• 설비공학논문집
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• 제5권3호
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• pp.198-206
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• 1993

Experimental results of two stage Gifford-McMahon cryorefrigerator are described. In-prototype experiments, drive mechanism is Scotch Yoke type driven by stepping motor, copper meshes and lead balls are used for regenerator's materials in the first stage and the second stage, respectively. To find optimal conditions of the cryopump, no load temperature and refrigeration capacity according to the variation of cycle frequency and operating pressure are measured, and the cool down and load characteristics at particular cycle frequencies are presented. In general, as the cycle frequency is lowered, no load temperature is dropped but refrigeration capacity is diminished. As the representative result, in a case that the cycle frequency is 70rpm and steady state pressure is 14 atm, no load temperature of second stage is lowered to 10.5K in 55 minuters, and in this situation the refrigeration capacity of the first stage is 42W at 80K, that of the second stage is 11 W at 20K.

• Mycobiology
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• 제38권1호
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• pp.70-73
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• 2010

Temperature-sensitive yeast mutants were used to screen for cell cycle-related genes from Pleurotus eryngii genomic DNA. A mushroom genomic DNA library was established and each gene was screened for the ability to rescue seven Saccharomyces cerevisiae temperature-sensitive strains. Hundreds of yeast transformants were selected at restrictive temperatures over $30^{\circ}C$. Plasmids from the transformants that survived were isolated and transformed back into their host strains. The temperature sensitivity of the resulting transformants was tested from $30^{\circ}C$ to $37^{\circ}C$. Ten DNA fragments from P. eryngii were able to rescue yeast temperature-sensitive strains, and their DNA sequences were determined.

• 오토저널
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• 제12권3호
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• pp.41-52
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• 1990

In this study are determined the unsteady temperature and thermal stress fields for a domestic 4-cylinder, 4-cycle gasoline engine cylinder head by the three-dimensional finite element method. A representative part of the cylinder head is modelled as a combination of hexahedron isoparametric elements, and the time-dependent temperature and the heat transfer coefficient of the gas are imposed as the thermal boundary conditions for the engine speeds of 500 rpm and 2000 rpm. The obtained results, which are represented graphically, indicate that the amplitudes of temperature fluctuation during a cycle are about 10.deg. C and 3.deg. C respectively on the surface of combustion chamber, and the maximum temperature fields occur at 30.deg. , 10.deg. respectively before the initiation of the exhaust stroke. Thermal stress fields due to non-uniform temperature distributions show that compressive stress is much larger than tensile stress throughout a cycle. It is also found that the compressive stress varies with substantial amplitude between the exhaust port and ignition plug hole, and the high tensile stress with small fluctuation occurs between exhaust port and the adjacent head bolt hole.

• 한국정밀공학회지
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• 제11권2호
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• pp.173-181
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• 1994

A Cold spot temperature control system for the batch annealing furnace has been estabilished in order to reduce energy consumption to improve productivity and stabilize the propertics of products. Therefore we confirmed a relation between annealing cycle time and atmospheric gas, variation of coil cold spot temperature with time during heating and actual temperature measurements at mid-width of each coil during heating and actual temperature measurements at mid-width of each coil during soaking. The results of the tempaeature variation effect on the batch annealing are as follows. 1) Heating time is reduced to one half with increasing atmospheric gas flow rate and changing of atmospheric gas component from HNx to Ax gas, and annealing cycle time is reduced to 2.7 times. 2) In case of short time healing, the slowest heating part is the center of B coil, in case of long time heating, the low temperature point moves from the center of coil to inside coil. And the temperature in this part is higher than other parts when cooling. When finished heating, the cold spot is located 1/3 of coil inside in case of HNx atmospheric gas. But center of coil in case of Ax atmospheric gas. 3) The outside of top coil is the highest temperature point when heating, which becomes the lowest temperature point when cooling. So, this point becomes high temperature zone at heating and low temperature zone at cooling, It has relation according to atmospheric gas component and flow rate. 4) Soaking time at batch annealing cycle determination is made a decision by the input coil width, and soaking time for quality homogenization of 1214mm width coil must be 2.5 hours longer than that of 914mm width coil for the same ciol weight. 5) Annealing cycle time with Ax atmospheric gas is extended 1 hour in of slow cooling during 5 hours in order to avoid rapid cooling.

• 설비공학논문집
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• 제11권3호
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• pp.422-430
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• 1999

This paper concerns the study of a two-stage absorption heat pump cycle to utilize treated sewage. This two-stage cycle consists of coupling double-effect with parallel or series flow type and single effect cycle so that the first stage absorber and condenser produces hot water to evaporate refrigerant in the evaporator of the second stage. The effects of operating variables such as absorber temperature on the coefficient of performance have been studied for two-stage absorption heat pump cycle. The working fluid is lithium bromide and water solution. The efficiency of the two-stage absorption heat pump cycle has been studied and simulation results show that higher coefficient of performance could be obtained for the first stage with parallel flow type. The optimum ratio of solution distribution can be shown by considering the COP, the crystallization of solution and the generator temperature.

