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마이크로핀 관의 기하학적 형상면화에 대한 열전달 특성(II) -증발 열전달-
곽경민,장재식,배철호,정모,Kwak, Kyung-Min,Jang, Jae-Sik,Bae, Chul-Ho,Jung, Mo 대한설비공학회 1999 설비공학 논문집 Vol.11 No.6
The evaporating heat transfer experiments with refrigerant HCFC 22 are performed for performance evaluation using 4 and 6 kinds of microfin tubes with outer diameter of 9.52mm and 7.0mm, respectively. Used microfin tubes have different shape and number of fins with each other, The experimental results are represented with effects of quality, mass flux and EPR. The evaporating heat transfer characteristics are represented by the existence of not only heat transfer area and turbulence promotion effect but also additional other enhancement mechanism, which are the overflow of the refrigerant over the microfin and microfin arrangement. Microfin tubes having a shape which can give much overflow over the microfin show large evaporating heat transfer coefficients. The effect of refrigerant overflow is much severe in evaporation than condensation. The effect of microfin arrangement is related to overflow effect of the refrigerant over the microfin.
마이크로핀 관의 기하학적 형상변화에 대한 열전달 특성 (I) - 응축 열전달 -
곽경민,장재식,배철호,정모,Kwak, Kyung-Min,Jang, Jae-Sik,Bae, Chul-Ho,Jung, Mo 대한설비공학회 1999 설비공학 논문집 Vol.11 No.6
To examine the enhancement mechanism of condensing heat transfer through microfin tube, the condensation experiments with refrigerant HCFC 22 are performed using 4 and 6 kinds of microfin tubes with outer diameter of 9.52mm and 7.0mm, respectively. Used microfin tubes have different shape and number of fins with each other The main heat transfer enhancement mechanism is known to be the enlargement of heat transfer area and turbulence promotion. Together with these main factors, we can find other enhancement factors by the experimental data, which are the overflow of the refrigerant over the microfin and microfin arrangement. The overflow of the refrigerant over the microfin can be analyzed by the geometric shape of the microfin. Microfin tubes having a shape which can give much overflow over the microfin show large condensing heat transfer coefficients. The effect of microfin arrangement is related to the heat transfer resistance of liquid film of refrigerant. The condensing heat transfer coefficients are high for the microfin tube with even distribution of liquid film.
곽경민,배철호,정모,이상천,Kwak, Kyung-Min,Bae, Chul-Ho,Jung, Mo,Lee, Sang-Chun 대한설비공학회 1998 설비공학 논문집 Vol.10 No.6
Prediction method for heat transfer coefficients in a horizontal smooth tube with forced convection condensation is proposed. In this paper, the analogy between momentum and heat transfer was applied to an annular flow regime and the logarithmic velocity distribution is applied to describe the velocity profile within the liquid film. Prediction results are compared with those of experimental ones. The test refrigerants are R113, R22, R134a, R407C(R33/R125/R134a, 23/25/52 wt%), R410A(R32/R125, 50/50 wt%) and R134a+R123(R134a/R123, 85.5/14.5 wt%) which are used under operating conditions in a condenser of air-conditioner. The proposed prediction method shows good agreement with experimental data within$\pm 30%$ for pure refrigerants. For the mixture refrigerants including the ternary mixture refrigerant R407C, condensation heat transfer from this study are higher than those from experiments. By correcting the constant in two-phase frictional multiplier, the predicated heat transfer coefficients become similar to the experimental results.
자동차용 증발기 판 내의 증발 열전달 및 유동 특성에 관한 실험적 연구
곽경민,주상우,정우열,김택근,김광일,Kwak, Kyung-Min,Joo, Sang-Woo,Jung, Woo-Youl,Kim, Taek-Keun,Kim, Kwang-Il 한국자동차공학회 2007 한국 자동차공학회논문집 Vol.15 No.2
An experimental study was performed to evaluate the in-plate evaporation heat transfer and flow characteristics of a evaporator used in automobile. Two test-cores with different heat transfer area, bead-shape and bead-array were tested, A type and B type. For the heat transfer, Nusselt number for B type test-core reaches a value nearly equal to the one for A type test-core, in the whole range of equivalent Reynolds number. But, for the same mass flow rate of refrigerant, hA for B type test-core becomes higher with the increase of the mass quality of refrigerant than for A type test-core. In a flow visualization experiment, the wake zone of refrigerant circulating at u-turn position of plate is observed.
