What is a Heat Exchanger?
The heat exchanger is a circuit element that provides heat transfer between two fluids (liquid or gas) with a temperature difference between them (without mixing with each other) without any physical contact.
In principle, heat exchangers are divided into three types;
– Tube type heat exchangers
– Plate type heat exchangers (Detachable type, Welded type, Semi-welded type, Brazed type)
– Special application Heat Exchangers (Platecoil Heat Exchangers, Econocoil Heat Exchangers, Spiral Heat Exchangers)
Plate Heat Exchangers
Plate Heat Exchangers are efficient heat exchangers with the widest product range in the world for different applications. Plate heat exchangers are created based on the concept of modular construction. Many different types of heat exchangers can be obtained by combining heat exchanger bodies, plates and customary inlet and outlet nozzles in different structures. The most important feature of Plate Heat Exchangers is that they can be made suitable for new conditions as a result of easily adding or removing plates depending on the change in working conditions, and they can be opened easily for cleaning and maintenance.
The patented plates for heat exchange are fixed by arranging them on the lower and upper carrier bars between the front and rear pressure plates made of steel by means of studs. The fact that each of these plates is pressed in one piece is very important for higher strength. There are no welds or connections on the plates. A standard unit has four holes on each plate, each in one corner. In addition, rubber-based gaskets are located inside the gasket slot around the plate in order to provide impermeability and create heat transfer channels. Inlet and outlet nozzles are located on the front platen in most applications. However, in special cases, the heat exchanger may need to be manufactured with multiple passes, in which case the inlet-outlet nozzles are located on both front and rear pressure plates. This is the general structure of the plate heat exchanger and this constructive structure allows the exchanger to be opened easily for control and cleaning purposes.
Plate Heat Exchanger Construction
The patented plates for heat exchange are fixed by arranging them on the lower and upper carrier bars between the front and rear pressure plates made of steel by means of studs. The fact that each of these plates is pressed in one piece is very important for higher strength. There are no welds or connections on the plates. A standard unit has four holes on each plate, each in one corner. In addition, rubber-based gaskets are located inside the gasket slot around the plate in order to provide impermeability and create heat transfer channels. Inlet and outlet nozzles are located on the front platen in most applications. However, in special cases, the heat exchanger may need to be manufactured with multiple passes, in which case the inlet-outlet nozzles are located on both front and rear pressure plates. This is the general structure of the plate heat exchanger and this constructive structure allows the exchanger to be opened easily for control and cleaning purposes.
What is the Working Principle of Plate Heat Exchanger?
In Plate Heat Exchangers, the fluids passing through the flow channels formed on the plates by means of gaskets flow without mixing with each other, while the desired heat transfer is realized due to the temperature difference. Plate Heat Exchangers; plate size and plate number are determined according to the flow rate of the fluid passing through, inlet-outlet temperature values, physical properties, pressure drops and the desired maximum strength value. Symmetrical or asymmetrical designs on the plates are in a structure that will allow the fluids to flow in a turbulent manner, which causes high heat transfer coefficients to be obtained. In Plate Heat Exchangers, the contact points created between the plates enable the plate package to reach the desired strength.
Plate Heat Exchanger Connection Diagram
What are the Advantages of Plate Heat Exchanger?
Special gasket design that prevents mixing of fluids:
Mixing of fluids for any reason is completely prevented thanks to the special gasket design. In case of any gasket failure, the flow is directly outward from the part open to the atmosphere. This can be detected externally.
Low weight and small installation volume thanks to its compact design:
Plate heat exchangers occupy 20-30% of the volume occupied by a tube heat exchanger of the same capacity. This provides a smaller volume and lower investment cost.
High efficiency – low cost thanks to full turbulence: In plate heat exchangers, high turbulent flow is created by the special shapes on the plates in the flow channels formed by the plates, which ensures high heat transfer coefficients to be achieved. These high heat transfer coefficients obtained provide lower costs by reducing the amount of material used in the heat exchanger.
Ability to easily increase capacity: Due to the modular structure of plate heat exchangers, the capacity can be increased by easily adding plates.
Lower maintenance costs: In plate heat exchangers, maintenance can be carried out without the need for any additional space, simply by removing the studs and easily accessing the heat transfer plates. In tube type heat exchangers, on the other hand, an additional space is needed as much as the volume used to take the tube bundle out.
