In this paper, the dynamic behaviour of the temperature profiles in the regenerator and in the gas near the hot and cold ends of the tube are discussed. The operation of a single-orifice pulse tube is described in general thermodynamical terms. This approach is extended to the double-inlet pulse tube. Expressions for the various sources of entropy are derived which lead to a relation for the coefficient of performance. It is determined when the second inlet improves the operation of the pulse tube and what are the optimum settings