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An Experimental Study on Heat Transfer in the Pulsating Pipe Flow
Hi-Yong Pak,Chang-Kee Kim 대한설비공학회 1993 International Journal Of Air-Conditioning and Refr Vol.1 No.-
An experimental result for the heat transfer of pulsating turbulent pipe flow was presented under the condition of uniform wall heat flux in a hydrodynamically fully developed region.<br/> Experiments were performed under the following conditions; Inlet time-averaged Reynolds number varying from 5000 to 11000; Pulsating frequency varying from 53 to 320 ㎐.<br/> The measurements showed that the effect of pulsation on local heat transfer was greater at the downstream location where the pulsating source exists and the averaged heat transfer rate over the pipe length was higher or lower depending upon the pulsating conditions when compared with a non-pulsating flow. In addition, the significant change of heat transfer rate was observed in acoustically resonant conditions, when the pulsating frequency of the flow corresponded to the pipes natural frequency.
Numerical Prediction for the Performance of Refrigeration System with the Scroll Compressor
Hi-Yong Pak,Kyoung-Woo Park 대한설비공학회 1996 International Journal Of Air-Conditioning and Refr Vol.4 No.-
A performance analysis of the refrigeration system using the HFC-134a and the scroll compressor is performed numerically. The refrigeration system mainly consists of various standard components such as heat exchangers, compressors, and expansion devices. The model for heat exchanger performance analysis is based on a tube-by-tube method which is analyzed separately by considering the cross-flow heat transfer with the outdoor air flow and the pressure drop. The system used the scroll-type compressor which has many merits such as high efficiency, low noise and vibration, and small size. Short-tube is included as an expansion device. Vapour and liquid lines are also considered for the performance analysis of refrigeration system.<br/> Using the modelings of various components of the refrigeration system, a performance comparison of CFC-12 and HFC-13a is performed numerically for the various outdoor air temperatures and various values of the short-tube diameter. As seen in the results of this study, the refrigeration system performance decreases as the outdoor air temperature increases, and the optimum short-tube diameter based on COP is 1.37㎜ for this system.
박희용(Hi-Yong Pak),이관수(Kwan-Soo Lee),김병규(Byoung-Kue Kim) 한국태양에너지학회 1990 한국태양에너지학회 논문집 Vol.10 No.1
단일 핀-관열교환기와 관련된 열역학적 최적설계법을 기준하여 핀-관열교환기의 엔트로피 생성율을 조사하였다. 엔트로피 생성율(비가역성) 해석법을 사용하여 최적설계조건을 구하였고 설계조건의 변화에 따른 총엔트로피 생성율과 핀의 길이, 관의 안지름과 바깥지름 및 핀간거리를 조사하였다.<br/> 이 연구의 결과에 따르면 바깥지름이 클수록 최적핀간거리와 핀높이는 커지고 엔트로피 생성율과 최적안지름은 작아진다. 또한 핀두께를 증가시키면 계의 엔트로피 생성율과 최적핀간거리는 증가하고 핀높이를 증가시키면 엔트로피 생성율과 최적바깥지름은 증가한다. The entropy generation rate in a fin-tube heat exchanger is investigated as a basis for thermodynamic optimization associated with single fin-tube heat exchanger. The entropy generation (irreversibility)analysis is used to find the optimum design factor and investigate total entropy generation, optimum dimensions of fin length, tube inner and outer diameters, and fin spacing on the variation of design factors.<br/> The results of this study are as follows: As the outer diameter increases, optimum fin spacing and fin length increase but the entropy generation and optimum inner diameter decrease; As fin thickness increases, the entropy generation of system and optimum fin spacing increase; As fin length increases, entropy generation and optimum outer diameter increase.
박희용(Hi-Yong Pak),차상명(Sang-Myung Cha),한철희(Chul-Hee Han) 한국태양에너지학회 1992 한국태양에너지학회 논문집 Vol.12 No.3
산업용 노의 폐열 회수를 위하여 노의 배기부에 설치되는 복사형 레큐페레이터 중에서 가장 대표적인 형태인 이중 원관식 레큐페레이터의 열전달 특성에 관하여 연구하였다. 내관에는 고온의 배기가스가 흐르고, 내관과 외관 사이의 환상공간에서는 공기가 흐르며 왼관의 외벽면은 단열되어 있는 원관식 레큐퍼레이터의 열전달 특성을 규명하였다. 고온의 배기가스 폐열은 내관의 내벽으로 전달되고 이는 다시 환산 공간내의 공기로 전달된다. 배기가스의 복사 열전달은 구조화 근사법을 사용하여 모델링한 후 이를 유동장과 연계하여 수치적으로 해석하였으며, 기존의 실험적연구와 일치하는 조건에서의 계산결과와 비교하였다. 또한, 내관의 동심축 상에 원동통형의 재복사기를 설치할 경우 내관에서 재복사 효과가 일어나는데 이에 따른 열전달 특성을 연구하여 레큐퍼레이터를 이론적으로 해석할 수 있는 방법을 제시하였다. In the concentric tube type recuperator, which is the most typical type of radiation recuperator, installed on the exhaust-secion of industrial furnace, air flows between the adiabatic outer tube and the inner tube in which exhausted gas flows with high temperature. The waste heat of the exhausted gas is transferred to the inner tube, and transferred from the inner tube to the flowing air.<br/> The heat transfer by radiation in the concentric tube type recuperator is modeled using spherical harmonics approximation, namely, P-N method and numerically analyzed considering the effect of dynamic flow field. The results are compared with the existing empirical data. In addition, a theoretical method is presented for the analysis of the heat transfer characteristics of a recuperator with a reradiator installed in the inner tube, which causes re-radiant in the inner tube, and the characteristics of the recuperator is analyszed and defined.