1. Optimization design direction of gasket plate heat exchanger
The technology of gasket plate heat exchanger
is improving day by day. In recent years, because of its advantages of high heat transfer efficiency, small volume, light weight, low fouling coefficient, convenient assembly and various kinds of plates, the plate heat exchanger has been widely used at heating industry . The gasket plate heat exchanger can be divided into dismountable, welded, brazed and shell type. Because the removable plate heat exchanger is easy to assemble and clean, and the area of heat exchanger is flexible, it is often used in heating solution. The removable plate heat exchanger is limited by the heat resistance of rubber gasket and is suitable for water to water heat transfer.
We should decide after comparing through technology economy. In order to improve the heat transfer efficiency of heat exchanger and reduce the resistance of heat exchanger, it is necessary to consider that improving the efficiency of gasket plate heat exchanger is a problem of comprehensive economic benefit. And we should reasonably choose the material and rubber gasket material and installation method, to ensure the safe operation of equipment, extend the service life of equipment.
2. Reduce heat resistance of dirt layer
Therefore, the key to reduce the thermal resistance of fouling layer in the heat exchanger is to prevent the plate from scaling. When the scale thickness of the plate is 1mm. It is necessary to monitor the water quality on both sides of the heat exchanger to prevent the plates from scaling and to prevent debris in the water from attaching to the plates. Some heating units in order to prevent water theft and steel corrosion, they add agents in the heating medium, so it is necessary to pay attention to water quality and adhesives caused by debris fouling heat exchanger plate. If there are viscous sundries in the water, a special filter should be used for treatment. When choosing agent, appropriate choice is not sticky agent.
3. Choose plates with high thermal conductivity
The thermal conductivity is about 14. 4W/mK, the material of plate can be selected from austenitic stainless steel, titanium alloy, copper alloy, etc. Stainless steel has good thermal conductivity. Stamping performance is good but not easy to be oxidized.
4. Reducing the thickness of plates
It is related to the pressure-bearing capacity of heat exchangers. When the plate is thicker, the design thickness of the plate has nothing to do with its corrosion resistance. It can improve the pressure-bearing capacity of heat exchanger. When the herringbone plate combination is adopted, the adjacent plates are inverted and the corrugated plates contact each other, forming the fulcrum of high density and uniform distribution, which makes the heat exchanger have good pressure-bearing capacity. The maximum pressure bearing capacity of domestic detachable plate heat exchangers has reached 2.5 MPa. The thickness of plate has a great influence on the heat transfer coefficient. When the thickness is reduced by 0.1 mm and the total heat transfer coefficient of symmetrical plate heat exchanger is increased by 600 W/mK and the asymmetrical plate heat exchanger is increased by 500 W/mK, the smaller plate thickness should be chosen as far as possible.
5. Ways to reduce heat exchanger resistance
It can increase the heat transfer coefficient, increase the average velocity of the medium in the inter-plate runner, and reduce the area of the heat exchanger. However, increasing the flow rate will increase the resistance of heat exchanger, increase the power consumption of circulating pump and equipment cost. The power consumption of the circulating pump is proportional to the third power of the medium flow rate. It is not economical to obtain a slightly higher heat transfer coefficient by increasing the flow rate. When the flow rate of hot and cold medium is comparatively large, the following methods can be used to reduce the resistance of heat exchanger and ensure a higher heat transfer coefficient.
(1) Using hot mixing plate
The plate is divided into hard plate H and soft plate L according to the angle of herringbone corrugation. The angle is generally 120 or so, and the plate greater than 90 is hard plate. The geometric structure of corrugation on both sides of the plate is the same. Inclusion angle is generally 70 or less than 90 for the soft board. The heat transfer coefficient of the hard plate of the hot mixing plate is high, the fluid resistance is high, and the soft plate is opposite. The combination of hard plate and soft plate can form three kinds of runners with high HH, middle HL and low LL, which can meet the needs of different working conditions. The plate area can be reduced by using heat mixing plate instead of symmetrical single-flow heat exchanger. The diameters of the corner holes on both sides of the hot and cold mixing plate are usually equal, and the flow rate of the hot and cold medium is comparable to that of the hot and cold medium. When the flow ratio of hot and cold media is too large, the L pressure loss on the side of cold media is very large. In addition, the design technology of thermal mixing plate is difficult to achieve accurate matching, which often leads to limited area saving. Therefore, when the flow ratio of hot and cold media is too large, the hot mixing plate should not be used.
(2) Using asymmetric gasket plate heat exchanger
A gasket plate heat exchanger with equal cross-section area of cold and hot runners is formed. According to the heat transfer characteristics and pressure drop requirements of cold and hot fluids, the symmetrical gasket plate heat exchanger consists of plates with the same corrugated geometry on both sides of the plate. By changing the waveform geometry of the two sides of the plate, a plate heat exchanger with different cross-sectional area of cold and hot runners is formed, and the angular L diameter on the side of the wide runner is larger. The heat transfer coefficient of asymmetric plate heat exchanger decreases slightly, and the pressure drop decreases sharply. When the flow rate of hot and cold medium is comparatively large, the plate area can be reduced by 15% to 30% by using asymmetric single-flow heat exchanger compared with symmetrical single-flow heat exchanger.
(3) Using multi-process combination
Multi-process combination arrangement can be adopted. When the flow rate of hot and cold media is large, more processes are used on the side of small flow rate to improve the flow rate and obtain higher heat transfer coefficient. In order to reduce the resistance of heat exchanger, less flow is used on the side of large flow rate. The multi-process combination presents mixed flow pattern, and the average temperature difference of heat transfer is slightly lower. Fixed plate and movable plate of plate heat exchanger with multi-process combination have nozzles, so the overhaul work is heavy.