Performance evaluation on radial turbines with potential working fluids for space closed Brayton cycle

Abstract

The performance of radial turbines with the He-Xe mixtures, helium, argon and air are examined in this paper. The published approach pertaining to Chapman-Enskog kinetic theory and corresponding states theory is adopted to calculate the transport properties of He-Xe mixtures with two different molecular weights of 15.9 g/mol and 40 g/mol. The independent or combined effects of the flow Euler number (Eu), Reynolds number (Re) and inflow velocity on flow similarity are discussed based on flat-plate flow. Under the consistent above conditions, the flows of these fluids are similar and the flow loss is merely a function of fluids properties. The established flow similarity conditions form a procedure to calculate the boundary conditions of similar turbines and its application makes the flow similar in radial turbines passages. It is reflected in the consistent topology skeleton of flow structures and the identical parameter distributions in the flow section. The turbines with He-Xe mixtures, Ar and air shares a pretty similar tendency of efficiency line and the values differ little. The differences between these turbines under the same working point have an upper limit of 0.3% before critical state. At the design point, a similar velocity triangle instead of an identical one can guarantee the flow similarity and an approximate efficiency compared with others. Once the working condition deviates from the design point, the efficiency error between the helium and other fluids widens as the working condition deviation increases.