A new selection principle of working fluids for subcritical organic Rankine cycle coupling with different heat sources

The low-grade heat sources coupled by ORC (organic Rankine cycle) are categorized into two groups. For the first one, the inlet temperature and the mass flow rate are known, and the working mass of the heat source is directly discharged after being used. For the second, the heat release is specific and the working mass of the heat source is usually recycled after releasing heat. The theoretical formulas of net power output and thermal efficiency for subcritical ORC coupling with the two kinds of heat source are proposed to elucidate the selection criteria of working fluids. The new mathematical relation of working fluid selection is given out. The selection of working fluids for subcritical ORC should couple with the types of low-grade heat sources. For the first heat source, both the theoretical analysis and numerical simulation results show that the working fluids with high liquid specific heat and low latent heat of evaporation should be selected as the working fluids. In contrast, the working fluids with low liquid specific heat and the high latent heat of evaporation are better for the second heat source. •A new selection principle of working fluids for subcritical ORC is proposed.•Low-grade heat sources coupled by ORC are categorized into two groups.•The net power output and thermal efficiency models are proposed for subcritical ORC.•The new mathematical relation of working fluid selection is given out.•The expected working fluids under different heat sources are different.