Weak current College】 【plate heat exchanger plate structure, combining form and seal.

<br> Summary: plate heat exchanger in the normal condition of the main failure mode is a seal failure. By stiffness on the slab, plate sealing structure including plate seals, gaskets, found the plate stiffness can improve heat exchanger capacity overall pressure; reasonably .design seal groove, can effectively improve the sealing gasket in the seal grooves in the stability and reliability seal. It also describes some prevent seal failure of practical experience. <br> <br> Keywords: plate heat exchanger; seal; fail; stiffness; .structural form <br> <br> Chinese book classification number: TH6 document identification code: A article number: 1671-3133 (2007) 01-0115-04 <br> <br> Introduction <br> <br> Plate heat exchanger is .a high efficient, energy saving heat transfer equipment, with high heat transfer coefficient, compact, supplies, forms, easy maintenance and many other advantages, the gradual expansion of the field of application, has been widely used in machinery, electric power, metallurgy, .chemical industry, textile, beverage, urban heating industries and areas that demonstrate strong competitiveness. <br> <br> 1 plate heat exchanger of the overall structure of the <br> <br> Plate heat exchanger to metal plate (thickness 05 ~ 10mm .) for heat exchanger components are made of stainless steel, industrial pure titanium or other materials for thin plate pressing. Will usually die plate pressed into a variety of Groove or wave shape, you can increase the stiffness of the plate to prevent plate deformation under pressure ., but also enhances the level of turbulent fluid, increasing heat transfer area. Each plate corners all open a hole, the slab is surrounded around the hole with sealing gasket tank pressure, and in the hole of the week is placed in the slot, to .allow the washer fluid or fluid into the plate surface blocked between the channel. If the number plate in accordance with the heat requirements then arrange on the stand, with fixed clamping plate and active clamping plate by clamping screw press, in the adjacent plate-form .fluid channel, with the help of the four corners of the orifice plate and gaskets. <br> <br> Plate heat exchanger plate structures vary, their design is the ultimate goal is to strengthen the plate heat exchanger increase plate surface effects, stiffness, .improve the heat exchanger capacity of pressure. Ideal form factor design, not only has a large heat transfer area, lower pressure drop, higher heat transfer coefficient, but also has good rigidity, so very thin plate in the fixed clamping plate, and activities of .the clamping plate clamping force of mutual support, to resist pressure to imbalances within the channel on the impact of its production. To this end, in the form factor design but also the supporting point of distribution as well as the layout of the rebar. < .br> <br> A piece of plate according to their functionality can be divided into diversion section, heat exchanger parts, sealing parts, edge support and a hanging position, five parts, which heat is the core of the slab structure, and its structure .depends on the nature of the heat transfer medium, according to the design of heat transfer and fluid dynamics. <br> <br> 2 plates of structural form <br> <br> Plate heat exchanger as a key element, its structure and design .sensible or not will have a direct impact on the plate of heat transfer performance, as well as the total resistance drop of carrying capacity. Currently there are over 100 species of core structure, its main corrugated form: Chevron wavy (including horizontal Chevron wavy and .Vertical Chevron wavy), horizontal wavy, vertical, diagonal ripple ripples. China's production of plate heat exchanger plate structure, mostly to Chevron wavy, belong to the typical mesh mobile plate-type structure, its characteristics are in the Board room of fluid channels, .the wrong column in full-contact, the contact points in the fluid surrounding the flow formation between spirals along tracks, resulting in strong disturbance. If you increase the degree of fluid flow, you can reduce the thickness of the laminar, effectively improve no transformation .of convective heat transfer coefficient, so as to achieve the aim of increasing the heat transfer coefficient. Experimental proof: for water, when the Reynolds number Re = 20 ~ 200, velocity-02 ~ 05m / s, the fluid that is entering turbulent state ., has a very high heat transfer coefficient. To this end, in the plate and decorate with uniform, and the appropriate contacts decrease spacing, in addition to greatly enhance the overall rigidity of the plate, can withstand a large differential pressure. <br> .<br> 3 plate combination forms <br> <br> Depending on the plate heat exchanger market research, our heat exchangers manufacturers design factor mainly Vertical Chevron wavy. <br> <br> Fluid in the above two forms of plate consisting of channel .flow can form a reticular flows, but the flow resistance and heat transfer coefficient. <br> <br> When horizontal Chevron corrugated slices, fluid after plate between the channel more smooth, fluid resistance is very small, very low pressure drop, but the .heat transfer coefficient than vertical Chevron corrugated plate slightly lower, thus more suitable for low-velocity, high viscosity and flow quite big occasions. <br> <br> When using vertical Chevron corrugated plate (ripple angle of 120 °), fluid in the .plate between the channel flow through time is extremely easy to generate turbulence, high heat transfer coefficient and thus can produce ideal heat effect, its main disadvantage is the pressure loss is relatively large, and therefore only apply to the pressure is not too big, not .applicable to high viscosity, low flow resistance requirements. <br> <br> Following to Tianjin a heat transfer equipment factory production of the BR100-plate and BRh070-plate for example (both plate duration aspect ratio closer) for instance, to compare the .same working conditions, two plate-type heat exchangers for the pressure loss value. The former is a landscape Chevron corrugated plate, the latter as vertical Chevron corrugated plate structure. <br> <br> Working conditions: 80 ¡ .