In this article, we will explore what is plate heat exchanger along with definition, working, parts, types, operations, etc. According to the laws of physics, when an energy flow is observed in a system, it continues to flow until the system has reached equilibrium. Mechanics states that when heat or temperature differences exist between two systems, then a flow of heat will occur from one system to another according to the law of thermodynamics. According to the equilibrium principle, the heat exchanger works on the basis of the exchange of heat.
A heat exchanger plays a critical role in the transfer of heat from one fluid to another by transferring heat from one fluid to another. In terms of heat exchanger types, plate heat exchangers are one of them, and they have different features and arrangements.
Plate heat exchangers are used to remove heat from a surface and to separate the cold fluid from the hot fluid by extracting heat from the surface. A plate heat exchanger is a device that consists of several different parts which are used to transfer heat.
What is Plate Heat Exchanger? Definition
It is known as a plate heat exchanger because it moves heat from one fluid to another using a series of metal plates. A series of channels are created between these plates by positioning them over each other to create a channelling pattern and facilitate fluid to move between them.
Due to the fact that the fluid is exposed to a larger surface area, the plate heat exchangers are able to distribute the fluid evenly throughout the plate and have better efficiency than conventional heat exchangers because the fluid is distributed over a greater area. In addition to increasing the heat transfer rate, this will also result in an increase in the rate at which the temperature is changing.
Features of Plate Heat Exchangers
- It has been well established over the past few decades that plate heat exchangers are widely used, and very small welded designs, which rely on millions of combi boilers, are used for hot water heating.
- Having such a small size and a high degree of heat transfer efficiency enables a combi boiler to heat up the home with much more efficiency by using less energy.
- Household heating and hot water are heavily influenced by small plate heat exchangers that can be found in households.
- In large business models, gaskets are frequently used between plates, while in smaller ones, the plates are often welded together.
History related to Plate heat exchanger
It was Dr. Richard Seligman, the founder of The Aluminum Plant and Vessel Company Ltd., commonly known today as APV, who introduced the first plate-and-frame heat exchanger to the world in 1923, which was the first successful plate-and-frame device ever made commercially.
As one of the world’s leading manufacturers of thin metal plate heat exchangers, Paraflow was the first to manufacture a plate and frame heat exchanger that was manufactured from cast gunmetal plates enclosed in a metal frame. This set the standard for today’s computer-designed thin metal plate heat exchanger.
Working Principles of Plate Heat Exchangers
Depending on its construction, function, and application, a plate heat exchanger works in a certain way according to its operating principle. It can be stated that plate heat exchangers could be defined as a type of heat exchanger in which metal plates are used to transfer heat from one fluid to another.
Due to the fact that the fluids are spread over a much wider surface area than conventional heat exchangers, the plate heat exchanger has a notable advantage over conventional heat exchangers in terms of exposure to the fluids. By doing so, heat is transferred more efficiently and the rate at which temperature changes is increased by a considerable amount, based on our preferences.
Let’s take a look at how the plate heat exchanger works
- With the Plat Exchange Heater, the principle of thermodynamics is employed in order to achieve its purpose. Normally, these exchangers consist of plates that have concave tubular shells that are enclosed inside a concave tube.
- It is arranged so that thin rectangular channels are developed as a result of the placement of the plate portions, so that heat can be transferred through partial pieces using the thin channels.
- As the operating fluid flows between these twisting and narrow channels, it forms a tight seal. It has girdled plates that are surrounded by gaskets so that the fluid flux can be controlled between the plates.
- This gasket arrangement is designed so that a particular liquid is distributed only on one plate, while a different liquid is distributed on the plate that follows.
- It is at this point that the cold and hot fluids alternately pass through the plate, causing a heat exchange to take place between the two fluids.
- It is important to note that the plates are designed to transfer heat quickly, and because of the large surface area, they perform better than tubes for heat transfer.
- There is a cooling fluid that flows upwards and fluid yet to be cold overflows in a downcast direction, which leads the cool fluid to transfer heat through the plates in an upward direction.
