Gasketed Plate Heat Exchangers
The plate heat exchanger is the most widely used configuration in geothermal system of recent design. A number of characteristics relative to geothermal application are responsible for this.
Those characteristics are:
Superior thermal performance
Plate heat exchangers are capable of nominal approach temperatures of 10 degree fahrenheit compared to nominal 20 degree for shell and tube units. In addition, overall heat transfer coefficients (U) for plate type exchangers are three to four times those of shell and tube units.
Availability of wide variety of corrosion resistant alloys
Since the heat transfer area is constructed of thin plates, stainless steel or other high alloy construction is significantly less costly than for a shell and tube exchanger of similar material.
Ease of maintenance
The construction of heat exchanger is such that, upon disassembly, all heat transfer areas are available for inspection and cleaning. Disassembly only requires small amount of loosening of tie bolts.
Expandability and multiplex capability
The nature of plate heat exchanger construction permits expansion of the unit should heat transfer requirements increase after installation. In addition two or more heat exchangers can be housed in a single frame, thus reducing space requirements and capital costs.
The superior thermal performance of the plate heat exchanger and the space efficient design of the plate arrangement results in a very compact piece of equipment. Space requirement for the plate heat exchanger generally run 10% and 50% that of a shell and tube unit for equivalent duty. In addition tube cleanings and replacement clearances are eliminated.
How it is constructed
It is a series of individual plates pressed between two heavy end covers. The entire assembly is held together by tie bolts. Individual plates are hung from the top carrying bar and guided by bottom carrying bar. For single pass circuiting , hot and cold side fluid connections are usually located on the fixed end cover. Multi-pass circuiting results in fluid connection on both fixed and movable end covers.
The primary and secondary fluid flow through the plate heat exchanger are in opposite directions on either side of the plates. Water flow and circuiting are controlled the placement of the plate gaskets. By varying the position of the gasket water can be channelled over a plate or past it. Gaskets are installed in such a way that a gasket failure cannot result in a mixing of fluids. In addition, the outer circumference of all gaskets is exposed to the atmosphere. As a result, should a leak occur, a visual indication is provided.
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