Study on heat transfer and fluid flow characteristics with short rectangular plate fin of different pattern

A detailed experimental investigation of the heat transfer and fluid flow characteristics of finned surfaces was conducted for airflow (ReL = 6250–25,000) at a flat plate boundary layer and narrow duct corresponding to 200 mm and 20 mm duct height, respectively. Short rectangular fins of either aluminum or resin material were attached in 7 × 7 arrays to a heating surface and the fin height, inclination angle and fin pattern (co-angular and zigzag) were varied. The fin spacing to length ratios along the streamwise and spanwise directions were kept at Sx/L = 2 and Sz/L = 1, respectively. T-type thermocouples and an infrared camera with a 160 × 120-point In–Sb sensor were used to measure the wall temperature and the detailed heat transfer at the endwall along with fin base. Dye flow in a water channel and titanium oxide oil film flow patterns around the fins were observed to study the flow behavior and its effect on heat transfer. In case of co-angular pattern flow stagnated in front of the fin and formed a strong horseshoe vortex around the fin while the longitudinal vortexes generated by the side top edges touched the fin surface and the endwall. On the other hand in case of zigzag pattern a weak horse shoe vortex appeared in front of the fin while the longitudinal vortex struck the endwall mainly and a sinusoidal wavy flow behavior was observed. The friction factor value was found to be almost constant and somewhat larger for a zigzag pattern of fins than for a co-angular pattern. The heat transfer results show that a narrow rectangular duct of 20 mm height with fin arrays in a zigzag pattern is the most effective, exhibiting a heat transfer enhancement at the endwall of more than four times over the case without fins wherein co-angular is the least recommended as it exhibits enhancement about a factor of more than three times. At flat plate boundary layer, i.e. in tall duct case both co-angular and zigzag patterns show almost same overall heat transfer enhancement about a factor of three times over the case without fins.