This dissertation first reviews non-traditional heat exchanger geometry, laser welding, practical issues with microchannel heat exchangers, and high effectiveness heat exchangers. Existing microchannel heat exchangers have low material costs, but high manufacturing costs. This dissertation presents a new microchannel heat exchanger design and accompanying continuous manufacturing technique for low-cost production. The cost optimization shows that with a lower cost per heat transfer ability, the resultant heat exchanger is less expensive and is higher effectiveness. This high effectiveness can be achieved even with a polymer heat exchanger, possibly with multiple serial stages. The dissertation discusses one possible joining method - a new type of laser welding named "forward conduction welding." The expanded heat exchanger can have counter-flow, cross-flow, or parallel-flow configurations. It can be used for all types of fluids, and the materials can be polymers, metals, or polymer-ceramic precursors. The cost and ineffectiveness reduction may be an order of magnitude or more. This dissertation uses the solar water pasteurizer, as an example, to demonstrate the application and optimization of the new heat exchanger. The prototype was fabricated with forward conduction laser welding with 28 micron thick low density polyethylene sheets. The measured effectiveness with water to water heat transfer was 72%. The predicted effectiveness was considerably higher, so a CT scan was performed to diagnose the problem with the channels not having the same heights at all points (causing flow maldistribution). A finite difference model was developed in Matlab to use this height data to predict the experimental effectiveness from first principles. This was compared to the experimental results, and reasonable agreement was found. The effect of manifold flow maldistribution and heat transfer was investigated. A number of effects, if modeled, would reduce error. Recommendations for future expanded heat exchangers and applications are made. The most promising avenue is multiple stages of cross flow.
|School||UNIVERSITY OF COLORADO AT BOULDER|
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