Comparison of Tube and Plate Heat Exchangers
Plate heat exchangers are more efficient than tube heat exchangers due to the high turbulent flow created in patented plate designs. They occupy 20% – 30% of the volume used by tube heat exchangers. They are lighter and cheaper than tube heat exchangers in terms of material used.
| Plate Heat Exchanger | Tube Heat Exchanger |
|---|---|
| Heat transfer coefficient is 3-5 times higher | Its yield is low. |
| It can achieve a temperature approximation of 1ºC. | It can achieve the temperature approximation of 5-10 ºC. |
| It does not require extra space for maintenance. | To remove the tube bundle, it needs an extra space of its own size. |
| It is very easy to repair and maintain. Simply remove the studs and push the rear pressure plate against the support column. | For repair, it is very difficult to disassemble and the bundle must be taken out. |
| Due to the high turbulence, the rate of contamination is less. | It has a higher contamination rate up to 3-10 times. |
| Due to the gasket design, mixing of two fluids is impossible. | Fluids can mix from both welds and pipes. |
| Plaka eklenerek kapasite artırımı yapmak mümkündür. | It is not possible to increase the capacity. |
| There is practically no heat loss. It does not require insulation. | It requires insulation due to the high heat loss. |
Importance of Material Used in Plate Heat Exchangers
One of the factors that ensure that plate heat exchangers operate smoothly for many years under the desired thermal conditions is that the materials that make up the heat exchanger are of a certain quality. In order to carry out the quality tests of the materials in accordance with ISO 9001, each material must be marked for retrospective examination.
Body Material; The quality of the heat exchanger bodies, which can also be made of different materials according to the working pressure of the system, should be at least St 37-2. (It can also be made of different materials such as St 44 and St 52). The most suitable body thickness is calculated by making strength calculations in accordance with the maximum working pressure of the heat exchanger. According to the process used, the body materials can also be manufactured as stainless. In applications where the cost is desired to be lower, the body made of carbon steel can be covered with stainless material. While the Plate Heat Exchanger body is being manufactured, it goes through the processing of hole centers, sandblasting, degreasing, phosphating and painting, respectively.
Plate Material; It is very important to choose the plate material suitable for the fluid used and the desired maximum working strength. In general, the following plate materials are used, and the most frequently used material type is 1.440 / AISI 316.
| AISI 304 | Nİ 200/201 |
| AISI 316 | G-30 |
| AISI 316 L | C- 4 |
| 254 SMO | INCONEL 625 |
| 654 SMO | INCONEL 825 |
| TİTANYUM | MONEL 400 |
| Tİ – PD | TANTALUM |
| C-276 | C – 22 |
Gasket Material; The limit factor in plate heat exchangers is the gasket. That’s why choosing the ‘right’ gasket material is so important. Various gasket types are listed below, depending on the application. One of the most important points that should not be forgotten is that heat exchanger gaskets are produced in three qualities: normal, sulphurous and peroxide. When these three quality gasket materials are compared among themselves, the peroxide material always provides the best performance in terms of working conditions.
Gasket materials commonly used in Plate Heat Exchangers
| Nıtrıle (Nbr) |
| Hnbr |
| Etilen Propilen (Epdm) |
| Florokarbon (Fpm) |
| Vıton Gf |
| PTFE Encapsulated NBR |
Calculation Method Used in Plate Heat Exchangers
While making plate heat exchanger calculations, each company generally uses a program developed by their own research and development departments, and the heat exchangers are dimensioned as a result of this program. In heat exchangers of different brands, with the same calorific value and capacity, the difference between heat transfer m² should be between 3-5%. If this difference is too high, the reason for this should be investigated thoroughly.
The Importance of Pressure Losses in Plate Heat Exchanger Design
In plate heat exchangers, since the shapes on the plate will create a resistance against the flow of the fluid in the installation, pressure loss will occur in the system. Pressure losses, which have an important place in the design of plate heat exchangers, directly affect the surface area of the plate heat exchanger and accordingly the costs. In plate heat exchangers, the higher the pressure loss, the smaller the surface area of the plate heat exchanger, while the lower the pressure loss, the larger the surface area of the plate heat exchanger. For this reason, when asking for proposals from companies, the desired maximum pressure losses should be given along with the same calorific values, and the result should be evaluated accordingly.
Considerations When Buying a Plate Heat Exchanger
Plate Heat Exchangers; It is very important to choose the right plate material, the right gasket material and both the plate and body thickness with the desired strength, suitable for the application and maximum pressure in which it will be used. In addition, the quality certificates of the product and its origin are of great importance.
Nowadays, unfortunately, there are companies that produce and market very low quality plates (by showing high quality) and gaskets both in China and in places where the manufacturing sites are unknown, just in order to sell materials at cheap prices.
Although almost every company has ISO 9001 certificate today, the marking (which is an indispensable part of ISO 9001) on their plates and gaskets is not included on the plates and gaskets of many companies, or even on the body material. This should give an idea of how accurate the certificates they use are.
For this reason, it will be very important to prefer companies that produce using today’s technology and have references both in the country and abroad, in order to have a product that provides the desired values and is worth the price paid.
Plate Heat Exchanger Installation
The plate heat exchanger is tested under pressure at the factory before delivery. A product control certificate is also supplied with the heat exchanger.
Placement and Assembly; The heat exchanger must be installed with space on both sides so that it can be intervened for later maintenance. These gaps vary according to the size of the heat exchanger, you can get information about this from the seller company.
All connections to the heat exchanger must be equipped with shut-off valves. The lower connections must be equipped with S2 and S3/M2 and M3 relief valves. The upper connections, on the other hand, should be equipped with ventilation devices at their highest points S1 and S4 / M1 and M4).