- This process eventually leads to the cooling of the heating medium, and the cooling medium ultimately becomes toast after this process has taken place.
Plate heat exchangers, as heat transfer systems, offer numerous benefits, including compact design, low heat loss, a wide range of applications, flexibility in operation, high heat transfer efficiency, a small installation size, and the ability to draw.
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Basic Functions of Plate Heat Exchangers
The basic functions of the Plate Heat Exchanger are as follow
- It is known that a plate heat exchanger is an electrical device for continuously transferring heat from one medium to another without consuming any energy in the process.
- In order to transfer heat between two liquids, a Plate and Frame Heat Exchanger is basically a thin corrugated metal plate with two liquids flowing in each direction, so heat may easily be transferred between them on either side of the plate.
- There is a tie bolt mechanism that ensures the compression of the plates by interconnecting a stationary frame component called the head with a moving frame component called the follower using the tie bolts.
- Compared to other types of Heat Transfer equipment, the plate Heat Exchanger requires less floor space and weighs less than other types. In applications with limited space, this makes it an excellent choice.
Various Parts used in Plate Heat Exchanger
Following are the major parts of a plate heat exchanger:-
There is no maximum number of plates that can be contained in a single plate heat exchanger. There is a constant tunnel or manifold created by the holes in the corners of the plate pack as it compresses, according to which fluid can easily flow through the plate pack and exit the device through the tunnel or manifold.
There is a quite tight channel of space between the thin plates that alternately traverses cold and hot fluids in the heat exchanger, which offers very low resistance to heat transfer due to its small size and space between the thin plates.
On top of the supporting column, the upper part is installed between the fixed plate and the pressure plates that are connected to the exchanger plates, and it sits between them.
Plates that are to be fixed
Plate heat exchangers consist of a number of fundamental parts, including the fixed plate. The plate is referred to as a fixed frame plate given that its name implies that it is a plate with a fixed frame. There is generally a connection between the pipes of the heat exchanger and the fixed plates of the heat exchanger.
Columns for support
Plate Heat Exchanger has a non-movable component, which means that it cannot be moved. There are two parts that are attached to this part, the guiding bar, and the carrying beam.
It comes with a mobile pressure plate frame mounted on the exchanger carrying beam, which is attached to the exchanger carrying frame. There is a frame attached to the exchanger that compresses the plates.
Units for tightening the framework
The plate pack is compressed using this device, which serves the purpose of compressing the frame components.
Gaskets and Plates
Plate packings are used to extend the width of the pressure plate between the fixed frame plate and the pressure plate. There is a screw-fastened between the two plates which acts as the compression mechanism when the screws are tightened. There are gaskets covering the plates in order to control the flow of air through the system.
Various Operations of Plate Heat Exchanger
Operations of Plate Heat Exchanger are as mentioned below
Dropping of Pressure levels
As much as possible, there should be little pressure drop so that the design value is kept near the actual value. Therefore, the demand for more energy is required in order to achieve the flow demand through the equipment which is asked for.
It should be noted that in order for the device to be able to hold the requested temperatures effectively, the device must be able to hold the pressure of the media that is applied in combination with a reduction in its capability to hold the temperature.
Comparing the actual inflow rate to the specified inflow rate is possible if you can measure it:-
- There is a possibility that the temperature program needs to be checked if the pressure drop is greater than specified.
- A congested bay area may lead to a low-temperature reading if the readings from the thermometer correspond to those certain.
- A narrowing of the passages can result in a temperature reading that does not correspond to the specified value.
Proper Installations criteria
A hard surface bottom is required for the device to be placed. As per the space conditions, 1.5 meters from the walls will also be sufficient to ensure that the plate device will have enough space around it.
Performing this exercise when servicing the machine, i.e. if you want to install new plates, tighten the plate package, etc., is absolutely necessary. In addition to the assembly description, the assembly delineation also states the amount of free space that is required.
