Performance assessment of a low grade waste heat driven organic flash cycle (OFC) with ejector

Organic flash cycle (OFC) appears as one of the preferable options for waste heat recovery due to better matching of temperature profiles in the heat recovery unit (HRU). However, efficiency of an OFC reduces appreciably due to higher irreversibilities of the high pressure and the low pressure throttling devices. In the present study, to overcome this drawback low pressure throttle valve of the conventional OFC is replaced by an ejector. The saturated liquid stream exiting the vapour separator is accelerated in the nozzle of the ejector as primary flow and the stream coming out of the turbine is entrained in the ejector as secondary flow. Due to the presence of the ejector, the dry saturated vapour leaving the vapour separator of the OFC can be expanded in the turbine to a pressure which is lower than the specified condenser pressure. The turbine exit pressure is such that total working fluid mass exiting the diffuser of the ejector is at condenser pressure. OFC with ejector yields an increment of about 9.50% in both first law efficiency as well as power output compared to that of the conventional OFC.