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김남수,김종보,김인석,최형진,Kim, N.S.,Kim, C.B.,Kim, I.S.,Choi, H.J. 대한설비공학회 1993 설비공학 논문집 Vol.5 No.3
Experimental investigations have been carried out to find the effect of drag reduction caused by effective polymer additives in turbulent flows. The experiments were undertaken with a test section of 9.8mm pipe diameter and 3500 mm pipe length(L/D=357) in a closed loop, and Copolymer-X and Polyacrylamide(PAAM) were used as polymer additives for comparisons. The tests were carried out under different polymer concentrations, and the temperatures of the flow considered were $26^{\circ}C$, $60^{\circ}C$ at the flow velocity of 5.3 m/s. The rate of drag reduction obtained by Copolymer-X is found to be considerably higher than that of PAAM in turbulent flows. Copolymer-X is also found to be very reliable for mechanical degradation, which has not been the case in any other additives. It is concluded that Copolymer-X is considered to be one of the most effective agents as an additive especially for long time hydraulic transports. It is also found that polymer degradation in more likely at lower polymer concentrations in the turbulent flows.
빙축열조내 부피축소 및 부양을 고려한 얼음의 용융과정에 관한 연구
장홍순(H.S.Jang),김동춘(D.C. Kim),김일겸(I.K.Kim),조남철(N.C.Cho),김종보(J.B.Kim),임장순(C.S.Yim) 한국태양에너지학회 1996 한국태양에너지학회 논문집 Vol.16 No.1
본 연구는 수평원통형 빙축열조 내에 채워진 얼음이 부양 및 부피가 축소되면서 내향용융될 때 얼음을 체적비((Vs/Vtot) 0.545, 1.00로 채운 후 얼음의 초기온도와 벽면 가열온도를 각각 변화시키면서 내향용융 시켰을 경우, 시간경과에 따른 상변화물질의 용융현상, 용융율 등을 실험적으로 구하여 이를 비교ㆍ검토한 것이다.<br/> 용융율은 얼음의 초기온도와 벽면 가열온도가 동일한 경우에는 얼음의 체적비(Vs/Vtot) 0.545가 1.00보다 크게 나타났으며, 체적비가 동일한 경우에는 얼음의 초기온도보다 벽면 가열온도의 영향을 크게 받는 것으로 나타났다.<br/> 용융진행시 얼음내의 전도열전달, 액상내의 자연대류에 의한 열전달, 얼음의 부양에 따르는 얼음과 열원 벽멱과의 접촉(close contact)에 의한 전도열전달 및 얼음의 회전등이 발생하는 복잡한 전열특성이 나타났으며 이러한 결과를 수평원통형 빙축열조 설계에 고려하여야 함을 알 수 있었다. In this study, melting process of the unfixed phase change material (ice) in horizontal ice storage tube was examined experimentally. Experiments were performed to investigate for heat transfer characteristics of ice melting process according to the change of initial ice temperature, tube wall temperature and initial ice volumetric ratio. The melting rate was more influenced by the wall temperature of tube than initial temperature of ice. Ice was closely contacted near the tube wall because of buoyancy. The remained buoyant ice was irregulary rotated in case of Vs/Vtot=1.00, but not rotated in casce of Vs/Vtot=0.545. Under the same wall and initial ice temperatures, the melting rate was higher for Vs/Vtot=0.545 than that for Vs/Vtot=1.00 due to the difference in the reduction of heating surface area. Therefore in the design of horizontal cylindrical ice storage tube, it should be in consideration of the contraction and rotation of P.C.M.(ice)
LiBr계 용액을 사용한 수직관 흡수기의 열 및 물질 전달에 관한 연구
조현철,김종보,정시영,강상우,이춘식,Cho, H.C.,Kim, C.B.,Jeong, S.Y.,Kang, S.W.,Lee, C.S. 대한설비공학회 1995 설비공학 논문집 Vol.7 No.2
Experimental investigations on heat and mass transfer characteristics in a vertical tube absorber have been carried out. Three different copper tubes with a length of 1.5m have been tested using LiBr solution and LiBr-$CaCl_2$ solution. The effects of solution flow rate, cooling water temperature, solution inlet temperature and evaporation temperature have been investigated in detail. It is found that heat transfer coefficient increases gradually with the increase of solution flow rate, but decreases rapidly for the flow rates less than 0.02kg/ms. The grooved tube generally shows better heat transfer performances than the smooth tube. LiBr solution shows almost no absorption capability for the cooling water temperatures over $40^{\circ}C$. LiBr-$CaCl_2$ gives less decreasing rate in absorption capability at these temperatures and the heat transfer coefficient becomes less dependent on the types of tubes in use. Considering heat and mass transfer rates, LiBr-$CaCl_2$ solution is found to be more suitable than LiBr solution for air cooled absorber, which operates at higher temperature than water cooled absorber.
정동수,김종보,Jung, D.S.,Kim, C.B. 대한설비공학회 1995 설비공학 논문집 Vol.7 No.3
In this paper, pressure drop through a capillary tube is modeled to determine the length of a capillary tube for a given set of conditions. HCFC-22 and its alternatives, HFC-134a, R407B, and R410A are used as working fluids. The conditions on which the model is tested are as follows : condensing temperature; 40.0, 45.0, 50.0, $55.0^{\circ}C$, degree of subcooling;0.0, 2.5, $5.0^{\circ}C$, capillary tube exit condition;choked flow, capillary tube diameter;1.2~2.4mm, mass flow rate;5.0~50.0g/sec. The results justify the use of Stoecker's model which yields the results very close to the values in ASHRAE handbook. While McAdams' method yields much better results than Duckler's in calculating the viscosity of the fluid in 2-phase, the friction factor suggested by Stoecker seems to be the best for capillary tubes of large diameter used in residential air conditioners. For each refrigerant, 372 data with various variables are calculated by the model. The results show that capillary tube length varies very uniformly with changes in condensing temperature and degree of subcooling. Based on this fact, regression analysis is performed to determine the dependence of mass flow rate on the length and diameter of a capillary tube, condensing temperature, and degree of subcooling. Thus determined correlation yields a mean deviation of 2.36% for 1,488 data, showing an excellent agreement.