In the case when the plate device has connections to the portable plate, it is important that the compressed dimension is checked before the pipes are connected to the pipes so that the compressed dimension can be compared to the delineation.
For the future possibility of further services, there must be room around the device in order for access to be made possible as well as to allow for future possibilities. For installation and conservation as well as service and maintenance, the confines suggested for the area are 1.5m in order to ensure good working conditions.
Various Types of Plate Heat Exchanger
Heat exchangers with plates can be categorized into four main types mentioned below:-
- Gasket-type Plate Heat exchanger
- Welded-type Plate Heat Exchangers
- Semi-welded-type Plate Heat Exchangers
- Brazed-type plate heat exchangers
Let’s explore all types of heat exchangers in brief:
Gasket-type Plate Heat exchanger
What is Gasket-type Plate Heat exchanger?
Typically, a gasket-style heat exchanger consists of multiple sheets of thin metal arranged in a channel configuration. A gasket plate heat exchanger, depending on whether internal plates are inserted or removed, can either increase or decrease the amount of heat that can be transferred and cooled. There is also the possibility of disassembling them for the purpose of washing or repairing them.
Stainless steel plates, as well as platinum ones, are normally used to present the plates, mild steel endplates are used to present the endplates, and rubber gaskets are generally used to present the rubber gaskets. In addition to heavy-duty HVAC, automotive, and process engineering applications, gasket plate heat exchangers can be used in a variety of different applications.
It is astonishing to find that despite their small size they are able to achieve such a high level of thermal efficiency. In order to keep plates together and prevent leaks, high-quality gaskets are used in plate heat exchangers and a well-designed seal is used to prevent leaks from these heat exchangers. In order to lower maintenance costs, it is also possible to quickly remove the plates to be washed, re-extended, or replaced.
Uses of Gasket-type plate exchange heater
In many heavy-duty applications, you will find these elements in HVAC, industrial, and process engineering applications as well as a variety of other kinds of heavy-duty equipment. Let’s take a look at some examples of these elements.
Heating and cooling in the district
This type of heat exchanger is used when connecting buildings to a district heating and cooling network, and you can find them in many buildings. District heating and cooling centers are also known as district cooling centers and they distribute fluids like hot water and cold water through some pipelines that form a network.
These central networks are connected to the buildings in order to take advantage of the fluids in these networks to heat and cool the buildings. As a means of connecting the buildings to the district network, a gasket plate heat exchanger is installed between the circuit that connects the building’s central plant to the district network that supplies the electricity.
A central plant circuit extracts heat or coolth from a network in order to be used at the desired time, usually through the use of a heat meter to determine how much energy is being used.
There are many HVAC applications that use gasket type of plate heat exchangers to connect chillers, boilers, and cooling towers indirectly to the central plant system, and they are used in these applications as well.
A number of cooling circuits can be configured in order to reduce the cooling load on the chillers, such as economizer circuits and heat recovery circuits.
Any kind of manufacturing units
Plate heat exchangers are used in many industrial plants as a means of pasteurization and reclaiming waste heat from processes like process chilling. In manufacturing plants, for example, water might be used as a means of cooling down the product that was just made, in order to keep it from overheating.
Before bottling the hot finished liquid product, it must be cooled down so it can be bottled. So the liquid product must go through one of these plate heat exchangers that is attached to the cooling circuit of a chiller. The purpose of doing this is to remove the unwanted heat from both fluids without mixing them together.
Merits and Demerits of Gasket-type plate exchange heater
- It is possible to disassemble the unit for cleaning purposes.
- There is the option to change the capacity of the heating or cooling system.
- In the event that parts are damaged, they can be replaced quickly.
- In spite of the fact that leaks are rare, they are usually caused by gaskets that fail.
- Shell and tubes have a higher pressure drop when compared to shells and tubes.
Welded-type Plate Heat Exchangers
There are two basic types of welded plate heat exchangers: gasket plate heat exchangers and welded plate heat exchangers, except that welded plate heat exchangers, have welded plates instead of bolted plates.
