Optimization of a Solar Bubble Dryer for drying rice and other commodities

Postharvest losses in Southeast Asian countries are typically 15–25% in weight and, when quality is factored in, can result in an additional 10–20% loss of value in the market. The reduction of postharvest losses would significantly improve food security and ensure healthy rice for consumers. Rice is harvested at 20-24% moisture content and needs to be dried within a day to safe moisture content of 14%. Due to high cost and complexity of conventional heated air dryers, farmers and the rice processing sector still rely mostly on sun drying done by spreading the paddy in the open under the sun. Delays due to unfeasible weather especially in the wet season, uncontrolled temperature and contamination with dirt and microorganisms cause 3-7% physical loss and a large portion of the quality loss. Solar drying is carbon neutral and as an alternative to heated air dryers prevents the emission of CO2 during drying. Existing mechanical dryers, however, require high investment cost and usually large amounts of paddy for drying to break-even and are therefore out of the reach of farmers in developing countries.

With funding from the Small Grant for IARC from BMZ a research consortium has developed the Inflatable Solar Dryer - ISD, which is commercialized by the trade mark “Solar Bubble Dryer”. The consortium consisted of the International Rice Research Institute (IRRI), Hohenheim University (UHOH) and the private company GrainPro Philippines, Inc.  UHOH has developed a computer model for simulating air flows in solar drying tunnels used for designing the tunnel, GrainPro did the prototyping for different ISD technology iterations and IRRI provided the knowhow on rice, did the testing on the IRRI experiment station and verification through IRRI programs with partners in different countries through IRRI’s postharvest networks.

This project aims at optimizing the Inflatable Solar Dryer in a continued collaboration between IRRI and University of Hohenheim in order to improve the drying process and to significantly reduce costs of the technology. Hohenheim researchers will employ advanced modeling techniques via Computational Fluid Dynamics (CFD) to simulate improvement scenarios and propose optimization strategies for the ISD. Simulations will be validated on optimized prototypes.