The plate and frame heat exchanger was one of the first compact exchanger to be used in the UK process industries, being originally introduced in 1923: the first plates were made of gunmetal. It is currently second to the shell and tube heat exchanger in terms of market share.
These exchangers are relatively compact and lightweight heat transfer surfaces, making them attractive for use in confined or weight-sensitive locations such as on board ships and oil production platforms. Pressures and temperatures are limited to comparatively low values because of the gasket materials and construction.he most variant of the plate and frame heat exchanger consist of a number of pressed, corrugated metal plates compressed together into a frame.
These plates are provided with gaskets, partly to seal the spaces between adjacent plates and partly distribute the media between the flow channels.
These exchangers are usually built of thin plates (all prime surfaces). Generally, exchangers cannot accommodate very high pressures, temperatures, and pressure and temperature differentials. The most common plate material is stainless steel.
The heat transfer surface consist of number of thin corrugated plates pressed out of a high grade metal. the pressed pattern on each plate surface induces turbulence and minimizes stagnant areas and fouling. Unlike shell and tube heat exchangers, which can be custom-built to meet almost any capacity and operating conditions, the plates of plate and frame heat exchangers are mass-produced using expensive dies and presses. Therefore, all plate and frame heat exchangers are made with may appear to be limited range of plate designs.
The plate pack is clamped together in a frame suspended from a carrying bar. Gaskets are fitted to seal the plate channels and interfaces. the frame consists of a fixed frame plate at one end and a movable pressure plate an the other. The movable plate facilitates access for cleaning or exchanging the heat transfer surfaces. The feature of this type of heat exchanger is the ability to add or remove surface area as necessary.
The plates are grouped into passes with each fluid being directed evenly between the paralleled passages in each pass. Whenever the thermal duty permits, it is desirable to use single pass, counter flow for an extremely efficient performance. Although plate and frame exchangers can accept more than two streams, this unusual. Two-pass arrangements are , however, common.
Plates can be produced from all press able materials . The most common construction materials are:
- Stainless steel (AISI304, 316)
Usually the frame is made of coated mild steel, as it should not under normal circumstances, come into contact with the process fluids. The surface coatings vary according to the exchanger environment. Frame can be stainless steel or clad with stainless steel as an alternative to mild steel.
Gasket properties have critical bearing on the capabilities of a plate heat exchanger. in the terms of its tolerance to temperature and pressure.
Gaskets are commonly made of:
- Nitrile rubber
Care should be taken in locating the gaskets during reassembly, as imperfect sealing is the main disadvantage of the plate and frame heat exchanger.
The operating limits of gasketed plate and frame heat exchanger vary slightly from manufacturer to manufacturer. Typically, the operating temperature range of the metal plates is from -35oC to +200oC. Design pressures up to 25 bar can be tolerated, with test pressures to 40 bar.
Heat transfer areas range 0.02 m2 to 4.45 m2 (per plate). Flow rates of up to 3500 m3/hr can be accommodate in standard units, rising to 5000 m3/hr with a double port entry. Approach temperature as low as 1oC are feasible with plate and frame heat exchangers.
The surface pattern on the plates tends to induce good mixing and turbulence, and in general this type of heat exchanger has a low propensity for fouling. Fouling resistances of typically 25% of those for shell and tube heat exchangers have been measured by Heat Transfer Research Incorporated (HTRI) in the USA.