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A study on heat transfer enhancement using straight and twisted internal fin inserts
Leonard D. Tijing,Bock Choon Pak(박복춘),Byung Joon Baek(백병준),Young I. Cho(조영일) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.11
The present study investigated the effect of internal aluminum fins with a star shape cross section on the heat transfer enhancement and pressure drop in a counterflow heat exchanger. A concentric tube heat exchanger was used with water as the working fluid. The heat transfer rate increased by 12-51% over the plain tube value, depending on the internal fin configuration used. However, the pressure drop also increased substantially by an average of 286-338%. The results showed that a straight fin configuration is good enough to produce a heat transfer increase in a counterflow heat exchanger. Twisted fin configurations did not further increase the heat transfer rate.
A novel viscosity measurement using a falling ball viscometer with a high-speed camera
Won Jin Jo(조원진),Bock Choon Pak(박복춘),Young I Cho(조영일) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.11
This study introduces a new approach to a falling ball viscometer by using a high speed motion camera to measure the viscosity of both Newtonian and non-Newtonian fluids from the velocity-time data. This method involves capturing continuous photographs of the entire falling motion of the ball as the ball accelerates from the rest to the terminal velocity state. Ball’s velocity was determined from the distance traversed by the ball by examining video tape frame by frame using the marked graduations on the surface of the falling ball cylinder. Each frame was pre-set at 0.01. Glycerin 74% was used for Newtonian solution, while aqueous solutions of Polyacrylamide and Carboxymethyl Cellulose were for non-Newtonian solutions. The experimental viscosity data were in good agreements with the results obtained from a rotating Brookfield viscometer.
Pak, Bock-Choon,Cho, Young-I 全北大學校 1995 論文集 Vol.39 No.-
본 연구는 전자 패키징에서 단위체로 사용되는 평행 유동 메니폴들에서 유동분포에 대한 레이놀즈 수와 헤더형상의 영향에 대해서 고찰하였다. 메니폴드내에서 유동 분포는 레이놀즈 수와 헤더 형상에 의해서 많은 영향이 있음을 알 수 있다. 설계측면에서 여러 가지 다른 형상의 헤더(직사각형, 삼각형, 경사형)를 고려한 결과, 삼각형 헤더가 레이놀즈수에 관계없이 가장 좋은 유동분포를 보이고 있다. 따라서, 통상적인 사각형헤더를 삼각형으로 변형할 경우 메니폴드내의 유동분포를 상당히 개선시킬 수 있음을 알 수 있다.