æ quenching oil cooling to 60 ° c, quenching oil processing capacity 8t / h. Quenching oil proportion of physical data: γ = 800kg/m3; dynamic viscosity μ = 13 × 10-3Pa · s. 31 of the BR100-type heat exchanger .<br> <br> Channel cross-section: 000289m2; equivalent diameter: 00082mm; its resistance-associated to: En = 19500Re-047. .Then: <br> <br> ΔP = Enμ2/γ/g <br> <br> Type: Re-Reynolds number, Re = d / V; V = υ pipeline average velocity (m / s); d is pipe diameter .(m); viscosity υ as movement (m2 / s); En; for resistance coefficient μ for dynamic viscosity (Pa · s); γ for weight (kg/m3); g = acceleration due to gravity (98m/s2); .Δ p is the pressure drop (MPa). <br> <br> Calculate: Δ P = 005MPa. <br> <br> 32 BRh070-type heat exchanger <br> <br> Channel cross-section: 000195m2; equivalent diameter .: 00074mm; its resistance correlations to En = 53641Re-0537. <br> <br> Calculate: Δ P = 015MPa. <br> <br> The calculation results can be seen, in the same condition, two form factors by pressure drop .considerably. <br> <br> Two form factors have advantages, there are also some limitations. For example, when asked to heat transfer coefficient of high and low resistance drop, use either form will not be reached relatively satisfied with the results. < .br> <br> If the horizontal Chevron wavy and Vertical Chevron corrugated plate mixed Assembly, can produce very different results. Its premise is that two form factors of the plate size, position, size, through-hole diameter dimension, gasket structure dimensions should .be identical. The mixed Assembly of the plate in the overlay, happens to be able to form the corresponding contacts, can form a network stream, its resistance drop and heat transfer characteristics between two corrugated plate between separate Assembly. <br> <br> .4 plate stiffness analysis <br> <br> Plate stiffness is the plate in accordance with the requirements of the Assembly, the fixed clamping plate and active clamping plate clamping on both sides of the resistance under different pressures media role and deformation ability. <br .> <br> In normal working condition, the plate must have sufficient strength, it also requires a certain stiffness in order to control the plate of the deformation process, making the heat transfer medium plate channel layer thickness uniform to ensure heat transfer efficiency. According .to the principle of thermal expansion or contraction, raise or lower the temperature will cause a plate of expansion or contraction, but the plate of expansion or contraction to vulnerability from the fixed clamping plate and active clamping plate restrictions. When the contract is not completely free .to do, will result in stress, this requires a heat transfer plates should have adequate stiffness and pressure resistance. In the slab structure design often requires reasonable layout support points and increasing rebar. Plate stiffness depends not only on the supporting point location of density and .precision, also depends on plates of length, width and thickness, and other factors. <br> <br> Currently, foreign and domestic heat plate plates vary, there are hundreds of forms. The aspect ratio is 1: 1, 2, 3 ., etc. In the special working conditions also have 1: 1.1: 4, 1: 5, 1: 6. Different conditions with different aspect ratios, its carrying capacity. The author after years of developing and manufacturing sheet-found that the plate of .the aspect ratio is impact plate stiffness of one of the important factors. <br> <br> Conditions for liquid-liquid, heat exchanger plates of design have to narrow the development trend of the long type. Narrow long plate can effectively reduce the fluid .flow phenomenon of edges, making it in the channel as possible uniform flow, heat transfer enhancement. In addition, also for improving the slab of lateral rigidity offers extremely favorable conditions. Plate of longitudinal stiffness can rely on 4-6 on clamping bolts and fixed .clamping plate, active clamping plate to calculation in guarantee; plate of lateral rigidity, not only to consider two plate clamping force and deformation after, but also the liquid pressure and tension, gasket and plate bearing point of deformation, dislocation, and many other factors .. When a plate of lateral rigidity is not sufficient to overcome the above deformation, likely in sealing gasket and leak happens between the plates. Practice shows that the plate of aspect ratio at 1: 25, 1: 3 or so, the plate heat exchanger .unit carrying capacity up to 2.5MPa and below this value of the form, the whole machine bearing capacity in 1.0-1.6MPa. <br> <br> 5 plate sealing structure analysis <br> <br> In the plate heat exchanger design, .plate's overall structure and seal strength has very close relations, reasonable structure design of the seal not only increases the stiffness of slab, improving heat exchanger for pressure resistance, and guarantees good tightness. Sealed structure is made of plates of seals and gaskets, sealing gasket .consisting of performance (performance of physical properties, chemical and technical properties), seal Groove forms, gasket compression ratios are the three elements of sealing design. <br> <br> 51 seal groove <br> <br> Seal groove shape directly related .to the gasket in the seal groove