Off-grid power generation has been demonstrated in data centers through the deployment of site-specific centralized power plants utilizing gas turbine or fuel cell-based power generation. Because power is centrally generated, power distribution requires a high voltage power grid within the data center with its ancillary storage and conditioning requirements and equipment. An alternative approach is a completely decentralized distributed power generation system in which fuel cells deployed within individual server racks provide power localized to that rack only. Among other advantages, such an approach also greatly increases the ability to modulate and control power to individual rack units. Because the Solid Oxide Fuel Cells (SOFC) proposed in this approach are air-cooled and have extremely high air exhaust temperatures, of order 800 oC, the optimal energy efficient design of an overall localized fuel-cell power generation system should also consider the opportunities to recover and re-use the waste heat. This paper reports on the development of a coupled thermal-electrical model of a thermoelectric generator (TEG) based energy recovery system operating between the fuel cell hot exhaust air temperature and a warm water cooling system deployed within the rack for server cooling. The power generation system consisted of a TEG module sandwiched between a hot air heat exchanger and a colder water based heat exchanger. The design of the TEG module for maximum power generation is heavily coupled with thermal and electrical conditions. Distribution of temperature on generator surfaces change the optimum design, hence the optimization of generator system required co-optimization with the design of the heat exchangers. This paper will present the results of a co-optimization study considering the effects of thermal parameters such as exhaust gas mass-flow-rate and temperature, cooling water volumetric-flow-rate and temperature, hot- and cold-flow parallel and counter-flow arrangements, as well as the thermal-electrical considerations in the TEG design including the design of the Thermo-Electric junctions, fractional area coverage of thermoelectric elements, and substrate thickness.
© 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. doi: 10.1109/ITHERM.2018.8419483
Ebrahimi, Khosrow; Ortega, Alfonso; Li, Calvin; Yazawa, Kazuaki; and James, Sean. (2018). "Waste Heat Recovery from Distributed Rack-Based Fuel Cells Using Thermoelectric Generators". Proceedings of the Seventeenth InterSociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems: ITherm 2018, 795-814.