• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.24 no.1
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• pp.23-28
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• 2012

In the present work, numerical analyses of air flow in HVAC duct have been carried out for enhancement of cooling/heating performance. For the analyses, three-dimensional Reynolds-averaged Navier-Stokes equations have been solved with the shear stress transport turbulence model. The numerical results were validated in comparison with the experimental data. Based on the numerical results, the HVAC duct was designed to reduce the pressure loss. The modified duct geometry shows largely reduced pressure drop in comparison with the reference geometry. And, through modified duct shape, the performance of air conditioning has been enhanced.

• Journal of the Korean Society of Marine Environment & Safety
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• v.18 no.5
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• pp.461-467
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• 2012

An experimental study was carried out to measure frictional pressure drop in flow boiling to deionized water in a microchannel having a hydraulic diameter of $500{\mu}m$. Tests were performed in the ranges of heat fluxes from 100 to $400kW/m^2$, vapor qualities from 0 to 0.2 and mass fluxes of 200, 400 and $600kg/m^2s$. The frictional pressure drop during flow boiling is predicted by using two models; the homogeneous model that assumes equal phase velocity and the separate flow model that allows a slip velocity between two phases. From the experimental results, it is found that the two phase multiplier decreases with an increase in mass flux. Measured data of pressure drop are compared to a few available correlations proposed for macroscale and mini/microscale. The homogeneous model well predicted frictional pressure drop within MAE of 29.4 % for the test conditions considered in this work.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2003.10a
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• pp.87-90
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• 2003

In Resin transfer molding (RTM), composite parts are produced by impregnation of a dry reinforcement with liquid matrix resin. Permeability is a key issue in this process. For thin parts, the resin flow in the thickness direction can be neglected. Therefore thin parts are considered as two-dimensional composites. However the resin flow through the thickness is important to thicker parts and we have to consider out-of-plane permeability. This work discusses a method to measure out-of-plane permeability. The flow rate and pressure drop across the porous media were measured. Also one dimensional form of Darcy's law is applied to calculate the out-of-plane permeability of various preforms. The flow is injected uniformly into layers of the preform. And a circular fiber mat with 6cm diameter was cut and flattened from cylindrical mandrel.

• Steel and Composite Structures
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• v.37 no.4
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• pp.391-404
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• 2020

Human-induced vibration could present a serious serviceability problem for large-span and/or lightweight floors using the high-strength material. This paper presents the results of heel-drop, jumping, and walking tests on a large-span composite steel rebar truss-reinforced concrete (CSBTRC) floor. The effects of human activities on the floor vibration behavior were investigated considering the parameters of peak acceleration, root-mean-square acceleration, maximum transient vibration value (MTVV), fundamental frequency, and damping ratio. The measured field test data were validated with the finite element and theoretical analysis results. A comprehensive comparison between the test results and current design codes was carried out. Based on the classical plate theory, a rational and simplified formula for determining the fundamental frequency for the CSBTRC floor is derived. Secondly, appropriate coefficients (β_rp) correlating the MTVV with peak acceleration are suggested for heel-drop, jumping, and walking excitations. Lastly, the linear oscillator model (LOM) is adopted to establish the governing equations for the human-structure interaction (HSI). The dynamic characteristics of the LOM (sprung mass, equivalent stiffness, and equivalent damping ratio) are determined by comparing the theoretical and experimental acceleration responses. The HSI effect will increase the acceleration response.

• Journal of Industrial and Engineering Chemistry
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• v.68
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• pp.274-281
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• 2018

Experimental studies of the hydrodynamic performance of the draft tube conical spout-fluid bed (DCSF) were conducted using pharmaceutical pellets. The experiments were carried out in a DCSF consisted of two sections: (a) a conical section with the cross section of $120mm{\times}250mm$ and the height of 270 mm, (b) a cylindrical section with the diameter of 250 mm and the height of 600 mm. The flow characteristics of solids were investigated with a high speed camera and a pezoresistive absolute pressure transducer simultaneously. These characteristics revealed different flow regimes in the DCSF: packed bed at low gas velocities, fluidized bed in draft tube at higher gas velocities until minimum spouting, and spouted bed. The stable spouting was identified by the presence of two dominant frequencies of the power spectrum density of pressure fluctuation signature: (i) the frequency band 6-9 Hz and (ii) the frequency band 12-15 Hz. The pressure drops across the draft tube as well as the annulus measured in order to better recognize the flow structure in the DCSF. It was observed that the pressure drop across the draft tube, the pressure drop across the annulus, and the minimum spouting velocity increase with the increase in the height of draft tube and distance of the entrainment zone, but with the decrease in the distributor hole pitch. Finally, this study provided novel insight into the hydrodynamic of DCSF, particularly minimum spouting and stable spouting in the DCSF which contains valuable information for process design and scale-up of spouted bed equipment.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.14 no.4
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• pp.20-26
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• 2018

