Analysis of plates and seals
In the design of plate heat exchanger, the overall structure of the plate has a close relationship with the sealing strength. The reasonable sealing structure design can not only improve the rigidity of the plate, improve the pressure resistance of the plate heat exchanger, but also ensure a good seal. Sex. The sealing structure is composed of the sealing groove and the sealing gasket of the plate. The performance (physical property, chemical property and process performance) of the sealing gasket, the form of the sealing groove and the compression ratio of the sealing gasket are the three major elements of the sealing design.
the seal groove
The shape of the sealing groove is directly related to the positioning of the sealing gasket in the sealing groove, which affects the stability of the sealing gasket during operation, and is also directly related to the sealing effect. The reasonable sealing groove should be designed so that the gasket does not shift at the designed position under the condition of being stressed and heated, and the original compression ratio is basically maintained. In order to meet the above requirements, in the design of the sealing groove, the closed form should be used as much as possible. In addition, under the premise of fully taking into account the tensile properties of the sheet material, the inclination of the sealing groove should be as small as possible. At present, in China's development of the plate type, the inclination of the sealing groove is generally between 25 ° ~ 35 °; and some well-known foreign brands, most of the plate sealing groove inclination angle is about 20 °, small to 7 ° .
At present, the design of various plate-type sealing grooves at home and abroad adopts a flat form, as shown in the figure. The utility model has the advantages that the sheet processing is simple and the sealing gasket has a simple structure, is easy to be bonded, and the sealing gasket has good stability in the sealing groove. However, there are also disadvantages. For example, when bonding the sealing gasket and the sealing groove, the alignment must be quite accurate, and no offset is allowed. Otherwise, the sealing gasket will break away from the sealing groove and lose the sealing effect when clamping. In view of this situation, this paper has done a lot of research and experiment on the form of the sealing groove, and developed a new type of structure. As shown in the figure, the sealing gasket has good stability during assembly, and the positioning is accurate, and the sealing groove is improved. The rigidity reduces the clamping force during assembly and reduces the degree of deformation of the plate. The results of many years of use show that the sealing groove form has good effect and has great promotion value.
Gasket
The gasket is an important part of the plate heat exchanger. In the assembly, the gasket is first adhered to the sealing groove of the plate, and the gasket is placed in the circumferential groove of the hole according to the fluid flow. In order to allow or prevent fluid from entering the passage between the plates, the purpose of heat exchange is achieved. The material, structural form and compression ratio of the gasket are directly related to the sealing effect of the plate heat exchanger.
Gasket material
At present, the commonly used gaskets are made of synthetic rubber and asbestos rubber. Synthetic rubbers commonly used are nitrile rubber, EPDM rubber and fluororubber. The physical properties of synthetic rubber gaskets mainly include permanent compression deformation and elongation at break under working conditions. The hardness index of rubber sealing gaskets should be determined according to the form of the sealing groove and the amount of compression.
Structural form of the gasket
There are also many types of structural forms of the gasket, and the cross-sectional form thereof is roughly rectangular, trapezoidal, hexagonal, pentagonal, and the like. There are two main types of common forms: one is shown in the figure, the upper part of the cross section of the gasket is pointed; the other form is as shown, and the upper part is flat. The former is to increase the degree of deformation of the gasket by the difference in size from the tip to the middle. The structural design is actually a flat seal, and the non-linear seal, because the bottom of the seal groove of the plate is flat, when the bottom of the plate seal groove is flat. This structure can offset some of the defects. The purpose of the latter design is to reduce the amount of compression of the gasket, which is in the form of a flat compression. The main disadvantage is that during the assembly process of the plate, the plate is easily misaligned, the clamping force is too large, and the deformation of the plate is easily caused. Through analysis and experiment, this paper designs the cross section of the gasket corresponding to the sealing groove shown in the figure as shown in the figure, which makes the assembly simple and improves the pressure bearing capacity of the plate.
Gasket compression ratio
Generally, the ratio of the compression amount of the gasket to its original thickness, that is, the compression ratio, is used as the design basis of the gasket. Based on years of design experience and analysis of a large number of plate heat exchanger sealing structures at home and abroad, the author believes that the compression ratio is between 20% and 25%.
The quality and service life of a plate heat exchanger is highly dependent on the quality and service life of the gasket. For most heat exchangers, the plates are generally not damaged, and the gaskets are prone to aging and cause leakage, so the quality of the gasket determines the quality and service life of the heat exchanger.
