• Membrane and Water Treatment
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• v.7 no.4
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• pp.297-311
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• 2016

Modeling and simulation of air humidification by hollow fiber membrane contactors are investigated in the current study. A computational fluid dynamic model was developed by solving the k-epsilon turbulence 2D Navier-Stokes equations as well as mass conservation equations for steady-state conditions in membrane contactors. Finite element method is used for the study of the air humidification under different operating conditions, with a focus on the humidity density, total mass transfer flux and velocity field. There has been good agreement between simulation results and experimental data obtained from literature. It is found that the enhancement of air stream decreases the outlet humidity from 0.392 to 0.340 (module 1) and from 0.467 to 0.337 (module 2). The results also indicated that there has been an increase in air velocity in the narrow space of shell side compared with air velocity wide space of shell side. Also, irregular arrangement has lower dead zones than regular arrangement which leads to higher water flux.

• Proceedings of the SAREK Conference
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• 2005.11a
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• pp.439-444
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• 2005

Steady state simulation and dynamic simulation were performed to analyze the operational characteristics of a multi-type refrigeration system, Fully distributed model was adopted to simulate the steady state and transient responses of the system. The main aim was to see the effect of one indoor unit on the other unit. Numerical simulations were carried out for various operation conditions of an indoor unit - secondary fluid inlet temperature, mass flow rate and expansion valve opening. The results showed that the inlet temperature and mass flow rate of the secondary fluid of one indoor unit had minor effect on the operation of the other unit. However, the opening of the expansion valve had significant effect on the performance of the other unit.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.7
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• pp.637-646
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• 2001

VOC(Volatile Organic Compound) removal characteristics in continuous flow reactors have been numerically investigated. The photocatalytic reaction have been simulated with the binding constant and the reaction rate constant obtained from experimental data for the constant-volume batch reactor, and then VOC abatement in continuous flow reactors with the same conditions as those of batch reactor has been analyzed. The standard 4\kappa-\varepsilon$ model and mass conservation equation have been employed for numerical calculation, and heterogeneous reaction rate has been used in terms of the boundary condition of the conservation equation. in the case of the continuous flow reactor, reaction characteristics have been estimated with various inlet velocities and with different number of baffles. The result shows that the concentration distribution and flow patterns are strongly affected by the inlet velocity, and that with the increased inlet velocity, VOC removal rate is increased, while removal efficiency is decreased. This result may be useful in the design of reactors with improved VOC removal efficiency.

• International Journal of Air-Conditioning and Refrigeration
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• v.12 no.3
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• pp.113-122
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• 2004

In case of heat exchangers operating under frosting condition, the thermal resistance and the air-side pressure loss increase with a growth of frost layer. In this paper, a transient characteristic prediction model of the heat transfer for a multi-inverter heat pump with frosting on its surface was presented by taking into account the change of the fin efficiency due to the growth of the frost layer. This dynamic simulation program was developed for a basic air conditioning system composed of an evaporator, a condenser, a compressor, a linear electronic expansion valve, and a bypass circuit. The theoretical model was derived from measured heat transfer and mass transfer coefficients. We also considered that the heat transfer performance was only affected by the decrease of wind flow area. The calculated results were compared with the experimental results for frosting conditions.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.6 no.4
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• pp.255-261
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• 1977

This study was concerned with the performance of solar air heater using parallel channels. Heat transmission model was developed and fabricated to increase the economic feasibility for solar heating system by using the cheap zinc plate. The prformance was discussed as a function of mass flow rate, and plate, inlet and outlet temperatures. Experimental results show that heat transmission model is sufficient for the analysis of thermal characteristics of air heater and collection efficiency is better than the domestic water heater, as the range 32-49 percent. Collection efficiency in the 2 layers of glass cover is better than that in 1 layer, so it is considered better to use the 2 layers of glass cover during the cold winter season in Korea.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.17 no.6
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• pp.696-707
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• 1988

This study simulates a typical solar system using the transient simulation program TRNSYS, and calculates the maximum cooling load of the model room of $50m^2$. In this study, energy rate control method is used in calculating a maximum cooling load. On the ground of the maximum cooling load of the model room, the variables that have an effect on the solar collection performance of the solar system are made a selection. Also in this study the trend of the solar collection performance is shown as the variables change. The results show that the variables which have an effect on the collection performance are collector area, collector mass flow rate, collector slope and the volume of storage tank, and the optimal value of Ac/Vt is not constant but varies as the collector area and the collector mass flow rate. Also the results show that for cooling system the optimal value of the collector slope is latitude minus $15^{\circ}$ during the seasonal operations, and twenty percent of the maximum cooling load is saved with the aid of the solar energy.

• International Journal of Air-Conditioning and Refrigeration
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• v.9 no.1
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• pp.39-49
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• 2001

Investigation of the performance of an autocascade refrigeration system using the refrigerant mixtures of R744 (carbon dioxide) and R134a (1,1,1,2-tetrafluoroethane) has been carried out by simulation and experiment. Cycle simulation using a constant UA model in heat exchangers has been performed for R744/134a mixtures of the compositions ranging from 10/90 to 30/70 by weight. Variations of mass flow rate of refrigerant, compressor work, refrigeration capacity and COP with respect to mass fraction of R744/134a mixture were presented. Performance test has been executed in the autocascade refrigeration system by varying secondary fluid temperatures at evaporator and condenser inlets. Experimental results match quite well with those obtained from the simulation.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.6
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• pp.880-890
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• 1999

The purpose of this study is to investigate the performance of an autocascade refrigeration system using the refrigerant miktures of R744 (carbon dioxide) and R134a (1,1,1,2-tetrafluoroethane) as working fluids by simulation and experiment. Cycle simulation using a constant UA model in heat exchangers has been performed for R744/134a mixtures of the compositions in the range of from 10/90 to 30/70 by weight percentage. Variations of mass flow rate of refrigerant, compressor work, refrigeration capacity and COP with respect to mass fraction of R744/134a mixture were presented. Performance test has been executed in an autocascade refrigeration system by varying secondary fluid temperatures at evaporator and condenser inlets. Experimental results show similar trend with those from the simulation.

• Journal of Environmental Science International
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• v.21 no.3
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• pp.327-337
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• 2012

Air pollution inventories are aggregated around south-eastern part of the Korean Peninsular including Busan, Ulsan, and Changwon cities. Because densely populated cities are concentrated in this region, air pollutants emitted from one of these cities tend to be impacted on the air quality of other cities. In order to clarify the seasonal movement pattern of emitted particles, several numerical simulations using WRF/FLEXPART were carried out. Four cases were selected for each season. The Weather Research and Forecasting model (WRF) reproduced atmospheric flow fields with nested grids. The seasonal pattern of air mass of study area was determined by backward and forward trajectories. As a result, the air parcel moves from northwest to southeast due to northwesterly winds in spring and winter. Also air parcel transports from south to north in summer, and moves from west to east. Because the air mass moves differently in each season, these characteristics should be considered when performing air quality analysis.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.511-516
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• 2001

The flow characteristics in a hot mill reheating furnace is numerically simulated in this study. Navier-Stokes equations for conservation of mass, momentum, energy are solved and the standard $k-\varepsilon$ model, mixture fraction/PDF model are used for the turbulent reacting flow in the furnace. Radiation heat transfer is incorporated by the P-1 method with the absorption coefficient evaluated using WSGGM. First, simulation results are obtained for the total furnace region with existing protective dam, and then the calculations are carried out only for the preheating zone in the furnace. In that zone, additional center darn is built in order to control the flow behavior of the inlet air and the combustion gas.