Integrated Absorption Refrigeration and Thermoelectric Based Cascaded Waste Heat Recovery
Open Access
- Author:
- Abbasi, Shahzaib
- Graduate Program:
- Mechanical Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- October 12, 2020
- Committee Members:
- Alexander S Rattner, Dissertation Advisor/Co-Advisor
Alexander S Rattner, Committee Chair/Co-Chair
Stephen P Lynch, Committee Member
Matthew J Rau, Committee Member
James Freihaut, Outside Member
Bed Poudel, Special Member
Daniel Connell Haworth, Program Head/Chair - Keywords:
- Thermoelectric
Absorption Refrigeration
Refrigeration
Energy Harvesting
Waste Heat Recover
Organic Rankine Cycle
Cascaded Waste Heat Recovery
WHR
ARS
TEG - Abstract:
- Waste Heat Recovery (WHR) methods that use only a single process to recover heat may be termed as single-pathway WHR methods. Common examples are technologies based on Thermoelectric Generators (TEGs), Organic Ranking Cycles (ORC), or absorption-based Thermally Activated Refrigeration (TAR). Most single-pathway WHR methods can only effectively harness heat sources in certain temperature ranges. A system in which heat is recovered as it cascades from a higher temperature to a lower temperature can be termed a cascaded WHR system. Cascaded WHR methods are of a particular interest for applications like refrigerated transport vehicles and industrial carburizing furnace operations where multiple outputs are needed, such as electricity, refrigeration, and process heating. This dissertation proposes a novel, integrated cascaded WHR system that uses a temperature matched approach that can increase process efficiency by providing electrical power and refrigeration through WHR. To investigate the potential of this approach, cycle models, thermoeconomic studies, and an experimental investigation of a cascaded approach of WHR, is performed. Thermoelectric generators (TEGs) are solid state devices that perform at their optimum when the temperature difference across their junctions is high. The efficiency of a TEG scales with the hot junction temperature. However, the efficiency of TEGs is low (~5%), hence the TEG pathway of WHR only harvests a small portion of a high-availability waste heat. Absorption Refrigeration Systems (ARS), however, can operate efficiently with low temperature heat sources. In this study, TEGs and Absorption Refrigeration (AR) subsystems are integrated using a coupling fluid, such that high-grade waste heat cascades through the TEGs, and the low-grade waste heat rejected by the TEG subsystem is used to operate an absorption refrigeration subsystem. Both systems have previously been investigated as single-pathway waste heat recovery methods but owing their respective temperature ranges in which they operate efficiently (high for TEGs and mid-to-low for Absorption Refrigeration), they are well-suited for integration. A thermoeconomic study of the proposed cascaded WHR system is performed, and the results from that study are compared to ORC based WHR systems. The study concluded that the payback periods for TEGs and AR based cascaded WHR systems are comparable to those of ORC based WHR systems. In order to investigate the challenges of integrated, cascaded WHR and to provide a basis for the thermoeconomic feasibility analysis, a 1/10th scale experimental facility was built based on the results from an engineering model created for the refrigerated transport application. This facility was experimentally tested at different inlet temperatures and flow rates for simulated exhaust and coupling fluid, to simulate the operating conditions of the vehicle application. An important part of the facility construction was the design and development of the Heat Acquisition Unit which extracts waste heat from the exhaust stream and transfers it through the TEGs to the coupling fluid, and the coupling fluid delivers heat to the absorption subsystem. Using this experimental approach, different design tradeoffs like electrical power output vs. cooling delivery and cost vs. WHR efficiency were explored. The experimental results were used for the validation of subsystem models.