Numerical Study On Vortex Generators Enhancing Flow And Heat Transfer Performance Of Vertical Rectangular Channel

In this paper, vortex generators strengthening the unsteady natural convection flow and heat transfer, which were set up on the collector surface in the solar chimney power plant system, was researched with numerical methods. Heat effects of the vortex generators were evaluated combining with the principle of field synergy. Then associative equations of the heat transfer and flow friction when ribs sizes were taken into account were fitted. All these would provide theoretical basis for the latter engineering design of the solar chimney power plant system with vertical collectors.Triangular winglets and rectangular diagonal inner rib pairs were respectively designed and arranged on the collector surface in vertical rectangular channel of the system, and the number of ribs, rib inclination and arrangement influence on the temperature and velocity difference of the airflow between the inlet and outlet were analyzed, so as the influence of ribs sizes on heat transfer and flow friction of the system. Based on these, the associative equations of heat transfer and flow friction of the airflow in the channel of the system were fitted as Reynolds number was in a certain range. The results show that:(1) Because of vortex generators arrangement, the velocity difference and temperature difference of the airflow between inlet and outlet increased sharply; As the number of ribs increased, the synergy angle between velocity and temperature gradient decreased because the disturbed effect enhanced, but energy loss increased as the flow friction increased; As the rib angles increased, average synergy angle decreased, the temperature difference between inlet and outlet increased; Heat transfer enhancement ratio Nu/NuO and friction ratio Cf/Cf0 were increased with the increase of Re; As Re increased, the thermal coefficient of performance was increasing and thermodynamic coefficient of performance of all channels were greater than 1.(2) From the heat transfer and flow friction characteristics correlations by multivariate regression, the relative rib length (relative rib width), the relative rib height, and circumferential rib density increases can enhance the effect of heat transfer, increasing the relative rib spacing would weaken the convective heat transfer because the disturbed effect of airflow was reduced; The flow friction increased when he relative rib length (relative rib width), and relatively high ribs circumferential rib density increased, or the relative spacing of the ribs decreased.(3) Comprehensive compared the synergy degree of air velocity and temperature gradient, the average heat transfer enhancement, the average flow friction and the average coefficient of thermal performance of the flow channels respectively arranged the two vortex generators, for the vertical channel in the solar chimney power plant system with vertical collectors, the strengthening effect of triangular winglets was more suitable.