EFFECT OF FIN PASSAGE LENGTH ON OPTIMIZATION OF CYLINDER HEAD COOLING FINS

摘要

The heat transfer performance of baffled cooling fins on cylinder heads of small, air-cooled, general-aviation aircraft engines was analyzed to determine the potential for improving cooling fin design. Flow baffles were assumed to be installed tightly against the fin end edges, an ideal baffle configuration for guiding all flow between the fins. A rectangular flow passage is thereby formed between each set of two adjacent fins, the fin base surface, and the baffle. These passages extend around each side of the cylinder head, and the cooling air absorbs heat as it flows within them. For each flow passage length, the analysis was concerned with optimizing fin spacing and thickness to achieve the best heat transfer for each fin width. Previous literature has been concerned mainly with maximizing the local fin conductance and has not considered the heating of the gas in the flow direction, which leads to higher wall temperatures at the fin passage exits. If the fins are close together, there is a large surface area, but the airflow is restricted. This leads to high air temperatures at the rear of the cylinder head and consequently a high wall temperature at that location. Increasing the fin spacing provides more flow but may excessively reduce the surface area and lead to high wall temperatures. Thus, there is an optimum fin spacing, which is investigated herein for each fin width as a function of fin passage length in the flow direction. The optimum spacing increased as the flow passage length increased.