Establishing Criteria for Fluids for Small Vapor Turbines

Four major criteria control the choice of a suitable fluid for small Rankine cycle turbines. They are molecular weight, boiling point, chemical stability, and the shape of the T-S diagram. The last criterion can be disregarded by employing a feedback heat exchanger to correct the shape. Losses normally associated with very small turbines can be kept to a minimum; units of 600 watts have been built and the design can be lowered to 150 watts without severe loss of efficiency.