• Journal of the Korean Society of Safety
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• 제33권3호
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• pp.92-98
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• 2018

The flow of cooling water in a passive containment cooling system (PCCS), used to remove heat released in design basis accidents from a concrete containment of light water nuclear power plant, was conducted in order to investigate the thermo-fluid equilibrium among many parallel tubes of PCCS. Numerical simulations of the subcooled boiling flow within a coolant loop of a PCCS, which will be installed in innovative pressurized-water reactor (PWR), were conducted using the commercially available computational fluid dynamics (CFD) software ANSYS-CFX. Shear stress transport (SST) and the RPI model were used for turbulence closure and subcooled flow boiling, respectively. As the first step, the simplified geometry of PCCS with 36 tubes was modeled in order to reduce computational resource. Even and uneven thermal loading conditions were applied at the outer walls of parallel tubes for the simulation of the coolant flow in the PCCS at the initial phase of accident. It was observed that the natural circulation maintained in single-phase for all even and uneven thermal loading cases. For uneven thermal loading cases, coolant velocity in each tube were increased according to the applied heat flux. However, the flows were mixed well in the header and natural circulation of the whole cooling loop was not affected by uneven thermal loading significantly.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 한국전기전자재료학회 2002년도 하계학술대회 논문집 Vol.3 No.2
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• pp.1063-1066
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• 2002

An equivalent circuit for the superconductor flux flow transistor(SFFT) was combined with high temperature cooling device, based on the analogy between thermal and electrical variables using the high-temperature superconductor(HTS), is proposed. The device is composed of parallel weak links with a nearby magnetic control line. A model has been developed that is based on solving the equation of motion of Abrikosov vortices subject to Lorentz viscous and pinning forces as well as magnetic surface barriers. The use of thermal models the global performance of thermal cooling circuit and signal system to be checked by using electrical circuit analysis programs such as SPICE.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 한국소성가공학회 2009년도 추계학술대회 논문집
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• pp.323-327
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• 2009

Silicone is recently used for LED chip encapsulment due to its good thermal stability and optical transmittance. In order to predict residual stress which causes optical briefringence and mechanical warpage of silicone, finite element analysis was conducted for both curing and cooling process during silicone molding. For analysis of curing process, a cure kinetics model was derived based on the differential scanning calorimetry(DSC) test and applied to the material properties for finite element analysis. Finite element simulation result showed that the curing as well as the cooling process should be designed carefully so as to reduce the residual stress although the cooling process plays the bigger role than curing process in determining the final residual stress state.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• 제25권7호
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• pp.398-405
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• 2013

Small and medium-size buildings employ a multi-distributed individual air-conditioning system that utilizes package air conditioners instead of centralized cooling systems, which can allow easier building management and maintenance, along with a diversification of facility use. Inverter driven system heat pumps have been developed to achieve not only an easy distribution control, allowing free combination of indoor units with different models and different capacities, but also wide applications to intelligent air conditioning. However, the control algorithms of the system heat pump are limited in the open literature, due to complicated operating conditions. In this paper, an inverter-driven system heat pump having two indoor units with electronic expansion valves (EEV) was simulated in the cooling mode. An integral optimum regulating controller employing the state space control method was also simulated, and applied to the system-heat pump system, to obtain efficient control of the MIMO (multi input multi output) system. The simulation model for the controller yielded satisfactory prediction results. The new control model can be successfully utilized as a basic tool in controller design.

• Structural Engineering and Mechanics
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• 제66권2호
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• pp.273-283
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• 2018

Currently, the dynamic amplification effect of suction is described using the wind vibration coefficient (WVC) of external loads. In other words, it is proposed that the fluctuating characteristics of suction are equivalent to external loads. This is, however, not generally valid. Meanwhile, the effects of the ventilation rate of louver on suction and its WV are considered. To systematically analyze the effects of the ventilation rate of louver on the multi-dimensional WVC of ultra-large cooling towers under suctions, the 210 m ultra-large cooling tower under construction was studied. First, simultaneous rigid pressure measurement wind tunnel tests were executed to obtain the time history of fluctuating wind loads on the external surface and the internal surface of the cooling tower at different ventilation rates (0%, 15%, 30%, and 100%). Based on that, the average values and distributions of fluctuating wind pressures on external and internal surfaces were obtained and compared with each other; a tower/pillar/circular foundation integrated simulation model was developed using the finite element method and complete transient time domain dynamics of external loads and four different suctions of this cooling tower were calculated. Moreover, 1D, 2D, and 3D distributions of WVCs under external loads and suctions at different ventilation rates were obtained and compared with each other. The WVCs of the cooling tower corresponding to four typical response targets (i.e., radial displacement, meridional force, Von Mises stress, and circumferential bending moment) were discussed. Value determination and 2D evaluation of the WVCs of external loads and suctions of this large cooling tower at different ventilation rates were proposed. This study provides references to precise prediction and value determination of WVC of ultra-large cooling towers.

