its temperature to a predetermined bottoming temperature in the extended part of this phase the heat transfer fluid flows through the system in the direction of arrows 96 therefore in the extended part of this phase the heat transfer fluid flows from pump 70 through the open valves in the following order 76a 84a and then back to pump 70 in the base part of the next phase which is not shown in the figures solenoid valves 76d and 84a are open while all the other six solenoid valves are closed in the extended part of this phase only solenoid valves 76d and 84d are open the heating and cooling of the chambers is continued in a series fashion through all the chambers and by opening only the identified solenoid valves and heating of the heat transfer fluid in one of lines 78a 78b 78c or 78d by an external burner in the following manner ______________________________________ base part extended partphase opened valves 34 on 34 burner opened valves______________________________________1 76a 84b 93c 76a 84a2 76d 84a 93b 76d 84d3 76c 84d 93a 76c 84c4 76b 84c 93d 76b 84b______________________________________ the thermal wave temperature profiles of the compressors in fig2 and 3 reading bottom to top are shown approximately in fig4 left to right profiles a b c d and e of fig4 correspond to phases 4 1 2 3 and 4 respectively the first stage and second stage compression zone cycles are depicted in fig5 wherein the first stage cycle is represented by the solid line rectangle abcd and the second stage cycle is represented.