Those types of plate heat exchangers are highly robust and can be used for moving fluids that are hot or eroding as they are capable of withstanding high temperatures. Unlike plate and frame heat exchangers, which are made from sheets of metal that are welded together, mechanical plate washing is not an option since the plates are welded together.
Semi-welded type plate heat exchanger
Heat exchangers with semi-welded plates combine both welded and gasket-tinned plates in their construction. Due to the fact that one fluid path is welded, and the other fluid path consists of gaskets, they are made up of pairs of two plate sets that have been welded together, and then the gasket has been placed over other pairs.
A plate heat exchanger that is formed in this manner, while still being able to transfer fluids of greater intensity, offers a combination of ease of maintenance and the ability to transfer more intense fluids.
Due to the relatively small chance of fluid loss that these types of plate heat exchangers have, semi-welded heat exchangers are widely used for moving heavy materials due to their low chance of fluid loss.
Uses of Semi-welded plate heat exchanger
There are usually patterns like chevrons or fish bones on the heat exchanger plate, which are pressed into the plate in order to improve the heat transfer from the plate to the heat exchanger. In micro plate heat exchangers, small dimples are used instead of microplates.
It can be said that this is a great design for a number of reasons, the first being that the fluid is spread across the plates much more evenly, which significantly increases the amount of surface area that can be used for heat exchange. This also results in much more turbulent flows of fluids as a result, which again increases the heat transfer through the fluids. Having small dimples on the surface of the product increases the surface area, thereby allowing for a greater transfer of heat. It has been possible to reduce the size of the heat exchanger by using these design improvements.
Merits and Demerits of Semi-welded plate heat exchanger
- These kinds of plate exchange heaters are much lighter in weight.
- Reduction of the amount of refrigerant required to operate this heater.
- The transfer of heat is comparatively higher.
- The cleaning procedure of these kinds of heaters is comparatively complicated.
- If damaged somehow the whole heat exchanger needs to be replaced.
- Capacity fluctuating cannot be possible.
Brazed-type plate heat exchangers
There are usually small applications for brazed plate heat exchangers, but in recent years, this has started to change, as larger and more powerful units are being manufactured and used in industry that are capable of handling greater heat loads.
In the automotive and refrigeration industries, these types of plate heat exchangers have been used widely over the years for a wide variety of applications. Stainless steel and copper brazing on the plates ensure that they are highly corrosion-resistant due to their composition of stainless steel plates.
The efficiency and lightweight of brazed plate heat exchangers make them a cost-effective choice for heat exchange. A heat exchanger using thin plates is often used to isolate the fluids from one another. However, to ensure a complete seal, the plates are brazed together to create a full seal.
The seal has two main components:
- brazing, which determines where the plates will be located, and
- positioning, which determines where each fluid will flow.
A heat transfer unit of this type is entirely composed of surfaces designed to facilitate accurate and efficient heat transfer. In addition to being able to withstand high temperatures, these surfaces can also withstand high pressures.
Uses of Brazed-type plate heat exchanger
In recent years, these units have started to change in terms of design and are now being produced and applied to larger applications in the industry in addition to smaller applications where they were typically used in the past. This type of heater is constructed of stainless steel plates welded together into one solid block, that is, they cannot be dismantled in their entirety, and thus they have a fixed heating and cooling capacity.
Use in apartments or Buildings
Individual apartments or homes that are connected to a central heating and cooling network will usually utilize heat interface units of the brazed plate kind in order to connect them to the network. To connect buildings to district heating and cooling networks, large brazed plate heat exchangers are sometimes used, however, the majority of these exchangers rely on gaskets at the moment.
In order to join the loops separated by the heat pump together, brazed plates will often be used to connect them. The use of brazed plates for the condenser and evaporator for refrigerant as well as coils for the water loops is quite common in the design of water source heat pumps that use condensers and evaporators to store refrigerant.
