Call number: LD2668 .T4 1985 S335 / Master of Science

Rising energy demands and the continual push to find more energy efficient technologies have been the impetus for the investigation of waste heat recovery techniques. Diesel engine exhaust heat utilization has the potential to significantly reduce the consumption of fossil fuels and reduce the release of greenhouse gases, because diesel engines are ubiquitous in industry and transportation. The exhaust energy can used to provide refrigeration by implementing an organic Rankine cycle coupled with a vapor-compression cycle. A critical component in this system, and in any waste heat recovery system, is the heat exchanger that extracts the heat from the exhaust. In this study, a cross-flow microchannel heat exchanger was geometrically examined and thermally tested under laboratory conditions. The heat exchanger, referred to as the Heat Recovery Unit (HRU), was designed to transfer diesel exhaust energy to a heat transfer oil. Two methods were developed to measure the geometry of the microchannels. The first was based on image processing of microscope photographs, and the second involved an analysis of profilometer measurements. Both methods revealed that the exhaust channels (air channels) were, on average, smaller in cross-sectional area by 11% when compared to the design. The cross-sectional area of the oil channels were 8% smaller than their design. The hydraulic diameters for both channel geometries were close to their design. Hot air was used to simulate diesel engine exhaust. Thermal testing of the heat exchanger included measurements of heat transfer, effectiveness, air pressure drop, and oil pressure drop. The experimental results for the heat transfer and effectiveness agreed well with the model predictions. However, the measured air pressure drop and oil pressure drop were significantly higher than the model. The discrepancy was attributed to the model's ideal representation of the channel areas. Additionally, since the model did not account for the complex flow path of the oil stream, the measured oil pressure drop was much higher than the predicted pressure drop. The highest duty of the Heat Recovery Unit observed during the experimental tests was 12.3 kW and the highest effectiveness was 97.8%. To examine the flow distribution through the air channels, velocity measurements were collected at the outlet of the Heat Recovery Unit using a hot film anemometer. For unheated air flow, the profile measurements indicated that there was flow maldistribution. A temperature profile was measured and analyzed for a thermally loaded condition. / Graduation date: 2012

The need for clean and renewable fuel such as hydrogen is driven by a growing worldwide population and increasing air pollution from fossil fuels. One of the major barriers for the use of hydrogen in automotive industry is the storage of hydrogen. Physisorption is the most promising storage technique due to its high storage density, reversibility and rapid sorption kinetics besides being safe and volume-efficient. A major challenge for physisorption is the need to manage the heat of adsorption at cryogenic temperatures. In this thesis, a 6061 aluminum microchannel cooling plate is designed to remove the equivalent heat flux required by the adsorption of hydrogen within an adsorption bed. Therefore, the objective of this thesis is to determine whether laser welding and heat treating strategies can be developed for a 6061 aluminum microchannel cooling plate as part of a larger hydrogen storage thermal management system. Key manufacturing process requirements include controlling the hermeticity, strength and dimensional stability of the heat-treated weld joint. A hermetic microchannel cooling plate was successfully laser welded and heat treated using free convection in air to quench the solution heat treatment. The weld strength and warpage obtained were within acceptable limits. Experimental testing of the fabricated microchannel cooling plate showed acceptable percent error with an experimental heat removal rate within 13.4% of computational fluid dynamics (CFD) analyses and an average pressure drop error of 25%. Calculations show that the cooling plate developed could support a hydrogen storage thermal management system taking up 5.0% and 10.3% of the system displacement volume and mass, respectively. / Graduation date: 2013