What are Heat Exchanger Plates Used For?

Sometimes referred to as a plate heat exchanger, plates used to facilitate the indirect transfer of heat between fluids have been around for about a century. The first ones were invented in 1923 by Dr. Richard Seligman. Heat exchanger plates were introduced to pasteurize milk at high temperatures for shorter periods, which has since become the standard method for pasteurizing milk. Unlike other heat exchangers, plates expose fluids to considerably more surface area, which speeds up temperature changes. Now used globally for multiple other applications that include pasteurization, heat exchanger plates have since developed to the point that more recent models are made with thin metal plates designed via computers, with certain types even utilizing laser technology.

What Is a Heat Exchanger Plate? 

Heat exchange between fluids involves heating or cooling a fluid by transferring heat from one liquid to another. Regarding a heat exchanger, plates are usually made from metal alloy or other thermally conductive material. Generally comprised of several plates used to transfer heat, a loose pressure plate holds together each against the fixed plate of the heat exchanger. Plates commonly feature a gasket arrangement that makes up two separate systems through which the heat is transferred, though heat exchanger plates can be of the brazed variety instead. While referred to as a heat exchanger, plates utilized to transfer heat can also be designed for condensation, cooling, evaporation, heating, and heat recovery, with corrugated plates providing an even larger surface that makes heat transference more efficient.

Types of Heat Exchanger Plates & Their Applications 

Two main types of heat exchanger plates are currently used for industrial purposes: gasket and brazed varieties. However, there are also micro-plate, plate-and-frame, and welded-frame designs, with a particularly innovative laser-welded frame design that offers additional advantages.

Gasket-Type Heat Exchanger Plates

This gasket arrangement allows heat to flow through single channels, with the primary and secondary media flowing counter to this. The gasket design keeps the media from mixing, with corrugated plates causing turbulence within the fluids as they pass through the unit. This turbulence provides information on how heat is effectively transferred. Consisting of multiple thin metal sheets that form channels, their gaskets lie between plates to form seals, which prevent the leaking or mixing of fluids and where they flow.

For this style of heat exchanger, plate gaskets are typically made with elastomers. These gaskets seal the channels, directing media along alternate pathways. Two bars – the upper carrying bar and lower guiding bar – support different heat exchanger parts, with a plate pack compressed by bolts between the frame and pressure plates. The upper carrying bar supports the channel and pressure plate, while the lower guiding bar remains fixed on the support column.

Gasket-style designs are simpler to clean and alter, requiring adding or removing plates to the heat exchanger. Gasket heat exchanger plates are used in various applications, including heavy-duty industrial and processing applications and utilization for heating, ventilation, and air conditioning (HVAC) systems.

Applications for gasket-style heat exchanger plates include: 

• District heating and cooling: Here, heat exchanger plates are used to heat and cool multiple connected buildings within a network. These systems comprise one or more central plants that produce chilled water, steam, and hot water. These flow through a series of insulated pipes to provide air conditioning, space heating, and heated water for the buildings within the network. Gasket heat exchanger plates are installed between the central plant and the rest of the piping system. The central plant controls the heat or cooling, using a heat meter to measure use.
• HVAC: In HVAC systems, gasket-style heat exchanger plates connect boilers, chillers, and cooling towers to a central system, decreasing the chillers’ cooling load.
• Industry and food processing: Heat exchanger plates are used in industry to recover waste heat, along with the processing of milk and other foods requiring pasteurization or similar heating.  For processing liquid products processed with heat, exchanger plates also help cool the fluid before bottling to lower their temperature.

There are numerous advantages to using gasket-style heat exchanger plates for the above purposes, including the ease of altering, cleaning, maintaining, and replacing components and adjusting the cooling or heating needed. On the downside, though leaks are rare, they’re more likely to occur with gasket-style heat exchanger plates due in part to higher pressure drops than other methods. Typically, these heat exchanger plates are made from stainless steel, though sometimes they’re made instead of titanium, with the end plates made from mild steel.

Brazed Heat Exchanger Plates

Rather than gaskets for holding plates together, brazed heat exchanger plates connect stainless steel plates by melding them at specific points where heat is transferred. These heat exchanger plates are pressed into specific shapes after being cut from a coil, from which copper foil cut from it forms to fit the plates. With a copper film wrapped around the brazed heat exchanger plates, numerous arrangements can be used to make them work optimally for various applications. These heat exchanger plates and foil are stacked to form a packed plate fitted with connections and frame plates.

