A Method for Determination of Porosity Change from Shrinkage Curves of Deformable Materials

The novel low-cost band thermodynamic dryer equipped with a solar collector, a parabolic focusing collector, a heat exchanger, screw fan, and a drying cabinet with a band was designed and tested. The maximum temperature in the solar collector reached 85°C, which was 55°C above the ambient temperature. The required drying time was 4.5 h, much reduced from the traditional solar drying time of 48 h. The final moisture content of the Roselle calyx was 12% w.b., which is the recommended storage moisture content. Measurements of ambient temperature and humidity, air temperature, and relative humidity inside the dryer as well as solids moisture loss-in-weight data are employed as a means to study the performance of the dryer. Solar drying was compared with conventional sun drying and heated air drying, using the following evaluation criteria: drying time, dried Roselle color, texture, taste, and production cost. For evaluation, a model-based Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) methodology was used. After the evaluation, the proposed continuous solar dryer was found to be better than conventional drying and heated air drying due to slower drying rate and better quality of the dried Roselle.