• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
• /
• v.38 no.12
• /
• pp.51-60
• /
• 2009

본 연구에서는 착상 조건 하에서 열교환기 휜의 열전도를 고려하여 휜 표면에서의 착상 거동을 예측하기 위하여 수학적 모델을 제시한다. 이 때, 공기측은 착상 현상에 대한 3차원 유동 변화의 영향을 고려한다. 서리층 두께에 대한 해석 결과는 실험 결과를 최대 10% 오차 내에서 잘 예측한다. 유동에 수직한 방향(z-dir.)의 서리층 두께 성장은 휜의 열전도에 의해 휜 바탕 근처에서 활발하고, 휜 끝으로 갈수록 지수함수적으로 둔화된다. 휜의 열전도를 고려한 경우에 비해 휜의 표면온도가 일정한 조건에서 서리층 두께는 최대 2배, 열전달량은 평군 10% 정도 과대 예측한다. 따라서, 열교환기 휜에서의 착상 거동을 정확하게 예측하기 위해 착상 모델 해석 시 휜의 열전도를 고려해야 한다. 휜의 열전도 고려 유무에 따른 착상 거동의 차이를 보완하기 위해 열전달량에 대한 등가온도를 산출하며, 이를 근거로 무차원 등가 온도 상관식을 도출한다.

• Journal of Energy Engineering
• /
• v.17 no.1
• /
• pp.1-7
• /
• 2008

The present study has been conducted to understand the heat and mass transfer characteristics of humid airflow in frosting conditions. A flat plate of aluminum was used for the simulation of flat surface part of the fin of the heat exchanger. The aluminum surface temperatures were measured and analyzed to clarify the heat and mass transfer characteristics under frosting conditions. Also, the pressure drops were measured to clarify the air-blocking effect of frost in the mini channel of the air-side hoot exchangers. A data reduction method was developed far the analysis of local characteristics of humid air under frosting conditions.

• Proceedings of the KAIS Fall Conference
• /
• 2010.05b
• /
• pp.1141-1144
• /
• 2010

본 연구에서는 난방운전시 저온 및 착상 조건에서 히트펌프 칠러의 성능을 조사하고자 하였다. 실험은 항온항습 기능을 가진 공기엔탈피 방식의 칼로리미터와 항온수조를 사용하여 수행되었으며, 실외온도조건을 설정한 후에 히트펌프 칠러의 성능을 실험으로 측정하였다. 외기조건이 $-7^{\circ}C$에서 $-15^{\circ}C$까지 변화함에 따라 시스템의 성능과 COP는 표준온도 조건의 실험값 보다 약 48~87%까지 감소하였다. 착상 실험에서는 시간 변화에 따라 출구수온이 표준온도를 기준으로 74% 감소하였다. 본 연구로부터 히트펌프 칠러의 설계 기초자료 획득 및 신뢰성을 확인할 수 있었다.

• Development and Reproduction
• /
• v.2 no.2
• /
• pp.197-203
• /
• 1998

DNA methylation seems to play an important regulatory role in gene expression and cell differentiation during postimplantation embryonic development. However, the significance of DNA methylation which is maintained by the DNA MTase during preimplantation embryonic development, is not fully understood. In order to study the role of DNA methylation in the preimplantation embryos, the expression of DNA MTase transcripts was monitored in the oocytes and preimplantation embryos. The mRNA of DNA MTase was detected in the oocytes and pleimplantation embryos. The relative mRNA levels of DNA MTase were high from the stages of GV-oocytes and pronuclear embryos, and thereafter decreased gradually. By the treatment of $\alpha$-amanitin, it was confirmed that the transcripts presented in pronuclear embryos was derived from the maternal genome. The presence of transcripts of DNA MTase in the oocytes and pronuclear embryos suggests that the maintenance of DNA methylation may be necessary and seems to play an important role in gene expression and cell differentiation during preimplantation embryonic develop-ment in mouse.

• Transactions of the KSME C: Technology and Education
• /
• v.3 no.1
• /
• pp.1-13
• /
• 2015

In this study, a new dynamic VRF-type heat pump simulation model is proposed which incorporates frosting and defrosting models. Toward this end, a simple frosting model based on the perfect analogy, and lumped system based defrost model, are proposed. Then, frosting and defrosting models are incorporated into a dynamic heat pump model which adopts segment-by-segment local heat exchanger model and map-based variable speed compressor model. Thus, the model can naturally represent locally uneven frosting and defrosting on the heat exchanger surface. Developed simulation model is validated against available experimental data to show good agreement within 10% error for capacity and COP. Finally, developed dynamic heat pump model is applied to annual heating season simulation to show that seasonal COP of heat pump is degraded by 7% due to frosting and defrosting.

