Tutorial on single- and two-component two-phase flow and heat transfer: Commonality and difference

It is assessed to what extent the results of two-phase two-component flow and heat transfer research can be usefully applied to support research on the flow and heat transfer in two-phase single-component systems. The latter single-component two-phase systems, envisaged for spacecraft thermal control applications, are Mechanically Pumped and Vapour Pressure Driven Loops, Capillary Pumped Loops, and Loop Heat Pipes. In these single-component systems the working fluid is a mixture of a liquid (for example ammonia, carbon dioxide, ethanol, or other refrigerants, etc.) and its saturated vapour. The two-component systems considered consist of liquid-gas mixtures, e.g. water-air. Various aspects are discussed qualitatively and quantitatively to determine commonality and difference between two physically looking similar and close, but essentially different systems. It is focused on the different pressure gradient constituents and total pressure gradients, on flow regime mapping (including evaporating and condensing flow trajectories in the flow pattern maps), on adiabatic flow and the impact of flashing, and on thermal-gravitational scaling issues. It is elucidated that, though there is a certain degree of commonality, the differences are appreciable. The conclusion is that one shall be very careful in interpreting two-component outcomes to develop single-component two-phase thermal control systems.