Numerical study on the heat transfer performance of trifoliate petal twisted helically coiled tube based on multi-objective optimization

In this study, the heat transfer and flow resistance characteristics of a trifoliate petal twisted helically coiled tube (TPTHCT) were numerically studied. First, a mathematical model of the TPTHCT was established and the enhanced heat transfer mechanism was analyzed. Secondly, the TPTHCT and the smooth helically coiled tube (SHCT) were comparatively investigated mainly on the parameters of heat transfer coefficient (h), pressure drop (|Δp|), heat transfer effectiveness (ε), and heat transfer exergy loss number (ξHT). Finally, a Multi-Objective Genetic Algorithm (MOGA) was utilized to optimize the TPTHCT. The results indicate that an additional torsional force exists in the TPTHCT, which causes a more complex flow state and makes the temperature distribution more uniform. For the same working condition, h increased (by a maximum of 40 %), |Δp| increased (by a minimum of 50 %). ξHT consistently exhibited an opposite variation trend with ε at the same inlet temperatures ratio (τ); further ξHT can describe the effect of changes in τ, whereas ε cannot. The best result from the optimization was achieved with the objective function being maximum h, minimum |Δp|, and minimum ξHT; and the optimal structural parameters were Rco = 25.1 mm, P = 93.2 mm, di = 8.8 mm, r2 = 0.3, θ = 432°, a = 0.16, E = 151 mm.