Plate Type Heat Exchangers

Plate type heat exchangers were originally developed for the milk industry where daily cleaning is necessary. They were first used at sea, as coolers, in the 1950s.

plate type heat exchangers

The plates are metal pressings, corrugated with horizontal or chevron pattern corrugations. These make the plates stiffer and therefore permit the use of thinner material. They also increase the heat exchange area and produce a turbulent flow. All these factors contributes to the efficiency of heat transfer. Turbulence, as opposed to smooth flow, causes more of the liquid passing between the plates to come in contact with them. It also breaks up the boundary layer of the liquid which adheres to the metal and act as a heat barrier in smooth flow. However, the turbulence can cause plate damage due to erosion and materials normally used in tube coolers for seawater contact, may not be suitable in plate coolers.

Plate material for seawater contact is titanium. This is an expensive metal but apparently able to withstand the conditions of service. Aluminium-brass has been used with poor results. Possibly failure of Aluminium-brass has been due to the presence of organic sulphides and other chemicals in coastal and inland waters. Titanium is immune from this type of attack. However, other factors such as turbulence in plates coolers or changes in the materials of the seawater system may be responsible for early failures. Stainless steel has been used in plate coolers for duty with seawater, but proved unsuccessful although it is suitable for other applications.

In plate type heat exchangers, the joint material is normally ‘nitrile rubber’ which is bonded to the plate with suitable adhesive such as ‘Plibond’. Other joint materials for higher temperatures are available, such as compressed asbestos fiber (CAF). The nitrile rubber is suitable for temperatures about 100 deg. Celsius. At higher temperatures the rubber hardens and looses its elasticity. The rubber joints are compressed when the cooler is assembled and clamping bolts tightened.

Over tightening can cause damage to the chevron corrugated plates. Also pressure drop across he cooler increases due to over tightening. At the same time loosely tightened plates results in inefficient sealing between plates. Dimensions are checked during tightening and loosening of plate cooler . Joints must be adequately clamped to prevent leakage.

All liquids inlets and outlets are a the fixed end plate. The movable ends sits in the horizontal carrying bars and he plates are also located and supported by these. The flow ports at the corners of the plates are arranged so that the cooling liquid and the liquid being cooled pass between alternate pairs of plates. Best efficiency is obtained by liquids moving in opposite directions. Joint leakage is visible externally except for the double joint at the ports on one side of the plate. A drain hole act as a tell-tale for his section.

REFERENCES

“General Engineering Knowledge” by H.D. McGeorge

 

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