Combined solar and membrane drying technologies for sustainable fruit preservation in low-income countries – prototype development, modelling, and testing

Abstract This investigation consisted of developing and evaluating solar dryers together with semi-permeable membrane pouches for drying juicy fruits in low-income tropical countries. Two design iterations were carried out including prototype modelling and testing. The latest developed solar dryers were a passive and an active solar dryer. Modelling was initially carried out mathematically using an equation solver software followed by computational fluid dynamics. Preliminary measurements were carried out on a small-scale solar dryer. Thereafter, full-scale models were developed and tested, both in laboratory and in real conditions in Mozambique. Results from modelling were validated against measurements in laboratory in Sweden and field trials in Mozambique. Prototype building and testing in Mozambique was undertaken in collaboration with local farmers and a university. Measurement results show that the dryers help to prevent microbial growth through increased temperatures. The drying flux was increased by 50% for the passive, and by 100% for the active solar dryers compared to the ambient controls that did not use a solar dryer. The total drying time was below four days for all pouches in the dryers. The active solar dryer was shown to have the shortest drying time and the highest capacity (more pouches) but also the highest costs. Mould growth and juice fermentation were observed on control pouches drying in open air. These problems were solved with the use of solar dryer technology. However, some challenges with the membrane pouches require further development including degradation of the membrane when exposed to direct sunlight.