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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.
실제기체의 물성을 이용한 Stirling 냉동기 단열해석
백종훈,장호명,Baik, J.H.,Chang, H.M. 대한설비공학회 1995 설비공학 논문집 Vol.7 No.1
A Finkelstein adiabatic analysis is performed for Stirling refrigerator with real gas properties of helium. The mass balance and the energy balance equations are formulated into the form that is convenient for incorporating an available computer code of the helium properties. The differential equations are solved numerically. The calculated coefficient of performance(COP) and the pressure variation are compared with the results obtained when helium is assumed to be an ideal gas. The relative errors in COP are presented as functions of the refrigeration temperature and the maximum cycle pressure.
65K 과냉 액체질소 생산을 위한 Brayton냉동사이클의 시스템 설계
정명진(M.J. Chung),정원상(W.S. Jung),장호명(H.M. Chang) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5
Bryaton refrigeration cycle is proposed and designed in detail for continuous cooling of liquid nitrogen from 75 K to 65 K at a rate of 5 ㎾. This refrigeration requirement is specified by the superconducting power devices under domestic development, where subcooled liquid nitrogen is used as cooling medium and high-voltage electrical insulator. Helium gas is the refrigerant of Brayton cycle and a plate-fin type of counter-flow heat exchanger is selected for both regenerative heat exchanger and subcooling heat exchanger. With given dimensions of standard plate-fin unit, detailed heat transfer analysis is performed to determine the necessary size of each heat exchanger which will satisfy the refrigeration requirement. It is rigorously shown that there exists a unique optimum in pressure ratio of Brayton cycle to minimize the power input to the refrigerator, when the sum of the two heat exchanger sizes is given as a constant. The practical parameters for selecting the compressor and expander are discussed, and an economic impact of the proposed design is also demonstrated in comparison with commercial G-M or Stirling coolers.
김승현,장호명,강병하,Kim, S.H.,Chang, H.M.,Kang, B.H. 대한설비공학회 1997 설비공학 논문집 Vol.9 No.3
A thermodynamic cycle analysis is performed for refrigerator-precooled Linde-Hampson hydrogen liquefiers, including catalysts for the ortho-to-para(o-p) conversion. three different configurations of the liquefying system, depending upon the method of the o-p conversion, are selected for the analysis. After some simple and justifiable models are introduced, a general analysis program to predict the liquid yield and the figure of merit(FOM) is developed with incorporating the commercial computer code for the hydrogen properties. The discussion is focused on the effect of the two primary design parameters-the precooling temperature and the high pressrure of hydrogen. When the precooling temperature is in the range between 45 and 60 K, the optimal high pressure for the maximal liquid yield is found to be in the range between 100 to 140 bar, regardless of the o-p conversion. However, the FOM can be maximized at slightly smaller values of high pressures. It is remarkable to observe that the lower precooling temperatures are favorable since both the liquid yield and the FOM can be obtained without compressing hygrogen to extremely high pressures.
백종훈,장호명,Baik, J.H.,Chang, H.M. 대한설비공학회 1996 설비공학 논문집 Vol.8 No.2
A cycle analysis is performed to investigate how the non-ideal gas behavior of helium reduces the heating capacity of VM heat pumps. Since the operating pressures of VM heat pumps are as high as 1 to 20 MPa, the compressibility factor of helium becomes clearly greater than 1 and the non-ideal behavior always represents a thermal loss in heating. To calculate the amount of the losses, an adiabatic cycle analysis is performed with the real properties of helium and the net enthaply flows through the two regenerators are numerically obtained. It is shown that the non-ideal gas losses could be as much as 8% in the heating capacity when the operating pressures are greater than 10MPa. The effects of the operating temperatures and the dead volumes on the loss are presented.
터보팽창기를 이용한 2단 팽창 Claude냉동사이클 해석
백종훈,장호명,Baek, J.H.,Chang, H.M. 대한설비공학회 1994 설비공학 논문집 Vol.6 No.2
A cycle analysis was performed for 2-stage expansion Claude refrigerators by a numerical method. The refrigerators are under recent development such that the reciprocating expanders of Collins cycle are replaced by new turboexpanders. A computer simulation program was written to predict the coefficient of performance of the refrigerators for several input parameters. It was found out that there exist unique optimum values for the ratio of expanded mass through the turboexpanders to the total mass and for the intermediate pressure of the 2-stage expansion. The maximum coefficient of performance was about $5{\times}10^{-4}$ at the optimal operation.