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In this paper, constructal optimization of the twice Y-shaped assemblies of fins with six freedom degrees (characteristic parameters of geometry) is performed by employing finite element method and taking dimensionless maximum thermal resistance as a performance index, and the heat transfer performance of the twice Y-shaped assemblies of fins under various conditions with different freedom degrees are analyzed. The results show that the twice assemblies can improve the heat transfer performance of Y-shaped fin remarkably, and the minimum maximum thermal resistance of the twice Y-shaped assemblies of fins decreases by 36.37% compared with that of once Y-shaped assembly of fins. It is also proved again that the larger the number of freedom degrees for evolving is, the more perfect the system performance is. The effects of different characteristic parameters of geometry on the performance of the twice Y-shaped assemblies of fins are different, one should pay different attention to these parameters in practical engineering designs. The effects of two angles on the maximum thermal resistance are larger, but the optima of the two angles are robust. The effects of two height ratios on the maximum thermal resistance are more remarkable than those of two thickness ratios.constructal theory, fin, multi-scale, enhanced heat transfer, generalized thermodynamic optimization Citation:Xie Z H, Chen L G, Sun F R. Constructal optimization of twice Y-shaped assemblies of fins by taking maximum thermal resistance minimization as objective.
In this paper, constructal optimization of the twice Y-shaped assemblies of fins with six freedom degrees (characteristic parameters of geometry) is performed by employing finite element method and taking dimensionless maximum thermal resistance as a performance index, and the heat transfer performance of the twice Y-shaped assemblies of fins under various conditions with different freedom degrees are analyzed. The results show that the twice assemblies can improve the heat transfer performance of Y-shaped fin remarkably, and the minimum maximum thermal resistance of the twice Y-shaped assemblies of fins decreases by 36.37% compared with that of once Y-shaped assembly of fins. It is also proved again that the larger the number of freedom degrees for evolving is, the more perfect the system performance is. The effects of different characteristic parameters of geometry on the performance of the twice Y-shaped assemblies of fins are different, one should pay different attention to these parameters in practical engineering designs. The effects of two angles on the maximum thermal resistance are larger, but the optima of the two angles are robust. The effects of two height ratios on the maximum thermal resistance are more remarkable than those of two thickness ratios.constructal theory, fin, multi-scale, enhanced heat transfer, generalized thermodynamic optimization Citation:Xie Z H, Chen L G, Sun F R. Constructal optimization of twice Y-shaped assemblies of fins by taking maximum thermal resistance minimization as objective.
Drag reduction in heavy oil transport systems is a key for high-efficiency oil transfer and, thus, for energy conservation. In this paper, we investigated the influence of viscosity, velocity, and velocity-gradient fields on drag resistance in fluid flow with variable viscosity in terms of the field synergy. The theoretical analysis indicates that the drag during varying viscosity fluid flow processes depends upon not only the synergy between the velocity and its gradient over the entire flow domain but also the viscosity and velocity gradient at the boundary. That is, for a given flow rate or inlet velocity, simultaneously reducing the fluid flow field synergy number over the entire flow domain and decreasing the fluid viscosity and the velocity gradient at the boundary will lead to a smaller flow resistance. In addition, starting from the basic governing equation and via the calculus of variations, we derived Euler's equation, essentially the momentum equation with a special additional volume force, using the criterion of the minimum viscous dissipation rate to optimize the flow processes for varying viscosity fluid. For fixed flow rate or inlet velocity, solving Euler's equation will result in the optimal velocity and viscosity fields, leading to the minimized flow resistance. Finally, a thermal insulating transport process for heavy oil was taken as a testing case to demonstrate the application of the theory. The results show that generating longitudinal vortexes to enhance the heattransfer performance of heavy oil will facilitate the flow drag reduction. For instance, when the inlet heavy oil velocity and the external effective heat-transfer coefficient are 0.01 m/s and 2 W m -2 K -1 , respectively, the total viscous dissipation rate with a certain presence of longitudinal vortexes is decreased by 19% compared to the result without the vortexes.
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