• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.5
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• pp.477-484
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• 2019

As the residence time in the vehicle increases, the passenger desires a pleasant and stable riding environment in addition to the high driving performance of the vehicle. The windshield defrosting performance is one of the performance requirements that is essential for driver's safe driving. In order to improve the defrosting performance of the windshield of a vehicle, relevant elements such as the shape of the defrost nozzle should be appropriately designed. In this paper, CFD based numerical analysis is conducted to improve defrost performance of small electric vehicles. The defrost performance analysis was performed by changing the angle of the defrost nozzle and the guide vane that spray hot air to the windshield of the vehicle. Numerical simulation results show that the defrosting performance is best when the defrost nozzle angle is $70^{\circ}$ and the guide vane installation angle is $60^{\circ}$. Based on the analytical results, the defrosting experiment was performed by fabricating the defrost nozzle and the guide vane. As a result of the experiment, it is confirmed that the frost of windshield is removed by 80% within 20 minutes, and it is judged that the defrost performance satisfying the FVMSS 103 specification is secured.

• Journal of Energy Engineering
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• v.19 no.3
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• pp.151-155
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• 2010

Adequate visibility through a vehicle windshield and frost melting period are critical aspects of major design parameters. To make progress in this area, a good understanding of the flow behavior and heat transfer characteristics produced by the HVAC module is required. The computational study was used to perform the parametric investigation into the defroster nozzle's performance with a full-scale model. The study highlights the drawbacks of current designs and points the way to improve passive defrosting mechanism. The results show that the current design of the defroster nozzles deliver the maximum airflow in the vicinity of the lower part of the windshield, which yields unsatisfactory visibility. Defrosting performance was excellent when the injection angle of the defrost nozzle was 45 degree. The numerical analysis satisfies the criteria provided by NHTSA.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.31 no.3
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• pp.53-58
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• 2002

대부분의 가정용 냉난방겸용 공기조화기(히트펌프)는 실외온도가 $5^{\circ}C$ 이하이고, 습도가 높은 저온고습조건에서 난방운전을 하면 열교환기 표변에 서리가 발생하고, 이로 인해 시스템의 성능이 떨어지게 된다. 이를 방지하기 위하여 어느 일정 조건이나 시간이 되면 히트펌프는 제상운전을 하게 되는데, 보통의 가정용 히트펌프의 경우 난방운전도중에 사이클을 냉방운전으로 전환하여 실외 열교환기의 온도를 높여 줌으로써 제상을 하는 방식 (Cycle reversing method)을 사용하고 있다. 이 방식은 부가적인 제상회로플 구성하 거나 히터를 첨가하는 등의 재료비 증가 없이 제상을 수행한다는 장점이 있으나, 시스템의 에너지 효율 측면에서 불리할 뿐만 아니라, 소비자의 입장에서 보면 제상운전이 진행되는동안에 따뜻한 바람이 공급되지 않아 쾌적한 공조를 제공받지 못한다는 단점이 있다. 본 자료에서는 먼저 제상방석에 관하여 그 종류와 특정을 알아보고, 최근에 진행되고 있는 착상 지연기술 중 어큐물레이터 내에 히터를 설치하는 방식(Viung C. Mei, et al., 2002, ASHRAE TRANSSACTIONS, V 108, Pt. 1)에 대하여 소개하고자 한다.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.23 no.1
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• pp.38-46
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• 2011

The hybrid defrost process combined with hot-gas bypass defrost and electric heater defrost was experimentally evaluated about its defrost performance in the fin-tube evaporators of household refrigerators. Also the hybrid defrost process was compared with only electric heater defrost process. The defrost efficiency of the hybrid defrost process was shown two times higher than electric heater defrost process. The defrost time of the hybrid defrost process was shorten about 10%~50% than electric heater defrost process. Thermal shock after defrost process was decreased about 50% for the case of the hybrid defrost. It was found that energy consumption ratio of defrost process was reduced up to 7.4% compared with 22.4% of electric heater defrost at the condition of $25^{\circ}C$ ambient temperature.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.6
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• pp.3389-3395
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• 2014