• 대한기계학회논문집B
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• 제31권2호
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• pp.116-124
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• 2007

An adsorption chiller is expected to have high energy-efficiency in utilizing the waste heat exhausted from a process. The objective of this paper is to investigate the performance of silica gel-water adsorption chiller from the cycle simulation and to provide a guideline for design of the adsorption chiller. The effect of cycle time, inlet temperature and water flow rate on the cooling capacity and COP is quantified during the cycle operation. It is found that the performance of adsorption chiller is more sensitive to the change of inlet water temperature rather than the water flow rate. It is concluded that the COP is 0.57 in the standard conditions(hot water $80^{\circ}C$, cooling water $30^{\circ}C$, chilled water inlet temperatures $14^{\circ}C$ and cycle time 420sec).

• International Journal of Air-Conditioning and Refrigeration
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• 제17권3호
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• pp.107-113
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• 2009

The objective of this study is to investigate performance characteristics of a household refrigerator using a two-stage compression cycle. The performance of the two-stage compression cycle was measured by varying the compressor speed, condensing temperature, and evaporating temperature. The COP of the two-stage compression cycle was analyzed and then compared with that of the single-stage compression cycle. The optimum combination of compressor speeds for a low- and a high-stage was determined. The COP of the two-stage compression cycle using a PTC (parallel two-stage compression) method was 5.85% higher than that of a STC (serial two-stage compression) method at optimum operating conditions.

• 열처리공학회지
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• 제4권3호
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• pp.31-38
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• 1991

Effect of thermal cycling on shape memory effect and stabilization of austenite was investigated in Fe-21%Mn alloy. The thermal cyclic treatment was carried out with two types, room temperature${\leftrightarrow}215^{\circ}C$ and room temperature${\leftrightarrow}260^{\circ}C$. In case of the room temperature${\leftrightarrow}215^{\circ}C$, the SME was rapidly increased up to 3 cycles and maintained nearly constant value regardless of further cycles. In case of the room temperature${\leftrightarrow}260^{\circ}C$, however, the SME was increased with increasing the thermal cycle up to 5 cycles and decreased gradually with further cycle. The variation of the ${\varepsilon}$ martensite volume pet with the thermal cycle was in good agreement with the variation of the SME. Therefore, the change of the SME due to the cyclic treatment was explained with the change of the ${\varepsilon}$ martensite content. As the thermal cycle was increased, the $M_s$ temperature was decreased, and the $A_s$ and $A_f$ temperatures were increased, respectively.

• Journal of Advanced Marine Engineering and Technology
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• 제40권6호
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• pp.476-483
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• 2016

해양온도차발전용 유기랭킨사이클은 해양의 표층수와 심층수사이의 온도차를 이용하여 발전하는 사이클이다. 작동유체는 유기랭킨사이클의 열역학적 성능에 있어 중요한 요소이다. 유기랭킨사이클의 열역학적 분석방법으로 핀치포인트분석이 있다. 본 연구는 열교환기내 핀치포인트온도차의 변화와 열원 및 열침의 출구온도의 변화에 따른 열역학적 성능분석을 수행하였다. 핀치포인트분석법에 따라 설계한 해양온도차발전용 단순랭킨사이클에 7종의 단일 작동유체를 적용하여 열역학적 성능을 분석하였다. 성능분석결과 열교환기에서 핀치포인트온도차와 열원 및 열침의 온도변화가 작을수록 사이클 총 비가역성 및 총 엑서지 파괴인자가 감소하였으며, 제2법칙 효율은 상승하였다. 또한 비가역성은 열역학적 변화가 발생한 곳에서 크게 변화하였다. RE245fa2는 선정한 작동유체 중에서 가장 우수한 열역학적 성능을 보여주었으며, 모든 작동유체의 성능은 유사하였다. 열교환기 및 작동유체 선정에 있어 열역학적 성능과 함께 다양한 요소들에 대해서도 엄밀한 이론적 근거가 필요하다.

• Journal of Advanced Marine Engineering and Technology
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• 제28권7호
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• pp.1082-1091
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• 2004

Analyzed Parametrically was an internal combustion engine combined with gas turbine the cycle of which is splitted into compression side cylinder and expansion side one, and heat adding of which is during constant volume pressure, temperature process. The advantages of each measures were analyzed by means of thermal cycle diagram. The thermal efficiency of partial load cutting off firstly isothermal heat adding and secondly isobaric heat adding also was analyzed The authors suggested some potentials about the performance as for thermal efficiency, mean effective pressure and reducing emissions and noise supposed were the operating parameter of the engine set to some values and were some problems solved.