Vapor Precooling in a Pulse Tube Liquefier

Experiments were performed to study the effects of introducing vapor into a dewar where a coaxial pulse tube refrigerator was used as a liquefier in the neck of the dewar. We were concerned about how the introduction of vapor might impact the refrigeration load as the vapor barrier in the neck of the dewar is disturbed. Three experiments were performed where the input power to the cooler was held constant and the nitrogen liquefaction rate was measured. The first test introduced the vapor at the top of the dewar neck. Another introduced the vapor directly to the cold head through a small tube, leaving the neck vapor barrier undisturbed. The third test placed a heat exchanger partway down the regenerator where the vapor was pre-cooled before being liquefied at the cold head. This experiment also left the neck vapor barrier undisturbed. Compared to the test where the vapor was introduced directly to the cold head, the heat exchanger test increased the liquefaction rate by 12.0%. The experiment where vapor was introduced at the top of the dewar increased the liquefaction rate by 17.2%. A computational fluid dynamics model was constructed of the dewar neck and liquefier to show how the regenerator outer wall acted as a pre-cooler to the incoming vapor steam, eliminating the need for the heat exchanger.