ABSTRACT
This chapter discusses the effect of the thermodynamics of the irreversible process in detail. It draws a whole series of experimentally determined isenthalps. The maxima of the different isenthalps lie on the inversion curve. Depending on where the initial and final points are chosen, both heating and cooling effects can be produced, in contrast to the free expansion, where there is always cooling. The inversion curve separates the region of heating from the region of cooling. The greatest cooling effect, for a given pressure drop and starting temperature, will occur when the initial state is on the inversion curve. The compressor drives the helium gas around the circuit and provides the necessary high pressure at the inlet side of the throttling valve. After compression and the consequent heating, the gas is cooled back to 20 K again by the liquid hydrogen cooler so that the helium always enters the heat exchanger.
