Pulse Tube Refrigerator - How IT Operates

How It Operates

The piston moves periodically from left to right and back. As a result the gas also moves from left to right and back while the pressure within the system increases and decreases. If the gas from the compressor space moves to the right it enters the regenerator with temperature T_H and leaves the regenerator at the cold end with temperature T_L, hence heat is transferred into the regenerator material. On its return the heat stored within the regenerator is transferred back into the gas.

The thermal environment of a gas element near X₂, that moves back and forth in the system, changes when it passes the heat exchanger. In the regenerator and in the heat exchanger the heat contact between the gas and its surrounding material is good. Here the temperature of the gas is practically the same as of the surrounding medium. However, in the pulse tube the gas element is thermally isolated (adiabatic), so, in the pulse tube, the temperature of the gas elements vary with the pressure.

Look at figure 1 and concentrate on gas elements close to X₃ (at the hot end) which move in and out of the pulse tube. A gas element that flows into the tube does so when the pressure in the tube is low (it is sucked into the tube via X₃ coming from the orifice and the buffer). At the moment it enters the tube it has the temperature T_H . Later in the cycle it is pushed out the tube again when the pressure inside the tube is high. As a consequence its temperature will be higher than T_H. In the heat exchanger X₃ it releases heat and cools to the ambient temperature T_H.

At the cold end of the pulse tube there is the opposite effect: here gas elements enter the tube via X₂ when the pressure is high with temperature T_L and return when the pressure is low with a temperature below T_L. They take up heat from X₂ : this gives the desired cooling power.