• Journal of the Korea Institute of Military Science and Technology
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• v.27 no.1
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• pp.43-50
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• 2024

Large planar military antenna boasts a range of electrical components, including TRA(Transmit-Receive Assembly), signal processors, etc. which engage in computations and calculations. These processes generate a significant amount of heat, leading to unforeseen consequences for the equipment. To mitigate these adverse effects, it's imperative to implement a cooling system that can effectively reduce heat-related issues. Given the antenna's intricate nature and the multitude of components it houses, a two-step estimation process is necessary. The first step involves a comprehensive model calculation to determine the total flow characteristics, while the second step entails a thermal analysis of individual TRA set. In this study, we depicted an antenna set using simplified 3D models of its components, considering their material and thermal properties. The sequential analysis process facilitated the calculation of branched flow rates, providing insights into the individual TRA. This approach also allowed us to design a cooling system for the TRA set, assessing its thermal stability in high-temperature environments. To ensure the optimal performance of TRA, breaking down the analysis into stages based on the cooling system's structure can assist operators in predicting numerical results more effectively.

• Nuclear Engineering and Technology
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• v.2 no.1
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• pp.19-25
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• 1970

A study was conducted on the coolant mixing between water flowing in two adjacent subchannels. Measurements were made of the quantity of mass transferred between a larger rectangular channel and a smaller triangular channel in a 19-rod fuel bundle under the conditions of single phase flow and air-water two-phase flow. The results of the experiments showed that the low mixing rate appears in single phase flow, and high mixing rate was measured in air-water two-phase flow Mixing rate decreases with the increasing of air void fraction during the air-water flow. It seems that the high mixing rate in the air-water flow was caused due to adequate agitation of the chaotic air void.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.4
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• pp.449-455
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• 2015

Owing to the trend of an increase in capacity and high-efficiency requirement, the life and reliability of power transformer depend significantly on the amount of heat generation per unit volume and the degradation of insulation oil. These problems can be solved by enhancing the cooling performance of the radiator. The purpose of this study was to find a suitable position of fans for a better cooling effect given by the forced-convection of air in an ONAF (Oil Natural Air Forced) type transformer. In the simulation, commercial software was used for flow analysis, and the cooling passage of the oil was simplified to shorten the time taken for computation. With the diameter of the fan fixed at a constant value, the analysis was performed only by changing the position of the fans. As a result, a vertical position change of the fans does not affect the cooling performance significantly. However, the temperature drop given by the fans positioned on the front region of the transformer is larger than that on the rear region.

• Journal of computational fluids engineering
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• v.19 no.4
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• pp.14-19
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• 2014

This study conducts shape optimization of rib turbulator on the internal cooling passage that has triangular cross-section of high pressure turbine nozzle. During optimization, various types of rib turbulator including angled, V-shaped, A-shaped and angled rib with intersecting rib are considered. Each type of rib turbulator is parameterized with attack angle(s), rib height, spacing ratio and bending/intersecting location. For optimization, Design of Experiment (DOE) and Kriging surrogate model are used to utilize computational resource more efficiently and Genetic Algorithm (GA) is used to search the optimum points. As a result, Pareto front of each type of rib turbulator with friction factor that relates to pressure drop in cooling passage and spatially averaged Nusselt number that relates to heat transfer on the wall is drawn and optimum points on the Pareto front are suggested.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.1241-1246
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• 2004

The heat flux on a chip is rapidly increasing with decreasing the size of one. It is necessary to properly cool the high heat flux chip. One of the promising cooling methods is to apply CPL heat pipes with porous materials, for example PVA, polyethylene, and powder sintered metal plate and with microchannels in the evaporator. A small scale CPL heat pipe with PVA as wick was designed and manufactured. Since the height difference between the evaporator and the condenser is a crucial parameter in the CPL heat pipes, the performance of the heat pipes depending on the parameter was investigated. The parameter is higher the performance is better. However, the improvement rate of the performance does not increase the increase rate of the height. In addition to, the parameter effect depending on heat input was investigated.

• The KSFM Journal of Fluid Machinery
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• v.14 no.6
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• pp.76-84
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• 2011

The effect of inlet velocity profile on the heat transfer coefficient in a rotating smooth channel was investigated experimentally. Three simulated inlet flow conditions of fully developed, uniform, and distorted inlet conditions were tested. The Reynolds number based on the channel hydraulic diameter was ranged from 10,000 to 30,000 and the transient liquid crystal technique was used to measure the distribution of the heat transfer coefficient in the rotating channel. Results showed that the overall heat transfer coefficient increased as the Reynolds number increased. Also, the distribution of the heat transfer coefficient was strongly affected by the inlet flow condition. Generally, the fully developed flow simulated condition showed the highest heat transfer coefficient.