Conventional methods, such as the clock time control method and temperature difference control method, for defrost control often encounter mal-defrost and a waste of energy. Therefore, a more efficient method is needed to control defrosting precisely. A photoelectric sensor unit consisting of an emitter and a collector was installed in the front of outdoor heat exchanger. Accurate defrost control was performed by monitoring and using the change in output voltage according to the presence of frost. In this study, experiments were performed to determine if the performance and characteristic curves obtained using the clock time control method can be reproduced using a photoelectric sensor under the heating and defrosting capacity test condition described at KS C 9306. The output voltage of the phototransistor (receiver) and heating capacity, power consumption, and surface temperature of the outdoor heat exchanger, were compared. The results showed that photoelectric sensors can be used as a defrost control method. On-off control timing of the clock time defrosting method was in good agreement with those predicted by the output voltage of the photoelectric sensor.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.2
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• pp.161-168
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• 2011

The heating, ventilating, air conditioning (HVAC) system is a very important part of an automotive vehicle: it controls the microclimate inside the passenger's compartment and removes the frost or mist that is produced in cold/rainy weather. In this study, the numerical analysis of the defrost duct in an HVAC system and the de-icing pattern is carried out using commercial CFX-code. The mass flow distribution and flow structure at the outlet of the defrost duct satisfied the duct design specification. For analyzing the de-icing pattern, additional grid generation of solid domain of ice and glass is pre-defined for conductive heat transfer. The flow structure near the windshield, streakline, and temperature fields clearly indicate that the de-icing capacity of the given defrost duct configuration is excellent and that it can be operated in a stable manner. In this paper, the unsteady changes in temperature, water volume fraction, and static enthalpy at four monitoring points are discussed.

• Proceedings of the SAREK Conference
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• 2004.06a
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• pp.165-165
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• 2004

• Korean Journal of Food Science and Technology
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• v.28 no.4
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• pp.624-631
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• 1996

Effect of fluctuation range and intervals of defrosting temperature on quality of frozen foods stored in a domestic refrigerator equipped with an automatic defrost system was evaluated. As defrost system was operated, temperatures of domestic refrigerators were elevated from $-18^{\circ}C\;to\;-5^{\circ}C\;and\;-15^{\circ}C$, and fluctuation intervals were l6 hrs and 30 hrs, respectively. Quality deterioration such as protein denaturation, vitamin loss, exudate production and changes in appearance of frozen foods was minimized by reducing temperature oscillation during storage. Considerable effects of thermal oscillation on ice crystal sizes were observed for frozen beef tissue and ice cream. TTI (time temperature indicator) system also proved that the temperature control of defrost system in domestic refrigerator can improve the quality of foods during storage.

• Transactions of the KSME C: Technology and Education
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• v.3 no.1
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• pp.1-13
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• 2015

In this study, a new dynamic VRF-type heat pump simulation model is proposed which incorporates frosting and defrosting models. Toward this end, a simple frosting model based on the perfect analogy, and lumped system based defrost model, are proposed. Then, frosting and defrosting models are incorporated into a dynamic heat pump model which adopts segment-by-segment local heat exchanger model and map-based variable speed compressor model. Thus, the model can naturally represent locally uneven frosting and defrosting on the heat exchanger surface. Developed simulation model is validated against available experimental data to show good agreement within 10% error for capacity and COP. Finally, developed dynamic heat pump model is applied to annual heating season simulation to show that seasonal COP of heat pump is degraded by 7% due to frosting and defrosting.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.6
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• pp.493-502
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• 2002

During the defrosting process, the temperature in the cabinet of a showcase becomes high as compared to the setting point, which is not desirable for stored foods or materials. It is necessary to develop a more efficient defrosting method to prevent large temperature fluctuation. In this study, the performance of a showcase refrigeration system with three evaporators is investigated by employing a hot-gas bypass defrosting technology in the system under frosting and defrosting conditions. The operating characteristics are compared with those for the on-off defrosting method that has been widely used in current products. As a result, the hot-gas bypass defrosting method shows higher refrigerating capacity and less temperature fluctuation than the on-off method under frosting/defrosting conditions, while the power input is relatively high for the hot-gas bypass method.