This article will give an in-depth discussion about plate heat exchangers.
This article will give a better understanding of:
A plate heat exchanger (PHE) is a compact and efficient device designed to facilitate the exchange of heat between two fluids, typically at different temperatures, using a series of thin metal plates.
This section delves into how plate heat exchangers operate.
PHEs work based on thermodynamic principles. Each plate is paired with a specific concave tubular shell. The arrangement creates narrow, rectangular channels, enabling effective heat transfer through these segmented regions.
Fluids flow through these narrow channels encased by gaskets, which help control the fluid movement. These gaskets ensure that one fluid type (potentially a heated canvas) passes over one plate while another fluid (like heated water) moves over the adjacent plate. The visual below displays two neighboring plates.
In this arrangement, cold and hot fluids alternate over the plates, enabling heat transfer between them. The extensive surface area of the plates enhances the rate of heat transfer compared to tubular heat exchangers.
As demonstrated in the diagram, the cold fluid inlet (blue) is positioned at the bottom, with the outlet at the top, while the hot fluid outlet (red) is also strategically located. This setup allows the cooler fluid to rise as the warmer fluid descends, transferring heat across the plates. This mechanism results in cooling of the heating medium and the warming of the cooling medium. Plate heat exchangers are celebrated for their compact design, efficient heat transfer, adaptability, and ease of installation and maintenance.
Operating a plate heat exchanger involves several steps:
Maintaining a specified pressure drop is critical. Excess energy may be necessary if it deviates from the design, signifying potential fouling or clogging. Monitor the flow rate against specifications to uncover discrepancies:
Install the device on a stable, level surface. Ensure at least 1.5 meters of clearance from walls for maintaining tasks like replacing or tightening plates. The installation manual specifies required free space.
Before pipe connections, confirm compressed dimensions match specifications if extensions are on a removable plate. Allow 1.5 meters of clearance around the device for optimal working conditions during installation and maintenance.
Ensure all bolts are secure and the plate pack is correctly assembled before startup. Initiate operation gradually, avoiding pressure shocks or water hammer to prevent equipment damage.
Key points include:
Consider these aspects when operating plate heat exchangers:
Employ the following essential procedure:
Follow these precautions:
Steps for disconnecting the unit include:
Plate heat exchangers come in various designs, including:
The upper section is secured between the supporting column and the fixed plate, where the pressure plates and exchanger plates are attached.
The fixed plate is a fundamental component of the plate heat exchanger. As its name suggests, it is a stationary frame plate. Typically, the heat exchanger pipes are attached to this fixed plate.
This is a stationary component of the plate heat exchanger. It features attached guiding bars and a supporting shaft.
The plate heat exchanger includes a movable pressure plate frame connected to the carrying shaft. This frame is capable of compressing the exchanger's plates.
This component guides the pressure plate and the heat exchanger plates into position.
This component is used to compress the frame corridor of the plate pack. It includes tensioning nuts, washers, and bolts.
The plate pack is installed between the pressure plate and the fixed frame plate. It is compressed by tightening screws that secure the two plates together. Gaskets around the plates help control the fluid flow.
The types of gaskets used in plate heat exchangers are:
The slit-in gasket is ideal for applications requiring frequent gasket replacement. It also reduces cement odor without the use of cement. This type of gasket is well-suited for processes such as water treatment or food processing.
Generally, EPDM gaskets are recommended for either high temperature or aggressive fluid operations. EPDM gaskets are high quality, unlike rubber gaskets that lose elasticity as time passes.
PTFE cushion gaskets are ideal for applications where traditional synthetic rubber gaskets would fail due to the nature of the fluid being handled. Their chemical resistance makes them suitable for a broader range of operations. The TCG gasket, with its elastic core, does not require a strong tightening collar during assembly, minimizing the risk of plate distortion from over-tightening. However, a TCG gasket is typically used on one side only, with a conventional gasket suitable for the other side if a non-corrosive fluid is present.
Plate heat exchangers come in the following types:
This type of heat exchanger makes use of top quality gaskets and construction. This gasket stops leakage by sealing the plates. Plates of this exchanger can be easily removed for the relief, expansion, or cleaning of the plates, which significantly reduces costs.
Brazed plate heat exchangers are widely used in refrigeration and industrial processes. The plates are brazed with copper, providing excellent corrosion resistance. Their compact design and efficient performance make them a cost-effective choice.
