Thermodynamics and heat transfer study of a circular tube embedded with novel perforated angular-cut alternate segmental baffles

Abstract

Baffles are used for heat transfer enhancement in heat exchanger tubes. However, they also increase the friction factor in the flow channel. Perforation in baffles further augments the heat transfer. Moreover, it was also noticed that the perforations in the baffles strongly reduce the associated pressure drop in the tube. Some novel ideas for baffles therefore need to be produced, which can cumulatively intensify the performance of the heat exchanger conduit. Therefore, in the present study novel design of perforated angular-cut baffles is considered for the experimental investigation in the turbulent flow regime for thermodynamic and heat transfer investigation. Air is taken as the working fluid with Reynolds number varying from 10,000 to 52,000. Two arrangements of baffles, viz. inline and alternate, are considered for the experimentation. The parameters considered for the investigation are as follows: three perforation ratios (H), two angles of attack, (α) and two pitch ratios (P). The results obtained from the investigation show an enhancement in Nusselt number, Nu, and friction factor, f, both. The highest augmentation in heat transfer is noted for alternate segmental baffles (ASB) with a perforation ratio (H) of 0.15, a pitch ratio (P) of 0.1 and an angle of attack (α) of 45°, while for segmental baffles (SB), a perforation ratio (H) of 0.20, a pitch ratio (P) of 0.2 and an angle of attack (α) of 30° give the minimum heat transfer. An increase in heat transfer coefficient is also noticed with an increase in angle of attack (α). ASB show superior heat transfer compared to SB, and ASB have an enhanced Nu compared to SB for a pitch ratio of 0.1, an angle of attack of 45° and a perforation ratio (H) of 0, 0.15 and 0.2, which is about 39.5%, 37.9% and 42.18%, respectively. Nusselt number, Nu, and friction factor, f, correlations were proposed, and a good agreement was found between the test obtained data and predicted data. The thermo-hydraulic performance parameter for all the examined cases was greater than unity.