Integrated dual cycle energy recovery using thermoelectric conversion and an organic Rankine bottoming cycle

Graduation date: 2011Hot engine exhaust and industrial process exhaust represents a resource that is often rejected to the environment without further utilization. This resource is prevalent in the transportation and industrial process sectors, but stationary engine-generator systems also typically do not utilize this resource. Engine exhaust is considered high grade heat and can potentially be utilized by various approaches to produce electricity or to drive heating and cooling systems. This thesis describes a model system that employs thermoelectric conversion as a topping cycle integrated with an organic Rankine bottoming cycle for waste heat utilization. This approach is being developed to fully utilize the thermal energy contained in hot exhaust streams. This thesis investigates several system configurations each composed of a high temperature heat exchanger which extracts thermal energy for driving the thermoelectric conversion\ud elements and a closely integrated bottoming cycle to capture the large amount of remaining thermal energy in the exhaust stream. The models differ by how they arrange specific heat exchangers in the system. Many interacting parameters that define combined system operation are employed in the models to determine overall system performance including output power, efficiency, and total energy utilization factors. In addition, the model identifies a maximum power operating point for the combined system. That is, the model can identify the optimal amount of heat to remove from the exhaust flow to drive the thermoelectric elements for maximizing the combined cycle output. The model has been developed such that the impact of heat exchanger UA[subscript h] values, thermal resistances, and the thermoelectric figure-of-merit (ZT) can be investigated in the context of system operation. The model also has the ability to simultaneously determine the effect of each cycle design parameter on the performance of the overall system, thus giving the ability to utilize as much waste heat as possible. Key analysis results are presented showing the impact of critical design parameters on power output, system performance and inter-relationships between design parameters in governing performance