Advantages of brazed plate heat exchangers include:
These heat exchangers operate similarly to gasketed heat exchangers, but their plates are welded together. They offer excellent durability and are suitable for handling hot fluids and abrasive substances. However, because the plates are welded, they cannot be cleaned mechanically like those in plate and frame heat exchangers.
This heat exchanger integrates two distinct types: gasketed plates and welded plates. It features a combination where one set of plates is welded together, while another set is sealed with gaskets. This design allows one fluid to flow through the welded section and another to pass through the gasketed section. The hybrid structure facilitates easier maintenance and enhances the exchanger's ability to handle more critical fluids. Additionally, this design minimizes the risk of fluid leakage.
A plate and frame heat exchanger is a type of heat exchanger where the plates form a structural framework. This design incorporates corrugated plates within a supporting frame. The unique construction of this heat exchanger generates substantial wall shear stress and turbulence, resulting in enhanced resistance to fouling and an improved rate of heat transfer.
This heat exchanger features gaskets that not only provide a sealing function but also direct the flow of fluids. These gaskets are placed in grooves along the edges of the plates. Plate and frame heat exchangers are designed to transfer heat between liquids at moderate to low pressures. They can also operate safely at elevated temperatures and pressures when configured without gaskets.
Features of plate and frame heat exchangers include:
The key components of plate heat exchangers and their respective functions are:
A single plate heat exchanger can accommodate up to 700 plates. As the plate stack is compressed, the corner holes in each plate form a continuous pathway or manifold, enabling fluid to move through the plate stack and exit the exchanger. The narrow gaps between the plates create a series of channels where hot and cold fluids flow alternately, resulting in minimal resistance to heat transfer.
Types of plate element patterns include:
The corrugated pattern, also known as the marsh board pattern, features reduced contact points between plates. This design facilitates the smooth flow of liquids containing fibers or sludge, minimizing the risk of blockages.
The "herringbone" pattern is named for its V-shaped press grooves, which resemble the bones of a herring.
By stacking V-shaped pressed plates and rotating them 180° in an alternating pattern, numerous contact points are created. This arrangement enhances resistance to high pressure and generates complex flow channels due to the V-shaped grooves, leading to superior heat transfer performance. Additionally, the reduced heat transfer resistance from the thinner plates results in heat transfer efficiency that is three to five times greater than that of S&T heat exchangers.
Different types of plates used in plate heat exchangers are outlined below:
This chapter will cover the applications, benefits, and maintenance of plate heat exchangers.
Plate heat exchangers are used in the following applications:
Although plate heat exchangers may have some drawbacks, such as high pressure drops and limitations on operating temperature due to the heat resistance of the sealing materials, their advantages often outweigh these issues. Some benefits of plate heat exchangers include:
The following steps outline the general maintenance procedures for a plate heat exchanger:
The initial step is to disassemble the plate heat exchanger.
Procedure for opening:
The plates are suitable for both manual cleaning and cleaning-in-place (CIP) procedures. Before disassembly, ensure that the unit is fully de-pressurized, locked out, and drained. Manual cleaning generally involves washing the plates with a mild detergent, water, and a non-abrasive cloth. To prevent bending, it's advisable to clean the plates on a flat surface. When reassembling, especially if the heat exchanger has been heavily fouled, make sure to remove all debris from the gasket sealing surfaces.
Steps for Cleaning-in-Place (CIP):
Procedure for Cleaning-in-Place (CIP):
During the inspection, it’s crucial to examine the plates for any cracks or perforations. Start with a visual inspection of the heat exchanger plates, paying special attention to areas where the plates make contact with each other. Perforations are often found at these contact points. To aid in the inspection, use a light to help identify potential issues. However, note that visual and light inspections may not uncover all defects in the heat exchanger plates.
After testing the gasket plates, proceed with their installation. Mechanical professionals should attach the gaskets to the plates. Ensure the gasket grooves are clean and free from debris. The flow paths can be either parallel or diagonal, depending on the plate model. Refer to the technical drawings in your plate manual for detailed guidance on the flow paths.
Ensure that each unit is operating correctly.
It has been seen that the PHE offers numerous advantages over other types of heat exchangers. However there is a variety of plate heat exchangers that are suitable in different applications and each having its own advantages and disadvantages. Therefore one must be aware of the specifications when choosing a heat exchanger for a particular application. The PHE must be generally well maintained for a long lasting life.
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