• Journal of Drive and Control
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• 제19권1호
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• pp.62-68
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• 2022

Considering the characteristics of industrial machines that lack vehicle-induced wind, forced convection by a cooling fan is mostly required. Therefore, numerical analysis of an engine room is usually performed to examine the cooling performance in the room. However, most engine rooms consist of a number of parts and components at specific positions, leading to high costs for numerical modeling and simulation. In this paper, a new methodology for three-dimensional computer-assisted design simplification was proposed, especially for the pile of components and parts at the engine room outlet. A porous media model and regression analysis were used to derive a meta-model for imitating the flow rate reduction at the outlet by the pile. The results showed that the fitted model was reasonable considering the coefficient of determination. The final numerical model of the engine room was then used to simulate the velocity distribution by changing the mass flow rate at the outlet. The results showed that both velocity distributions were significantly changed in each case and the meta-model was valid in imitating the flow rate reduction by some piles of components and parts.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• 제12권5호
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• pp.486-493
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• 2000

A theoretical model for the transient performance of vapor-compression air-conditioning system has been developed to evaluate the influence of the refrigerant charge on the system performance. A set of mass and energy equations for the simulation of the heat exchangers and the capillary tube and a polytropic compression model for the compressor are used. The present model successfully predicts the transient behavior of the vapor-compression air-conditioner from the startup. As the refrigerant charge is increased, both the evaporating and condensing pressures increase gradually, and the cooling rate and the COP show a maximum in the range of 0.75-0.8 kg of refrigerant charge. This amount of refrigerant mass is determined to be the optimum charge of the model system. Also, the effect of outdoor air temperature on the optimum refrigerant charge is discussed.

• Journal of the Korea Academia-Industrial cooperation Society
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• 제19권9호
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• pp.69-76
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• 2018

The present study analyzed the effect of film hole position of 45 degree ribbed cooling channel on film cooling performance of gas turbine blades. We also investigated the influence of the ribs under the fixed blowing ratio. Three-dimensional numerical model was constructed and extensive simulation was conducted using the commercial code (Fluent ver. 17.0) under steady-state condition. Base on the simulation results, We investigated the cooling effectiveness, flow velocity, streamline, and pressure coefficient. Moreover, We analyzed the effect of cooling hole position on ejection of the secondary flow caused by the rib structure. From the results, It was found that internal flow of the cooling channel forms a vortex pair in the counterclockwise from the top side, and clockwise from the bottom side. For the channels with ribs, the vortex flow generated by the ribs caused a higher pressure difference near the hole outlet, resulting in at least 12% higher cooling effectiveness than the channel without ribs. Additionally, when the hole is located on the left side of the ribbed channel (Rib-Left), it can be found that the secondary flow generated by the ribs hits against wall surface near the hole to form a flow in the direction of the hole inclination angle. Therefore, It is considered that the region where the cooling gas discharged to the blade surface stays in the main flow boundary layer is wider than the other cases. In this case, The largest pressure coefficient difference was observed near the outlet of the hole, and as a result, the discharge of the cooling gas was accelerated and the cooling efficiency was slightly increased.

• Solar Energy
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• 제18권4호
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• pp.95-100
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• 1998

Indoor environment of the classrooms in most school buildings have not been maintained comfortably during the heating and cooling seasons due to the insufficient installation of the heating and cooling systems and their operation in our country. This study aimed to suggest the guideline for installing the appropriate heating systems to make a better environment of the classrooms in the elementary school buildings. Field survey and the computer simulation of the model school were carried out, and the cost of the both installation and operation were compared with different heating systems.

• Proceedings of the KSME Conference
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• 대한기계학회 2001년도 춘계학술대회논문집C
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• pp.251-256
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• 2001

Deformation analysis of injection molded articles whose geometry is considered as the assembly of the thin flat plates has been conducted. For the in-mold analysis, thermo-viscoelastic stress calculation of rheologically simple amorphous polymer and in-mold deformation calculation considering the in-plane mold constraint has been done. Free volume theory has been used for the non-equilibrium density state by the fast cooling. At ejection, the redistribution of stress together with instantaneous deformation has been considered. During out-of-mold cooling after ejection, thermoelastic model based on the effective temperature has been adopted for the calculation of deformation. Two typical mold geometries are used to test the numerical simulation.