positioning, affect the sealing gasket on a running stability, also directly linked to the sealing effect. Reasonable seal groove design should make the sealing gasket on stress, heat conditions, where the design does not occur on the basic .of displacement, and to maintain the original compression ratio. In order to achieve the above requirements, the design of the seal groove, should as much as possible to adopt the enclosed form. In addition, to take full account of plate material tensile properties, .you should make the seal groove angle possible. At present, China has developed a form, the seal grooves in the inclination of 25 ° ~ 35 °; and some well-known brand abroad, the majority of plate seal groove angle is 20 ° left .and right, most small-to-7 °. <br> <br> At present, domestic and international variety of plate-type seal groove design uses the plane form, as shown in Figure 3a. Its advantages are simple sheet molding processing, .gasket structure is simple, easy-to-bonding, sealing gasket in the seal grooves and good stability. But there are disadvantages, for example in adhesive sealing gasket and seal groove, bit must be quite accurate, is not allowed to have offset, or .clamping, gasket be divorced from the lost seal seal groove. In response to this situation, this article on the seal Groove Forms has done a lot of research and testing, developed a new type of structure, as shown in Figure 3b, The sealing gasket .assembling time good stability, positioning, improved sealing Groove parts of stiffness, reduced Assembly process of the clamping force, reducing the degree of deformation plate. For many years with the result shows that the seal Groove Forms drastically, greater promotion value. <br> .52 gasket <br> <br> Gasket is the plate heat exchanger is an important part in the Assembly by using the adhesive will put in jail in plate gasket tablets in the seal groove, hole week trough under fluid flow needed to place the gasket and .thus to allow or block a fluid into the plate between the channel, the purpose of achieving heat. Gasket material, structure, format and compression ratio is directly related to the plate heat exchanger sealing effect. <br> <br> 521 gasket material < .br> <br> Currently used for sealing gasket material is synthetic rubber and asbestos rubber. Synthetic rubber commonly used with NBR, EPDM and Viton. Synthetic rubber sealing gasket of physical performance indicators mainly in working condition of permanent deformation and elongation, rubber sealing rubber .hardness indicators should be under the seal grooves in the form and the amount of compression. <br> <br> 522 gasket of structural form <br> <br> Gasket of structure, there are a variety of forms, the forms are generally have .rectangular cross sections, trapezoid, Hexagon, Pentagon, etc. Commonly used in the form of two types: a form as shown in Figure 4a, its sealing gasket cross section in the upper part of the pointed; another form as shown in Figure 4b, .the upper plane. The former is through sophisticated to the size difference in the middle to increase the degree of deformation gasket, its structure design actually remains flat seal, seal, because the plate nonlinear tablets seal groove bottom is flat, when the plate seal groove .bottom plane defects, this structure can be offset by some. The latter is designed to reduce the amount of compression sealing gasket, its compact form flat clamping. Its main disadvantage is the Assembly of the plate, the plate is easy to misplace, clamping force .is too large, easily plate deformation. Through the analysis of research and testing, this design and the PCT as shown in Figure 3B sealing Groove corresponding gaskets section shown in Figure 4c, makes Assembly easier, also improves the ability of the pressure plate. < .br> <br> 523 gasket compression ratio <br> <br> General to gasket compression ratio of its original thickness that compression ratio as gasket design basis. According to many years of design experience, as well as domestic and foreign large amounts of heat .exchanger analysis of sealing structure, the author believes the compression ratio is in 20% to 25% is ideal. <br> <br> 6 conclusion <br> <br> Plate with mixed combinations, you can make today's plate heat exchanger applications more .widely. Not only that the plate heat exchanger greatly enhance adaptive capacity, and also has higher heat transfer coefficient, low flow resistance, and high efficiency, energy saving, good value for money. <br> <br> At the same time, depending .on the plate of stiffness, reasonable design seals and gaskets, can effectively improve the sealing gasket in the seal grooves in the stability and reliability seal, is to ensure that the seal effect of the important conditions. Through the use of the user tracking survey and .feedback information, as shown in Figure 3b sealing Groove forms and shown in Figure 4c gasket is best design, its bearing capacity and service life of a previous design of product has greatly improved. <br> <br> In order to adapt to the heat .exchanger for multi-purpose development trends, but also continually explore research, development of better, newer products, further improve our plate heat exchanger products level. <br> <br> Reference documents: <br> <br> [1] Zhang source .of chemical principles [M] Chengdu: Chengdu University of science and technology press, 2003 <br> <br> [2] Xu guozhi, anyuan benign fluid in the plate heat exchanger within the shape channel Dynamics [M] Beijing: petrochemical equipment press ., 2004 <br> <br> [3] Jin Ming Cong, Cheng still die, Zhao Yong xiang heat exchanger [M] Chongqing: Chongqing University Press, 2001. <br> <br> [4] Hu guozhen chemical sealing technology [ .M] Beijing: chemical industry press, 2002 <br>.