• 수산해양교육연구
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• 제25권2호
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• pp.301-306
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• 2013

In this paper, cycle performance analysis of two-stage compression and two-stage expansion refrigeration system using alternative freon refrigerants is presented to offer the basic design data for the operating parameters of the system. Alternative freon refrigerant for freon refrigerant R22 were used as working fluids in this study. The operating parameters considered in this study included evaporation temperature, condensation temperature, subcooling degree, superheating degree, and mass flow rate ratio of inter-cooler. The main results were summarized as follows : The COP of two-stage compression and two-stage expansion refrigeration system increases with the increasing subcooling degree and mass flow rate ratio of inter-cooler, but decreases with the increasing evaporating temperature, condensing temperature and superheating degree. Therefore, subcooling degree, mass flow rate ratio of inter-cooler of two-stage compression and two-stage expansion refrigeration system using alternative freon refrigerants have an effect on COP of this system.

• 동력기계공학회지
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• 제13권6호
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• pp.70-75
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• 2009

In this paper, cycle performance analysis of R744($CO_2$) two-stage compression and one-stage expansion refrigeration system is presented to offer the basic design data for the operating parameters of the system. The operating parameters considered in this study include superheating degree, compressor efficiency, gas cooling pressure, mass flowrate ratio, outlet temperature of gas cooler and evaporating temperature in the carbon dioxide two-stage refrigeration cycle. The main results were summarized as follows : The cooling capacity of two-stage compression and one-stage expansion refrigeration system increases with the increasing superheating degree, compressor efficiency and gas cooling pressure, but decreases with the increasing mass flowrate ratio and evaporating temperature. The compression work of two-stage compression and one-stage expansion refrigeration system increases with the increasing superheating degree, outlet temperature of gas cooler, gas cooling pressure and evaporating temperature, but decreases with the increasing compressor efficiency and mass flowrate ratio. The COP of two-stage compression and one-stage expansion refrigeration system increases with the increasing compressor efficiency, but decreases with the increasing superheating degree, gas cooling pressure, mass flowrate ratio and evaporating temperature. Therefore, superheating degree, compressor efficiency, gas cooling pressure, mass flowrate ratio, outlet temperature of gas cooler and evaporating temperature of R744($CO_2$) two-stage compression and one-stage expansion refrigeration system have an effect on the cooling capacity, compressor work and COP of this system.

• Clinical and Experimental Reproductive Medicine
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• 제32권4호
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• pp.337-346
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• 2005

Objective: The oligosaccharide moieties of glycoproteins and proteoglycans have a vital function in blastocyst differentiation. Concanavalin (ConA), a lectin, is known to bind on the preimplantation embryos, especially on blastocyst. In this study, we investigated whether ConA can modulate the trophoblast development and about the regulating mediator. Also, we investigated whether expansion is enough for hatching procession of the mouse blastocyst. Method: Embryos were collected at 72 h post hCG injection and chemicals were treated after 24 h (96 hr post hCG injection). ConA or calcium ionophore A23187 were exposed to blastocyst and than analysis the developmental process for 48 hr. Intracellular free-$Ca^{2+}$ concentration in trophectoderm was measured with confocal laser microscope after exposing to ConA or calcium ionophore A23187. ConA-pretreated blastocyst exposed to the calcium ionophore A23187 and then analyzed the developmental process. Otherwise ouabain was treated to the blastocyst to block the $Na^+/K^+$-ATPase activity. Results: In contrast to the control blastocyst, the ConA-exposed blastocysts developed beyond the expansion stage with significantly high rate (90.4%) at 12 h post administration. ConA induced an increase the intracellular $Ca^{2+}$ concentration in trophectoderm. Calcium ionophore A23187 also stimulated expansion of blastocyst. Most of the control blastocysts developed to the hatching stage at 144 h post hCG injection. However, strongly 65% of the ConA-exposed embryos were arrested at expanded stage at same time point. The developmental progression rates to hatching stage of both ConA- and calcium ionophore A23187-expose blastocysts were significantly lower than that of the control. However ConA-pretreated embryos developed to the hatching stage like control embryos. Ouabain showed a tendency to delayed the progress to expansion stage but did not inhibit the development to the hatching stage. Conclusion: ConA-mediated expansion is the result of the increase of intracellular free-calcium in blastocyst stage embryo. It is suspected that expansion of the blasocyst is a essential indirect factor in hatching and the calcium may triggering the cellular mechanisms for the both expansion and hatching progression.

• 한국가스학회지
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• 제16권3호
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• pp.42-47
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• 2012

본 논문에서는 규제 프레온냉매 R22의 대체 자연냉매의 후보인 R290(프로판), R600(부탄), R717(암모니아), R1270(프로필렌)을 작동유체로 사용하는 2단압축 1단팽창 냉동시스템의 성능 특성을 비교하였다. $-20^{\circ}C{\sim}-50^{\circ}C$ 정도의 저온을 얻기 위해 사용되는 2단압축 1단팽창 냉동장치에서의 증발온도, 응축온도, 과열도 및 과냉각도의 변화에 따른 성능계수(COP) 변화를 규명하고자 하였다. 성능특성 규명 결과, 과냉각도 및 중간냉각기에서의 냉매유량 증가에 따라 시스템의 COP는 증가하였으나, 증발온도, 응축온도 및 과열도가 증가할수록 COP는 저하되는 결과를 나타내었다. 또한, 자연냉매를 사용하는 2단압축 1단팽창 냉동시스템의 COP는 규제 프레온냉매 R22를 사용하는 경우보다 높기 때문에 자연냉매를 사용하고자 하는 냉동시스템의 안전성이 확보되면 충분히 대체 냉매로서의 경쟁력이 있을 것으로 판단되었다.

