Performance evaluation of an Organic Rankine Cycle (ORC) connected to two-phase closed thermosyphons

This paper aims at evaluating the performance of a waste heat-to-power plant using an organic Rankine cycle (ORC) connected to two-phase closed thermosyphons (or gravity-assisted heat pipes or wickless heat pipes). The heat exchanger, made up of two-phase closed thermosyphons, is used for transferring heat from exhaust stream to ORC working fluid. In practice, a hot oil loop or a pressurized hot water loop or a saturated steam loop or even a direct evaporator is often used to transfer heat from heat source to ORC system. However, installing a heat exchanger directly in the hot gas paths of ORC system evokes the concerns for the flammability and/or toxicity of organic working fluids especially when the heat source has a relative high temperature. Also the use of an intermediate heat carrier loop such as thermal oil or saturated steam or pressurized water loop is relatively expensive and involves installation of relatively heavy components. A priori, the use of two-phase closed thermosyphons for capturing and transferring heat from a waste heat source to organic working fluid is less expensive than the use of an intermediate heat transfer loop and eliminates safety concerns as in the case of direct installation of an ORC evaporator in the hot gas paths.