• Transactions of the Korean hydrogen and new energy society
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• v.32 no.1
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• pp.1-10
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• 2021

Water electrolysis technology, which generates hydrogen using renewable energy resources, has recently attracted great attention. Especially, the polymer electrolyte membrane water electrolysis system has several advantages over other water electrolysis technologies, such as high efficiency, low operating temperature, and optimal operating point. Since research that analyzes performance characteristics using test bench have high cost and long test time, however, model based approach is very important. Therefore, in this study, a system model for water electrolysis dynamics of a polymer electrolyte membrane was developed based on MATLAB/Simulink®. The water electrolysis system developed in this study can take into account the heat and mass transfer characteristics in the cell with the load variation. In particular, the performance of the system according to the stack temperature control can be analyzed and evaluated. As a result, the developed water electrolysis system can analyze water pump dynamics and hydrogen generation according to temperature dynamics by reflecting the dynamics of temperature.

• Progress in Superconductivity and Cryogenics
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• v.8 no.4
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• pp.30-33
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• 2006

Several crucial issues are discussed in the design of cryogenic cooling system for high field magnets. This study is mainly motivated by our ongoing program to develop a 21 T Fourier Transform Ion Cyclotron Resonance Mass Spectrometer (FT-ICR MS). The magnets of this system will be built horizontally to accomplish the requirement of user friendliness and reliability, and the replenishment of cryogen will not be necessary by a closed-loop cooling concept. The initial cool-down and safety are basically considered in this paper. The effects of the helium II volume and the gap distance of the weight load relief valve (or safety valve) on the cool-down time and temperature rising during an off-normal state are discussed. The total amount of cryogenic cooling loads and the required helium flow rate during cool-down are also estimated by a relevant heat transfer analysis. The temperatures of cryogen-free radiation shield are finally determined from the refrigeration power of a cryocooler and the total cryogenic loads.

• Journal of computational fluids engineering
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• v.16 no.4
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• pp.7-13
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• 2011

A comparative analysis of thermal models in the lattice Boltzmann method(LBM) for the simulation of laminar natural convection in a square cavity is presented. A HYBRID method, in which the thermal equation is solved by the Navier-Stokes equation method while the mass and momentum conservation are resolved by the lattice Boltzmann method, is introduced and its merits are explained. All the governing equations are discretized on a cell-centered, non-uniform grid using the finite-volume method. The convection terms are treated by a second-order central-difference scheme with a deferred correction method to ensure stability of the solutions. The HYBRID method and the double-population method are applied to the simulation of natural convection in a square cavity and the predicted results are compared with the benchmark solutions given in the literatures. The predicted results are also compared with those by the conventional Navier-Stokes equation method. In general, the present HYBRID method is as accurate as the Navier-Stokes equation method and the double-population method. The HYBRID method shows better convergence and stability than the double-population method. These observations indicate that this HYBRID method is an efficient and economic method for the simulation of incompressible fluid flow and heat transfer problem with the LBM.

• Journal of Sensor Science and Technology
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• v.20 no.6
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• pp.363-367
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• 2011

This paper proposes a highly-sensitive gas flow sensor with a simple structure. The sensor is composed of a micro-heater for heating the gas medium and a pair of temperature sensors for detecting temperature differences due to gas flow in a sealed chamber on one axis. Operation of the gas flow sensor depends on the transfer of heat through the air medium. The proposed gas flow sensor has the capability to measure gas flow rates <5 $cm^3$/min with a resolution of approximately 0.01 $cm^3$/min. Furthermore, this paper reports some additional experiment results, including the sensitivity of the proposed gas flow sensor as a function of operating current and the flow of different types of gas(oxygen, carbon dioxide, and nitrogen). The fabrication process of the proposed sensor is very simple, making it a good candidate for mass production.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.11
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• pp.867-873
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• 2006

Vertical falling liquid film is extensively used in heat and mass transfer processes of many applications, such as evaporative coolers, cooling towers, and absorption chillers. In such cases, it is required that the falling film spreads widely in the surface forming thin liquid film to enlarge contact surface. An addition of surface active agent to a falling liquid film or hydrophilic surface treatment affects the fluid physical properties of the film. Surfactant addition not only decreases contact angle between the liquid and solid surface but also changes the surface from hydrophobicity to hydrophilicity. In this study, the effects of contact angle on falling film characteristics over a vertical surface have been investigated experimentally. The contact angle is varied either by an addition of surfactant to the liquid or by hydrophilic surface treatment. It is found that the wetted area is increased and film thickness is decreased by the hydrophilic treatment as compared with those of other surfaces. With this hydrophilic treatment, the falling liquid film spreads out widely in the surface. As surfactant concentration is increased, wetted area is also increased and the film thickness is substantially decreased.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.1536-1537
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• 2011

