Thermochemical cycle | EPFL Graph Search

Thermochemical cycles combine solely heat sources (thermo) with chemical reactions to split water into its hydrogen and oxygen components. The term cycle is used because aside of water, hydrogen and oxygen, the chemical compounds used in these processes are continuously recycled. If work is partially used as an input, the resulting thermochemical cycle is defined as a hybrid one. History This concept was first postulated by Funk and Reinstrom (1966) as a maximally efficient way to produce fuels (e.g. hydrogen, ammonia) from stable and abundant species (e.g. water, nitrogen) and heat sources. Although fuel availability was scarcely considered before the oil crisis efficient fuel generation was an issue in important niche markets. As an example, in the military logistics field, providing fuels for vehicles in remote battlefields is a key task. Hence, a mobile production system based on a portable heat source (a nuclear reactor was considered) was being investigated with utmo

Installation, instrumentation and testing of an exhaust gas heat recuperator for hybrid cycle

Thomas Wicht

This report presents the work done in the frame of a Minor in Energy project in the school of Mechanical Engineering at the Swiss Institute of Technology of Lausanne (EPFL), in order to obtain 10 ECTS credits. It is to install, instrument and test an exhaust gas heat recuperator and to assess its performances. The project fits into the topic of hybrid cycles based on fuel cells and inverted Brayton-Joule cycles. The system is first presented and the instrumentation is detailed. The tests are then described and the results are presented and discussed. The heat exchanger appears to be very large versus the gas flowrate and the flue gases are cooled down to low temperatures. The condensation is an issue and the condensed water collection system is not efficient, leading to problems in doing power estimations. Finally some possible improvements of the system are proposed and described. A smaller heat exchanger is also computed and presented as an example.

2011

Dynamic flow control and performance comparison of different concepts of two-phase on-chip cooling cycles

Jackson Braz Marcinichen, Bruno Michel, John Richard Thome, Duan Wu

A hybrid on-chip two-phase cooling cycle specifically designed to cool server boards with chips of high performance computers was experimentally evaluated considering steady-state and transient operation of two parallel pseudo-chips and auxiliary electronics mimicking a real server board. Control strategies were developed and evaluated by reference tracking and disturbance rejection tests considering several setpoints of controlled variables. The hybrid cycle, operating with a common refrigerant R134a as the working fluid, was energetically and exergetically compared with two other cooling cycles experimentally evaluated in a previous study, one driven by an oil-free gear pump and another by an oil-free mini-compressor. The results showed that, for a specific steady state condition and heat load, respectively 28.9%, 51.9% and 62.5% of the energy out of the pump, compressor and hybrid cycles were associated with heat losses. The differences observed between the three cycles were justified firstly due to the concept of the cycles, i.e. cycles with the compressor showed as expected lower thermal performance than that with pump since its appeal is for energy recovery (benefitting from a higher condensing temperature) and secondly due to the irreversibilities observed in drivers, condenser and piping (thermal insulation). In summary, the three cycles proved to be efficient, simple and reliable concepts to cool server boards (CPUs, DIMMs etc.), showing high thermal performance and potential for heat recovery when compared with traditional air-cooling systems in current use in data centers. It can also be said that the pump cycle showed the best results in terms of energy and exergy, with the cooling and heat recovery performances reaching a maximum of about 5 and 1.8 times higher than the other cycles (worth noting that the focus in the present study was two-phase flow control and proof-of-concept of different cooling loops, meaning that no "optimal" system design was attempted and the differences above can be reduced). (C) 2013 Elsevier Ltd. All rights reserved.

Elsevier2014

Dynamic flow control and performance comparison of different concepts of two-phase on-chip cooling cycles

Jackson Braz Marcinichen, Bruno Michel, John Richard Thome, Duan Wu

Elsevier2014