HOW HEAT EXCHANGER PLATES INFLUENCE HEAT TRANSFER EFFICIENCY

Advantages of plate heat exchangers in terms of plates

Spiral plate heat exchangers actually use metal plates (generally 0.5-10mm in thickness) as heat exchange elements, which are made of stainless steel, industrial pure titanium or thin plates of other materials. Generally speaking, a mold is used to directly press the plate into various grooves or corrugations, which can increase the rigidity of the plate to prevent the plate from being deformed when it is compressed, and it also enhances the turbulence of the fluid and increases The heat exchange area of the spiral plate heat exchanger equipment is improved.

The four corners of each plate on the spiral plate heat exchanger will have a hole in each corner, and a gasket groove is pressed around the plate and the hole. Later, when it is actually used, it will be around the hole as needed. A gasket is placed in the groove to allow fluid or prevent fluid from entering the channel between the plates. If several plates are arranged on the support in sequence according to the heat exchange requirements, then the fixed compression plate and the movable compression plate should be compressed by the compression screw, and a fluid channel is formed between the adjacent plates. With the help of the holes and spacers at the four corners of the plate.

Murphy’s spiral plate heat exchanger is designed mainly with longitudinal herringbone corrugations. Herringbone waves are divided into horizontal herringbone waves and longitudinal herringbone waves. When the fluid flows in the channels formed by the two types of plates, it will inevitably form a network flow, but the flow resistance and heat transfer coefficient are different.

When the spiral plate heat exchanger equipment adopts transverse herringbone corrugated plates, the fluid will appear smoother when passing through the channels formed between the plates, the flow resistance is also relatively small, the pressure drop is very low, but its heat transfer coefficient It is also slightly lower than the longitudinal herringbone corrugated plate, so it is more suitable for occasions with low flow velocity, high viscosity and relatively large flow.

If the spiral plate heat exchanger equipment adopts longitudinal herringbone corrugated plates (the corrugation angle is 120°), it is easier to produce turbulence when the fluid flows through the channels formed between the plates, and the heat transfer coefficient is high, so it can Produce ideal heat exchange effect.

Improve the heat transfer coefficient of the plate surface and increase the heat transfer coefficient in the heat exchanger.

The heat transfer coefficient of the spiral plate heat exchanger has an important relationship with the heat transfer coefficient of the plate surface. Increasing the surface heat transfer coefficient of the plate itself is because the corrugation of the spiral plate heat exchanger can cause the fluid to produce turbulence at a small flow rate. It is also because of this that a relatively high surface will be obtained to a large extent. The heat transfer coefficient and surface heat transfer coefficient are related to the geometric structure of the plate corrugation and the flow state of the medium.

The waveforms of the plates on the spiral plate heat exchanger mainly include herringbone, straight and spherical shapes. After years of research and experimentation, it is found that the corrugated cross-section shape is actually a triangle (the heat transfer coefficient of the sinusoidal surface is large, the pressure drop is relatively small, and the stress distribution is uniform when compressed, but the processing is difficult).

It will have a higher surface heat transfer coefficient, and the greater the angle of the corrugation, the higher the flow velocity of the medium in the flow channel between the plates, and the greater the surface heat transfer coefficient.

In the spiral plate heat exchanger, the heat transfer coefficient is improved. At this time, it is necessary to pay attention to choosing the plate material with high thermal conductivity, and you can also choose austenitic stainless steel, titanium alloy, copper alloy, etc.

For stainless steel, its thermal conductivity is good, the thermal conductivity is about 14. 4 W/(mK), high strength, good stamping performance, not easy to be oxidized, and the price will inevitably be lower than titanium alloy and copper alloy , It is used more in heating engineering, but its resistance to chloride ion corrosion will also appear to be relatively poor.

In the spiral plate heat exchanger, the heat transfer coefficient is improved, the thermal resistance of the fouling layer is reduced, and the key to reducing the thermal resistance of the fouling layer of the heat exchanger is to prevent the plate fouling. When the fouling thickness of the plate is 1 mm, the heat transfer coefficient is reduced by about 10%. Therefore, at this time, it is necessary to monitor the water quality on the hot and cold sides of the spiral plate heat exchanger to prevent the plates from scaling.

Reduce the thickness of the plate and improve the heat transfer of the heat exchanger

Spiral plate heat exchangers improve heat transfer, in fact, in order to improve the efficiency and capacity of spiral plate heat exchangers. We should pay attention to reducing the thickness of the plate. The design thickness of the plate has nothing to do with its corrosion resistance, but It is related to the pressure bearing capacity of spiral plate heat exchanger equipment.

If the plates are thicker, the pressure bearing capacity of the heat exchanger can be improved. After that, if the plates on the spiral plate heat exchanger are combined with herringbone plates, this time it is also necessary to pay attention to the inverted adjacent plates, and the corrugations will also contact each other. In this regard, we actually need to pay attention to it. At this time, a fulcrum with high density and uniform distribution will be formed. The corner holes of the plate and the edge sealing structure have been gradually improved, so that the heat exchanger equipment has a good The pressure capacity.

The pressure-bearing capacity of the Murphy detachable spiral plate heat exchanger has reached 2.5 MPa, and the plate thickness has a relatively large influence on the heat transfer coefficient. The thickness is reduced by 0.1mm. The total heat transfer of the symmetrical plate heat exchanger The coefficient is increased by about 600W/(m.K), and the asymmetric type is increased by about 500 W/(m.K). Under the premise of satisfying the pressure-bearing capacity of the heat exchanger, it should be noted that a relatively small plate thickness should be selected .

Spiral plate heat exchangers can improve the heat transfer energy from the perspective of increasing the logarithmic average temperature difference. The flow patterns on the equipment include counterflow, cocurrent and mixed flow (both countercurrent and downstream). Under the same working conditions, the logarithmic mean temperature difference is large in countercurrent flow and small in downstream flow, and the mixed flow pattern is between the two.

When spiral plate heat exchanger equipment is in use, the method of increasing the logarithmic mean temperature difference of the heat exchanger should also pay attention to the use of countercurrent or a mixed flow pattern close to countercurrent as much as possible. At this time, it is also necessary to pay attention to increasing the heat as much as possible. The temperature of the cold side fluid should then be lowered.