• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.24 no.4
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• pp.351-357
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• 2012

To reduce the summertime cooling load of a plant factory, a concept design was performed for the double skin window which utilizes the low temperature air from a ground coupled heat exchanger. The design parameters were selected as the number of cavity air inlet, the cavity thickness, the location of cavity air inlet, and the configuration of cavity air outlet. A parametric study was conducted in a systematic way to evaluate the heat transfer characteristics of the double skin window. As the number of cavity air inlet and the cavity thickness increase, the heat flux from outside air to indoor air was decreased. The effect of the location of cavity air inlet was not significant and the larger cavity air outlet area gave us relatively better heat blocking performance from outside hot air. This study demonstrated that it is possible to develop an improved double skin window by utilizing a ground coupled heat exchanger.

• Journal of the Korean Institute of Gas
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• v.7 no.4 s.21
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• pp.7-13
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• 2003

This study was carried out to optimize premixed burner and heat exchanger of the condensing gas boiler which can save energy by utilizing latent heat of combustion gas and reduce pollutant in exhaust gas. The heat exchanger of the gas boiler was composed of three parts, which were an upper, lower, and coil heat exchanger. The upper heat exchanger was placed outside of the premixed burner and a lower heat exchanger was located under the upper heat exchanger. And, coil heat exchanger rounded the outer surface of an upper and lower heat exchanger. The boiler designed by this research reaches turn-down ratio 4:1 in the domain of equivalence ratio 0.75${\~}$0.8 and thermal efficiency of $97\%$. Emission of NOx and CO concentration was under 20ppm and 140ppm at equivalence ratio 0.8. When diameter of the burner is replaced from 60mm to 50mm, emission of CO was reduced about 50ppm remarkably.

• Nuclear Engineering and Technology
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• v.32 no.1
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• pp.46-56
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• 2000

Numerical results are presented for the 2-dimensional turbulent transient heat transfer of the shell/tube heat exchanger with a step change of the inlet temperature in the primary side. Heat transfer boundary conditions outside the pipe are given partially by the convection heat transfer conditions and partially by insulated conditions. Calculation results were obtained by solving the unsteady two-dimensional elliptic forms for the Reynolds-averaged governing equations for the mass, momentum and energy. Finite-difference method was used to obtain discretization equations, and the SIMPLER solution algorithm was employed for the calculation procedure. Turbulent model used is the algebraic model proposed by Cebeci-Smith. Results presented include the time variant Nusselt number distribution, average temperature distribution and outlet temperatures for the various inlet temperatures and flow rates.

• Journal of the Korean Society of Industry Convergence
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• v.11 no.4
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• pp.157-163
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• 2008

The present study investigated the pressure drop and the total frost mass of the louvered fin type heat exchanger, which is widely used at the air-conditioning system. The pressure drop due to the frosting phenomenon and the total frost mass were investigated by changing the wet bulb temperature condition of the inlet air. Hence the brain of 55wt% was used as a cooling solution instead of a common refrigerant. The temperature difference between the brine and the tube outside wall at the outlet of heat exchanger was $10^{\circ}C$, at maximum, higher than that at the inlet of heat exchanger. As the wet bulb temperatures were increased, the pressure drop was linearly increased due to the increment of frost mass. And the increment of heat exchange rate was smaller than that of inlet air enthalpy due to the increment of frost mass. The pressure drop of air side was rapidly increased due to the progress of frosting phenomena. The run time that the pressure drop occurred rapidly was decreased by the growth of frost.

• Journal of Power System Engineering
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• v.18 no.5
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• pp.22-27
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• 2014

The objectives of this paper are to obtain an empirical equations regarding the correlations between heat transfer and pressure drop of oval fin-tube heat exchanger having large diameter using wilson plot method. It was difficult to find any recommendable heat transfer and friction factor correlation available for our large diameter experimental cases. Overall heat transfer coefficients are composed of the heat transfer coefficients both inside and outside tubes. The resulting empirical correlations for the Nui and f-factor are given as $Nu_i=0.0146Re^{0.809}Pr^{0.3}$ and $f=4.366Re^{-0.64}$, respectively. The empirical correlations of the Nui and f-factors were developed for the large diameter oval finned-tube heat exchanger as a function of the Reynolds number. As the EG(Ethylene glycol) and air flow rate increases, the heat transfer rate and pressure drop is increased largely.

