• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.5
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• pp.1725-1734
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• 1996

Experimental condensation and evaporation heat transfer coefficients were measured in a horizontal smooth tube and a horizontal micro-finned tube with HFC-134a. The test sections are straight, horizontal tubes with have a 9.52mm outside diameter and about 5000mm long. The micro-finned tube had 60 fins with a height of 0.12mm and a spiral angle of 25.deg.. The condensation test section was a double-pipe type with counter flow configuration. The evaporation test section employed an electic heating method. Enhancement factors which is defined as a ratio of the heat transfer coefficient for micro-finned tube to that for smooth tube, varied from 1.3 to 1.6(mass flux:110~190kg/m$^{2}$s) for condensation and 1.2 to 1.5 (mass flux:70~160kg/m$^{2}$s) for evaporation. The experimental data of condensation and evaporation heat transfer coefficients were compared to several empirical correlations. Based on these comparisons, modified correlations of the condensation and evaporation heat transfer coefficient for both smooth and micro-finned tubes were proposed.

• Proceedings of the KSME Conference
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• 2005.11a
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• pp.10.2-10.2
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• 2005

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.5
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• pp.713-723
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• 1997

Performance and heat transfer characteristics of an air conditioning system filled with hydro- carbon refrigerants are experimentally investigated. Single component hydrocarbon refrigerants (propane, isobutane, butane and propylene) and binary mixtures of propane/isobutane and propane/butane are considered as working fluids in the air conditioning system. Performances of each refrigerant are obtained at several compressor speeds and temperature levels of secondary heat transfer fluids. The cooling capacity and the coefficient of performance are obtained as test results. Heat transfer data of selected refrigerants are achieved from overall conductance measurement. Average heat transfer coefficients at different mass fluxes are shown and they are also displayed for different heat capacities of the system. Experimental results show that some hydrocarbon refrigerants have better characteristics than R22.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.8
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• pp.698-706
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• 2004

Heat transfer coefficients of enhanced tubes in a flooded evaporator are measured through Wilson Plot method. And the correlations are proposed to design a flooded evaporators. Overall heat transfer coefficients are composed of the heat transfer coefficients both inside and outside tubes. Usually the experiments have been conducted separately. But there have been many difficulties like setting up the equipments and measuring the wall temperature. Wilson Plot method makes it possible to measure the separated transfer coefficients at the same equipment through experimental skills. So the cost and time can be reduced. And the results are reliable enough to use for design. Heat transfer coefficients inside the tube were able to be correlated uniquely in spite of various outside conditions. Boiling heat transfer of R134a is more dependent on the saturation temperature and much higher than that of R123.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.11
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• pp.1127-1133
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• 2012

A finned-tube-type evaporator module has been proposed for a 2 t/h-class water-tube-type industrial boiler with multiple burners. The geometry of the fins was changed at each module to equalize the evaporation. The modules were designed by considering the energy balance at each row rather than by following a conventional bulk design procedure. The designed module was built into a 2 t/h-class water-tube-type boiler, and its performance was tested. A numerical simulation was also conducted to evaluate the two- or three-dimensional effects of factors such as the inlet conditions. The numerical simulation also included the conjugate heat transfer problem to predict the fin tip temperature. The heat transfer coefficient with fins is lower than that obtained from the empirical correlation of a bare tube. The fin tip temperature from CFD is higher than that from the analytical solution.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.12
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• pp.1007-1017
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• 2003

An experimental study on the air-side pressure drop and heat transfer coefficient of slit fin-tube heat exchanger has been carried out. The data reduction methodology for air-side heat transfer coefficients in the literature is not based on a consistent approach. This paper focuses on new method of data reduction to obtain the air-side performance of fin-tube heat exchanger using R22 and recommends standard procedures for dry and wet surface heat transfer estimation in fin-tube heat exchanger having refrigerant on the tube-side. Results are presented as plots of friction f-factor and Colburn j -factor against Reynolds number based on the fin collar outside diameter and compared with previous studies. The data covers a range of refrigerant mass fluxes of 150∼250 kg/$m^2$s with air flows at velocity ranges from 0.3 m/s to 0.8 m/s.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.6
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• pp.789-798
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• 1999

