Young Chul Kwon

Experimental Study of Heating Surface Angle Effects on Single Bubble Growth

Nucleate pool boiling experiments were performed using pure R11 for various surface angles under constant heat flux conditions during saturated pool boiling. A 1-mm-diameter circular heater with an artificial cavity in the center that was fabricated using a MEMS technique and a high-speed controller were used to maintain the constant heat flux. Bubble growth images were taken at 5000 frames per second using a high-speed CCD camera. The bubble geometry was obtained from the captured bubble images. The effects of the surface angle on the bubble growth behavior were analyzed for the initial and thermal growth regions using dimensional scales. The parameters that affected the bubble growth behavior were the bubble radius, bubble growth rate, sliding velocity, bubble shape, and advancing and receding contact angles. These phenomena require further analysis for various surface angles and the obtained constant heat flux data provide a good foundation for such future work.

Experimental Study on Heating Performance Characteristics of Air Source Heat Pump with Air to Water Type

ABSTRACT:This paper presents the heating performance characteristics of the air source heat pump with air to water type. The heating capacity, COP, P-h diagram were measured at various operating conditions, air-side temperatures, relative humidities, and inlet/outlet water temperature under the standard heating condition of KS B 6275. The experimental data for the heat pump were measured using the air-enthalpy calorimeter and the constant temperature water bath. As the air-side temperature increases, the heating capacity and COP increase. The effect of the air-side relative humidities on the heat pump performance is insignificant. The heat pump performance on inlet and outlet water temperatures and air-side temperatures(-7, -11, -15℃) were studied. Heating capacity and COP increased about 27～39% with the air-side temperature increasing. Enthalpy between the front and the rear of condenser decreased about 6% by increasing of the inlet water temperature. These results can be utilized in the design of the air source heat pump system with air to water type.Keywords:Air to water(공기-물), COP(성능계수), Heating capacity(난방능력), Heat pump(히트펌프), Performance(성능)

Experimental Study on Heating Performance of Heat Pump Chiller under Overload, Frost and Defrost Conditions

ABSTRACT:In the present study, the performance characteristics of the heat pump chiller under heating conditions were experimentally investigated. Capacity, input power and COP under overload, frost and defrost conditions were obtained. The experimental data for the heat pump chiller were measured using the air-enthalpy calorimeter and the constant temperature water bath. At overload condition, the heating capacity and COP increase about 25.7% and 19.1%, respectively. The variations of the evaporator, the compressor outlet and the condenser temperature were ob-tained under frost and defrost conditions. The frost and defrost period of the heat exchanger decreases about 36.0～56.1%.Keywords:Chiller(칠러), COP(성능계수), Defrost(제상), Frost(착상), Heat pump(히트펌프), Overload(과부하) †Corresponding author Tel.: +82-41-530-2396; fax: +82-41-530-2986 E-mail address: yckweon1@sunmoon.ac.kr 1. 서 론 공조 수요의 확대와 함께 고효율과 고성능화를 추구하는 공조기기 시장에서 히트펌프는 효율성 높은 공조기로 주목받고 있다. (1-3) 또한 공기 열원을 사용하여 기름 및 가스 등을 직접 연소하지 않아 이산화탄소 배출량을 감축하여 친환경적이다. 그러나 외기 온도가 저온으로 갈수록 효율이 급격히 감소하고 실외 열교환기에 발생하는 서리로 효율감소와 서리를 제거하기 위한 에너지소비 증가는 해결해야할 문제로 지적되고 있다.