Thermal drying technologies : new developments and future R&D potential

Abstract

Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.

Thermal dehydration processes are highly energy-intensive and are found in almost all industrial sectors, accounting for 10 to 20 percent on national industrial energy consumption in developed countries. With escalating energy costs and need to mitigate environmental pollution due to emissions from combustion of fossil fuels, it is increasingly important to develop innovative drying technologies. Furthermore, drying also affects quality of the dried product due to physical and/or chemical transformations that may occur during the heat and mass transfer operation. With tens of thousands of products that are dried in hundreds of dryer types, it is a formidable task indeed to develop design and scale-up procedures of wide applicability. Attempts have been made over the past three decades to make fundamental and applied contributions to transport phenomena and material science aspects in drying of various forms of wet solids, pastes and liquids. This presentation will attempt to summarize the state-of-the-art as far as theoretical understanding of drying processes and provide examples of some new technologies being developed. Opportunities for challenging fundamental and modeling studies to enhance drying technologies will be identified. Illustrative results will be presented to show how mathematical modeling of spray, spouted bed and heat pump dryers can be utilized to develop new conceptual designs and to optimize operating conditions as a cost-effective route to intensify innovation in thermal dryer design.