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Comparisons of upwind numerical scheme for a hyperbolic two-fluid model
Moon-Sun Chung(정문선),Youn-Gyu Jung(정연규),Sung-Jae Lee(이성재) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.10
A lot of upwind scheme has been developed for simulating high speed, single-phase flows and some of them prove to be very successful. However, all of these numerical schemes cannot be applied for two-phase flow problems due to their complexity relating the interfacial phenomena between two phases of fluid. For this reason, sometimes we need to find an optimal numerical scheme in order to adopt a prominent upwind scheme to the hyperbolic two-fluid model for two-phase flows. Before choosing an upwind numerical scheme, we need to compare some candidates by solving benchmark problems. In this study, we compare the Flux Vector Splitting (FVS) scheme with the Harten, Lax and van Leer (HLL) scheme for a hyperbolic two-fluid model for 1D. equation system and analyze their advantage and disadvantage by calculating the two-phase shock-tube problem.
마이크로 pin fin 화학반응기에서 수소화붕소나트륨 수용액의 압력강하 및 탈수소 화학반응 연구
정기문(Ki Moon Jung),최석현(Seok Hyun Choi),정문선(Moon-Sun Chung),이희준(Hee Joon Lee) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11
Many types of hydrogen storages have been studied recently paying attention to hydrogen storage and release. Among those, dehydrogenation from the hydrolysis of a sodium borohydride (NaBH₄) solution has been of much interest owing to its high theoretical hydrogen storage capacity (10.8 wt.%) and potentially safe operation. However, most of researchers have focused on chemical characteristics such as NaBH4 hydrolysis, catalysts, and synthesis, but not on the mechanical design of a chemical reactor for hydrogen generation. To design an efficient chemical reactor, size (which should be compact) and pressure drop, reaction rate are of great importance. Therefore, a microchannel is promising for the design of a dehydrogenation reactor owing to its very large reacting surface area per unit volume. Moreover, micro size pin fin structures could be manufactured on the bottom of microchannel surface for even more extended reacting surface area and contact catalytic reaction. An experiment study has been performed on catalytic reaction rate and pressure drop of NaBH4 solution over both a single microchannel with a hydraulic diameter of 300 ㎛ and a staggered array of micro pin fins with hydraulic diameter of 50 ㎛ in the microchannel. Catalytic reaction rates and pressure drops were obtained over Reynolds numbers from 1 to 60 and solution concentration from 5 to 20 wt.%. Moreover, reacting flows were visualized using a high-speed camera with a macro zoom lens. As a result, both the amount of hydrogenation and pressure drop are 2.45 times and 1.5 times more in pin fin microchannel than in a single microchannel, respectively.
2-유체 모델을 위한 “개선된 Semi-Implicit 기법”
이성재(Sung-Jae Lee),정문선(Moon-Sun Chung) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.4
Introducing the interfacial pressure jump terms based on the surface tension into the momentum equations<br/> of two-phase two-fluid model, the system of governing equations is turned mathematically into the hyperbolic<br/> system. The eigenvalues of the equation system become always real representing the void wave and the<br/> pressure wave propagation speeds as shown in the previous manuscript. To solve the interfacial pressure jump<br/> terms with void fraction gradients implicitly, the conventional semi-implicit method should be modified as an<br/> intermediate iteration method for void fraction at fractional time step. This advanced semi-implicit method<br/> (ASIM) then becomes stable without conventional additive terms. As a consequence, including the interfacial<br/> pressure jump terms with the advanced semi-implicit method, the numerical solutions of typical two-phase<br/> problems can be more stable and sound than those calculated exclusively by using any other terms like virtual<br/> mass, or artificial viscosity.
정연규(Youn-Gyu Jung),정문선(Moon-Sun Chung),이성재(Sung-Jae Yi),장근식(Keun-Shik Chang) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11
In this study, we are planning to discuss on the implementation of an upwind method for a new 2-dimensional 2-fluid model including the surface tension effect in the momentum equations. This model consists of a complete set of 8 equations including 2-mass, 4-momentum, and 2-internal energy conservation equations having all real eigenvalues. Based on this equation system with upwind numerical method, we first make a pilot 2-D. code and then solve some benchmark problems in order to check whether this model and numerical method is able to properly solve some fundamental one-dimensional two-phase flow problems or not.