The evaporating heat transfer experiments with refrigerant HCFC 22 are performed for performance evaluation using 4 and 6 kinds of microfin tubes with outer diameter of 9.52mm and 7.0mm, respectively. Used microfin tubes have different shape and number of fins with each other, The experimental results are represented with effects of quality, mass flux and EPR. The evaporating heat transfer characteristics are represented by the existence of not only heat transfer area and turbulence promotion effect but also additional other enhancement mechanism, which are the overflow of the refrigerant over the microfin and microfin arrangement. Microfin tubes having a shape which can give much overflow over the microfin show large evaporating heat transfer coefficients. The effect of refrigerant overflow is much severe in evaporation than condensation. The effect of microfin arrangement is related to overflow effect of the refrigerant over the microfin.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.4
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• pp.343-352
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• 2013

In this study, a smooth flat surface, low fin, Turbo-B, and Thermoexcel-E surfaces are used to examine the effect of the flow velocity on the pool boiling heat transfer coefficients (HTCs) and critical heat fluxes (CHFs). HTCs and CHFs are measured on a smooth square heater of $9.53{\times}9.53mm^2$ at $60^{\circ}C$ in a pool of pure water at various fluid velocities of 0, 0.1, 0.15, and 0.2 m/s. Test results show that for all surfaces, CHFs obtained with flow are higher than those obtained without flow. CHFs of the low fin surface are higher than those of the Turbo-B and Thermoexcel-E surfaces due largely to the increase in surface area and sufficient fin spaces for the easy removal of bubbles. CHFs of the low fin surface show even 5 times higher CHFs as compared to the plain surface. On the other hand, both Turbo-B and Thermoexcel-E surfaces do not show satisfactory results because their pore sizes are too small and water bubbles easily cover them. At low heat fluxes of less than $50kW/m^2$, HTCs increase as the flow velocity increases for all surfaces. In conclusion, a low fin geometry is good for application to steam generators in nuclear power plants.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.25 no.9
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• pp.484-492
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• 2013

Nucleate pool boiling heat transfer coefficients (HTCs) are measured with HFC32/HFC152a mixture at several compositions. All data are taken at the liquid pool temperature of $7^{\circ}C$, on a horizontal plain square surface of $9.53{\times}9.53$ mm, with heat fluxes of 10 $kW/m^2$ to 100 $kW/m^2$ with an interval of 10 $kW/m^2$, in the increasing order of heat flux. Test results show that the HTCs of these mixtures are up to 45% lower than those of the ideal HTCs calculated by a linear mixing rule with pure fluids' HTCs, due to the mass transfer resistance associated with non-azeotropic refrigerant mixtures. Pool boiling data show the deduction in HTCs with an increase in GTD of the mixture. The present mixture data agree well with five well known correlations, within 20% deviation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.2
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• pp.113-120
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• 2010

An experimental investigation was carried out to examine the evaporative heat transfer characteristics of R-134a in a micro-channel heat exchanger. The micro-channel heat exchanger used in this study was a sort of plate heat exchanger. Micro-channels were fabricated on the SUS304 plate by the photo-etching process: 13 sheets of plates were stacked and bonded by the diffusion bonding process. The effects of the evaporating temperature, mass flux of R-134a, and inlet temperature of water were examined. As the difference between the inlet temperatures of R-134a and water increased, the heat transfer rate increased. The evaporative heat transfer coefficients obtained in this study range from 0.67 to 6.23 kW/$m^2{\cdot}^{\circ}C$. The experimental correlation for the Nusselt number as a function of the Reynold number and $\Theta$ was suggested for the micro-channel heat exchanger.