COMPONENTS, CONFIGURATION, AND APPLICATIONS OF GASKETED PLATE AND FRAME HEAT EXCHANEGRS

Nicholas Brian Muha Nbm5064@psu.edu

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Components, Configuration, and Applications of Gasketed Plate and Frame Heat Exchangers

A heat exchanger is a mechanical device that uses conduction to transfer heat between two moving fluids. Within a heat exchanger two fluids cross paths, and heat is transferred from the hot fluid to the cold fluid. More specifically, gasketed plate and frame heat exchangers are heat exchangers that use tightly packed metal plates to facilitate counter-flow between two fluids. This document will focus primarily on the gasketed plate and frame heat exchanger design. In this design, thin metal plates paired with rubber gaskets are used to alternate fluid flow and promote heat transfer. The following sections of the document will analyze the components, configuration, and applications of gasketed plate and frame heat exchangers.

Overall System Operation In a plate and frame heat exchanger fluids travel over the surface area of tightly packed metal plates. Heat transfer occurs by alternating the fluid paths between the plates. For example, fluid #1 may flow through the first, third, and fifth plates and fluid #2 may flow through the second, fourth, and sixth plates. This concept is illustrated in figure 1 below.

Figure 1- Plate and Frame Heat Exchanger

Flow over many plates creates an extremely large surface area for heat transfer to occur. This large surface area is what makes plate and frame heat exchangers extremely efficient. In a standard design the hot fluid will enter the heat exchanger on the top left, and exit on the bottom left. On the other hand the cold fluid will enter on the bottom right, and exit on the top right. This arrangement is known as counter-flow since the two fluids are flowing in

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opposite directions when they interact. Counter-flow is the most popular flow pattern as it allows for the highest rate of heat transfer per unit area.

Main Heat Transfer Components The main benefit of the plate and frame design is the large surface area where heat transfer occurs. This large surface area allows for maximum heat transfer efficiency, and is accomplished with a complex plate and gasket system. This section will describe how plates and gaskets function, and it will also describe how the two components interact.

Plates

Plates in a plate and frame heat exchanger are specifically designed to allow for efficient heat transfer between fluids. The plates contain grooves which direct the flow along the entire surface area of the plate. Plates can contain various grove designs which can be seen below in figure 2. Different plate designs are chosen based on the type of fluid, the application, and the required fluid velocity.

Figure 2- Plate Groove Designs

Plates are also available in various materials depending on the application. Examples of plate materials include stainless steel, titanium, nickel, and tantalum. Plates are also available in thicknesses ranging from 0.023 inches to 0.039 inches. The number of plates in a plate and frame heat exchanger depends solely on the desired physical footprint.

Gaskets

Gaskets are used to direct fluid flow across the plates in plate and frame heat exchangers. Each individual plate is lined with a gasket to ensure that all fluid remains within the system. In a plate and frame heat exchanger the two fluids contained in the system never come in physical contact. The lack of physical fluid interaction allows reactive fluids to be used with one another, which is a huge benefit of the plate and frame design. Gaskets are used to ensure that the fluids do no come in contact by directing flow down alternating plates. This concept is illustrating more clearly in figure 3 below.

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Gaskets come in a variety of materials depending on the specific fluid being used. The most common gasket materials are EPDM rubber and Nitrile Rubber. EPDM is used in non-fatty/oily applications, while Nitrile Rubber is used in higher fat/oil applications. Other less common gasket materials include Fluorocarbon rubber, Butyl and Styrene Rubber. These less common materials come at higher costs and are mainly used either with corrosive fluids or in harsh environments.

Additional Structural Components Although the combination of plates and gaskets are responsible for the heat transfer in the plate and frame design, additional components are necessary to complete the functioning system. Although they dont necessarily play a role in heat transfer, components such as the frame, side plate, and carrying bar are integral features in the plate and frame design. These additional components are depicted in figure 4, and are briefly described below.

Frame

The frame of the heat exchanger is the component that houses the flat metal plates. The frame consists two structural plates that are secured around the thin metal plates using rods and tightening bolts. The frame is regularly handled for maintenance, therefore it is imperative that it remains at room temperature. This is accomplished by keeping the first plate on either side of the device free of flow, ensuring that no heat is transferred to the frame. This feature can be observed in figure 1.

