Browsing by Author "Kheradmand, Saeid"

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Compound Heat Transfer Enhancement of Wavy Fin-and-Tube Heat Exchangers through Boundary Layer Restarting and Swirled Flow
(2018-08-01)
Sadeghianjahromi, Ali
;
Kheradmand, Saeid
;
Nemati, Hossain
;
Liaw, Jane-Sunn
;
Wang, Chi-Chuan
This study performs a 3D turbulent flow numerical simulation to improve heat transfer characteristics of wavy fin-and-tube heat exchangers. A compound design encompassing louver, flat, and vortex generator onto wavy fins can significantly enhance the heat transfer performance of wavy fin-and-tube heat exchangers. Replacement of wavy fins around tubes with flat fins is not effective as far as the reduction of thermal resistance is concerned, although an appreciable pressure drop reduction can be achieved. Adding two louvers with a width of 8 mm to the flat portion can reduce thermal resistance up to 6% in comparison with the reference wavy fin. Increasing the louver number and width can further decrease the thermal resistance. Also, it is found that the optimum louver angle is equal to the wavy angle for offering the lowest thermal resistance. Therefore, compound geometry with three louvers, a width of 12 mm, and the louver angle being equal to wavy angle with waffle height to be the same as fin pitch of the reference wavy fin has the most reduction in thermal resistance of 16% for a pumping power of 0.001 W. Adding punching longitudinal vortex generators on this compound geometry can further decrease thermal resistance up to 18%.
Heat transfer enhancement of wavy fin-and-tube heat exchangers via innovative compound designs
(2020-03-01)
Sadeghianjahromi, Ali
;
Kheradmand, Saeid
;
Nemati, Hossain
;
Wang, Chi-Chuan
;
機械工程學系
The present study examines some novel improvements in association with the airside performance of wavy fin-and-tube heat exchangers. Effects of waffle height, adding slits on wavy fins and vortex generators on the thermal resistance of wavy fin-and-tube heat exchangers are investigated. Increasing waffle height, imposing slits on the wavy fin, or adding vortex generators can provide 6-10% reduction in thermal resistance subject to constraints of the same pumping power. Yet, the compound design including all these three features together is even more powerful to achieve a 16% reduction of thermal resistance. Increasing waffle height will decrease thermal resistance, but the accompanied pressure drop is even higher. Hence, it is highly recommended that the waffle height should be less than the fin pitch or at a corrugation angle being less than 15 degrees. Punching slits on the top of wavy fin surface can result in 6-7% decrease in thermal resistance. Effect of increasing the width of slits on heat transfer characteristics is negligible. Conversely, increasing the length of slits is much more effective. It can be seen from the results that slits with a length of 12 mm and a width of 1 mm yield 8-10% reduction in thermal resistance.
OPTIMIZATION OF THE LOUVER FIN-AND-TUBE HEAT EXCHANGERS-A PARAMETRIC APPROACH
(2020-01-01)
Sadeghianjahromi, Ali
;
Kheradmand, Saeid
;
Nemati, Hossain
;
Wang, Chi-Chuan
;
機械工程學系
3D turbulent flow numerical simulations are performed to study heat transfer and flow friction characteristics of louver fin-and-tube heat exchangers. The effects of louver angle, fin pitch, transversal tube pitch, and longitudinal tube pitch on Colburn and friction factors are investigated in detail. Three stages of the effect of louver angle on the Colburn j factor are identified, including rising, level-off, and increasing again. A wide range for louver angle ranging from 0 degrees (plain fin) to 80 degrees is considered. Results show that the Colburn factor increases from a louver angle of 0 degrees (plain fin) to 20 degrees, followed by a level-off or slight decline until the louver angle reaches 45 degrees, and finally, the Colburn factor is increased again with a further rise of louver angle. However, the friction factor increases with an increase in louver angle from 0 degrees (plain fin) to 80 degrees. Colburn and friction factors are almost independent of fin pitch while they decrease with an increase in transversal and longitudinal tube pitches. The optimum louver angle is around 20 degrees upon carrying out the full factorial method in maximizing Colburn factor and minimizing friction factor.