The high-voltage circuit breaker plays an important role in the electrical system because there has been a need for suitable switching devices capable of initiating and interrupting the flow of the electric fault current. It continues as the contacts recede from each other and as the newly created gap is bridged by a plasma. The arc plasma happens inside the insulation nozzle of SF6 self-blast interrupter which is newly developed as the next-generation switching principle. The ablation of PTFE nozzle is caused by this high temperature medium, the PTFE vapor from the nozzle surfaces flows toward the outlets and the pressure chamber. The vapor makes the pressure of the chamber increased by heat and mass transfer from the arcing zone. Because the rate of ablation depends on the magnitude of applied current, it decreases when the current goes to zero. The compressed gas inside the chamber flows reversely toward the arc plasma during this moment. According to this principle, the arc can be cooled down and the fault current can be interrupted successfully. In this study, we calculate arc plasmas and thermal-flow characteristics caused by fault current interruption inside a SF6 self-blast interrupter, and to investigate the effect of PTFE ablation on the whole arcing history.

• Computers and Concrete
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• v.30 no.2
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• pp.143-150
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• 2022

In this paper, the non-linear mathematical problem is solved via numerical scheme by utilizing shooting method. Brownian diffusion and thermophoresis along mass and heat transfer are accounted for. Non-linear expression is reduced via non-dimensional variables. The simplified ordinary differential equations are tackled by shooting technique. Behavior of distinct influential parameters is investigated graphically and analyzed for temperature and concentration profile. Our finding indicates that temperature profile is enhanced for the thermophoresis, Brownian motion coefficient, Prandtl number, Eckert number and temperature slip parameter. Comparison of numerical technique with the extant literature is made and an acceptable agreement is attained. Graphs are plotted to examine the influence of these parameters.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2989-2994
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• 2007

Gas hydrates are ice-like crystalline compounds that form under low temperature and elevated pressure conditions. Although hydrate formation can pose serious flow-assurance problems in the gas pipelines or facilities, gas hydrates present a novel means for natural gas storage and transportation with potential applications in a wide variety of areas. An important property of hydrates that makes them attractive for use in gas storage and transportation is their very high gas-to-solid ratio. In addition to the high gas content, gas hydrates are remarkably stable. The main barrier to development of gas hydrate technology is the lack of an effective method to mass produce gas hydrate in solid form. The first objective of this study is investigating the characteristics of gas hydrate formation related to several factors such as pressure, temperature, water-to-storage volume ratio, concentration of SDS, heat transfer and whether stirred or not respectively. And the second objective is clarifying the relation between the formation efficiency and each factor in order to find the proper way or direction to improve the formation performance.

• Korean Journal of Human Ecology
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• v.21 no.3
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• pp.539-550
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• 2012

In-depth knowledge of fabric microstructure is essential for understanding clothing comfort since it plays a significant role in heat and mass transfer between the human body and clothing. In this study, a novel method was employed for investigating 3D surfaces and solid construction characteristics of specific fabrics by using a reverse engineering technique. The surface construction data were obtained by a confocal laser scanning microscope and then manipulated by a 3D analysis program. Triangle mesh was used for connecting each 3D point, with clouds and fabric surface characteristics created by rendering techniques. For generating a 3D solid model, determinants of radius of curvature was used. According to the proposed method, actual surface expression of the real fabric was achieved successfully. The results from this methodology can be applied to the detailed analysis of clothing comfort that is highly influenced by the microstructure of the fabric.

• Journal of Soil and Groundwater Environment
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• v.17 no.2
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• pp.7-14
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• 2012

Batch tests were carried out to evaluate the thermal treatment of low volatile organic compounds in low-permeability soil. The chemical oxidation by sodium persulfate catalyzed by heat and Fe (II) was evaluated. Enhanced persulfate oxidation of n-decane (C-10), n-dodecane (C-12), n-tetradecane (C-14), n-hexadecane (C-16), and phenanthrene was observed with thermal catalyst, indicating increased sulfate radical production. Slight enhancement of the pollutants oxidation was observed when initial sodium persulfate concentration increased from 5 to 50 g/L. However, the removal efficiency greatly decreased as soil/water ratio increased. It indicates that mass transfer of the pollutants as well as the contact between the pollutants and sulfate radical were inhibited in the presence of solids. In addition, more pollutants can be adsorbed on soil particles and soil oxidant demand increased when soil/water ratio becomes higher. The oxidation of the pollutants was significantly improved when catalyzed by Fe(II). The sodium persulfate consumption increased at the same time because the residual Fe(II) acts as the sulfate radical scavenger.