Side Plate

Figure 3- Individual Plate Gasket Pattern

Fluid entering this corner will not flow across the plate

Fluid entering this corner will flow across the plate

Gaskets bordering each plate ensure that all fluid remains within the system

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Figure 4- Additional Plate and Frame Heat Exchanger Components

The side plate on a plate and frame heat exchanger is another important component of the overall system. The side plate is a piece of sheet metal that borders the tightly packed metal plates. The sheet metal is a safety component that acts as a barrier between the tightly packed plates and the outside air. The fluid within the plates is highly pressurized, therefore if a breach were to occur on the surface of a plate the pressurized fluid would shoot out at dangerously high velocities. For this reason, the side plate is necessary to act as a boundary in the case of plate failure.

Carrying Bar

The final component of a plate and frame heat exchanger is the carrying bar. The carrying bar is a solid metal beam that sits atop the structure. This component is a structural element that is also used when the heat exchanger is transported.

Plate and Frame Heat Exchanger Applications Plate and frame heat exchangers are used in a variety of applications in industries such as chemical, pharmaceutical, food & beverage, dairy, HVAC, Marine, and oil cooking. Plate and frame heat exchangers are extremely versatile in terms of fluid compatibility, size, and cost therefore they can be utilized in many different energy systems. Two of the main plate and frame heat exchanger applications in the HVAC industry are described below.

Cooling Tower Isolation

Carrying Bar

Front and Back Frames

Side Plate

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A central energy plant consists of many components including chillers, heat exchangers, pumps, and cooling towers. Cooling towers are considered open systems because they operate outdoors and contain unpressurized fluid that is open to the atmosphere. Since fluid within a cooling tower is open to the environment, it is very common for particles and debris to enter the system. As the water continues to flow through the system, debris is carried from the cooling tower to the other plant components. This debris can cause major issues for downstream machinery, therefore it is imperative that the water is filtered prior to entering the equipment. For this reason many buildings utilize plate and frame heat exchangers as a means to isolate the cooling tower from the rest of the energy plant. In this application, all water leaving the cooling tower will first flow through the heat exchanger. Plate and frame heat exchangers are relatively inexpensive, and they are very easy to disassemble and clean therefore they make a great filter for the overall energy system. Any debris accumulated from the cooling tower water will become trapped in the plate and frame heat exchanger due to the turbulent fluid flow, and can be removed from the system before damaging pumps or chillers. This process is depicted in the image below.

Figure 5- Cooling Tower Isolation Configuration

Free Cooling

Most buildings utilize chilled water plants for cooling purposes during warm summer months. In this process heat is extracted from water using chillers, and then the water is sent through the building and utilized for air conditioning purposes. However, chillers consume the most energy out of all energy plant components. Any time that a plant manager can turn off the chillers, money is being saved. In situations when the ambient air temperature is sufficient to chill water, chillers can be turned off and the cooling tower/heat exchanger combination can sufficiently cool the building. In this configuration water is first chilled in the cooling tower using the cool outside air. The chilled water then flows through a heat exchanger, where it absorbs heat from a second fluid. The second fluid, now cooler, can be used to cool the building while the hot water cycles back through the cooling tower to repeat the process. This process is illustrated in the image below.

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Figure 6- Free Cooling Configuration

Conclusion Cooling tower isolation and free cooling are just two of many plate and frame heat exchanger applications. Plate and frame heat exchangers should always be considered when designing a central energy plant due to the low cost, ease of assembly, and heat transfer efficiency. When adding a plate and frame heat exchanger to an energy system it is important to choose a reasonable plate and gasket combination. Plate material, plate groove design, and gasket material will all change based on the specific application. With the correct planning, design, and implementation plate and frame heat exchangers can be used to increase the efficiency of nearly all central energy plants.

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Image Citations:

Cover Page:

http://www.dhtnet.com/images/galpf.jpg

Figure 1:

http://www.bing.com/images/search?q=plate+and+frame+heat+exchanger+flow&FORM=HDRSC2#view=detail&id=4711B8930132D51A0F2DF51204A5526413302DAF&selectedIndex=9

Figure 2:

http://www.genemco.com/catalog/CA39plateheatexchanger.pdf

Figure 3:

http://www.separatorequipment.com/uploads/images/Products/Technologies/Gea_Optiwave_Plates.png

Figure 4:

http://influx.dk/wp-content/uploads/2012/05/pladevarmeveksler-Alfa-Laval.gif

Figure 5:

http://www.gea-phe.com/typo3temp/pics/3aecb6ca82.jpg

Figure 6:

http://www.alabamapower.com/business/save-money-energy/energy-know-how/images/c00123.gif

Additional Resources:

http://deltathx.com/contentpg.aspx?itemid=655

http://www.genemco.com/catalog/CA39plateheatexchanger.pdf

http://www.graham-mfg.com/gasketed-and-brazed-plate-heat-exchanger-applications

http://www.wcrhx.com/plate-heat-exchanger-gasket-materials