| Summary: | 碩士 === 國立成功大學 === 機械工程學系 === 107 === In this article, we have investigated the effect of forced convection on the heat exchanger efficiency of non-Newtonian turbulence in the heat exchanger system. Therefore, we simulated the forced convection of a non-Newtonian fluid in a uniform three-dimensional twisted elliptical tube with uniform wall temperature are investigated using the finite volume approach. Flow resistance and heat transfer characteristics of nanofluids in the twisted elliptical tube are studied with the parameters including Reynolds number, power law index, and the twist pitch.Effects of the above-mentioned parameters on the performance of the twisted elliptical tubes are analyzed and the overall thermal-hydraulic performance is evaluated.
The simulation results show that the twisted elliptic tube with different pitches produces a rotation when the fluid flows through the twisted elliptic tube, which enhanced the heat transfer performanc. Although the heat transfer capacity can be improved, the disturbance caused by the pressure increases pressure drop.In addition, the effect of secondary flow on heat transfer is explained by the field synergy theory, and calculated the entransy dissipation rate in the elliptic twisted tube. When the Reynolds number and the n value increase and the pitch length is shortened, the entransy dissipation will increase, but the thermal resistance reduces. The overall heat transfer efficiency is better; but considering the influence of frictional impedance, there will be a higher thermal performance factor when the Reynolds number is lowered. The above conclusions have high added value and applicability for the design of the new heat exchanger.
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