Can be used in Chillers
The use of brazed plate heat exchangers is now being used in the production of chillers. There are two types of chillers, air cooled chillers are equipped with brazed plates as the evaporator, and water-cooled chillers are equipped with brazed plates as the condenser as well. This depends on the cooling load, but on both, the evaporator and condenser can be replaced with brazed plates.
Can be used in Calorifiers
A brazed plate heat exchanger is able to connect a calorifier or hot water tank indirectly to the heating circuit by connecting it to the wiring. With this arrangement, the two components are separated and hot water can be supplied instantaneously or hot water can be drained from the storage vessel depending on how much hot water is required at any point in time.
Merits and Demerits of Brazed-type plate heat exchanger
- There is a reduced likelihood of leaks occurring in the system.
- Compared to gasket types, this type of seal is slightly more efficient.
- An improvement over gaskets in terms of compactness.
- Cleaning these surfaces is more difficult.
- As a precaution, it is imperative that if any damage is caused to the blazed plate exchanger, the entire unit must be replaced.
Heat Transferring of Plate Heat Exchanger
In a plate heat exchanger, the total heat transfer rate can be expressed as follows:
- Q = UAΔTm
The heat transfer coefficient, total plate area, and effective mean temperature difference are represented by U, A & ΔTm respectively. Follow these steps to calculate the total plate area:
- A= NpAp
There are Np and Ap plates except for the end plates and each plate has an area. As well as this, the overall heat transfer coefficient is calculated as follows:
The convective heat transfer coefficients of hot and cold fluids, respectively, are hot and cold.
Plate thickness and conductivity are measured by tp and Kp, respectively. In addition, Rf, hot and Rf, cold are fouling factors for hot and cold fluids, respectively.
Thermal effectiveness and log-mean temperature difference are two basic methods used to calculate heat transfer in plate heat exchangers. The following equation gives the heat transfer rate in the first approach:
- Q = UA(FΔTm)
F is the correction factor, a function of the configuration of the heat exchanger, and ΔTm is the log means temperature difference.
Merits of using Plate Heat exchanger
Heat exchangers with plates have several advantages, they are mentioned below
- It is very simple to clean a plate heat exchanger by taking off the tie bolts and sliding back the movable frame part of the unit. It is then possible to inspect, pressure clean, or remove the plate pack so that it can be refurbished if it is needed.
- Plate Heat Exchangers have a very significant feature in that they can be expanded to suit a wide variety of applications.
It will save you both time and money to simply add plates to your existing Heat Exchanger rather than investing in a brand new Heat Exchanger in order to increase your heat transfer requirements.
- As a result, the Heat Transfer coefficients are very high because of the combination of the counter-directional flow and this technology.
- Plate Heat Exchangers are typically required to occupy between 20-40% of the space that is required by tube and shell Heat Exchangers, depending on the model.
- In the course of heat recovery and regeneration applications, it is particularly important to achieve close approach temperatures, which are very important.
- When you have a high heat transfer coefficient, you have a smaller heat exchanger and less Heat Transfer area. In some cases, you can have even fewer Heat Exchangers.
Demerits of using Plate Heat exchanger
Heat exchangers with plates have several disadvantages, which are mentioned below
- It is a well-known fact that the standard plate gaskets found on plate heat exchangers are not able to withstand pressures exceeding a certain limit, and temperatures above a certain level.
- Due to the corrugated surface and the small flow space on the plates, high-pressure drops are caused due to friction, therefore raising the cost of pumping because of higher pressure drops.
- As the plates rub against each other, friction can cause the plates to wear and form small holes, making it difficult to locate them once they have formed.
- It is true that plate heat exchangers are sometimes used in the process of condensation or evaporation, but these heat exchange devices should not be used for gases or vapors due to the narrow channels and the high pressures that might be encountered.
- Furthermore, the plate heat exchanger is not suitable for processing highly viscous fluids or those containing fibrous materials due to the high-pressure drop associated with the exchanger and the difficulties associated with flow distribution in a high-viscous fluid.
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