Bidirectional Upstream Pumping Mechanical Seal Performance

With the sustained and rapid development of world economy, the unceasingly expanding of industrialized scale, long distance transport of oil and nuclear power, the rapid development of oil refining and chemical industry, more and more mechanical seal machinery and equipments are needed with high parameters such as high temperature, high pressure or high speed. In the condition of high pressure or easy vaporization environment, mechanical seal is facing many problems, one of which is the premature failure caused by the friction and serious wear or hot crack without inefficient lubrication. Non-contact surface technique is one of the important means of solving this problem, which includes dry gas seal, oil film mechanical seal and upstream pumping mechanical seal. But it seems too complicated when non-contact mechanical seal is applied to pump device. If there is a type of mechanical seal that can solve the problem just with simple improvement of the ordinary mechanical seal, then it is undoubtedly the most practical one.There was a bi-directional self-upstream pumping mechanical seal with a simple structure and a small leakage rate since the recent years, which could meet the needs of high parameter conditions in operation. As a type of mechanical seal with high parameters, it has widely used in many fields. But its operation is more complex, and the related properties have not been known very clearly at present.The theoretical calculations in this paper used an approximate calculation method of the surface pressure regarding circular slot and thermal wedge mechanical seal, mechanical seal with liquid membrane was simulated and calculated by using Fluent software, and the theoretical calculation and the simulation results were compared. The main research contents are as follows:(1)By the theoretical calculations, the pressure distributions of liquid membrane surface were obtained in this type of mechanical seal, when the inner pressure was an atmospheric pressure, and the outside pressures were 1.5MPa,2.5MPa,3.5MPa,4.5MPa, 5MPa, respectively. The pressure distributions of liquid membrane surface were obtained in the five cases by using the numerical simulation method.(2)Compared with the results by the two methods, it could be found that the result by the theoretical calculation was basically the same as that by the numerical simulation. The result by the numerical simulation showed that the liquid membrane pressure along the radius direction was non-linear, especially by the area of slot.(3)According to the theoretical formula, it is known that the leakage rate has a very close relation among the pressure difference on the end surface, the dynamic viscosity of liquid membrane, the film thickness and the sealing structure. The relationship graphs among the leakage rate, the pressure difference and film thickness on the end surface were drawn. It could be also clearly known that, the pressure difference on the end surface increased and the leakage rate increased linearly with the pressure at the outer diameter increased; the leakage rate increased with the liquid membrane thickness increased. When the film thickness ho was less than 1.5μm, the leakage rate change was smooth. When the film thickness ho was more than 1.5μm, the leakage rate of growth rate rapidly rosen.(4)The numerical simulation results showed that the slot number of sealing surface and geometrical parameters had the obvious effect on the pressure of liquid membrane surface. However, the approximate theoretical calculation method did not reveal this phenomenon. That is why in the approximate theoretical calculation of liquid membrane pressure, the slot area was the only factor affecting slot profile in the formulae, and the magnitude of the slot area was mm2 but the magnitude of pressure was MPa. While in the numerical simulation, more parameters were involved and the neglected or approximate conditions were less. The numerical simulation results showed that the increase of slotnumber could cause the increase of moving pressure effect on the end surface.