• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1540-1545
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• 2004

This paper presents a semi-empirical model to predict the frost growth formed on the cold cylinder surface. The model is composed of the correlations for frost properties including the various frosting parameters and local heat transfer coefficient. The effects of varying the correlations for local heat transfer coefficient on the frost growth are examined to establish the model. The numerical results are compared with experimental data obtained by the previous researchers. The results agree well with the experimental data within a maximum error of 13%. As the results, the frost thickness decreases with changing angular position from front stagnation to separation point. Also the effects of air velocity on the frost growth are negligible, as compared to the other frosting parameters.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1576-1581
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• 2004

An experimental study has been carried out to investigate the frosting behaviors of thermally conductive plastic(PBT based resin) resin by comparing with those of aluminum and some plastic(PTFE based resin) test specimens. It is found that the frosting behavior of plastic specimens with 1 mm thickness show similar trend with aluminum except PTFE. The properties of frost formed on the specimens are affected by both thermal conductivityand surface characteristics (hydrophilic/hydrophobic) of the materials. It can be said that the heat and mass transfer rate of plastic materials are almost equivalent with those of aluminum.

• International Journal of Air-Conditioning and Refrigeration
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• v.13 no.3
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• pp.138-144
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• 2005

In order to select a new material for a heat exchanger, the frosting behavior of a thermally conductive plastic based on PBT was compared to the frosting behavior of aluminum and three types of plastics based on PTFE. The frosting behavior on the 1 mm thick PBT specimen was similar to that of the aluminum specimen but not that of the pure PTFE specimen. The properties of the frost formed on the specimens were affected by both the thermal conductivity and surface characteristics of the materials. The heat and mass transfer rates of the thermally conductive plastic were almost equivalent to those of the aluminum specimen.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.1
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• pp.62-70
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• 2005

In this study, the air-side heat transfer coefficients of several types of evaporators in the household freezer/refrigerators are investigated. The types considered in this work are: discrete flat plate fin-and-tube type(in-lined tube array), continuous flat plate fin-and-tube type(staggered tube array), and spine fin-and-tube type(in-lined tube array). The heat transfer correlations obtained from this study for each heat exchangers could expect heat transfer coefficients less than $5\%$ of errors. The result indicates that the air-side heat transfer performance of spine fin-and-tube type evaporator shows the highest value under dry conditions, but discrete flat plate fin-and-tube type evaporator shows the highest value among these three evaporators under frosting conditions.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.4
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• pp.307-316
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• 2008

The objective of this study is to provide numerical and experimental data that can be used to investigate the performance characteristics of a flat plate fin-tube evaporator in household and commercial refrigerators under frosting conditions. Computer simulations with variations of operating conditions such as air inlet temperature, relative humidity, and geometries were performed to find out optimal design parameters of a fin-tube evaporator for household and commercial refrigerators. The tube-by-tube method was used in the simulation and the frost growth model was considered under frosting conditions. The developed analytical model predicted the decreasing rates of heat transfer capacity and air flow rate ratio within ${\pm}$10% compared to the experimental results for a refrigerator under real operating conditions. As a result, the frost thickness at $3^{\circ}C$ & 80% is increased 40% than that of $-3^{\circ}C$ & 80%, and the frost thickness at $3^{\circ}C$ & 90% is increased 30% than that of $3^{\circ}C$ & 60%. Accordingly, the operating time of the evaporator in the refrigerator was reduced with the increase of the decreasing rate of air flow rate ratio at each condition.

• 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.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.6 no.2
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• pp.155-165
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• 1994

In this study, the following factors are investigated from experiments for a vertical parallel plate heat exchanger under the frosting condition ; the growth of frost layer, the characteristics of heat and mass transfer, the change of mass flow rate of the air passing through the heat exchanger, and the pressure drop of the air in the heat exchanger. The amount of heat and mass flux of water vapor transferred from the air stream to the heat exchanger surface is large at the early stage of frosting and then decreases dramatically, and the extent of decreasing rate becomes moderate with time. The frost layer formed near the inlet of the heat exchanger is thicker and denser than that formed near the outlet. It is found that the gradient of the amount of frost along the flow direction increases with time. In the early period of frost formation, the thermal resistance between the air and the cooling plate increases dramatically and then the extent of change decreases with time. Initially the convective thermal resistance is dominant. Then, while the convective thermal resistance decreases with time, the conductive thermal resistance continues to increase with time and finally the conductive thermal resistance becomes dominant.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.7 no.1
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• pp.161-170
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• 1995

This study is concerned with the numerical analysis of performance on fin-tube heat exchanger under frosting condition. In this work, tube-by-tube method using LMED is employed. The present results are compared with O'Neal's experimental and numerical results. A standard evaporator model with 2rows-2columns is selected to investigate the effects of the various parameters such as fin pitch, air flow velocity, and humidity. The results show that frost thickness and the amount of frost per unit area decrease as fin-pitch becomes narrower. In the meantime, frost thickness and accumulation rate increase with higher inlet air humidity. It is shown that heat transfer rate increases during 30minutes and then it decreases. Heat transfer rate and the amount of frost increase with air velocity, however frost thickness does not increase over a certain velocity.

• Proceedings of the SAREK Conference
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• 2007.11a
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• pp.252-257
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• 2007

The present study investigated the effect of air velocity on frost formation of slit fin-and-tube heat exchanger under frosting condition. The slit fin-and-tube heat exchanger with outer tube diameter 7.0mm and 1 row was used. Air side pressure drop, photographs of frost distribution, frost accumulation and frost thickness were presented with respect to the frosting time. In the early stage of experiment, the case with air velocity of 1.5m/s showed 403% higher for the air pressure drop than the case with the air velocity of 0.5m/s. As the frost was accumulated, the effect of air velocity on air pressure drop was decreased. In the end stage of test, air pressure drops of two cases were very close and air pressure drop for the air velocity of 0.5m/s was higher than that of 2.0m/s. It was also shown in the photographs of frost distribution, frost accumulation and frost thickness. From frost thickness, fanning friction factor was presented.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.12
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• pp.1071-1078
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• 2010

The objective of this study is to investigate the heat transfer characteristics of evaporators that have various fin configurations and are used in household refrigerators. The frosting and defrosting characteristics of a spirally coiled circular fin-tube evaporator, a discrete-plate fin-tube evaporator, and a continuous-plate fin-tube evaporator were measured and compared. Under non-frosting conditions, the heat transfer coefficient of the spirally coiled circular fin-tube evaporator was 22.3% and 40.2% higher than the coefficients of the discrete- and continuous-plate fin-tube evaporators, respectively. Under frosting conditions, the heat transfer coefficient of the spirally coiled circular fin-tube evaporator was 27.0% and 46.3% higher than the coefficients of the discrete- and continuous-plate fin-tube evaporators, respectively. In addition, the defrosting water amount of the spirally coiled circular fin-tube evaporator was 3.2% and 9.4% lower than the amounts in the case of the discrete- and continuous-plate fin-tube evaporators, respectively.