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장호명,Chang, H.M. 대한설비공학회 1994 설비공학 논문집 Vol.6 No.1
An optimal design for Gifford-McMahon/Joule-Thomson(GM-JT) refrigerators was performed by a numerical method. The design goal was to meet the cooling requirement for MRI systems, which was 3 Watt at 4 K. A general cycle analysis program was written to calculate the cooling capacity of the GM-JT refrigerators for the givenstage GM refrigerator. The program was executed for a specific refrigerator with various design parameters. The optimal values for the maximum cooling were found for the sizes of the heat exchangers, the mass flow rate of helium, and the compression pressure.
Estimation of surface emissivity for conduction-cooled metal plates at cryogenic temperatures
장호명,이경현 한국초전도.저온공학회 2008 한국초전도저온공학회논문지 Vol.10 No.2
The relation between surface emissivity and temperature distribution is experimentally and analytically investigated for a conduction-cooled metal plate in vacuum. Experimental set-up consists of a rectangular metal plate placed vertically in a cryostat and thermally anchored to the coldhead of a GM cryocooler at the top. Temperature is measured at a number of locations over the plate with platinum resistors mounted on the plate. A parallel analysis on the balance of heat conduction through the plate and thermal radiation on its surface is performed to numerically calculate the temperature distribution having the same boundary conditions as experiment. By comparing the two results, an average emissivity of the plate is roughly estimated for different metal plates and different surface conditions. The estimated emissivity in present study is less than the listed values for highly polished stainless steel, and meets a fairly good agreement for oxidized copper surface.