브라운관용 플런저 냉각표면의 온도분포 개선을 위한 연구
곽경민(Kyung Min Kwak),배철호(Cheol Ho Bai),박지열(Ji Yeol Park) Korean Society for Precision Engineering 2008 한국정밀공학회지 Vol.25 No.3
The main objective of the present study is to achieve linear temperature distribution of cooling surface of plunger. K type thermocouples are attached at the surface of plunger to measure temperature. Nozzle and insulating material are inserted in the pin hole of the plunger for this study. Cooling water flow enters at one nozzle and leaves at three nozzles. Flow through nozzle can be activated in the pin hole, temperature of hot point around hole is decreased. Meanwhile, insulating material blocks off heat transfer, temperature of cold point around hole is increased. By combination of nozzle and insulation, heat transfer of hole is controlled effectively, as result its, temperature of plunger surface shows linear temperature distribution.
수중 위치 추정을 위한 3차원 전자기파 센서 노드 개발
곽경민(Kyung Min Kwak),김진현(Jinhyun Kim) 제어로봇시스템학회 2013 제어·로봇·시스템학회 논문지 Vol.19 No.2
In this paper, we discuss a 3-dimensional localization sensor node using EM waves (Electromagnetic waves) with RSSI (Received Signal Strength Indicator). Generally EM waves cannot be used in underwater environment, because the signal is highly attenuated by the water medium according to the distance. Although the signal quickly reduces in underwater, the reducing tendency is very clear and uniform. Hence EM waves have possibility as underwater distance sensors. The authors have verified the possibility by theory and several experiments, and developed calibration methods in case of linear and planer environment. For 3-dimensional localization in underwater, it must be known antenna’s radiation pattern property in electric plane(called E-plane). In this paper, we proceed experiments to verify attenuation tendency with z axis movement, PLF(Polarization Loss Factor) and ILF (Inclination Loss Factor) with its theoretical approach.
수치해석에 의한 버터플라이 밸브의 유량계수 및 유동특성에 관한 연구
곽경민(Kyung-Min Kwak),조지승(Ji-Sung Cho),김진대(Jin-Dae Kim),이중형(Jung-Hyung Lee) 한국기계가공학회 2012 한국기계가공학회지 Vol.11 No.4
The objective of this study is to simulate flow coefficient and flow characteristics such as velocity and pressure distribution for butterfly valve. Butterfly valves used in this study are 65A, 80A and 100A, in size, and of which the opening angle is varied. The flow coefficient, Kv, increases as the disc opening and valve size are increase. When using flow coefficient meanwhile specific curve of flow rate is also determined. The flow velocity between disc and seat increase as the disc opening decrease. The re-circulating zone is also observed in downstream behind disc.
곽경민(Kyung-Min Kwak),이중형(Joong-Hyoung Lee),조경철(Kyung-Chul Cho),이은하(Eun-Ha Lee) 한국기계가공학회 2021 한국기계가공학회지 Vol.20 No.4
The objective of this study is to prevent or decrease condensation on the surface of aluminum butterfly valves used in high humidity air conditions. We proposed a new valve with an anti-condensation device, a heat resistance medium, instead of a conventional valve. We, then, compared the surface temperature distribution between the proposed and conventional valves using experimental and analytical methods. The size of the evaluated valve is 100A and fluid conditions are 35℃/RH 75% in the air outside the valve and 5℃ in the cooling water inside the valve. The experimental results show that the surface temperature of the proposed valve is 23~42% higher than that of a conventional valve, thereby exhibiting an anti-condensation effect. As a result, we observed the complete prevention of condensation on a gear box mounted to the proposed valve, showing surface temperature distribution above the dew point temperature of air. The analytical results are in agreement with the trends in experimental results.