Numerical evaluation of improved solar dryer for agricultural applications

In the present work, performance of solar dryer having evacuated tube collector was enhanced by artificial roughness with circular rib for agricultural applications. The influence of roughness geometry parameters i.e. relative roughness pitch (P/e) of 12 and relative roughness height (e/D_h) of 0.057 on Nusselt number and friction factor has been investigated. Reynolds number considered for investigation varied from 2500 to 8000. Rughened solar evacuated tube collector performed better than smooth solar evacuated tube collector. Nusselt number augments with the increase in Reynolds number while friction factor shows an opposite trend with increase in Reynolds number. Maximum enhancement ratio of Nusselt number and friction factor is 1.54 and 2.43, respectively, obtained at Reynolds number of 8000. The value of thermo-hydraulic performance parameter for circular rib roughened solar evacuated tube collector varied between 1.09 - 1.15 over the entire range of Reynolds number.