What is a Plate Heat Exchanger: A Simple Guide

Plate heat exchangers, or PHEs, offer a big advantage over conventional fluid heat exchangers that use coiled pipes. Their design has enabled highly efficient energy transfer for over 90 years.

PHEs were invented in 1923 by Dr. Richard Sligman and initially manufactured with aluminum plates. Because plate heat exchangers are often used in industrial applications where they are exposed to aggressive or corrosive liquids, the preferred plate metal is usually stainless steel or titanium.
Plate heat exchangers are found in a wide variety of markets around the world including pharmaceutical, food, petroleum, chemical and marine industries. Brazed plated heat exchangers are commonly used domestically in on-demand water heaters. An example of a high-quality industrial PHE is the Alfa Laval heat exchanger, which features state-of-the-art design and materials.
How Plate Heat Exchangers Work
The science behind a plate heat exchanger is simple. Two separate fluids are separated by a metal plate. Heat transfers from the hotter liquid to the cooler one. The plates are held within a frame that directs each fluid’s flow in opposite directions through every other plate in order to maximize energy transfer.
To achieve the highest performance in heat transfer, each plate must be as thin as possible and have a large surface area. Furthermore, the flow of liquid on both sides of each plate must be turbulent but uniform. PHEs such as Alfa Laval plate heat exchangers utilize a unique herringbone pattern to increase surface area and maximize energy transfer even when the temperatures of the two fluids are very close to one another.
Heat Exchangers for Any Application
PHEs come in base designs to meet the needs of a wide variety of industrial applications:

• Gasketed PHE – A versatile heat exchanger used for heat recovery, condensing, evaporating, cooling and heating processes.
• Semi-welded PHE – Designed to handle refrigerants such as ammonia. They are particularly easy to inspect, clean and modify.
• Fully welded PHE – Used in corrosive, high-temperature processes. Their compact size makes installation easy.
• Brazed PHE – Designed for high temperature and pressure applications. They are particularly good where space is tight.
• Fusion bonded PHE – A gasket-free design for aggressive liquid applications requiring a high degree of corrosion resistance or hygiene.

Generally, top manufacturers such as Alfa Laval offer design services that can recommend the correct type of PHE for a particular application.
The best plate heat exchangers are designed to facilitate inspection and maintenance with user-friendly frames that are easily opened for plate examination, cleaning or gasket replacement. If a manufacturer offers frames in a wide variety of sizes, they can be easily customized to suit specific applications.
General Applications
Heating
Plate heat exchangers are a cost-effective and efficient means of capturing and transferring heat in water systems. They also separate water circuits that contain incompatible solutions and pressure differentials. For energy efficient heating of tap water, PHEs are the preferred solution. Unlike coil and tank water heaters, plate heat exchangers heat the water instantly and require far less space. Heat exchangers can also extract energy from building heating systems during warmer weather months. The excess heat can be used, for instance, to heat an outdoor pool.
Cooling
Many cooling applications demand high thermal efficiency where the difference between input and output stream temperatures is small. The best PHEs perform efficiently with temperature approaches as little as half a degree centigrade. A four-port counter flow design allows thermal transfer to occur in a single pass. In applications where air conditioning equipment is using an open cooling source such as fresh or salt water, a heat exchanger protects A/C equipment by creating a separate secondary circuit. This technique significantly improves equipment life and reduces maintenance costs.
About the author: 
Allied Heat Transfer deals in Industrial cooling and heat transfer systems with a range of heat exchanger products including Oil Coolers, Industrial Radiators, Shell and Tube Heat Exchangers, Air Coolers, Plate Heat Exchangers and Cooling Towers.