Most heat exchangers transfer heat between a fluid that is either heated or cooled by another fluid in a contained vessel. Many times this is a coiled metal pipe passed through the liquid that is to be heated or cooled. The liquid is typically contained in a reservoir constructed of a non-conductive material and lined with a thermal lining to prevent the increase or loss of heat.
With a plate heat exchanger, a number of thin metal plates compressed into a plate pack are used instead of coils of pipe. Because the plates have a greater surface area than a coil, tube, or wheel, plate heat exchangers transfer heat at a greater rate, thus heating or cooling the liquid at a much greater and more efficient speed. Because of their size and efficiency, plate heat exchangers are becoming more and more common. Despite their increased popularity, there are some things you may not know.
- Plate heat exchangers date back to the early part of the last century, with the first being developed in 1923. Advances in metallurgy and fluid compositions have resulted in significant improvements in the technology over the past (almost)100 years. Today, the devices are smaller than ever before and have moved from predominately industrial applications to include residential use in many boilers and hot water heaters, as well as refrigeration units.
- While plate heat exchangers are typically used for transferring heat from liquid to liquid, they do not just work with liquids. Plate-style heat exchangers can also be used during the transfer of heat from gases such as steam. The plates simultaneously run hot and cold fluids through alternating channels so they can be used to heat or cool just as efficiently based on the need, i.e., heating water in a boiler or dispelling heat in a refrigerator. There are hundreds of different uses, and they have become very popular in the pharmaceutical, dairy, and food and beverage industries.
- A key advantage of plate technology is the ease of modification and adaptation. Another advantage of plate heat exchangers over other varieties is the opportunity for expansion. In fact, the expansion is as simple as adding additional plates.
- There are four main styles of plate heat exchangers: gasketed, brazed, welded, and semi-welded. The gasketed exchangers are the easiest to clean and expand. They are one of the best choices for low-cost maintenance. Your best bet for corrosion resistance is the stainless steel plate with copper brazing. The least adjustable is the welded model, since the plates are welded together. The benefit of this style is the durability and ability of the sealed plates to contain corrosive materials. Blending the best of all worlds, the semi-welded exchanger alternates welded and plate pairs with gaskets. The welded pairs can contain liquids that the gasketed parts cannot, but the gaskets allow for expansion, alteration, and ease of cleaning.
- Because the frames and plates can be created in many different sizes and shapes, imagination is one of the only limits to the design of plate-style heat exchangers. Modular designs further enhance the many potential applications and expand its usefulness beyond the larger single design styles. Adding to the space savings is the efficiency factor, which allows a much smaller unit to produce the same effects as other styles twice their size.
- High heat transfer rates make plate-style heat exchangers highly efficient. Certain models can perform up to six times the U or K thermal value of other types of heat exchangers, such as the shell and tube. The secret lies in the high surface area of the plates. Even though the plates may be smaller than shell and tube or adiabatic wheel exchangers, the liquid is in contact with a vastly larger percent of the transfer surface.
- Plate-styled heat exchangers can often lead to significant cost savings since their smaller size, modular designs, and lighter weight components lead to major savings on transportation costs and required rigging. They also require far less material to produce, and, since they are designed to not lose liquid, even more money is saved. The ability to quickly disassemble several of the varieties for cleaning and maintenance also saves vast amounts of time and money. If one part of plate-style heat exchanger is faulty, leaks, or simply fails, it can be taken out and replaced instead of purchasing an entire new heat exchange unit.
- One major difference between plate heat exchangers involves the internal pattern of grooves. Known as the corrugation pattern, the internal flow of liquid is different based on the direction of flow. The pattern affects the pressure of the liquid and the speed of pressure drop, which impacts the heat gain or loss. The type of metal also plays a part in the efficiency of heat transfer and the type of fluid that can be used with the plates. Some metals that are commonly used include stainless steel, titanium, nickel, and several metal combinations, such as titanium-palladium.
- The main limitations of plate heat exchangers are their inability to work with high fluid temperatures (greater than 180 degrees) or with great temperature differentials between the fluids. Choosing the wrong style for the temperatures or liquids could also limit effectiveness and lead to leakage.
- Even though the reservoir is typically thermally lined, a tremendous amount of energy can radiate out since the ambient temperature will almost always be dramatically different along the external wall. This is especially true as the units get larger or if there are many units being used. In order to reduce the loss of energy, insulation is highly suggested. Because of the frequent maintenance and inspection, however, standard insulation applications are not feasible. As a result, the best solution is often a customized thermal barrier that can be easily and quickly removed and reattached.
Plate heat exchangers have evolved tremendously over the last 90+ years and have made significant impacts in the industrial and residential sectors. While these devices are designed to give you an incredible value, even the best devices need to be serviced and maintained. Don’t allow corroded gaskets, blockages, fouling, or pressure loss to rob you of your time and money. Through standard and routine maintenance, not only is your investment kept running optimally, but a lot of money is saved by increasing peak efficiency and limiting downtime.