A. Introduction

The scraped surface exchanger (SSHE) is a specialised heat exchanger which is invaluable for certain difficult applications. Although it is sometimes described as a combination of a mixer and a heat exchanger it is really only the enhanced heat transfer, induced by the scraper blades, that is the main feature.

Most applications involve highly viscous liquids (i.e. liquids having large molecules) or liquids containing particulates. As a consequence the fluid behaviour then becomes non-Newtonian. Furthermore this non-Newtonian viscosity changes significantly during the progression through the heat exchange process, particularly in cooling applications.

For this reason there are, as yet, no straightforward design equations that can easily be applied to any specific process application. Most selections are made on the basis of comparison with prior experience or through the use of pilot plant tests and subsequent scale up. This service is offered by most SSHE manufacturers.

On the other hand, by examining the detailed behaviour characteristics of the SSHE, it is possible to assess the main factors that affect design, selection of the equipment or choice of operating conditions. This is the approach followed in this note.