• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.8
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• pp.1062-1068
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• 2000

The effect of heat exchanger surface treatment on the frosting/defrosting behavior in a fin-tube heat exchanger is investigated experimentally. It is found that the hydrophilic surface mainly influences on the frosting behavior, however, the hydrophobic surface gives some influence on the defrosting behavior. In view of frosting performance, surface-treated heat exchanger with either hydrophilic or hydrophobic characteristic shows a little improvement in the thermal performance than the aluminium heat exchanger with no surface treatment. The result reveals that the heat exchanger with hydrophobic surface treatment is more effective in view of the defrosting efficiency and time. The amounts of residual water on the surface-treated heat exchangers are shown to be smaller than those of the bare heat exchanger, therefore further improvements on the performance of re-operations are expected.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.7
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• pp.667-672
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• 2004

An experimental study has been carried out to investigate the frosting behavior on the plate of thermally conductive plastic (PBT based resin) by comparing it with those of aluminum and some plastic test specimens (PTFE based resin). It is found that the frosting behavior of plastic specimens with 1 mm thickness shows similar trend to that of aluminum except PTFE. The properties of frost formed on the specimens are found to be affected by both thermal conductivity and surface characteristics of the materials. The results indicate that the heat and mass transfer rates of PBT resin are almost equivalent to those of aluminum.

• International Journal of Air-Conditioning and Refrigeration
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• v.7
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• pp.101-111
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• 1999

The effect of various conditions of frosting and defrosting on the defrosting behavior of a fin-tube heat exchanger has been examined experimentally. An electric heater is used for defrosting in a fin-tube heat exchanger. There are several local maxima in the water draining rate. The amount of residual water on the heat exchanger after completion of defrosting is kept constant due to surface tension on the heat exchanger. Without considering degradation of the thermal performance due to the frosting, the defrosting efficiency is improved with increasing amount of frost irrespective of the frosting condition. The defrosting behavior is affected by frosting density as well as frost accumulation, both of which vary with the experimental operating conditions. The heat loss to the surrounding air decreases, and melting and defrosting efficiencies show high values with decreasing heat input.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.6
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• pp.649-657
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• 1998

In this study, the effects of the various conditions of frosting and defrosting on the behavior of defrosting in a fin-tube heat exchanger have been examined experimentally. The electric heater is used for defrosting in a fin-tube heat exchanger It is shown that there are several local maxima in the water draining rate. The amount of residual water on the heat exchanger after the completion of defrosting is kept constant due to surface tension on the heat exchanger. Without considering the degradation of the thermal performance due to the frosting, the defrosting efficiency is improved with increasing amount of the frost irrespective of the frosting condition. The defrosting behavior is affected by the frosting density as well as the frost accumulation, which vary with the experimental operating conditions during the frosting period. The heat loss to the surrounding air decreases, and the melting and defrosting efficiencies show high values with decreasing heat input.

• 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.

• 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.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2334-2339
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• 2008

This paper proposes an improved mathematical model for predicting the frosting behavior on a two-dimensional fin considering the heat conduction of heat exchanger fins under frosting conditions. The model consists of laminar flow equation in airflow, diffusion equation of water vapor for frost layer, and heat conduction equation in fin, and these are coupled together. In this model, the change in three-dimensional airside airflow caused by frost growth is accounted for. The fin surface temperature increased toward the fin tip due to the fin heat conduction. On the contrary, the temperature gradient in the airflow direction(x-dir.) is small throughout the entire fin. The frost thickness in the direction perpendicular to airflow, i.e. z-dir., decreases exponentially toward the fin tip due to non-uniform temperature distribution. The rate of decrease of heat transfer in the airflow direction is high compared to that in the z-direction due to more decrease in the sensible and latent heat rate in x-direction.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.20 no.11
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• pp.727-732
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• 2008

This paper presents a mathematical model to predict the behavior of frost formed on an one-dimensional fin of heat exchanger, considering fin heat conduction under frosting conditions. The computational domain consists of air-side, the frost layer, and fin region, and they are coupled to the frost layer. The frost behavior is more accurately predicted with fin heat conduction considered (Case A) than with constant fin surface temperature assumed (Case B). The results indicate that for Case B, the frost thickness and heat transfer are overpredicted in most regions of the fin, as compared with those for Case A. In addition, for Case A, the maximum frost thickness varies little with the fin length variations, and the extension of the fin length after 30mm contributes insignificantly to heat transfer.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.1
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• pp.95-101
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• 2000

The effect of surface contact angle on the behavior of frost formation in a fin-tube heat exchanger is investigated experimentally. It is shown that both heat exchangers with hydrophilic and hydrophobic surfaces appear to have a better thermal performance than bare aluminium heat exchanger, but the improvements are very small. There is a little increase in the amount of the frost deposited onto the heat exchanger with both hydrophilic and hydrophobic surface. However, the effect of contact angle on the frost density is observed ; the frost with high density forms on the heat exchanger with hydrophilic surface ; and the frost with low density is deposited onto the heat exchanger with hydrophobic surface when compared with the frost deposited onto the heat exchanger with bare aluminium surface. This may be attributed to the fact that the shape of water droplets which condense on the surface of heat exchanger at the early stage of frosting varies with contact angle, and thus makes a difference on the structure of frost formation. From the experiments with different relative humidity of inlet air, it is shown that the variations of operating parameter make no influence on the effect of surface contact angle on the frosting behavior in the heat exchanger.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2091-2096
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• 2007

This paper presents a mathematical model for predicting the frost behavior formed on heat exchanger fins, considering fin heat conduction under frosting condition. The model is composed of air-side, the frost layer, and fin region, and they are coupled to the frost layer. The frost behavior is more accurately predicted with fin heat conduction considered (Case A) than with a constant fin surface temperature assumed (Case B). The results indicate that the frost thickness and heat transfer rate for Case B are over-predicted in most regions of the fin, as compared to those for Case A. Also, for Case A, the maximum frost thickness varies little with the fin length variations, and the extension of the fin length over 30 mm contributes insignificantly to heat transfer.