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• Selection of cooling system for superconducting machines requires a series of high-level considerations. • Different components of cooling system are discussed based on the prerequisites of a machine engineer and designer. • Technical and economic aspects of choosing a cryogenic fluid and the related system were discussed. • Specific considerations for aerospace, marine, and wind applications of superconducting machines were discussed. • Hydrogen and Turbo Brayton cryocoolers are discussed as future of cooling systems for superconducting machine in aviation. In this paper, general considerations for selecting a cryogenic cooling system for superconducting machine in different applications were explained with respect to the design, operation, and condition monitoring constraints. These considerations are explained so that they help electric machine engineers and designers to get familiar with cryogenic aspects of selecting and using cryogenic cooling system of superconducting machines. In fact, the main questions are: what are the important factors that one should take into account when selecting a cooling system for a superconducting machine application? Also, which one of these factors could later affect the performance of the cooling system so that it can efficiently cope with the expected heat load withoutfacing a thermal breakdown? To adress these questions, common cooling system structures, different cryogenic fluids, the associated parameters with the value of heat loads, and safety margins were discussed to help the machine engineers to choose the most appropriate cryogenic cooling system that adjusts better with their superconducting machine and the specific considerations that they might have. Some considerations regarding the auxiliary devices such as heat exchangers and pumps, were explained as the next priority in selecting a cooling system. Special challenges and considerations imposed to the cooling systems of superconducting machines in aerospace applications such as electric- and hydrogen-powered aircraft, naval applications, and wind energy application were also discussed. Although all of these applications share similar concerns like weight, cost, and specific mass of cooling systems, each one of them have their specific concerns and constraints which come with higher priority. [ABSTRACT FROM AUTHOR]

Future, high-performance military aircraft will likely use vapor compression systems to manage the temperatures of multiple loads which are time-varying, dissimilar, and have high-turndown ratios. Experiments were performed using a scaled vapor compression system over a hypothetical flight profile to compare the temperature control performance and energy consumption of a superheat and capacity control strategy (Method A) against those of an alternate cycle-based strategy (Method B). Method B modulated the compressor speed to control the saturated suction temperature (SST) and modulated the expansion valves to directly control the evaporator heat load outlet temperature. The vapor compression system used two evaporators with dynamic and dissimilar heat loads. Method B offered better temperature control performance for the profile examined. The coefficient of performance (COP) of Method B was slightly greater than that of Method A. However if the overcooling produced by Method A was penalized, the useful COP of Method B would be meaningfully higher. Lastly, Method B did not require back pressure control valves. The use of fewer components is important for aircraft weight and reliability concerns. [ABSTRACT FROM AUTHOR]

Abstract: Water is always present in the atmospheric air in the form of vapour. As air of low temperature expands through the turbine condensation may occur. Condensation gives rise to several problems in materialization of the air cycle as it results in temperature rise thus to different conditions than the expected at the turbine exit. Also in most air cycle applications, liquid water must be removed from the air stream before it gets to the cooled space. In the case that turbine exit temperature is very low; there is the possibility of ice particles formation. A method allowing the evaluation of air properties when condensation occurs is required in order to examine its effect on the cycle and optimize the operating envelope. The present paper describes a thermodynamic equilibrium method for predicting the occurrence of condensation and calculating the mixture properties once condensation has occurred. The method has been validated against the experimental results from a turbocharger turbine. The experimental results show that condensation can cause significant alteration to the turbine exit conditions. It is demonstrated that condensation can be predicted and the mixture properties after condensation can also be accurately evaluated. [Copyright &y& Elsevier]