Development and performance evaluation of a refractance window drying system for production of quality bioproducts

Abstract

Reliance on low-level technology in Uganda, is one of the key constraints to reducing postharvest losses and producing high value processed products that can fetch good prices not only locally but also in the export markets. Refractance Window Dryer (RWD) system, therefore, is one of the novel drying technologies that have been identified to reduce postharvest losses in Uganda. The purpose of the study was to develop and carry out a performance evaluation of a cost-effective RWD miniature. Using SolidWorks 2019 CAD software, the machine was simulated and meshed using the finite element method (FEM). The system was simulated and analyzed for stress, displacement, and thermolysis. The meshing tool made the problem solvable (Maximum stress was determined by meshing nodes and elements) which reduced the degrees of freedom from infinite to finite with the help of discretization. The results showed that the highest stress 1.645 N/m2 was below the machine’s selected material (stainless steel) yield strength of 6.20422 x 108 N/m2, with maximum and minimum strain of 4.96 x 10-9 and 1.124 x 10-12 respectively, which indicated that the boiler moved slightly out of position with no significant bending. A maximum heat flux of 81.2 kW/m2K, occurred at a maximum acoustic power of 3.084 x 10-14 W/m3. The heat flux and the computational fluid dynamics analysis (CFD) results, confirmed that the material selected for the hot water flume does not undergo thermolysis (thermal deterioration) at the selected working parameters. The machine’s throughput was 1 kg/hr at an evaporative energy of 171 kJ/kgH2O. The drying time was 40 minutes for tomato puree from 1567 % to 15.0 % MC db. and 55 minutes for mango pulp from 614 % to 11.0 % MC db. at a pre-heating temperature of 95℃. The machine consumed 4.41 kWh and 4.08 kWh while drying mango pulp and tomato puree respectively. The machine’s thermal efficiency was 23.81% and 21% while drying mango pulp and tomato puree respectively. The project economic analysis was done, and the results indicated that the project is feasible; the total project cost was US$ 2,322, the annual operational cost predicted was US$ 6,013.68 and the annual overhead cost was US$ 712.8. The total annual expenditure was US$ 6,726.4, and the predicted total expenditure after five operational years was US$ 35,953.4. The predicted yearly gross income was US$ 8,553.6 with a net income stream per year of US$ 1,827.12. The machine was efficient, economically viable and a suitable unit for dehydrating moist materials for laboratory use (pilot-scale study) and medium-scale industries for drying of bio-products.