and trapezoidal prisms) commonly used in the literature, raindrop geometry was used in heat exchanger arrangements. Also, flow guiding vanes having rectangular prism geometry was added to the plane of the inlet diffuser of the separator plate. Exhaust gas temperature and flow rate values obtained in the experimental study performed at 2200 rpm of a single-cylinder spark-ignition engine was used in the computational fluid dynamics analyzes performed for exchanger arrangements. For each heat exchanger arrangement, computational fluid dynamics analyzes were performed steady-state, and the contours of temperature distribution, velocity vectors, inlet-outlet temperatures, pressure drop inside the exchanger were obtained. According to the results of the computational fluid dynamics analysis performed for the designed exhaust exchanger arrangements; the reverse direction serial plate arrangement having six flow guiding fins and 15°, 30°, and 45° angled raindrop geometries have more optimum values in terms of heat exchanger surface temperature, distribution and pressure drop in the exchanger compared to other models. Furthermore, with the heat exchanger arrangements with raindrop fin structure, a higher and homogeneous heat exchanger surface temperature was achieved despite higher pressure drop compared to the reference (empty) heat exchanger arrangement.

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