טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentTzabar Nir
SubjectMixed-Gas Joule-Thomson Sorption Cryocoolers
DepartmentDepartment of Mechanical Engineering
Supervisor Professor Emeritus Gershon Grossman
Full Thesis textFull thesis text - English Version


Abstract

Joule-Thomson (JT) cryocoolers are widely in use for a variety of applications. The absence of moving parts at the cold end increases their reliability and eliminates any vibrations emission. JT cryocoolers operate with pressurized fluids that may be provided either from pressure vessels or compressors. Cooling to 80 - 100 K with JT cryocoolers is often implemented with either of two pure gases: nitrogen or argon. Alternatively, mixed gases have been suggested as refrigerants.

Sorption compressors have no moving parts, do not emit vibrations, and are highly reliable. JT sorption cryocoolers constitute the most mature technology for cooling from a normal Room-Temperature (RT) down to temperatures below 100 K in the absence of moving parts. Nitrogen is usually used as the working fluid for cooling to temperatures between 80 and 100 K and activated carbons are the best adsorbents for this purpose.

In the present research we suggest a novel sorption JT cryocooler that operates with a mixed refrigerant. Merging of sorption cryocooling and a mixed refrigerant shall enable the use of a simple, single stage compressor for cooling to 80 - 100 K, lower operating temperatures of the sorption cycle, and thus - reduced power consumption.

In this work we present measurements of nitrogen, methane, and ethane on a commercial pelleted activated carbon. Analytical models are fitted to the experimental results and further modified to incorporate the temperature dependence. A sorption compressor prototype has been fabricated and tested with nitrogen. The calculated sorption cycle has been verified with a reasonable accuracy by the compressor's experimental results.

The adsorption of mixed gases is usually investigated under steady conditions. However, the sorption process in a compressor goes through varying states and mass changes. In this research a numerical analysis for mixed gas sorption compressors is developed, based on pure gas adsorption characteristics. Two binary mixtures are investigated: nitrogen-methane and nitrogen-ethane. The analysis is then verified against experimental results. Binary mixtures have also been investigated as refrigerants for Joule-Thomson cryocoolers. Experimental results are presented to verify some of the analytical results.

Finally, the option of mixed refrigerant sorption JT cryocoolers is explored. The considerations for developing mixed refrigerants to be driven by sorption compressors and to be utilized with JT cryocoolers are provided. It appears that, unlike with pure nitrogen, mixed refrigerants can be suitable for JT cryocooling with a single stage sorption compressor.