In case of welding, the Plate Heat Exchanger should not be used as grounding. Otherwise, an electric arc may occur between the heat transfer plates.
Commissioning – Operation of Plate Heat Exchangers
First, check to make sure that the operating data does not exceed the values on the nameplate of the heat exchanger and that all studs are properly tightened.
Pumps; Pumps feeding the heat exchanger should be used together with balancing valves. If the pumps are strong enough to produce a pressure higher than the nominal pressure of the heat exchanger, they must be used with a safety valve. Pumps must not suck air.
Operating; To prevent pressure shock, the pumps must be started with the valves closed. All valves should be opened at the same time as possible. The flow rate is then gradually increased until the operating temperature is reached. Impacting must be avoided, otherwise the rubber seals may slip out of place and cause leakage.
Ventilation; In multi-pass heat exchangers, the air of the heat exchanger must be bled immediately after the first start-up. Trapped air can lead to airlocking and excessive superheating of the plates; as a result, the heat transfer capacity is reduced and the risk of wear increases.
Maintenance of Plate Heat Exchangers
If possible, do not operate the heat exchanger overnight and wait for it to cool.
Disconnect all connections to the collapsible cover plate.
– Unscrew the screws.
– Ensure that the hinged door is moved parallel to the frame plate by loosening the nuts alternately.
Cleaning the Plates
– Brushes made of steel or carbon steel should not be used; Likewise, stainless steel should not be used for titanium plates.
– First, a strong water jet is sprayed onto the surface that transfers the heat, and then the surface is cleaned by rubbing with a nylon or similar brush.
– Be careful not to damage the gaskets.
– Oxide or lime residues are cleaned with a soft brush and a 2-5% nitric acid solution. (Hydrochloric acid or sulfuric acid should not be used). Organic deposits containing protein can be removed with a soft brush and 2% sodium hydroxide solution at 50°C.
– Oily deposits are cleaned with a soft brush using kerosene. After cleaning, rinse thoroughly with water and rinse.
Applying adhesive to gaskets or clip gaskets; The adhesive is applied with a small flat brush to the parts of the plate where the gasket will be placed. The gasket is then placed in its place on the plate. After drying for approximately 30 seconds (this time depends on the thickness of the adhesive layer and how thin the adhesive is), the adhesive holds the rubber gasket securely in the gasket seat, thus facilitating assembly. Then, with the help of other plates or a material of suitable weight from another material, a light pressure is applied to the plate for about ½ hour. Place the gasket on the plate, When the right side is up, the code number of the gasket is also visible around the air vent passage. Make sure that the clips of the gaskets align with the places on the gasket seat of the plate. Insert each clip into the overlying part and push the gasket until the clip snaps into place. Gasketed plates are now ready to be mounted on the heat exchanger body.
Mounting of Plates to the Heat Exchanger; Before installing the heat exchanger, check all gaskets and all surfaces against gaskets. Particles that could compromise sealing or damage gaskets or sealing surfaces must be removed.
With the help of the grouping scheme of the Plate Heat Exchanger made from the computer, the plate is placed in the heat exchanger according to the position of the plate in the heat exchanger. Make sure the plate pack is installed correctly. Plate edges should be in the shape of a normal honeycomb.
Compressing the heat exchanger; The plate pack must be compressed to a certain thickness (A-size). A-dimension * Indicates the inner length in millimeters between the 3% fixed front pressure plate and the movable rear pressure plate.
Dimension A may differ * 3% depending on the tolerance of the plate thickness and the pressing depth. If dimension A is correct, the plates stop with metallic contact between them.
When compressing the heat exchangers:
– Tighten the screws.
– Tighten the nuts as the resistance increases.
Important Note: More compression may cause deformation of the plates. Never clamp the exchanger under pressure!
Duct Designs Used in Plate Heat Exchangers
In plate heat exchangers, the higher the turbulence flow in the flow channels formed by the plates, the higher the heat transfer coefficients will be. Therefore, plate heat exchanger manufacturers use high cost AR on channel designs in the plates in order to obtain a higher heat transfer coefficient (k). -Does GE studies. The higher the heat transfer coefficient, the lower the need for heat transfer areas. In other words, the same application can be solved using fewer plates.
A. ULTRAFLEX (Asymmetrical) Design
In the Ultraflex plate design, there are both wide-angle and narrow-angle plates. In this design, the opposite (diagonal) flow direction is used. The most important feature of this design is the ability to create six different channel designs that can respond to different applications as a result of turning or turning a pair of narrow-angle and wide-angle plates. In this way, plate heat exchangers are designed according to the characteristic data of each application and the design that gives the highest heat transfer coefficient is selected.
B. Symmetrical Design
Symmetrical plate design also consists of wide-angle and narrow-angle plates. In this design, either parallel or diagonal flow can be used. In symmetrical design, three different channel designs can be obtained by using only wide-angle, narrow-angle only or both narrow-angle and wide-angle plate pairs.
Kaynak: tesisat.com / ekinendustriyel.com
