광센서를 이용한 제상제어 방법에 대한 연구

전창덕(ChangDuk Jeon) 대한설비공학회 2017 설비공학 논문집 Vol.29 No.4

This study attempted to investigate the value of photoelectric sensors in terms of a defrost-control method. Tests were conducted in a calorimeter room under the heating with the defrost-performance test conditions described in KS C 9306. Accordingly, the photoelectric technology is a competitive defrost-control method that can precisely control the operational defrost cycle using the output voltages that are proportional to the frost height. The heating period is gradually reduced because the complex defrost-control method, for which the sensors initiate the defrosting process and the defrosting process is terminated by the time parameter, could not adjust the net defrosting time by itself. Therefore, a complex defrost-control method, for which the photoelectric sensors start the defrosting process and it is terminated by the temperature parameter, is preferred because of the adjustment of the net defrosting time. Regardless of the defrost-control method, the first defrosting cycle is activated earlier than the times that are determined in the second and third cycles and so on, because the first operation cycle can decide the characteristics of the subsequent cycle.

하이브리드 제상 방식을 적용한 냉장고용 핀-관 열교환기의 제상 성능 평가

이수원(Suwon Lee),박용주(Yongjoo Park),권래언(Laeun Kweon),정영만(Youngman Jeong),이재근(Jaekeun Lee) 대한설비공학회 2011 설비공학 논문집 Vol.23 No.1

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℃ ambient temperature.

AN EXPERIMENTAL STUDY ON THE DEFROSTING PERFORMANCE OF A PCM-BASED REVERSE-CYCLE DEFROSTING METHOD FOR AIR SOURCE HEAT PUMPS

MINGLU QU,SHIMING DENG,YIQIANG JIANG 대한설비공학회 2010 International Journal Of Air-Conditioning and Refr Vol.18 No.4

When an ASHP unit operates in heating mode, frost can be accumulated on the surface of its outdoor coil. Currently the most widely used defrosting method for ASHPs is reverse cycle defrost. However, the fundamental problem for such a method is that there is insufficient heat available for ASHPs during defrosting. This paper reports on an experimental study of developing a novel reverse-defrosting method which was thermal energy storage (TES) based on using phase change material (PCM). Comparative experiments were carried out at two operating conditions: standard defrosting condition and the PCM-based defrosting condition. Results indicated that the use of this PCM-based reverse defrosting method could help shorten defrosting time, increase defrost COPd, enhance system reliability, reduce transition duration from defrost to normal space heating operation, and improve indoor thermal comfort for occupants during defrosting and heating resumption process while without degrading the quality of space heating provided by the ASHP during heat operation.

AN EXPERIMENTAL STUDY ON THE DEFROSTING PERFORMANCE OF A PCM-BASED REVERSE-CYCLE DEFROSTING METHOD FOR AIR SOURCE HEAT PUMPS

Qu, Minglu,Deng, Shiming,Jiang, Yiqiang The Society of Air-Conditioning and Refrigerating 2010 International Journal Of Air-Conditioning and Refr Vol.18 No.4

When an ASHP unit operates in heating mode, frost can be accumulated on the surface of its outdoor coil. Currently the most widely used defrosting method for ASHPs is reverse cycle defrost. However, the fundamental problem for such a method is that there is insufficient heat available for ASHPs during defrosting. This paper reports on an experimental study of developing a novel reverse-defrosting method which was thermal energy storage (TES) based on using phase change material (PCM). Comparative experiments were carried out at two operating conditions: standard defrosting condition and the PCM-based defrosting condition. Results indicated that the use of this PCM-based reverse defrosting method could help shorten defrosting time, increase defrost $COP_d$, enhance system reliability, reduce transition duration from defrost to normal space heating operation, and improve indoor thermal comfort for occupants during defrosting and heating resumption process while without degrading the quality of space heating provided by the ASHP during heat operation.

Frosting and defrosting behavior of slippery surfaces and utilization of mechanical vibration to enhance defrosting performance

Heu, Chang Sung,Kim, Sun Woo,Kim, Jihyun,Lee, Seojin,Kim, Jin Man,Lee, Kwan-Soo,Kim, Dong Rip Elsevier 2018 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.125 No.-

<P><B>Abstract</B></P> <P>We experimentally investigate the frosting and defrosting performance of slippery surfaces which have low sliding angles of water droplets and low ice adhesion strengths. The frosting and defrosting characteristics of slippery surfaces are compared with those of bare aluminum, hydrophilic, and superhydrophobic surfaces. The enhanced sliding properties of water droplets on the slippery surfaces effectively promote the drainage of the condensate on their surfaces, which not only leads to significant frost retardation under frosting conditions, but also substantially reduces the mass of the retained water on the surfaces after defrosting by heat. In addition, when mechanical vibration is applied together with heating during defrosting process, the low ice adhesion strengths of the slippery surfaces enable the effective detachment of the lumped frost layer from their surfaces, thereby significantly reducing the defrosting time.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Frosting and defrosting performance of slippery surfaces are experimentally investigated. </LI> <LI> Slippery surfaces lead to effective frost retardation and reduced retained water after defrosting. </LI> <LI> The effects of applying mechanical vibration to heat defrosting of slippery surfaces are studied. </LI> <LI> Slippery surfaces exhibit significant reduction of defrosting time with mechanical vibration. </LI> </UL> </P>

