Plate exchangers are constructed of nearly rectangular plates rounded at the corners and separated by gaskets located near their edges (Figure 8-1). Their assembly is shown in Figure 8-2. The volume bounded by two or more plates and their gaskets contains the flowing fluids. This applies to each side of each plate. The area within these boundaries is heat transfer surface. This construction is ideal in many applications. Several improvements have been made in the basic concept to enhance the heat transfer characteristics of this construction. Seal welds are sometimes used, omitting the need for gaskets. Other improvements will be described in this chapter.