Exergo-economic criteria for performance evaluation of enhanced heat transfer duct with constant wall temperature

Combining the first and second laws of thermodynamics with the exergo-economic theory, the exergy-economic performance of enhanced duct in comparison with reference smooth duct subjected to constant wall temperature have been examined comprehensively under three design constraints. Extended exergo-economic performance evaluation criteria formulas, i.e., the net profit per unit transferred heat load (ηp) and the total cost per unit transferred heat load (ηc) have been obtained from the perspectives of exergy recovery and exergy destruction respectively, accounting for all potential factors such as heat transfer, flow and investment costs. The application of exergo-economic performance evaluation based on ηp and ηc is illustrated by selecting a spirally corrugated duct as an example. The results for different design constraints show that the exergo-economic performance of enhanced duct is largely determined by Reynolds number (Rea) and dimensionless inlet temperature difference (θ). There exist critical values of Rea and θ exceeding which ηp of enhanced and smooth ducts would be less than zero, showing no engineering significance; however, ηc of enhanced and smooth ducts is unconditionally greater than zero due to their specific physical meaning. For all the three design constraints, better exergo-economic performance for enhanced duct can be achieved provided that Rea and θ are in the desirable ranges.