Views:1 Author:Site Editor Publish Time: 2020-06-18 Origin:Site
Plate heat exchangers (PHE) consist of a series of thin corrugated plates hung from a carrying bar and clamped between a fixed and movable head plate. The corrugated plates or heat transfer plates are normally stainless steel or other materials ductile enough to allow pressing. Each heat transfer plate is fitted with an elastomeric gasket, partly to seal and partly to distribute the process fluids. Connections in the fixed or movable head plates permit the entry of the process fluids into the plate pack. Differentiating a heat transfer plate from a channel is extremely important and fundamental to the analysis of PHEs. The heat transfer plate separates the two process fluids; the channel is the space established by two heat transfer plates, through which process fluids are distributed and heat transfer is carried out. Figure 1 details the major components of a PHE. Nomenclature describing PHEs is not standardized, and alternate names are used by various manufacturers.
CONVENTIONAL HEAT EXCHANGERS
Today’s conventional heat transfer plate designs are classified as chevron or herringbone type, with the corrugations forming a series of patterns. Each plate size is pressed with two different chevron angles, Figure 2, the low theta plate and high theta plate, and have acute and obtuse apex angles, respectively.
The gasket groove on these conventional-style plates is recessed 100%, Figure 3, so that there is always a front and back to each plate. By having the gasket groove recessed 100%, the plates can only be rotated about the Z axis. The channels are formed by alternately rotating adjacent plates 180° about their Z axis so that the arrow heads of the chevron angles point in the opposite direction. When two plates are adjacent to each other, the thermal and pressure drop characteristics of that channel depend strongly on the angle at which corrugations cross each other. With two different patterns, low and high theta, three distinctly different channels can be formed, each having their own hydrodynamic characteristics.
• H Channel. Two plates with obtuse angles and high theta are placed together forming a high-theta channel, characterized by high pressure drop and high temperature changes across the plate, Figure 2.1.
• L Channel. Two plates with acute angles and low theta are placed together forming a low-theta channel, characterized by low pressure drop and modest temperature changes across the plate, Figure 2.2.
• M Channel. Combining one high-theta plate and one lowtheta plate to form a medium-theta channel, having characteristics that fall somewhere between those of an H and L channel, Figure 2.3.