Design and Manufacturability of an Aluminum Cross Corrugated Primary Surface Heat Exchanger
Wong, Tjung Yeung
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In this thesis, a consideration is given to the design and manufacturability of a cross corrugated primary surface heat exchanger utilizing aluminum plate material. The unitary cell geometry of the cross corrugated surface as well as the main geometrical quantities are considered based on studies by others. An investigation was conducted in order to find the optimum shape of the heat exchanger as well as the flow direction. The investigation shows that the rectangular with triangular ends heat exchanger with countercurrent flow is the preferred design over the other shapes and flow paths considered in this thesis. This configuration provides the largest LMTD which reduces the required total heat transfer surface area for a given duty as well as hedging the risk of maldistribution flow that might exists in the heat exchanger. The Nusselt Number and the Friction Factor were considered in the heat transfer calculations. The result shows that lower pitch over height ratio (P/H i ) will result in a higher heat transfer coefficient and a lower pressure drop. Two cross corrugated angles were considered and the results shows that the cross corrugated angle of &thetas; = 75 degree shows superior performance over &thetas; = 60 degree. Optimization methods were utilized in designing the heat exchanger based on setting restrictions on criteria such as heat transfer surface area and allowable pressure drop. The resulting sizes of the heat exchangers differ depending upon the cross corrugated shape, corrugated angle as well as the plate thicknesses. The theoretical results show that decreases in the pitch over height ratio (P/Hi) will result in a lighter weight and smaller volume heat exchanger. The focus of the manufacturability of the heat exchanges is on producing the cross corrugated surface using aluminum plate. Thin aluminum plate was selected due to the consideration of producing a light weight and cost effective heat exchanger. However, the material's % elongation (stretchability and thinning) limits producing the most cost effective heat exchanger. The maximum % elongation of Aluminum 3003-O that was tested using the UB die set was about 25% (before it breaks); thus, resulting in a higher pitch over height ratio (P/H i ) than desired. This suggest the strong need for further research into alternate materials and manufacturing techniques that would results in achieving the desired, lower P/H i ratio = 2.2.