This type of heat exchanger plate system resists fatigue from both heat and pressure, making it ideal for an array of heating and cooling solutions. Though previously used for more modest applications, this technology has recently seen larger units for industrial use becoming more prevalent. Though less easy to clean and maintain than the gasket-style heat exchanger plates, brazed-style plates offer advantages as they’re more firmly sealed together. Instead of gaskets, it’s the plates’ alignments and brazing that form a seal, guiding fluid toward the channel into which it will flow.  

Applications for brazed-style heat exchanger plates include:

• Calorifiers: Brazed-style heat exchanger plates connect indirectly to heating circuits when installed with either calorifiers or hot water tanks. This enables hot water to be produced on demand or drawn from heated water in the storage container.
• Chillers: The evaporator can be replaced with brazed heat exchanger plates in both water-cooled and air-cooled chillers. They can also replace condensers in water-cooled chillers, though this depends on how large the cooling load is.
• Heat pumps: Often using brazed heat exchanger plates to connect separated loops, heat pumps connected to a water source commonly use brazed plates for the condenser. The evaporator provides refrigerant, and coils connect water loops.
• Heating and cooling: Heating and cooling networks for apartment buildings or other connected residential areas use the brazed heat exchanger. Larger plates are sometimes used for heating and cooling networks for larger areas, though these usually use gasket-style heat exchanger plates.

Generally, brazed heat exchanger plates are made with stainless steel, though the brazing points that join plates together are often made from copper. Brazed-style heat exchanger plates offer better efficiency than gasket-style models and are less likely to leak, offering a more compact profile. However, this comes with a cost. Brazed-style systems are more challenging to clean, and when damaged, the entire unit requires replacement.

Micro-Plate Heat Exchangers

These types of heat exchanger plates can be either gasket or brazed models. They provide better efficiency than either of these two traditional types of heat exchangers. The plate is what differentiates micro-plate heat exchangers from other varieties. Microplate heat exchangers use minute dimples instead of a fishbone or chevron pattern pressed into the plate to facilitate heat transfer. It helps maximize heat transfer by allowing a more even spread of fluid and ensuring a more turbulent flow to augment heat transfer.

This design also makes heat exchanger plates lighter and more compact. They’re used for variable refrigerant flow (VRF) units, condensers, chiller evaporators, and chillers cooled by water or air. Micro-plate designs save energy and space over more conventional heat exchanger plates. Yet, while they are lighter, more efficient, and require a lower refrigerant charge, they’re more challenging to clean, and their capacities aren’t adjustable. Also, brazed-style heat exchanger plates can’t be repaired, so they must be replaced when damaged.

Plate-and-Frame Heat Exchangers

Offering high thermal efficiency, these heat exchangers are made up of stacked plates, making their profile more compact so that they need less space. They’re also flexible, with heat exchanger plates that can be removed for cleaning, maintenance, and repair or even reconfigured to adjust heat transfer requirements or fluid flow. However, it’s necessary to consider the fluid type before choosing this type of heat exchanger. Plates don’t deal well with extreme temperature differentials between the two fluids in this heat exchanger system, so it’s essential to consider the amount of heat to be transferred and the pressures and temperatures involved in the application.  

Welded-Frame Heat Exchanger Plates

A variation of the plate-and-frame heat exchanger is the weld-frame heat exchanger. Plates in this design are welded together into a single block, fixing the capacity to heat or cool as they can’t be dismantled entirely. These heat exchanger plates can handle higher pressures and temperatures; however, they are used widely for heavy industrial applications, such as oil refineries or power plants. One iteration of this design involves laser-welded heat exchanger plates, which are combined by welding a circular pattern with a laser to create a barrier that resists pressure within the heat exchanger. Plates are filled with either nitrogen or water, creating a hollow space through which media can flow to control cooling or heating.

Advantages of laser welded-frame heat exchanger plates include: 

• Allows thinner plates to be used, saving costs for material
• Better overall heat transfer
• Enables a plethora of shapes and designs with CNC-programmed lasers
• Lower welding costs with lasers
• Requires less fluid to heat or cool as heat exchanger plates require less fluid and thus lower pump capacity
• A welded pattern assures higher turbulence, reducing algae, lime, or other deposits.

With countless industrial applications, laser-welded heat exchanger plates produce beer, milk, soft drinks, wine, and other consumable liquids. These heat exchanges are also used in chemical, meat processing, pharmaceutical, and other industries.

Heat Exchanger Plates from Hayes Pump 

As the largest distributor of pumps and pump implements in the Northeast, Hayes Pump carries a variety of heat exchanger plates for pumping systems. We are especially pleased to offer an innovative and dependable design by Omega Thermo Products. Their laser welded-frame heat exchanger plates provide consistent performance for various applications, including chemical, food and beverage processing, HVAC, and pharmaceutical sectors. For more information on heat exchanger plates and other products we carry, contact the pump experts at Hayes Pump.