Drying: a fascinating unit operation

This special issue contains a selection of papers presented at the 12th International Drying Symposium, held from 28 to 31 August 2000, in Noorwijkerhout, The Netherlands. Other selections are presented in special issues of Drying Technology [1,2]. The proceedings are published by Elsevier Science [3]. The final programme and some background information can be found at website http://www.ids2000.tue.nl. In this journal, it might be worthwhile to make a few statements about drying in the context of chemical engineering. In 1972, Keey [4] wrote in the preface to his first book: “Drying is a commonly practised art, but a neglected science, at least by workers whose mother-tongue is English.” And in Chapter 1 of his book: “The reasons for drying are almost as diverse as the materials that are dried.” And one more statement: “The diversity of purpose is matched by the diversity of methods.” Now, three decades later, the diversity has not decreased; but what about the art and science? For extending drying as a science, the development of a “drying community” was very important. The following initiatives in the past have been invaluable: organising of the International Drying Symposia by Arun Mujumdar, start of the journal Drying Technology, and the publication of a series of handbooks and monographs. As a result of the founding of national working parties on drying in a number of countries, the EFChE has incorporated a Working Party on Drying. All these initiatives have roused great interest, enthusiastic participation and cooperation from workers in the field, all coming from a very diverse world. Meanwhile, the International Drying Symposium has found a firm basis in the International Advisory Panel. In many respects, drying remains still an art, but its character is changing from alchemy and craftsmanship to inspired virtuosity. The science of drying is no longer neglected; it is flowering. However, both in the world of drying itself and in that of chemical engineering, appreciation and application still have considerable room for improvement. For this reason, we will touch upon a few aspects of drying in general,