• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.9
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• pp.830-838
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• 2005

The present study investigated the optimization of the absorption performance of the vertical absorber tube with falling film by considering heat and mass transfer simultaneously. Effects of film Reynolds number, geometric parameters by insert device (spring) and flow pattern on heat and mass transfer performances have been also investigated. Especially, effects of coolant flow rate and the flow pattern by geometric parameters has been observed for the total heat and mass transfer rates through both numerical and experimental studies. Based on both predicted values, the optimal coolant flow rate was predicted as 1.98 L/min. The maximum absorption rate of the spring inserted tube was increased by the maximum of $20.0\%$ than those for uniform film of bare tube. Average Sherwood numbers and Nusselt numbers were increased as Reynolds numbers increased under the dynamic and geometric conditions showing the maximum absorption performance.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2003.10a
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• pp.14-18
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• 2003

Feul-cell system consists of fuel reformer, stack and energy translator. Among these parts, slack is a core part which produces electricity directly. In order to set a stack module, fabrication of appropriate stack, design of water flow path in stack, and control of coolant are needed. Especially, water or air is used as a coolant to dissipate heat. The different temperature of each electric cells after cooling and the high temperature of the stack affect the performance of the stack, Therefore, it is necessary that the relationship between coolant, healing rate, width of slack, properties of stack, and the shape of water flow path must be understood. For the optimal design, the computational simulation by CFD-ACE has been conducted and the resulting database has been constructed.

• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.2
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• pp.48-59
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• 2017

In this study, an analysis of the thermo-fluid dynamic and missile-motion performance was carried out through a numerical simulation inside the missile canister. Calculation was made in an analytical volume using dynamic grid and evaporated water was used as a coolant. To analyze the interaction among the hot gas, coolant, and mixture flow, Realizable $k-{\varepsilon}$ turbulence and VOF (Volume Of Fluid) model were chosen and a parametric study was performed with the change of coolant flow rate. As a result of the analysis, pressure of the canister showed a large difference depending on the presence or absence of the coolant, and also showed a dependancy on the amount of coolant. Velocity and acceleration were dependent on the canister pressure.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.247-253
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• 2011

An experimental study on performance characteristics of an evaporative heat exchanger based on tests for various operating conditions was presented. The heat exchanger maximizes the heat transfer rate per unit volume by applying mini-channels for both the air and coolant flow paths, and minimizes the amount of the coolant by using its latent heat of evaporation. The heat exchanger was manufactured by etching the flow paths, brazing the heat exchange plates, and welding the in/out ports of the media. The basic performance test has confirmed that the heat exchanger met its design requirements, and the results of the map test were analyzed to produce the performance characteristics quantitatively depending on the air inlet temperature, the air flow rate, and the coolant flow rate.

• Nuclear Engineering and Technology
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• v.54 no.10
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• pp.3919-3927
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• 2022

This study presents an optimal design of the coolant system of a non-refueling full-life small reactor by analyzing the space-integrated geometrical and electromagnetic variables of an extra vessel electromagnetic pump (EVEMP) for the circulation of a lead-bismuth eutectic (LBE) coolant. The EVEMP is an ideal alternative to the thermal-hydraulic system of non-refueling full-life micro reactors as it possesses no internal structures, such as impellors or sealing structures, for the transportation of LBE. Typically, the LBE passes through the annular flow channel of a reactor, is cooled by the heat exchanger, and then circulates back to the EVEMP flow channel. This thermal-hydraulic flow method is similar to natural circulation, which enhances thermal efficiency, while providing a golden time for cooling cores in the event of an emergency. When the forced circulation technology of the EVEMP was applied, the non-refueling full-life micro reactor achieve an output power of 60 MWt, which is higher than that achievable via the natural circulation method (30 MWt). Accordingly, an optimized EVEMP for Micro URANUS with a flow rate of 4196 kg/s and developed pressure of 73 kPa under a working temperature of 250 ℃ was designed.

