How to give a full play to the advantages of zeotropic working fluids in organic Rankine cycle (ORC)

Abstract

Improving the efficiency of organic Rankine cycle (ORC) is the ultimate goal of the researchers with thermodynamic background. As the “blood” of ORC, the working fluid plays a vital role to the improvement of the performance. The thermos-physical properties parameters, transport parameters and other parameters of working fluids could directly affect the efficiency, safety, stability and economy of ORC. With the increasing requirements on working fluids, it is difficult to find a pure working fluid not only with satisfied thermodynamic performance but also permissible enverimental protection and safety. In contrast, zeotropic working fluid, which is mixed with two or more pure working fluids, is easier to meet the requirements of thermos-physical properties, environmental and safety. But at the present stage, the application of zeotropic working fluids in ORC still adapted or employed the methodology originated from what we learn from pure working fluids. Under such circumstances, the temperature glide of zeotropic working fluids improves system efficiency while the composition shift would in turn reduce system efficiency. Thus, 3D-ORC is proposed in this paper to provide zeotropic working fluids a full play on performance improvement of energy conversion. The performance of 3D-ORC is calculated for the recovery of waste heat of internal combustion engines and compared with the simple ORC using pure and zeotropic working fluids. The results show that the performance of 3D-ORC is better than simple ORC under the same conditions.