Experimental Investigation of heat transfer and fluid flow characteristics of circular tube with perforated inserts

Abstract

The thermal performance of heat exchangers is increased using the passive technique in which the nature of fluid flow in the boundary layer is revived. However, the enhanced heat transfer is accompanied by a considerable rise in frictional losses. newlineAn experimental set-up is designed and fabricated according to literature review. Multiple perforations are drilled along the center line of the tape to attain the porosity ratio of 0.045. V cuts are introduced in the perforated twisted tape on one of its longitudinal edges. The relative pitch ratio is the ratio of pitch length of V cuts to the pitch length of twisted tape and is varied from 1 to 2. Later V cuts are introduced on both the longitudinal edges of the tape. Subsequently, multiple V cuts are made on both edges of tape by keeping the distance between the consecutive V cuts equal to half of the pitch length. newlineThe present study investigates the thermal and frictional characteristics of the tube fitted with modified twisted tape. It is found that V cut in the twisted tape brings considerable enhancements in the Nusselt number concerning the simple and perforated twisted tapes. Nusselt number of twisted tapes increases in the order of solid twisted tape, perforated twisted tape, perforated twisted tape with double V cuts having dcW equal to 0.2 and wcW equal to 0.2, and perforated twisted tape with double V cuts having dcW equal to 0.27 and wcW equal to 0.27. The formation of double V cuts, i.e., on both sides of twisted tape edges brings out considerable enhancement in heat transfer. The optimum value of thermos hydraulic performance parameter reaches 1.88 by the use of perforated twisted tape with multiple double V cuts having dcW equal to 0.27 and wcW equal to 0.27. The entropy generation analysis reveals that the perforated twisted tape having a twist ratio of 3 enhances the heat transfer at the cost of minimum exergy destruction. The minimum value of the entropy generation number corresponds to PTT. newline newline