Heat Transfer and Flow Characteristics Through Acentric Twisted Oval Tubes: A 3D Numerical Investigation

Tube oval- twisting techniques have been consistently used to promote heat transfer and flow turbulence properties within tubes, enhancing flow mixing, disturbing boundary layers, and hence, offering higher thermal efficiency. However, the acentric twisted oval tubes have more intricacy as compared with twisted oval tubes due to the eccentricity of their twisting pattern and using them in heat transfer. The current study performs 8 configurations of the acentric twisted heating oval tube that is exposed to a constant heat flux of 1750W/m². In addition, 2 cases of the typical centric twisted oval and plain circular tubes for comparison purposes under a turbulent flow regime, 10000 ≤ Re ≤ 50000. The momentum, continuity and energy equations were solved by the chosen RNG k-ε model. The main parameters of Nusselt number Nu, friction factor f and thermal performance factor TPF for the air flows are examined at various aspect and eccentricity ratios. The results are compared to each other in all cases and with the typical plain tube and the well-established centric twisted oval tube. The results show a maximum increase in Nusselt number and friction factor of 196% and 182%, respectively, more than those of the plain tube. The acentric twisted oval tubes provide better thermal performance with an optimal value of TPF=1.61, which is 61% higher than the plain tube. The Nusselt number is almost 30% greater than that of the typical centric twisted oval tube, and the thermal performance factor is (TPF=1.24) at the same conditions. This valuable enhancement may support the heat exchanger industry, boosting energy savings and carbon dioxide emissions.