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다수의 팬코일유닛에 작동유체를 공급하는 헤더에서 하부 유동저항 변화에 따른 유량분배 특성 평가
김진섭(Jinsub Kim),정지환(Ji Hwan Jeong) 대한설비공학회 2021 설비공학 논문집 Vol.33 No.8
If a working fluid is not properly distributed in a heating and cooling system, the energy loss will increase. The flow distribution is affected by the flow resistance of piping, valves, heat exchangers, and so on. In addition, flow distribution can be controlled by the change of flow resistance of valves. Therefore, it is necessary to study flow distribution considering the flow resistance. In the present study, a numerical flow network model was developed to predict the flow distribution in a flow distribution system supplying the working fluid to multiple fan coil units. The flow resistance generated in each channel was represented by the valve flow coefficient. The variation of flow distribution was analyzed by changing the flow coefficient. The numerically predicted flow distribution was compared with experimental data for validation of the flow network model.
김진섭(Jinsub Kim),정지환(Ji Hwan Jeong) 대한설비공학회 2020 대한설비공학회 학술발표대회논문집 Vol.2020 No.6
The Hydronic System efficiency can improve by controlling the flow in the system. Therefore, it is necessary to quantitatively study the flow resistance of value considering effective parameters such as pipe length, type of valve, fan coil unit, and so on the flow distribution. In the present study, the flow distribution characteristics are experimentally analyzed according to the flow resistance, and the hydronic System flow distribution is simulated in which water was supplied to fan coil unit through a header. The flow resistance generated in the valve, pipe length, fan coil unit, and so on in each loop was represented through the valve flow coefficient. Moreover, the flow rate distributed in each branch pipe was measured. Variation of the flow rate based on the flow resistance was measured by changing the valve flow coefficient. As a result of the experiments, the distribution condition and flow coefficient range of control valve were derived.
김진섭(Jinsub Kim),이정호(Jungho Lee) 대한기계학회 2016 대한기계학회 춘추학술대회 Vol.2016 No.12
Surface characteristics such as surface roughness and surface wettability are the most important factors that affect heat transfer coefficient (HTC) and critical heat flux (CHF) in pool boiling. Effect of surface characteristics on pool boiling heat transfer of water was investigated using various surfaces having different roughness and different wettability. Surface roughness (R<SUB>a</SUB>) on the copper surfaces having moderate wettability (θ = 65°) was varied from 0.041 μm to 2.36 μm. It is verified that both HTC and CHF increase with increasing surface roughness. Three surfaces having similar surface roughness (R<SUB>a</SUB> ~ 0.11 μm) and different contact angles of 12° (superhydrophilic), 65° (moderate), and 122° (hydrophobic) were examined. While HTC increases with contact angle increase at low heat flux, CHF on the hydrophobic surface was merely 55 kW/m², which is over 20 times smaller than those on hydrophilic surfaces.
Long-Distance Microscope Lens를 이용한 직교유동 가시화
김재윤(Jaeyun Kim),서진혁(Jinhyeuk Seo),이준식(Junsik Lee),김진섭(Jinsub Kim),이정호(Jungho Lee) 대한기계학회 2016 대한기계학회 춘추학술대회 Vol.2016 No.12
Cross flow is a current of flow that flows against or across the main current. It has been widely used in engineering applications for film cooling of gas turbine, smokestack pollution dispersion, fuel injection, aircraft control, etc. The jet in cross flow has various characteristics compared with normal flow in flow structure, general dynamics and mixing properties. Although there are a variety of flow analysis methods, flow visualization and numerical analysis are regarded as two major methods. Flow visualization was utilized to analyze the cross flow in this study. The cross flow was made by visualization test rig and oil droplets which are mixed with the cross flow are illuminated by the diode pumped solid state (DPSS) laser and captured with a high speed camera according to change of blowing ratio. Also, the flow near the jet hole was observed in detail utilizing Long-Distance Microscope Lens. This work is intended to examine a distinguished structure of the jet in cross flow through flow visualization and to get better understandings of the flow physics.
Hyunjung Lee(이현정),Jinsub Kim(김진섭),Chu Young(추용),Kwang Pyo Kim(김광표),Kabrai Park(박갑래) 대한기계학회 2020 대한기계학회 춘추학술대회 Vol.2020 No.12
A cryogenic circuit for large scaled superconducting device like a tokamak is installed quite complex. In the KSTAR tokamak, the five cryogenic circuits are managed for cooling of each components (Toroidal Field magnets, Poloidal Field magnets, structures current leads, thermal shield, buslines) independently. The circuit for the Poloidal Field magnets branches into one hundred cooling channels. Five cryogenic valves are controlling the flow rates according to cooling channel length. The KSTAR PF1 upper and lower magnets have ten cooling channels parallel respectively. The pressure drop of the magnets is adjusted by cryogenic valve and is maintained by a supercritical helium circulator. The flow rate should be uniform among the cooling channels or magnets but the flow imbalance was observed during the flow test of magnet individually. The measured imbalance was around 10 % between KSTAR PF1 upper and lower. To investigate for effect of the flow imbalance on the magnet, the simple model of the PF1 upper and lower magnets has been developed using SUPERMAGNET code. The maximum temperature trends are studied in details depending on the imbalance.