Organic Rankine Cycles

Description:

Waste heat from engines or other sources can be used for co-generation of electrical power and heat at a lower temperature level which can be used for district heating. Although water is used in normal Rankine cycles very successfully, it is not always the best choice for cycles powered by heat sources at intermediate temperature levels.

Numerous organic compounds can be used instead, and the choice of a fluid depends on many criteria. Besides the long-term stability and toxicity, the achievable thermodynamic efficiency is one of the most important factors. In the investigations of the Thermodynamics group at the University of Duisburg-Essen, the overall energy utilization is determined with respect to the available energy (exergy) of the heat source. It turns out that the overall efficiency generally differs considerably from the pure cycle efficiency, due to unavoidable exhaust heat losses and also due to a mismatch in heat capacities and temperature levels along the heat transfer process.

figure: simple rankine cycle

Reference:

• M. Aslam Siddiqi and Burak Atakan (Lecture); Investigation of the criteria for fluid selection in Rankine cycles for Waste heat recovery .ecos²⁰¹⁰ ; 23rd International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy systems; June 14, 2010 - June 17, 2010; EPFL Rolex Learning Center, Lausanne, CH