• Korean Chemical Engineering Research
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• v.59 no.1
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• pp.77-84
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• 2021

To control hot spot in a plug flow reactor (PFR) is important for the yield and purity of products and safety. In this paper, coolant temperature is set as a state variable, and radial distributions of heat and mass are considered to model the PFR more realistic than without considering radial distributions. The model consists of three state variables, reactant concentration, reactant temperature, and the coolant temperature. The flow rate of the isothermal coolant is a manipulated variable. This paper shows that the controller considering the radial distributions of heat and mass is more effective than the controller without them. Assuming that u3,0 is 0.7, the suggested control equation was robust when St is bigger than 1.3, and Ac/A is smaller than 2.0. Under this condition, the hot spot temperature changed within the relative error of one percent when the temperature of input altered within the range of five percent.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.05a
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• pp.187-192
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• 2006

The combustion performance tests of a 30 tonf-class full-scale combustion chamber performed with water as a coolant were described. The combustion chamber has chamber pressure of 53bara and propellant flow mass rate of 90kg/s. Since it was first firing test for 30tonf-class combustion chamber using channel cooling, water coolant mass flow .ate of 35kg/s and 18kg/s were performed which correspond to 110% of kerosene design volume flow rate and equivalent cooling performance of kerosene. The test results are described and the results showed that the water cooling performance of this combustion chamber is sufficient and the firing test is feasible using the kerosene as a coolant.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05b
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• pp.29-35
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• 1996

For the Reactor Coolant System(RCS) flow rate measurement by the secondary calorimetric heat balance method, the coolant temperature of the hot leg is needed. Several Resistance Temperature Detectors(RTD) are installed in the hot leg to measure the temperature, but the average value of RTDs does not correctly represent the energy-averaged(bulk) temperature because of the thermal stratification phenomenon. Therefore some correction is introduced to predict the bulk temperature, but the correction inevitably contains uncertainty because the stratification is not defined well quantitatively yet. Therefore a large uncertainty for the correction has been used for the conservative estimation. But unrealistically large uncertainty causes degradation of the measurement method and yields difficulty to meet the acceptance criterion in start-up flow measurement test. In this paper, an analytical estimation is made on the correction and the related uncertainty using the measured hot leg velocity profile of System 80 reactor flow model test and the measured temperatures of YGN 3&4 and PVNGS 1&2 start-up tests. The results reveal that the magnitude of the correction uncertainty is much smaller than that used in the previous design. Therefore, the confidence on the flow rate measurement method can be improved and the difficulty in start-up flow measurement test can be lessened if the smaller correction uncertainty obtained through this estimation is applied.

• Transactions of the Korean hydrogen and new energy society
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• v.18 no.3
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• pp.292-300
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• 2007

A dynamic system model of a proton exchange membrane fuel cell(PEMFC) has been developed. The PEMFC of this study has large active area with water cooling in order to simulate the performance of the commercially viable PEMFC system for the transportation. A PEMFC stack model is a transient thermal model which is respond to the dynamic change of the coolant temperature and the flow rate. The dynamic cooling system model has been developed to determine the coolant flow rate and the coolant temperature. Prior to the system level study, thermal management criteria have been set up and brought to the control command of the cooling system. Since the system model is designed to evaluate the effect of thermal management on the system performance, it is attempted to determine the proper control algorithm of the cooling system so that the PEMFC system is working on the thermal management criteria. As a result of simulation, feedback controlled cooling system consumes less power and produce more power comparing with that of conventionally controlled cooling system.

• Proceedings of the SAREK Conference
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• 2007.11a
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• pp.216-221
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• 2007

An experiment was carried out to investigate the effect of a coolant circuit arrangement on the heat transfer and air pressure drop of a fin-tube sensible heat exchanger with the corrugated fin surface. The air inlet temperature was set to $23^{\circ}C$,the relative humidity to 50% and the air inlet flow rate to 20, 22, $25m^3/min$, respectively. while the coolant temperature was set to $7^{\circ}C$, and the coolant mass flow rate to 10, 16, 22kg/min, respectively. Experiment showed that the exchanger having a diameter of 12.7mm with parallel circuit does better performance in sensible heat transfer and air pressure drop than those three of diameter of 12.7mm with a series circuit and that with diameter of 15.88mm with a parallel circuit.