• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.6
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• pp.1621-1628
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• 1990

Numerical solutions are presented for the heat transfer from radiating and convecting fins. Consideration is given to thin, annular fins attached to a tube surface for which the temperature is constant. Fin to fin, fin to base, and fin to environment radiative interactions are considered. It is assumed that the radiating surface is diffuse-gray, the environment is black, and the surrounding fluid is transparent. The radiation terms are formulated by using Poljak's net-radiation methoad. The mathematical description of the simultaneously heat transport by conduction, convection, and radiation leads to a nonlinear integro-differential equation. This has been solved for a wide range of the pertinent physical parameters by using finite difference method and iteration method based on the Newton-Raphson technique. The temperature distributions, heat transfer rates, fin efficiencies, and fin effectivenesses are presented in dimensionless form. The results definitely indicate that the use of fins leads to a significant increase in heat transfer compared with the unfinned tube.

• Journal of Energy Engineering
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• v.22 no.1
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• pp.44-50
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• 2013

This study was experimentally investigated NOx and CO emissions characteristics with various equivalence ratios using premixed type of burner installed small heat exchanger. The effectiveness of heat exchanger and the entropy generation number were also calculated. As results, the heat transfer rate increases with increasing equivalence ratio due to increase the flame temperature. According to the emission characteristics and the effectiveness, the optimal operating equivalence ratio is 0.75 in the range of this experiment. Consequently, the area of the heat exchanger should be increased to reduce the entropy generation number and to increase the effectiveness.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.5
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• pp.531-537
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• 2010

This paper optimized the design parameters of the offset strip fin in a heat exchanger. To decrease the pressure drop and increase heat transfer, the performance factors such as j/f, $j/f^{1/3}$, and JF, which could be used to estimate the pressure drop and heat transfer simultaneously, were employed as the criteria for optimization. In the present study, STDQAO, PQRSM, and MGA were used for solving the constrained nonlinear optimization problem. The JF factor and heat transfer performance of the optimized offset-strip fin were greater than those of the reference offset-strip fin by 36% and 280%, respectively.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.11
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• pp.1044-1050
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• 2004

The present study has been conducted to develop a heat pipe heat exchanger for middle-high temperature ranged from 300 to $600^{\circ}C$. Heat transfer rate, overall heat transfer coefficient and temperature effectiveness were investigated using a heat pipe heat exchanger with Dowtherm A as working fluid. Theoretical analysis was also conducted, and the followings were obtained: (1) Heat exchange rate increased as waste gas temperature supplied to evaporator and frontal velocity in condenser increased, (2) Overall heat transfer coefficient increased by $3{\sim}7\%$ as frontal velocity in evaporator and condenser increased, (3) Temperature effectiveness was about $30\%$ in evaporator and was about $40\%$ in condenser, (4) Heat recovery rate was about $38\%$, (5) Pressure drop did not exceed $8\;mmH_{2}O$ under the running condition of $1{\sim}3Nm/s$, (6) Simulation results were corresponded with experimental results.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.3
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• pp.315-323
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• 1998

This paper contains a verification of simulation program to predict the capacity of a condenser used in car air-conditioners. Verification of simulation program is carried out with the comparison error between experiment and simulation bounds within 3.5%. The present investigation shows the results for heat transfer rates of condenser under different operating conditions, such as velocity and degree of superheat. The range of front velocity of air is 1∼5m/s. As the front velocity is increased, the heat transfer rate of condenser is largely increased at a low velocity range. In a meanwhile, heat transfer rate of condenser is almost constant in a range of velocity over 3m/s. As for the effect of inlet pressure of refrigerant on the heat transfer rate, we obtained the similar trend of heat transfer rates as like varying the front velocity, Also we have calculated the heat transfer rates with varying inlet superheats of refrigerant, the larger the superheat is, the more heat transfer rate is obtained.

• Journal of the Korean Society of Propulsion Engineers
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• v.6 no.4
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• pp.25-35
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• 2002

A calculation procedure for designing LRE regenerative cooling system is introduced. In LRE thrust chamber, heat is transfered from the hot gas to the wall by convection and radiation, then conduction through the wall and finally convection to the liquid coolant. A cooling channel is designed on the basis of heat transfer rate calculated by using criterial method and integral method. The result is compared with existing Russian cooling channel design code. Also a design logic and quantitative effect of various parameters were introduced to help better understanding for those who is not familiar to LRE system.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.16 no.1
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• pp.9-16
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• 2020

In this study, a numerical study was conducted to evaluate the performance improvement when CuO nanofluid was used in the plate heat exchanger. As a result, the heat transfer amount is increased by 5.45% when 2 vol% CuO nanofluid is used. The influence on the CuO nanofluid on the performance of heat exchanger is decreased by increasing the flow rate of working fluid. In addition, the overall heat transfer coefficient using 2 vol% CuO nanofluid decreased compared to the base fluid. However, the pressure drop and the consumption of the pump power is increased as the concentration of CuO nanofluid increased because the increase of the viscosity. These are increased up to 15.4% compared to those of the base fluid. Moreover, the performance index of CuO nanofluid is decreased by 12.6% compared to that of the base fluid.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.12
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• pp.1049-1059
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• 2003

R410A is considered as an alternative refrigerant to R22 for air conditioners. An experimental investigation was made to study the characteristics of the heat transfer and pressure drop for R410A flowing in a fin-and-tube heat exchanger used for commercial air-conditioning units. Experiments were carried out under the conditions of inlet refrigerant temperature of 6$0^{\circ}C$ and refrigerant mass flux varying from 150 to 250 kg/$m^2$s for refrigerant side. The inlet air has dry bulb temperature of 35$^{\circ}C$, relative humidity of 40% and air velocity varying from 0.68 to 1.6 m/s. Experiments show that air velocity decreased by 16% is needed for R410A than that of R22 for subcooling temperature of 5$^{\circ}C$, which resulted in air-side pressure drop decrease of 15% for R410A as compared to R22. As a consequence, in order to provide the same design condition of a condenser, the fan requires lower electric-power consumption with R410A than that with R22.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.1
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• pp.112-121
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• 1992

A numerical analysis was carried out to study two-dimensional turbulent natural convection in a square enclosure containing fluid of Prandtl number 6.05 within internal energy sources. The square enclosure was bounded by four rigid planes of constant equal temperature. Inclination angles of 0, 15, 30 and 45 deg. from the horizon for Rayleigh numbers from 1 * 10$^{6}$ to 1 * 10$^{9}$ were studied. Local and average Nusselts numbers are obtained on all four walls. If inclination angle exists, the average Nusselt number appears in increasing order at bottom, left, right and top wall.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.15 no.4
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• pp.46-54
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• 2019

In this study, the performance of a shell and tube heat exchanger (STHE) and welded plate heat exchanger (WPHE) was measured experimentally. The pass numbers of the STHE was changed by 1, 2 and 4. As a result, the WPHE showed 2.1 times higher heat exchange capacity than that of the STHE. In case of pressure drop, the STHE with 1 and 2 pass number has a lower pressure drop than the WPHE, while the STHE with 4 pass presented higher pressure drop than the WPHE. The performance index considering the heat exchange capacity and pump consumption power, showed in oder of STHE_Pass1 > STHE_Pass2 > W PHE > STHE_Pass4 under the same flow rate. Therefore, when the WPHE was designed optimally under same operating condition with STHE, the maintenance fee and space can be reduced effectively by using the WPHE.