الفهرس | Only 14 pages are availabe for public view |
Abstract According to the objective of this research, an investigation of the performance of transposed-fluids heat exchangers to be used in Stirling engine design, eight simple heat exchangers were designed, manufactured, and tested experimentally to be used as a heater and a cooler in the alpha type Stirling engine. Each specimen was a shell-and-tube, air-to-water, and elbow bend heat exchanger. As a first step a number of five heat exchangers were designed, manufactured, and tested. Each specimen of this group has a different tube bank arrangement and geometrical configuration. The specimen which has minimum dead volume, low pressure DROP and high rate of heat transfer was selected as the best one to be improved in the second step. From the discussion of the first step experimental results, it was found that a specimen of (quadrant cross-section) and circular tube arrangement can be selected as the best one. Three specimens were manufactured similar to the best one. These specimens have the same geometrical configuration and tube bank arrangement, but have different tube spacing. So they have different number of tubes consequently different dead ” volumes. from the discussion of the second step experimental results, it was found that the specimen of the least number of tubes has the minimum pressure drop, but does not have the minimum dead volume, while it has a reasonably high rate of heat transfer Each one of the eight tested specimens was employed individually as a heater and a cooler in a computer program (Excel program) to study the engine performance analytically. Based on the Schmidt analysis the engine work space was divided into three isothermal regions. This program considers the friction losses and consequently the pressure DROP due to the working fluid flow through each part of the engine. The dimensions of the engine parts were optimized analytically according to two schemes to get a maximum output power. In the first scheme, different strokes of the expansion and compression were assumed. In the second scheme, they were assumed to be equal. For all calculations the optimum performance was calculated at a charging pressure, which insures 40 bar maximum pressure inside the machine. The cooling water mass flow rate and its inlet temperature to the cooler were assumed constant. Also the hot gasses mass flow rate and its inlet temperature to the heater were assumed constant. The inner diameter of the expansion and compression spaces was assumed to be equal. The optimum dimensions of the engine were found. The optimum engine power was found for a specimen which has square cross-section, in-line tube bank arrangement. |