Entropy generation analysis for laminar thermal augmentation with conical strip inserts in horizontal circular tubes

• Thermal augmentation with conical strips is studied based on entropy generation.
• Entropy generations of tubes with non-staggered strips are ∼81% of staggered ones.
• Effects of geometrical parameters of inserts on irreversible losses are studied.
• Entropy generation is sensitive to geometry angle with relative variation of ∼30%.
• The concave curve between entropy generation number and Re has a pit at Re = 600.

Our previous investigations demonstrated that conical strip inserts have good thermo-hydraulic performances based on evaluation criteria of the First Law of Thermodynamics. The present work is dedicated to further analyze the performances of these inserts from a viewpoint of entropy generation. Effects of alignment method and geometrical parameters on entropy generations of laminar heat transfer in the tubular flow are investigated. Local entropy generations are presented for discussion. Results show that entropy generation rates caused by non-staggered strips are about 81.1% that of staggered alignment, while the heat transfer rates and PECs of the former are about 33.8% and 13.5% larger than the latter counterparts, respectively. Moreover, the entropy generation rate (and thus irreversible loss) caused by heat transfer process overwhelms the counterpart by viscous flow. The total entropy generation number of enhanced tube, ranging between 0.0657 and 0.0975, is most sensitive to geometry angle with a maximum averaged relative variation of 32.2%. Its variation trend with Re is concave with a pit at Re = ∼600. In brief, non-staggered inserts with a larger geometry angle and smaller strip-wall gap and pitch, facilitate a better thermo-hydraulic performance at Re = ∼600 from the viewpoint of exergy loss reduction.