Solar drying of henna (Lawsonia inermis) using different models of solar flat plate collectors: an experimental investigation in the region of Biskra (Algeria)

In this article, an experimental study is presented in two parts: First, the best performing solar dryer is selected between two models of flat plate solar collectors (FPCs). The second part investigates the drying behavior of henna (Lawsonia alba, syn. Lawsonia inermis Linn.) using the best selected FPC. The aim of this study is to get a clean product in a reduced time by using solar FPCs. Therefore, we first present the results of an experimental investigation on the thermal performances and pressure drops of two models of FPCs for indirect drying applications: i) simple-pass collector with trapezoidal obstacles (model I) and ii) double pass collector with trapezoidal obstacles in the air flow duct (model II). In the second part, we compare different methods of henna drying; we have proceeded to the application of the best indirect dryer (model II) for drying of henna under climatic conditions of Biskra, Algeria. As a result, some conclusions are made on the drying behavior of henna by the study of the influence of: drying process, air flow rate and masse of the product on the drying kinetic of the product for the forced convection hot air drying and their temperature dependence.