• Journal of Radiation Protection and Research
• /
• v.21 no.4
• /
• pp.273-284
• /
• 1996

Embryos and fetuses are more sensitive to various environmental agents than are adults or children. The biological effects such as intrauterine death and malformation are closely connected with prenatal exposure very various agents. The sensitivity of these embryonic/fetal effects depends on the stage of pregnancy. From the viewpoint of fetal development, embryonic and fetal stages can be divided into three stages : Preimplantation, organogenetic and fetal. Each stage corresponds to 0 to 4.5days, 4.5 to 13.5days, and 13.5days of gestation in mice, respectively. Many studies on the biologcal effects of mice irradiated by ${\gamma}-rays$ at various stages during organogenesis and fetal period have been performed. Based on these results, the dose-effect and dose-response relationships in malformations, intrauterine death, or retardation of the physical growth have been practically modeled by the ICRP(International Commission on Radiological Protection) and other international bodies for radiation protection. Many experimental studies on mice have made it clear that mice embryos in the preimplantation period have a higher sensitivity to radiation for lethal effects than the embryos/fetuses on other prenatal periods. However, no eratogenic effects of radiation at preimplantation stages of mice have been described in many textbooks. It has been believed that 'all or none action results' for radiation of mice during the preimplantation period were applied. The teratogenic and lethal effects during the preimplantation stage are one of the most important problems from the viewpoint of radiological protection, since the preimplantation stage is the period when the pregnancy itself is not noticed by a pregnant woman. There are many physical or chemical agents which affect embryos/fetuses in the environment. It is assumed that each agents indirectly effects a human. Then, a safety criterion on each agent is determined independently. The pregnant ICR mice on 2, 48, 72 or 96 hours post-conception (hpc), at which are preimplantation stage of embryos, were irradiated whole body Cesium-gamma radiation at doses of 0.1, 0.25, 0.5, 1.5, and 2.5 Gy with dose rate of 0.2 Gy/min. In the embryos from the fetuses from the mice irradiated at various period in preimplantation, embryonic/fetal mortalities, incidence of external gross malformation, fetal body weight and sex ratio were observed at day 18 of gestation. The sensitivity of embryonic mortalities in the mice irradiated at the stage of preimplantation were higher than those in the mice irradiated at the stage of organogenesis. And the more sensitive periods of preimplantation stage for embryonic death were 2 and 48 hpc, at which embryos were one cell and 4 to 7 cell stage, respectively. Many types of the external gross malformations such as exencephaly, cleft palate and anophthalmia were observed in the fetuses from the mice irradiated at 2, 72 and 96 hpc. However, no malformations were observed in the mice irradiated at 48 hpc, at which stage the embryos were about 6 cell stage precompacted embryos. So far, it is believed that the embryos on preimplantation stage are not susceptible to teratogens such as radiation and chemical agents. In this study, the sensitivity for external malformations in the fetuses from the mice irradiated at preimplantation were higher than those in the fetuses on stage of organogenesis.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.34 no.12
• /
• pp.1071-1078
• /
• 2010

The objective of this study is to investigate the heat transfer characteristics of evaporators that have various fin configurations and are used in household refrigerators. The frosting and defrosting characteristics of a spirally coiled circular fin-tube evaporator, a discrete-plate fin-tube evaporator, and a continuous-plate fin-tube evaporator were measured and compared. Under non-frosting conditions, the heat transfer coefficient of the spirally coiled circular fin-tube evaporator was 22.3% and 40.2% higher than the coefficients of the discrete- and continuous-plate fin-tube evaporators, respectively. Under frosting conditions, the heat transfer coefficient of the spirally coiled circular fin-tube evaporator was 27.0% and 46.3% higher than the coefficients of the discrete- and continuous-plate fin-tube evaporators, respectively. In addition, the defrosting water amount of the spirally coiled circular fin-tube evaporator was 3.2% and 9.4% lower than the amounts in the case of the discrete- and continuous-plate fin-tube evaporators, respectively.

• Proceedings of the SAREK Conference
• /
• 2005.06a
• /
• pp.100-100
• /
• 2005

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.16 no.9
• /
• pp.5795-5801
• /
• 2015

The low temperature distribution of the refrigerated and frozen food has been increased gradually. Refrigeration industry is using R134a refrigerant, which GWP is 1300. R1234yf is an alternative refrigerant of R134a because GWP of R1234yf refrigerant is just 4. Evaporator used in refrigeration truck refrigeration system is operated on low temperature condition. Accordingly, evaporator is formed frost and the formation of frost is rapidly decreased performance of evaporator. In this study, the performance of evaporator using R134a and R1234yf refrigerant was analyzed with operating conditions under frost condition. As a result, the performance of R134a evaporator according to air inlet temperature, relative humidity and evaporating temperature was more sensitive than R1234yf evaporator. Besides, the frost growth of R134a evaporator is steeper than that of R1234yf one.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.18 no.12
• /
• pp.3305-3314
• /
• 1994

In this study, the influence of a frost formed on the vertical plate for different operating conditions(the temperature of the air, the humidity of the air, the velocity of the air, and the temperature of the cooling plate) is investigated. The performance of the heat exchanger is examined by introducing a parameter such as the energy transfer resistance. Correlations which relate frost density, frost thickness and energy transfer resistance to Reynolds number, air temperature and humidity, and cooling plate temperature are developed. Static pressure drop and air flow rate are expressed as a function of free flow area of air.