Relationship between Expansion Ratio and Stress to act on the Copper Tube Assembling the Plate Fin Tube Type Heat Exchanger

摘要

A plate fin tube type heat exchanger has been widely used as a heat exchanger fur an air conditioner. It is composed of copper tubes and aluminum fin stocks, and, in general. assembled by means of mechanical tube expansion. Two tube expansion methods are available: shrinking method and shrink-less method. In this paper, we report on measurement result of stress acting on copper tubes when they are expanded, tube expansion ratio of a heat exchanger, and reduction ratio of tube wall thickness. For each of the shrinking and shrink-less methods, by using smooth bare copper tubes and inner grooved copper tubes having an outside diameter of 7mm and average wall thickness of 0.30mm, and aluminum fin stocks having an hole diameter 7.33mm and thickness of 0.100mm, we made 4sample heat exchangers. Following are our measurement result: In tube expansion of the shrinking method, from start to finish, almost constant compression stress in given to copper tube, and thus we had observed no great change in the tube expansion ratio. In tube expansion of shrink-less method, compression stress acted on copper tube temporality during pre-expansion of the tubes. However, as tube expansion progressed, tensile stress grew, reducing the tube expansion ratio accordingly. (For smooth bare tube: 0.4 percent, inner grooved tube 0.7 percent) As for reduction of copper tube wall thickness, the tube expanded with the shrink-less method has a higher ratio than the tube expanded with the shrinking method. In the case of shrink-less method, tubes were expanded with tensile stress acting on the copper tubing. Thus, it is inferred that the reduction ratio of tube wall thickness grew in the latter stage of tube expansion when tensile stress increased, thus reducing the tube expansion ratio.