Maximizing Run Time of a Fixed Orifice Joule-Thomson Cryocooler

• Published in: Advances in Cryogenic Engineering; Volume 49B Vol. 710; pp. 1661 - 1668
• Main Author: Maytal, B-Z
• Format: Journal Article
• Language: English
• Published: 23.06.2004
• ISBN: 9780735403840; 0735403848
• ISSN: 0094-243X
• DOI: 10.1063/1.1774864

A typical mode of Joule-Thomson cryocooling is the employment of a fixed orifice through which a pressure vessel is discharged. Present analysis is based on ideal gas volumetric behavior of the compressed coolant and linearization of the pressure dependence of coolant's integral isothermal Joule-Thomson effect. The instantaneous pressure in the vessel and the period of operation are derived for the two extreme discharge regimes, the isothermal and the adiabatic and any polytrophic discharge in between. Argon and nitrogen are the discussed refrigerants. The model predicts the longest achievable run and the associated optimal orifice as function of actual heat load and the intensity of the Joule-Thomson effect. Run time degrades sharper by reducing the optimal size of the orifice than by enlarging it. Stretching the orifice by a factor of 5 has a similar degrading effect as shrinking to half of its size, in both cases halving the optimal longest discharge period. In terms of cut off pressure, the optimal orifice is the one that terminates the run at about sixty percent of the initial pressure of the vessel.