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마이크로 열전냉각기의 열성능에 대한 열전소자 두께의 영향
이공훈,김욱중 대한설비공학회 2006 설비공학 논문집 Vol.18 No.3
The three-dimensional numerical analysis has been carried out to figure out the effect of the thermoelectric element thickness on the thermal performance of the thermoelectric micro-cooler. The small-size and column-type thermoelectric cooler is considered. It is known that tellurium compounds currently have the highest cooling performance around the room temperature. Thus, in the present study, Bi2Te3 and Sb2Te3 are selected as the n- andp-type thermoelectric materials, respectively. The thermoelectric leg considered is less than 20 m thick. The thickness of the leg may affect the thermal and electrical transport through the interfaces between the leg and metal conductors. The effect of the thermoelectric element thickness on the thermal performance of the cooler has been investigated with parameters such as the temperature difference, the current, and the cooling power.
비직교좌표계에 대한 P-1 근사법 및 유한체적법을 이용한 주유동 중의 원형실린더 주위의 복사열전달 해석
이공훈,이준식,최만수 대한기계학회 1995 대한기계학회논문집 Vol.19 No.3
A study of radiative heat heat transfer has been done in the non-orthogonal coordinate system utilizing the finite volume method and the P.1 approximation. Radiation of absorbing, emitting and scattering media in a concentric annulus has been solved using the non-orthogonal coordinate and the calculations were compared with the existing results. The results obtained from the analysis using the finite volume method are in good agreement with the existing calculations for all optical thicknesses. It was also shown that for only optically thick cases, P-1 approximation can be used in a non-orthogonal coordinate. Convective heat transfer analysis has been carried out to obtain the temperature fields in a cross flow around a circular cylinder and the finite volume method was applied in the non-orthogonal coordinate system to analyze radiative heat transfer. Effects of the optical thickness, the ratio of the surface temperature of the cylinder tot he free stream temperature, and the scattering albedo on radiation have been presented.
Low GWP 혼합 냉매의 열역학 물성치를 위한 상태방정식의 선정
이공훈,김동호,김우경,김진섭,김영,류진우 대한기계학회 2022 大韓機械學會論文集B Vol.46 No.10
Low GWP refrigerants are required to manufacture the refrigeration systems owing to the worldwide global warming issue. The refrigerant replacements for most refrigeration systems have been developed with a GWP value of less than 150. However, the replacement for R410A with a GWP value of less than 150 has not been developed to date. Thus, an attempt has been made to develop the refrigerant replacement as a mixture refrigerant. To develop this refrigerant, the thermodynamic properties must be calculated with the equation of state (EOS) to investigate its performance. In the present study, several types of EOS have been investigated to calculate the thermodynamic properties for pure fluids and mixtures, and the Helmholtz energy explicit EOS showed the best results.
유한체적 복사전달해석법을 이용한 주유동중에 놓인 원형실린더 주위에서의 복사-대류 열전달해석
이공훈,이준식,Lee, Gong-Hun,Lee, Jun-Sik 대한기계학회 1996 大韓機械學會論文集B Vol.20 No.1
A finite volume radiation solution method was applied to a non- orthogonal coordinate system for the analysis of radiative-convective heat transfer about a circular cylinder in crossflow. The crossflow Reynolds number based on the cylinder radius was 20, and the fluid Prandtl number was 0.7. The radiative heat transfer coupled with convection was reasonably predicted by the finite volume radiation solution method. The investigation includes the effects of conduction- to-radiation parameter, optical thickness, scattering albedo and cylinder wall-emissivity on heat transfer about the cylinder. As the conduction- to-radiation parameter decreases, the radiative heat transfer rate increases and conduction rate as well due to the increase in temperature gradient on the cylinder wall which is caused by radiation enhancement. With an increase in the optical thickness, the Nusselt number increases significantly and the temperature gradient shows similar behavior. Though the radiative heat transfer increases with the scattering albedo, the total heat transfer decreases. This is because the decrease in the conduction heat transfer exceeds the increase in the radiation heat transfer. As the wall- emissivity increases, the radiation absorbed in the vicinity of the cylinder wall increases and thereby the total heat transfer increases, even though the conduction heat transfer decreases.