공랭식 VRF 시스템의 연속난방에 관한 연구

장지영(Ji Young Jang),이상헌(Sang Hun Lee),김병순(Byung Sun Kim) 대한설비공학회 2013 대한설비공학회 학술발표대회논문집 Vol.2013 No.6

AN EXPERIMENTAL STUDY ON PERFORMANCE IMPROVEMENT FOR AN AIR SOURCE HEAT PUMP BY ALTERNATE DEFROSTING OF OUTDOOR HEAT EXCHANGER

정훈,황정호,전창덕 대한설비공학회 2014 International Journal Of Air-Conditioning and Refr Vol.22 No.3

For a space heating air source heat pump (ASHP) in the condition of low temperature and high humidity, frost on the surface of heat exchanger becomes the major cause decreasing heating surface area and thus the performance of heat pump. In this study, we showed a method of delaying the implantation of frost using alternate defrost control. First, we acquired the performance data for conventional periodic reversed-cycle defrosting with a 5RT heat pump. After the experiment, the heat pump was modified to verify the effects of newly introduced alternate defrosting and compared with the conventional periodic reverse cycled method. It was found that heating coefficient of performance (COP) of heat pump using newly proposed alternate defrost method was about 17% higher than conventional heat pump using periodic reverse cycled defrosting.

Study of thermal phenomena in the cabin of a passenger vehicle using finite element analysis: human comfort and system performance

Ji, HoSeong,Kim, YoonKee,Yang, JangSik,Kim, KyungChun Professional Engineering Publishing Ltd 2014 Proceedings of the Institution of Mechanical Engin Vol. No.

<P>A numerical simulation is performed to evaluate the thermal comfort of passengers and the performance of a defroster. In this study, a grid system based on a real vehicle and a finite element human model are used with an appropriate time step. The turbulent nature of the flow is modelled using a standard <I>k–ε</I> model according to the logarithmic law of the wall. The complex flow characteristics inside the passenger compartment are shown with simultaneous velocity and temperature fields in several sections of the flow domain. Through a predicted mean vote analysis, the thermal comfort of the passengers is discussed, in particular with respect to the measured location of the seat and the measured position of the passenger. An additional study is conducted on the defrost mode with respect to the defrosting performance which is closely related to passenger safety. The velocity profile at the defrost nozzle is interpolated to the inlet boundary surface node through a defrost duct simulation. The monitored points on the ice boundary indicate the melting time, the phase-change duration, the change in the enthalpy and other useful information.</P>

착상조건에서 연속난방이 가능한 히트펌프 성능 향상 기술

전창덕(Jeon, Chang-Duk) 한국산학기술학회 2013 한국산학기술학회논문지 Vol.14 No.2

히트펌프는 에너지 효율이 높고, 지열, 폐열, 공기열 등 다양한 열원 사용이 가능하기 때문에 보급이 빠르게 확대되고 있다. 공기를 열원으로 이용하는 공랭식 히트펌프의 경우는 실외기 표면에 형성되는 서리를 제거하기 위해 제상운전이 요구된다. 일반적으로 사용하는 역사이클(reverse cycle) 제상운전 방법은 연속난방이 불가능하며 이로 인 해 성능계수가 감소하는 원인이 된다. 본 연구에서는 실외기 코일용 휜-관 열교환기를 3열로 구성하고 난방과 제상이 동시에 가능하도록 일정시간 간격으로 열교환기의 한 개의 열을 응축기로, 나머지 열은 증발기로 교번 운전을 수행하 여 KS C 9306에 규정된 제상-난방 시험조건(건구온도 2℃, 습구온도 1℃)에서 최소 180분 이상 연속난방이 가능함을 실증하였으며 역사이클 제상방법을 사용하는 일반적인 히트펌프 대비 COP가 약 20% 향상됨을 알 수 있었다. Heat pumps come into wide use because high energy efficiency can be obtained and diverse heat sources like geothermal heat, waste heat and air are available. It is necessary for an air source heat pump to defrost in order to remove frost on the surfaces of an outdoor heat exchanger. It is impossible for continuous heating if reverse cycle operation is used as defrosting method, furthermore it causes the degradation of COP. In this study an fin-tube heat exchanger with three rows was used as an outdoor coil. One row among three rows of the heat exchanger was used like a condenser in order to remove frost on it, the others were used as evaporator to accomplish continuous heating. Each row was switched in order from a condenser to an evaporator in specified time interval. Tests were carried out during minimum 180 minutes at the defrost-heating test condition(dry bulb temperature 2℃, wet bulb temperature 1℃) described in KS C 9306. Time-averaged COP was about 20% higher than that of conventional defrosting method.

제상모드에 대한 실차 내부 환기유동의 정량적 가시화 연구

이진평(Jin Pyung Lee),이상준(Sang Joon Lee) 한국가시화정보학회 2010 한국가시화정보학회지 Vol.8 No.2

Thermal comfort inside a passenger car has been receiving large attention in automobile industries. Especially, the performance of windshield defroster is important in the design of a car to ensure passenger comport and safety. Thereby, better understanding on the ventilation flow along the vehicle windshield is essential to evaluate the performance of windshield defroster. However, most previous studies dealt with the defrost flow using CFD (computational fluid dynamics) calculations or scale-down model experiments. In this study, a real commercial automobile was used to investigate the flow discharged from the vehicle defroster and the ventilation flow along the windshield using a PIV velocity field measurement technique. The experimental data would be useful to understand the flow characteristics in detail and also call be used to validate numerical predictions.