Numerical optimization of flow-heat ducts with helical micro-fins, using Entropy Generation Minimization (EGM) method

摘要

An enhancement of heat transfer in heat exchangers channels is always associated with increased pressure drop and energy for pumping - especially when the channel wall is not smooth. Bearing in mind entire channel as a thermodynamic system, there are two irreversible "competing" processes - fluid flow and heat transfer, which cause entropy generation in it. In the literature, this method of analysis was called Entropy Generation Minimization (EGM) or Thermodynamic Design (THD). In this paper are presented theoretical basis and geometry formulation for considering cases and results of numerical simulations for fully developed 3D flow in tubes with micro-fins on the wall. As a parameter, was examined helical angle of micro-fin (referred to the axis tube). This angle was changed in the range from 0 (grooves parallel to the axis) to 90 degrees (grooves perpendicular to the axis). To realize numerical simulation ANSYS-CFX code was used. Before numerical investigation, for tube with helical angle of 30 degrees, verification of calculation code has been carried out. Comparison results of numerical simulations and experiment (obtained from a specially built stands) gave a good correlation, especially for the SST turbulence model. On this basis, the results obtained from simulations, for other angles are also credible. The 3D-chart presents results in dimensionless and normalized coordinates. Generated entropy and its minimum is shown as a function of the helical angle and Reynolds number. Additionally, on the graph, the distributions of the heat transfer coefficient on the grooved surface for studied angles were shown - as an example of visualization capabilities.