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소수성 코팅된 수평관내에서의 적응축 유도를 통한 응축 열전달 성능 증진
강주원(Joo Won Kang),황경원(Kyung Won Hwang),박현선(Hyun Sun Park),Moriyama Kiyofumi,김무환(Moo Hwan Kim) 대한기계학회 2016 대한기계학회 춘추학술대회 Vol.2016 No.12
We measured how the condensation heat transfer coefficient h inside a horizontal tube changes by hydrophobic coating on the condensing surface. We built horizontal test sections in which steam flows inside a tube and coolant flows outside as counter flow. The 2-meter-long stainless steel tubes were used as condensing tubes, which were two types: one as purchased and the other tube coated internally with polytetrafluoroethylene (PTFE). The outer diameter of the tubes was 50.8 mm, and the inner diameter was 47 mm. Steam at saturation temperature was supplied to the test section with maximum mass flux of 12.2 kg/m2/s at a pressure 1.5 bar. Tube outer wall temperatures, coolant temperature difference between inlet/outlet, and coolant mass flow rate were measured for calculation of h. The value of h was 53% increased in the PTFE-coated tube than in the normal tube. This result shows usefulness of the present method for the improvement of the efficiency of heat exchangers.
피동안전계통의 수직관과 수평관내 순수증기 응축 열전달 성능 비교
강주원(Joo Won Kang),황경원(Kyung Won Hwang),박현선(Hyun Sun Park),Kiyofumi Moriyama,김무환(Moo Hwan Kim) 대한기계학회 2014 대한기계학회 춘추학술대회 Vol.2014 No.11
Condensation heat exchangers cooled by a water pool have growing attention in nuclear power plants as the passive cooling systems can cool down the core heat energy without any power sources. In this study, the average and local condensation heat transfer were experimentally investigated inside a vertical tube which is submerged in a water pool for designing a new condensation heat exchanger as a passive safety system. In the experiment, the system pressure of 0.6~1.4 MPa and mass flux of 8.7~26.2 kg/m2-s were tested. The condensation heat transfer coefficient increased as both of the system pressure and the mass flux increased. In case of a horizontal tube, several correlations were used to calculate heat transfer coefficient. It showed that the condensation heat transfer coefficients were higher inside the horizontal tube than the vertical one under the same conditions. Liquid film formation in each tube orientation was theoretically analyzed to support the results.
양기훈(Ki Hoon Yang),김동억(Dong Eok Kim),황경원(Kyung Won Hwang),하영호(Young Ho Ha),김무환(Moo Hwan Kim) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11
An experimental study was performed to investigate local condensation heat transfer coefficients (HTCs) of high pressure steam. The test section was a single vertical tube with an inner diameter of 15.8㎜, a length of 1.5m, and composed of SUS 316. Experiments were conducted for mass fluxes from 20.4 to 51.0㎏/㎡s and pressures from 10 to 60bar. HTCs were compared with several correlations. The predictions of those correlations were largely deviated from the experimental HTCs, because the correlations did not directly reflect the local effects of the liquid film and vapor shear stress. However, in Nusselt equation, although the absolute values of prediction had large differences to measured values, in the aspect of tendency, the equation was outstanding compared to other correlations. Thus, for predicting efficiently the condensation heat transfer phenomena, the modification of the Nusselt theory equation based on the effects of liquid film and vapor shear stress would be promising.