ABSTRACT

Research and development activity in the inter- and cross-disciplinary area of thermal drying has been escalating rapidly over the past two decades. It is clearly motivated by economic incentive to improve the operation to produce a better quality product at a lower cost in terms of resources, energy consumption as well as environmental impact. The focus to date has been on improving the engineering aspects of design and operation to produce “engineered” products of desired characteristics. Much remains to be achieved in the area of the material science aspects of drying e.g. the   prediction of quality parameters, which are product-dependent. What is needed is a generalised drying theory that incorporates the transient transport phenomena involved in drying along with appropriate models to account for the morphological changes as well as chemical processes that may occur during drying.

This paper focuses on the current developments in drying as well as recent trends. Some areas where more R&D is needed, which provide opportunities to make definitive contribution, will be identified. For example, sophisticated analytical measurements at the micro-scale are needed to examine the movement of moisture during drying and also any changes in the physical structure as well as solute transport that can occur in drying of foodstuffs or solids containing a dissolved solid in the liquid phase. Even today, there is need to devise more efficient and compact dryers. Whether we will ever need “micro-scale” dryers is a speculative question but certainly there will be the need to design dryers with high “volumetric” efficiency unlike most dryers built today.  Finally, there will be further developments and extended applications for superheated steam dryers, heat pump-assisted hybrid dryers and multi-stage dryers using different dryer types in each stage. Mathematical models for drying as well as dryers will continue to be in demand to allow reliable design and scale up as well as control of industrial dryers.