In this study, the performance characteristics of a welded plate heat exchanger was investigated experimentally. Performance tests were carried out according to the flow rate and inlet temperature of working fluid. As a result, the heat transfer capacity increased by 335.5 kW with an increasing the flow rate and temperature difference between hot and cold side. However, the overall heat transfer coefficient was increased with the increase of flow rate, and it was not effected significantly from inlet temperature difference between hot and cold working fluid. The pressure drop was increased by 55.78 kPa with an increasing the frow rate when the flow rate ratio between hot and cold side 1:1. However, the tendency of pressure drop was difference when flow rate ratio wasn't 1:1. In case that the flow rate ratio between hot and cold side was not 1:1, the pressure drop at the low flow rate side was higher than that when the flow rate ratio was 1:1, while pressure drop of the other side was decreased compared to that when the flow rate ratio was 1:1.

• Journal of Welding and Joining
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• v.28 no.6
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• pp.28-34
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• 2010

This paper was described on investigation to prevent porosity in high speed MIG Welding of Al 6082-T6. Porosity measurement was carried out by using image analysis of micrographs with the help of an analysis software. The main parameter was arc length and torch progressive angle. The porosity ratio was increased as arc length was increased. The arc length was increased depending upon the output voltage. By proper selection of pulse waveform parameter, the stable arc of one pulse one drop was generated. The porosity ratio of optimum condition in one pulse one drop was lower than high voltage condition. When torch progressive angle was an angle of advance $10^{\circ}$, porosity ratio was minium.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.24 no.12
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• pp.823-829
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• 2012

In this study, the performance of mobile air conditioner(MAC) systems to which the refrigerants R134a and R1234yf were used was evaluated to compare the characteristic of automotive refrigeration cycles with refrigerant. The experimental setup of a MAC consists of an belt driven compressor, a condenser, an evaporator and a block type thermal expansion valve. The drop-in test on MAC were carried out under variable compressor speed from 800 to 2500 rpm. Performance test by using R1234yf and R134a in the same system revealed low the charge amount and mass flow rates for using R1234yf, that is, up to 10% and 17%, respectively. The compressor discharge temperature of R1234yf is $8^{\circ}C$ lower than that of R134a. The cooling capacity with R1234yf system decreased by 4~7% compared with R134a system. In addition, The COP of R1234yf system is lower 3~4% than that of R134a system.

• Transactions of the Korean hydrogen and new energy society
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• v.14 no.1
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• pp.53-60
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• 2003

Performance evaluation on thermal transport of a plate heat exchanger has been carried out. The $\varepsilon$-Ntu method is employed to evaluate the performance of a brazed type of plate heat exchanger. This problem is of particular interest in the design of a plate heat exchanger. The characteristics of heat transfer as well as pressure drop are studied in the wide range of Reynolds numbers in the cold side while that of hot side is fixed at 620. f-factor correlation in a plate heat exchanger is obtained from the pressure drop data. It is also found that the effectiveness of the plate heat exchanger is increased as the Ntu is increased.

• Journal of Energy Engineering
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• v.20 no.3
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• pp.191-199
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• 2011

The char burn-out and NOx emissions from sub-bituminous coal were investigated in drop tube furnace under $O_2/N_2$ and $O_2/CO_2$ environments with different $O_2$ concentrations of 12, 21 and 31%. Results show that the char burn-out rate is faster as $O_2$ concentration increases higher and char burn-out rate under $O_2/CO_2$ decreases due to the lower oxygen diffusion into coal surface through the $CO_2$ rich boundary layer. NO concentration increases with increasing $O_2$ concentration, but declines at $O_2$ concentration of 31%. Meanwhile, NO emission indexes decreases monotonically with increasing $O_2$ concentration, which indicates that more NO reduction occurs with higher $O_2$ concentration probably due to greater HCN formation. For all conditions of $O_2$ concentration, the NO concentration under $O_2/N_2$ maintains higher than those of $O_2/CO_2$ due to presence of thermal NO.