• 설비공학논문집
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• 제6권2호
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• pp.130-139
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• 1994

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.

• Journal of Advanced Marine Engineering and Technology
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• 제41권3호
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• pp.191-196
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• 2017

20세기에 대두된 HCFC나 CFC계의 냉매들의 환경에의 악영향을 극복하기 위하여 보다 환경 친화적인 이산화탄소와 같은 자연냉매에 대한 관심이 커지고 있다. 겨울철 대기의 열원을 이용하여 증발을 유도하는 이산화탄소 열펌프는 증발기의 온도가 높아 효율이 상대적으로 낮아지고, 130bar가 넘는 고압으로 인하여 열펌프 설비 부품들의 제작의 어려움이 따르게 된다. 본 연구는 보다 낮은 압력의 새로운 2단 팽창식 $CO_2$ 오토 캐스케이드 열펌프를 고안하여 이러한 단점들을 해소하고 보다 효율을 증가시키고자 하였다. 새로운 오토 캐스케이드 열펌프에 2단 팽창방식과 효과적인 냉각방식의 시스템 구성을 하여 혼합냉매인 $CO_2$ 와 R32를 적용하였다. 공정에 고압 70bar, 중간 팽창압은 25bar, 최종 저압은 10bar를 적용하여 해석한 결과, 현재의 오토 캐스케이드 열펌프 공정의 COP는 1.629이었으나, 개선된 중간 압력 25bar의 2단 팽창 오토 캐스케이드 공정은 2.332로 현재의 공정보다 43.15% 향상되었다. 또한 저압측 증발기의 온도도 $-10^{\circ}C$ 이하가 되어 찬 외기에도 증발이 용이하게 발생되는 공정이 되었다. 본 공정이 향후 $CO_2$ 열펌프의 성능계수를 보다 향상시키고 고압에 따른 부품 문제들의 해소에 기여할 수 있는 공정으로 분석되었다.

• 한국발생생물학회지:발생과생식
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• 제15권1호
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• pp.17-24
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• 2011

Lipid metabolites involved in cellular regulation as signaling mediators. Prostaglandins (PGs), metabolites of lipid are involved to pregnancy at the time of implantation but the functional roles of PGs on embryo development are still controversy and largely unknown. In previous report, the levels of $PGE_2$ and $PGF_{2a}$ at embryos of morula stage and blastocyst stage were explored (Cheon et al., 1998). In this study, the previous suggestion was confirmed and the possible downstream mediator of prostaglandin $E_2$ and prostaglandin $F_{2a}$ on the expansion and hatching of mouse embryo was examined. As expected, developmental rate of the blastocyst to expanded stage was a concentration-response curve that showed the highest expansion rate at 10 ${\mu}M$ $PGE_2$, but at 100 ${\mu}M$ $PGE_2$, the rate was decreased. In contrast to the $PGE_2$, $PGF_{2a}$ stimulated expansion without toxicity at highest concentration. Cotreatment of PGs with indomethacin overcame the inhibitory effects of indomethacin in expansion. Exogenous PGs also improved the development of expanded embryos to the hatching stage. Besides, PGs receptors' transcripts detected at blastocyst. $PGE_2$ was caused of calcium fluctuation in the blastocyst but $PGF_{2a}$ did not. The changes of intracellular calcium concentration were different between indomethacin pretreated embryos and non-treated embryos. Based on these results it is suggested that PGs work as paracrine and/or autocrine factors through calcium and the others which were not identified in this study.

• 설비공학논문집
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• 제20권5호
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• pp.295-303
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• 2008

The objectives of this study are to predict actual system performance and effective operating range of the 2-stage compression heat pump system using river water. An electronic expansion valve was applied to the simulation to analyze the effects of operating conditions on the system performance. The developed program was verified by comparing the predictions with the measured data. The results from the present model showed a good agreement with the measured data. In addition, the heat pump simulation was conducted by increasing condenser reservoir inlet temperature to investigate the benefits of the 2-stage compression over the 1-stage compression in the heating mode. The performance of the 2-stage compression cycle was better than that of the 1-stage compression when the inlet temperature of the condenser reservoir was higher than $40^{\circ}C$.

• 동력기계공학회지
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• 제19권6호
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• pp.82-88
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• 2015

In this paper, cycle performance analysis of two-stage compression and one-stage expansion refrigeration system applied various refrigerants is presented to offer the basic design data for the operating parameters of the system. The operating parameters considered in this study include degree of superheating and subcooling, compressor efficiency, evaporation temperature, condensing temperature, mass flow rate ration into inter-cooler, effectiveness of internal heat exchanger. The main results were summarized as follows : The COP of two-stage compression and 1-stage expansion refrigeration system increases with the increasing subcooling, mass flow rate ration of inter-cooler, evaporation temperature, but decreases with the increasing condensing temperature and superheating degree. Therefore, subcooling degree, mass flow rate ratio of inter-cooler of two-stage compression and 1-stage expansion using substitute refrigerant have an effect on COP of this system. The COP of alternative refrigerants was higher than the COP of R22 in this study, although the COP of some mixed refrigerants were lower than COP of R22.

• 한국수소및신에너지학회논문집
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• 제30권2호
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• pp.188-192
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• 2019

Comparative studies between single- and two-stage expansion process using LNG cold heat have been performed for a closed Rankine power generation cycle. PRO/II with PROVISION release 10.0 from Schneider Electric Company was used, and the Peng-Robinson equation of state model with Twu's alpha function was selected for the modeling and optimization of the power generation cycle using LNG cold heat. In two-stage power generation cycle, 6.7% more power was obtained compared to that of single-stage power generation cycle through the optimization works.