# The critical temperature of the fluid should be well above the highest temperature existing in the proposed cycle. Evaporation of the working fluid — and thus the significant addition of heat — can then ensue at the maximum temperature of the cycle. This results in a relatively high cycle efficiency.
# The slope ds/dT of the saturated vapour line in T–s diagram (see Chapter Classification of pure (single-component) working fluids) should be nearly zero in the applied pressure ratio of the expander. This prevents significant moisture (liquid droplet) formation or excessive superheat occurring during the expansion. It also ensures that all the heat rejection in the condenser occurs at the minimum cycle temperature, which increases the thermal efficiency.
# A low value for the specific heat of the liquid or, alternatively, a low ratio of number of atoms per molecule divided by the molecular weight and a high ratio of the latent heat of vaporisation to the liquids specific heat should appertain. This reduces the amount of the heat required to raise the temperature of the subcooled liquid of the working fluid to the saturation temperature corresponding to the pressure in the Rankinecycles evaporator. So most of the heat is added at the maximum cycle temperature, and the Rankine cycle can approach more closely the Carnot cycle.