Development of Air Cycle Technology for Transport Refrigeration

Developments for air cycle systems with respect to special requirements concerning the use of compression and expansion machines for transport refrigeration are discussed in this paper. Historic aspects are mentioned briefly and the present situation in Germany is sketched in the example of an air cycle air-conditioning system for the new generation of the German high speed train ICE 2.2. In order to develop air cycle systems for transport refrigeration, it is a challenge to select adequate machine concepts. This is one of the most important points to be considered because of the significant influence of the isentropic efficiencies with respect to the coefficient of performance. Especially the efficiency of the expansion machine has to be considered. Two fundamentally different concepts are described. The first concept consists of a motor-comp;ressor-expander-unit using turbo machines. Characteristic data of the machines are used to simulate the full and part load behavior of this concept within an air cycle unit for use in transport refrigeration. The second concept consists of a pressure wave machine. Measurement results are shown and difficulties in obtaining serious efficiency data are discussed. In addition to this two finite difference schemes for fluid dynamics which have been developed and applied to evaluate fluid dynamic properties for the pressure wave machine are introduced.