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정사각 덕트 내에서 열/물질전달 촉진을 위한 경사진 단락 요철의 좁은 틈새 효과
우성제,이세영,최청,조형희,Wu, Seong-Je,Lee, Sei-Young,Choi, Chung,Cho, Hyung-Hee 대한기계학회 2002 大韓機械學會論文集B Vol.26 No.1
Local heat/mass transfer and friction loss in a square duct roughened with various types of continuous and discrete rib turbulators are investigated. The combined effects of the gap flows of the discrete ribs and the secondary flows are examined for the purpose of the reduction of thermally weak regions and the promotion of the uniformity of heat/mass transfer distributions as well as the ;augmentation of average heat/mass transfer. The rib-to-rib pitch to the rib height ratio (p/e) of 8 and the rib angles of 90° and 60° are selected with e/D$\_$h/=0.08. The vortical structure of the secondary flows induced by the parallel angled arrays are quite distinct from that induced by the cross angled arrays. This distinction influences on heat/mass transfer and friction loss in all the tested cases. The gap flows of the discrete ribs reduce the strength of the secondary flows but promote local turbulence and flow mixing. Consequently, the angled discrete ribs with the small gaps provide a more uniform heat/mass transfer distribution sustaining high average heat/mass transfer.
터빈 기익 내부관 열전달 증대를 위해 설치된 요철의 형상 효과
우성제,권혁진,조형희,Wu, Seong Je,Kwon, Hyuk Jin,Cho, Hyung Hee 대한기계학회 1999 大韓機械學會論文集B Vol.23 No.1
Heat transfer in a duct is augmented remarkably by rib turbulators. However, increasing friction loss is accompanied due to ribs disturbing flows. Hence, pressure drops and heat transfer are considered simultaneously to decide heat/mass transfer performance in a rib-roughened duct. In the present study, the effects of rib cross section shape on pressure drop through a duct are investigated as well as those on heat transfer characteristics. The results show that the characteristics of heat/mass transfer and friction loss in the duct roughened with triangular ribs are similar to those with square ribs, while significantly different from those with semicircular ribs. The best performance in the duct is obtained by using semicircular shaped ribs among three types of ribs for the large rib angles of ${\alpha}{\geq}63^{\circ}$.
우성제(Seong Je Wu),신창환(Chang Hwan Shin),조형희(Hyung Hee Cho) 대한기계학회 2001 대한기계학회 춘추학술대회 Vol.2001 No.9
Single-phase convection and partial nucleate boiling in free-surface and submerged jet impingements of subcooled water through a 2 ㎜-diameter circular pipe nozzle were investigated by local measurements. Effects of jet velocity and nozzle-to-impinging surface distance as well as heat flux on nucleate boiling were considered. Heat flux increase reduced the temperature difference between stagnation and far-downstream regions with the increasing influence of boiling in partial boiling regime. The change in nozzle-to-impinging surface distance from H/d=1 to 12 had a significant effect on the stagnation heat transfer of the submerged jet, not the free-surface jet. The submerged jet provided a worse cooling performance due to the temperature increase of the pool, thereby being more sensitive to the elocity variation from 1 to 3.9 ㎧.
권혁진,우성제,조형희,Kwon, Hyuk-Jin,Wu, Seong-Je,Cho, Hyung-Hee 대한기계학회 2000 大韓機械學會論文集B Vol.24 No.5
The influence of arrangement and length of discrete ribs on heat/mass transfer and friction loss is investigated. Mass transfer experiments are conducted to obtain the detailed local heat/mass transfer information on the ribbed wall. The aspect ratio (width/height) of the duct is 2.04 and the rib height is one tenth of the duct height, such that the ratio of the rib height to hydraulic diameter is 0.0743. The ratio of rib-to-rib distance to rib height is 10. The discrete ribs were made by dividing each continuous rib into 2, 3 or 5 pieces and attached periodically to the top and the bottom walls of the duct with a parallel orientation The combined effects of rib angle and length of the discrete ribs on heat/mass transfer ae considered for the rib angles $({\alpha})\;of\;90^{\circ}\;and\;45^{\circ}$. As the number of the discrete ribs increases, the uniformity of the heat/mass transfer distributions increases. For $(\alpha})=90^{\circ}$, the heat/mass transfer enhancement with the discrete ribs is remarkable, while the heat/mass transfer performances are slightly higher than that of the transverse continuous ribs due to the accompanied high friction loss penalty. For $(\alpha})=90^{\circ}$, the average heat/mass transfer coefficients and the heat/mass transfer performances decrease slightly with the discrete ribs compared to the case of the angled continuous ribs.
평면 충돌제트에서 노즐 깃이 단상 및 비등 열전달에 미치는 영향
신창환(Chang Hwan Shin),임성환(Seong Hwan Yim),우성제(Seong Je Wu),조형희(Hyung Hee Cho) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.4
The water jet impingement cooling is one of the techniques to remove heat from high heat flux equipments. We investigate the local heat transfer of the confined water impinging jet and the effect of nozzle collar to enhance the heat transfer in the free surface jet and submerged jet. Boiling is initiated from the furthest downstream and the wall temperature increase is reduced with developing boiling, forming the flat temperature distributions. The reduction in the nozzle-to-surface distance for H/W≤1 causes the significant increases and distribution changes in heat transfer. Developed boiling reduces the differences in heat transfer for various conditions. The nozzle collar is employed at the nozzle exit. The distances from heated surface to guide plate, H<SUB>c</SUB> are 0.25W, 0.5W and 1.0W. The liquid film thickness is reduced and the velocity of wall jet increase as decreased spacing of collar to heated surface. Heat transfer is enhanced for region from the stagnation to x/W~8 in the free surface jet and to x/W~5 in the submerged jet. For nucleate boiling region of further downstream, the heat transfer by the nozzle collar is decreased in submerged jet compare with higher velocity condition. It is because the increased velocity by collar is de-accelerated at downstream.