Screening analyses and thermal-hydraulic performance optimization of flat-plate solar air heaters with longitudinal vortex generators

Abstract

The thermal-hydraulic performance of solar collectors depends on the ability of the working fluid to remove the heat stored on those devices. Basically, the benefits of heat transfer enhancement by using special surface geometries are due to an increase of the convective heat transfer coefficient or/and surface area. The use of modified surfaces reduces the thermal resistance and thus provides an increase of the convective heat transfer coefficient. However, the heat transfer enhancement is always associated with pressure drop increasing. This research deals with the numerical investigation of the thermal-hydraulic performance of flat-plate solar air heaters with two kinds of longitudinal vortices generators (LVGs): delta and rectangular winglets vortex generators. The LVGs enhance the heat transfer through secondary vortices generation with low pressure losses. It is well known that there are a lot of parameters which can affect the thermal-hydraulic performance of LVGs. Thus,it is evident that the amount of the design of experiments to maximize the thermal-hydraulic performance of this type of surface can be enormous. Based on this,it used a non-parametric method for screening the input parameters (via Smoothing Spline ANOVA method)to evaluate the contribution of the input variables and their interactions on the thermal-hydraulic performance. A surrogate-based optimization process has been proposed in order to maximize the thermal-hydraulic performance through the selection of the most important LVG geometrical parameters. (AU)