• Transactions of the Korean Society of Automotive Engineers
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• v.23 no.4
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• pp.428-435
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• 2015

This paper presents the experimental study of cabin thermal comfort using a cold storage heat exchanger in a vehicle air-conditioning system. Recent vehicle-applied ISG functions for fuel economy and emission, but when vehicles stop, compressors in the air-conditioning system stop, and the cabin temperature sharply increases, making passengers feel thermal discomfort. This study conducts thermal comfort evaluation in the vehicle, which is applied to a cold storage system for the climate control wind tunnel test and the vehicle fleet road test with various airflow volume rates and ambient temperatures blowing to the cold storage heat exchanger. The experimental results, in the cold storage system, air discharge temperature is $3.1-4.2^{\circ}C$ lower than current air-conditioning system when the compressor stops and provides cold air for at least 38 extra seconds. In addition, the blowing airflow volume to the cold storage heat exchanger with various ambient temperature was examined for the control logic of the cold storage system, and in the results, the airflow volume rate is dominant over the outside temperature. For this study, a cold storage system is economically useful to keep the cabin at a thermally comfortable level during the short period when the engine stops in ISG vehicles.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.4
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• pp.225-232
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• 2001

An experimental study is carried out to investigate the characteristics of heat transfer of outside helical tubes. The main heat exchanger consists of twelve curved columns with each 300mm diameter and the total length of 1.2m copper tube having an outer diameter of 19.05mm with 1.5mm thickness. Water flows down the outside of helical tube, where flow patterns are the vertical film falling flow, immerged flow, and mixed-flow which is the combination of film falling flow and immerged flow. Refrigerant 11 flow the inside of the tube countercurrently. The experimental range of inside flow rate is 1.7~3.2$\ell$/min and outside flow rate is 21-33$\ell$/min. The results are presented as Nusselt number with corresponding Reynolds number for variety of outside and inside flow rates. The heat transfer rates of the mixed flow are 8 to 56% higher than those of film falling flow or immerged flow only. Interpretation of the results is given on the basis of physical reasoning and the correlation equations.

• Journal of Hydrogen and New Energy
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• v.30 no.6
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• pp.578-584
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• 2019

The occurrence of white plume in the cooling tower is phenomenon that the steam in the air through the cooling tower fan is condensed again by the cold ambient air to become saturated moist air. Accordingly, this can cause many problems like spoiling landscape around the cooling tower, odor of ambient air, falling accident by frozenness in the winter, and traffic accident, etc. This study was to install the heat exchanger in the inside of the cooling tower in order to prevent the white plume phenomenon in the cooling tower without affecting the performance of cooling tower. In addition, this study was to discharge the part of cooling water into the atmosphere through the recirculation of heat exchanger after creating dry air by heating the saturated moist air to the dew point temperature. At that time, this study was to conduct the experimental study in order to secure the optimal design data to prevent the white plume in the cooling tower because it checked the dry·moist temperature and relative humidity in the inside·outside of cooling tower on the moist air, and evaluated the performance of the heat exchanger.

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.1
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• pp.71-80
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• 1985

The various sizes of wires are attached to the outside of the inner tube in a double pipe heat exchanger to enhance the thermal performance. The diameters of the wires range from 0.5mm to 1.6mm while the pitches are chosen between 5mm and 50mm. Experiments have been performed with the range of Reynolds numbers from 15000 to 30000 in annular space where air flows. The friction factors are increased by 1.5 to 4.5 times depending on the sizes and the pitches of the wires. However, the Nusselt numbers are increased by the factors of 1.8 to 2.8 within this experimental range. It is suggested that there should be an optimum configuration rendered when the weighting values of the heat transfer promotion and the pumping power are given.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.26 no.11
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• pp.504-511
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• 2014

The objective of this study is to theoretically analyze the performance of an open wet air-cycle refrigeration system, which nowadays is increasingly generating environmental concern. The temperature and relative humidity of the outside air are selected as the most important parameters. As the temperature and relative humidity of the outside air increase, the pressure ratio of the ACM compressor is determined to be nearly constant, the air temperature at the exit of the system increases, and the amount of condensed water, the cooling capacity, the COP, and the total entropy production rate increase overall. The effects of the effectiveness of the heat exchanger and the efficiency of the turbine on the performance are greater than that of the efficiency of the ACM compressor. Also, the performance of the wet air-cycle refrigeration system with two heat exchangers is enhanced, with a high COP and low total entropy production rate, compared to the system with a single heat exchanger.