• Journal of Energy Engineering
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• v.28 no.4
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• pp.103-110
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• 2019

The domestic innovative power reactor named iPOWER will employ the passive molten corium cooling system(PMCCS) to cool down and stabilize the core melt in the severe accident. The final design concept of the PMCCS is yet to be determined, but the in-vessel retention through external reactor vessel cooling has been also considered as a viable strategy to cope with the severe accident. In this study, the two-phase natural circulation flow established between the reactor vessel and the insulation was simulated using a thermal-hydraulic system code, MARS-KS. The flow path of cooling water was modeled with one-dimensional nodes, and the boundary condition of the heat load from the molten core was defined to estimate the naturally-driven flow rate. The evolution of major thermal-hydraulic parameters were also evaluated, including the temperature and the level of cooling water, the void fraction around the lower head of the reactor vessel, and the heat transfer mode on its external surface.

• Nuclear Engineering and Technology
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• v.23 no.1
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• pp.66-80
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• 1991

The LOFT intermediate break experiment L5-1, which simulates 12 inch diameter ECC line break in a typical PWR, has been analyzed using the reactor thermal/hydraulic analysis code RELAP5/MOD2, Cycle 36.04. The base calculation, which modeled the core with single flow channel and two heat structures without using the options of reflood and gap conductance model, has been successfully completed and compared with experimental data. Sensitivity studies were carried out to investigate the effects of nodalization at reactor vessel and core modeling on major thermal hydraulic parameters, especially on peak cladding temperature(PCT). These sensitivity items are : single flow channel and single heat structure (Case A), two flow channel and two heat structures (Case B), reflood option added (Case C) and both reflood and gap conductance options added (Case D). The code, RELAP5/MOD2 Cycle 36.04 with the base modeling, predicted the key parameters of LOFT IBLOCA Test L5-1 better than Cases A,B,C and D. Thus, it is concluded that the single flow channel modeling for core is better than the two flow channel modeling and two heat structure is also better than single heat structure modeling to predict PCT at the central fuel rods. It is, therefore, recommended to use the reflood option and not to use gap conductance option for this L5-1 type IBLOCA.

• Journal of the Korean Society of Propulsion Engineers
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• v.24 no.5
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• pp.43-55
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• 2020

The effect of cutted pin in front of pin-fin array was analyzed for increasing the cooling performance of gas turbine blade. The numerical simulations were conducted to figure out the flow and thermal characteristics. The base case which is staggered pin-fin array, cut pin case 1 which has X₂/D_p=1.25 cut pin and cut pin case 2 which has X₃/D_p=1.75 cut pin were compared. The results showed that cut pin increases the strength of the horseshoe vortex which occurred at the leading edge of pin-fin array. Furthermore, the wake effect is reduced at the trailing edge of pin-fin array. As a result, the heat transfer distribution on the endwall increases. However, the friction factor increases owing to the installation of cut pin, but the thermal performance factor is increased maximum 23.8% in cut pin case 2. Therefore, installation of cut pin will be helpful for increasing the cooling performance of pin-fin array of gas turbine blade.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1993.04a
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• pp.1-19
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• 1993

기계적 mechanism에 의해 동력의 전달 또는 방향을 전환할때 상대적으로 움직이는 두 면에서 필연적으로 발생하는 마찰, 마모를 감소시켜 원활한 작동을 유지시켜 주는 물질을 윤활유라 한다. 이러한 윤활유의 기능은 두 마찰면 사이에 유체막을 형성하여 마찰 및 마모를 감소시키는 마찰, 마모 작용과 같은 1차 기능과 두 마찰면 사이에서 발생하는 열을 냉각시키는 냉각작용, 금속표면의 청정성을 유지시키는 방청작용, 두 마찰면을 밀봉시켜주는 밀봉작용과 같은 2차 기능으로 대별할 수 있다. 윤활유의 구성은 크게 윤활기유와 기유의 물성을 보완 또는 기유에 없는 물성을 나타내는 첨가제들로 구성되어 있는데 기유로는 주로 Paraffine계, Naphthenic계, Aromatic계로 탄소수 20~50의 탄화수소 혼합물로 이루어진 광유계 깅유와 물성과 용도에 따라 인위적으로 합성된 여러가지 합성기유가 사용된다.