• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.15 no.1
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• pp.1-8
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• 2019

In this study, the effect of operating conditions of fan-coil unit with an oval tube type heat exchanger on its non-dimensional performance coefficient has been investigated. Pressure drops and heat transfer rates were measured under heating condition for various water flow rates, inlet temperatures and wind speeds. As a non-dimensional performance coefficient, Colburn j-factor was evaluated. The results show that the most sensitive parameter on heat flux is the inlet temperature, which affects the heat flux 4.7 and 7.2 times more than the wind speed and water flow rate, respectively. On the other hand, the Colburn j-factor as a non-dimensionalized index decreases with the wind speed, and has an maximum when the wind speed is about 1 m/s. the Colburn j-factor increases slowly with the water flow rate and inlet temperature but at a certain range of inlet temperature, the opposite phenomenon is found.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.37-42
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• 2003

An experiment was performed to study heat transfer characteristics between corrugated heat exchanger and flat plate type one. While heat capacity(13.86kW) was provided constantly and the flow speed was varied from 2.8 to 17.9m/s, The temperature and the pressure drop were measured. Furthermore, Heat transfer coefficient, Colburn factor and Nusselt number were calculated using them. With increase of the flow speed for both exchangers, the coefficient and the pressure drop increased, but Colburn factor decreased. The coefficient, pressure drop and Colburn factor of the corrugated type were all higher than those of the flat one, which is due to the flow interruption with recirculation and reattachment of the corrugated type. The empirical correlations of Nusselt number were suggested for the tested two heat exchangers.

• Proceedings of the SAREK Conference
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• 2009.06a
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• pp.1443-1448
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• 2009

Numerical analysis has been carried out to investigate air-side convective heat transfer characteristics in compact heat exchangers with continuous plate fins. Simulation results such as air flow and temperature distributions are presented, and heat transfer characteristics are compared for various inlet conditions. Results from various turbulence models are also compared for applicability. There is large difference between the local heat transfer coefficient distributions along the cylinder wall for circular tubes. Colburn j factors from the calculated results of circular and flat tubes in the heat exchangers are compared for various Reynolds number. The predicted results in this study can be applied to the optimal design of air conditioning system. with compact heat exchanger.

• Journal of Mechanical Science and Technology
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• v.18 no.7
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• pp.1258-1266
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• 2004

It is important to completely understand heat/mass transfer from a flat plate because it is a basic element of heat/mass transfer. In the present study, local heat/mass transfer coefficient is obtained for two flow conditions to investigate the effect of boundary layer using the naphthalene sublimation technique. Obtained local heat/mass transfer coefficient is converted to dimensionless parameters such as Sherwood number, Stanton number and Colburn j-factor. These also are compared with correlations of laminar and turbulent heat/mass transfer from a flat plate. According to experimental results, local Sherwood number and local Stanton number are in much better agreement with the correlation of turbulent region rather than laminar region, which means analogy between heat/mass transfer and momentum transfer is more suitable for turbulent boundary layer. But average Sherwood number and average Colburn j-factor representing analogy between heat/mass transfer and momentum transfer are consistent with the correlation of laminar boundary layer as well as turbulent boundary layer.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.12
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• pp.994-1001
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• 2007

Numerical analysis has been carried out to investigate air-side convective heat transfer characteristics in a compact heat exchanger with circular tubes and continuous plate fins. Simulation results such as air velocity and temperature distributions are presented, and heat transfer coefficients are compared with previous experimental correlations. Three models of standard and RNG $k-{\varepsilon}$, and Reynolds stress are applied for turbulence model applicability. Predicted heat transfer coefficient from the models of standard and RNG $k-{\varepsilon}$ are very close to those of the heat transfer correlations while there are relatively large difference, more than 17 percentage in the result from the Reynolds stress model. From the calculated results a correlation for Colburn j factor in the compact heat exchanger system is suggested.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2001.11a
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• pp.28-35
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• 2001

The heat transfer and pressure drop characteristics of R718 flowing in smooth horizontal copper tubes with inner diameter of 3.36 mm, 5.35 mm, 6.54 mm and 8.12 mm were investigated. The test section is a counterflow heat exchanger with refrigerant flowing in the inner tube and water flowing in the annulus. Experiments were peformed for the flowing range of variables : Reynolds number (1000 to 20000), mass flow rate of brine (450 kg/h) and refrigerant temperature (5$0^{\circ}C$). The main results were summarized as follows : (1) The heat transfer coefficient of 3.36 mm ID was about 10% to 30% higher than that of 5.35 mm, 6.54 mm and 8.12 mm ID, and the heat transfer coefficients for small diameter. tubes are about 20% to 27% higher than these predicted by Gnielinski. The new correlation is proposed to predict the experimental data. (2) As a result of comparison with correlation prosed by Blasius. the deviation of the experimental data slightly increased as the tube diameter decreased. (3) The ratio of heat transfer to friction factor (j/f) correlated by all experimental data increased as the tube diameter decreased.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.9-13
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• 2001

In the present study, the friction coefficients (Fanning and Moody coefficients) and the Nusselt number is reviewed from an educational point of view. It is discussed that these dimensionless numbers can be treated with two lengh scales. Also, the similarity between the momentum and heat transfer is discussed based on the length scales.

• 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.15 no.3
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• pp.220-229
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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 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 0.6 m/s to 1.6 m/s.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.11
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• pp.999-1007
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• 2013

The present work reports numerical results of the pressure drop and heat transfer characteristics of pipes with various shapes such as circular, elliptical, circumferential wavy and twisted using a three-dimensional simulation. Numerical simulations are calculated for laminar to turbulent flows. The fully developed flow in pipes was modeled using steady incompressible Reynolds-averaged Navier-Stokes (RANS) equations. The friction and Colburn factor of each pipe are compared with those of a circular tube. The overall flow and heat transfer calculations are evaluated by the volume and area goodness factor. Finally, the objective of the investigation is to find a pipe shape that decreases the pressure loss and increases the heat transfer coefficient.