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File Last modified on: Wed Nov 18, 2020 22:50:34
Sterlingly cool !

A unique Sterling cooler (coolers employing the Stirling cycle of operation) has been designed by Prof. S L Bapat of Department of Mechanical Engineering. In a Stirling cycle, a working fluid such as helium or hydrogen is first compressed and this hot gas is allowed to cool down to the desired temperature while passing through a regenerator (porous matrix) and then allowed to expand to cool down further. The resultant cooling or refrigeration effect is extracted and used for cooling applications. During return of the cold gas for the next cycle of compression, it is allowed to pick up heat from the regenerator. Stirling coolers used for cryogenic applications are also known as Stirling cryocoolers.

The unique designed Stirling cooler developed consists of a compressor which has a piston disposed in a compressor cylinder. It has an expander comprising a piston rotatably and reciprocally disposed in an expander cylinder. A regenerator is placed within a cavity formed in an extension at the top of the expander piston. A circumferential groove is formed on the extension adjoining the bottom wall of the cavity and the top end of the expander piston and gas passages formed in the top wall and bottom wall of the cavity. A pair of helical grooves is provided along the length of the expander piston with their ends meeting each other. The pitch of the helix formed by the helical grooves is twice the expander piston stroke.

The compressor cylinder is connected to the expander cylinder through a connecting tube and helical grooves provided along the length of the expander piston and the circumferential groove. At least one seal is provided between the sidewall of the cavity and expander cylinder to prevent gas leakage and a conductor material cap is provided over the top of the expander cylinder, which corresponds to the expansion space formed within the expander cylinder between the top end of the extension and the closed end of the cap.

The unique design of the cooler makes it very compact and effective in cooling. The coolers have long life, attained through the use of non-contact running surfaces. Gas bearings allow the two moving parts to "ride on a cushion of gas" keeping the running surfaces from making contact while the machine is operating. Unlike vapor compression systems outfitted with capillary tubes that have optimized performance at only one temperature condition, Stirling coolers maintain their high performance over a wide range of temperature conditions.

Cooler uses the environmentally safe inert gas, helium, as the working fluid. Light weight makes portable cooling a reality. Stirling coolers perform well in harsh temperature environments and high ambient temperatures and are limited only by the materials of the cooler. These are some of the advantages of the designed cooler.

Indian patent application no. 299/MUM/2006 Patent grant no. 225128
Inventors: S L Bapat


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