The organization of the coolant flow pattern is determined so that the heating and heated mediums mix on different sides of the same plate. Hot and cold channels are arranged alternately through them. The heat-exchanger is one type of recuperative device for heat exchange.
How the Heat Exchanger Works
The principles of their operation are based on the movement of heat exchange between two mediums, for which a non-mixing contact plate is required. There are openings on the front and rear plates of the heat exchanger through which the heat consumer and the coolant enter the unit. The corrugated type of wall layer in conditions of a flow moving at high speed gradually becomes turbulent. The mediums move towards each other from different sides of the plate, avoiding mixing. Plates, which are arranged in parallel, form working channels. Moving through them, each medium carries out heat exchange and leaves the internal limits of the equipment. Thus, plates are an important element of the heat exchanger. Flows inside the plate heat exchanger follow single-pass and multi-pass schemes depending on the technical characteristics and conditions of the problem being solved.
Heat Exchanger Design
The design of the heat exchanger for the heating system consists of several disassemblable elements:
- Plates – static and movable;
- Plates;
- Guides – heat movement occurs along them, they have a rounded shape;
- Fasteners – designed to collect the plates into a common structure.
There are several variants of plate heat exchangers differing in accordance with the dimensions of the frames. This parameter determines the power of the equipment used in the system and the level of heat transfer produced. It is quite simple to increase the productivity of the heat exchanger: increase the number of plates. Depending on this, the dimensions and weight of the equipment change.
Types of Heat Exchangers
Plate heat exchangers are divided into several types according to their design features. When organizing a heating system, you can choose:
Disassemblable: In the design of the secondary disassemblable plate heat exchanger, the main function of heat movement from one coolant to another is performed by a plate pack. They are arranged alternately, and dense rubber gaskets are placed between them, so the likelihood of displacement of mediums is completely excluded. The structure of the coolant allows organizing two circuits of movement.
Brazed: The basis of the brazed device system is also a plate pack. But the elements are brazed and cannot be disassembled. Copper and nickel are used as brazing materials in brazed models. You can find nickel-brazed and copper-brazed plate and shell-and-tube heat exchangers on the market. If aggressive mediums act as heat carriers in brazed devices, nickel solder is recommended.
Semi-welded: The secondary plate heat exchanger is equipped with a plate pack, which is placed in a combined way:
- brazing is carried out in pairs;
- seals are placed outside the paired mini-pack;
- then the next mini-pack is installed.
The design features of the device make it possible to use secondary plate heat exchangers not only with water but also with aggressive mediums, as well as in cooling. The welding method allows completely eliminating the possibility of freon leakage.
Welded: In this case, the plates are welded without a seal. The coolant flow moves through the corrugated channel, and the second flow – through the tubular one. The welded model is designed to operate at extremely high parameters, the maximum temperature can reach 900 °C, and the pressure – up to 100 bar. The same applies to the choice of mediums in the system, due to the absence of rubber sealing elements and the welded mounting method, the likelihood of leakage is completely excluded. Such brazed devices are intended for production conditions.
Heat Exchangers by Heat Transfer Type
A heat exchanger is used to transfer heat from one medium to another. Implementation can be done in two ways:
- Regenerative: The secondary plate device has a wall made of a material with high thermal conductivity. It separates and prevents the mixing of two circulating mediums.
- Recuperative: Heat exchange here occurs on a single surface. Liquid heat-conducting mediums come into contact with it alternately.
Heat Exchangers by Application
Brazed, semi-welded, and disassemblable heat exchangers, regardless of the features of their construction, work only because they allow heat exchange between adjacent mediums without the possibility of mixing them. Plate models are applied in housing and communal services for organizing individual heating systems, in the energy sector, and other areas.
The wide range of application options and the popularity of plate devices for heating are due to the small dimensions of the heat exchangers, operation at different pressure ranges, and their high efficiency, which is primarily due to the turbulent circulation of the heat carrier substance. This same feature allows completely eliminating the possibility of scale formation on the internal surfaces and overall any sediment.
The main element of the secondary plate heat exchanger is thin steel plates. They are distributed into packs.
The principle of operation is based on the ability to transfer heat from a hot medium to a cold one. The medium flow circulates constantly inside the system under high pressure, and the mixing of water or another heat carrier is completely excluded due to the presence of rubber gaskets placed precisely in the zones of possible contact. Modern plate heat exchangers are efficient because the mediums under pressure move through slit channels with a complex shape.
Depending on the application area, heat exchangers are divided into several types:
- Shell-and-tube: The installation structure consists of tubes assembled into a single bundle. A grid element is used for connection. Fixation occurs by welding and brazing.
- Plate: This type of heating device is a construction of plates. It has certain dimensions and is connected by welding.
- Coiled: The heating construction consists of coils. The heat carrier moves through a system of curved tubes, passing through the entire device in addition to the circuit.
- Spiral: They use sheets of steel bent into a spiral.
- Water and air heating devices.
In general, there are many options for heat exchangers, but those listed are the most common. Plate heat exchangers are the most popular, so it is recommended to study their features first.
Heat Exchangers by Medium Flow Direction
The efficiency of a plate heat exchanger is based not only on the design features of the device but also on the direction of the flow of mediums under pressure:
- Cocurrent flow: The heat carrier, for example, water, moves along the circuit in one direction. This is a good option for heat exchange, however, at the output, heat exchange will end, and both flows will have the same temperature. If the characteristics of the flows in the system are different, then equilibrium will occur earlier, meaning heat exchange will end within the circuit.
- Countercurrent flows in heating systems: Flows move in opposite directions, which allows optimal heat exchange throughout the movement. After passing through the entire circuit of the system, the temperature of the heated water or other medium will be equal to the temperature of the heat carrier at the inlet, and vice versa.
It can be difficult to choose which model you need. It is wise to consult a specialist on this matter.
Heat Exchangers by Medium Interaction Type
Depending on the type of interaction between the mediums, secondary heat exchangers are divided into:
- Surface: Mediums do not mix, and their contact in the circuit occurs through a special surface. If it is a plate model, plates are used, and in shell-and-tube exchangers, tubes are used.
- Mixing: In some cases, heat exchange is carried out by mixing mediums. An example of such a device is a cooling tower. They are used in production for cooling large volumes of water using an air stream. These include steam bubblers, nozzle heaters, cooling towers, and barometric condensers.
Application Areas of Heat Exchangers
Plate and shell-and-tube heat exchangers are used everywhere. They are indispensable devices in the gas, refrigeration, petrochemical, and oil refining industries. The construction of the equipment depends on the intended conditions of use:
- Food industry: The equipment is indispensable in the production process of dairy products, sugar, vegetable oils, and alcohol.
- Metallurgy: The use of plate heating heat exchangers is due to the need for cooling. During operation, the hydraulic systems of furnaces and other functional heating elements heat up, so the installation of a plate brazed, welded, or spiral heat exchanger becomes mandatory.
- Shipbuilding: Used in systems as a source of cooling as well. Sea water can be used to cool the engine in the circuit. It is possible to use in the heating system, but usually on large vessels.
- Municipal heating supply: The heating secondary plate or shell-and-tube heat exchanger is ideal for heating water in a heating system. Plates made of anti-corrosion steel are required.
Plate models, whether welded or simply assembled, are the most convenient, efficient, and overall advantageous option for a heat exchanger. They are easy to install and set up, require no special maintenance, and in case of breakdown and system failure, you can easily find a master capable of repairing it. This heating system option is chosen to provide heat for residential and commercial buildings.