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Study on Opening Characteristics of Dry Gas Seals with Typical Spiral Grooves

Author: LiuKun
Tutor: PengXuDong; BaiShaoXian
School: Zhejiang University of Technology
Course: Chemical Process Equipment
Keywords: dry gas seal typical spiral grooves opening characteristics radial tapereddepth critical opening rotational speed
CLC: TB42
Type: Master's thesis
Year: 2012
Downloads: 56
Quote: 0
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Abstract


Owing to the high gas film stiffness and stable operation under the high-speed condition, spiral groove dry gas face seals have been widely applied to high-speed rotating equipment such as centrifugal compressor, expansion engine and turbomachinery. But under the low-speed and low-pressure conditions, the spiral groove dry gas seals still have a problem that the open force is not enough so that the seal faces open hardly during the startup process, which restricts the application on the rotating machinery. In order to improve the opening performance of the dry gas seal(DGS) under low-speed and low-pressure operating conditions, tipical spiral groove dry gas seals were investigated by both theoretical and experimental method.First, based on the theory of gas mixed lubrication, a dynamic opening model for a DGS was developed by considering the effects of gaseous slip flow and surface roughness, where the structure parameters and opening characteristic ones were difined. By compared the calculated results with the ones pulished on the literatures, the model and solving method were proved to be correct and dependable.Then, hydrodynamic opening characteristics of dry gas seals with tipical types of spiral grooves were studied. The gas film pressure distributions between the two faces of the tipical types of spiral grooves under different operating conditions were numerically analyzed. A series of simulations were carried out to study the influences of structure parameters, seal medium pressure, balance ratio and spring pressure on the hydrodynamic opening performances. After that, the opening experiments were also carried out to compare the differences of opening performances of the tipical types of spiral grooves. The results showed that the tiny differences of groove structures had greatly influenced the gas film pressure distribution between the seal faces. Dynamic opening characteristic was greatly affected by balance ratio and spring pressure and seal medium pressure. Compared with the spiral grooves DGS and the annular grooves DGS, the opening performances of the goose grooves are the best under the same operating conditions.Finally, In order to improve the opening performance of the typical spiral grooves under low velocity and low pressure condition, four kinds of bottom types of spiral grooves, namely convergent tapered bottom groove, convergent ladder-like bottom groove, divergent tapered bottom groove, divergent ladder-like bottom groove, was introduced by optimizing the equal deep spiral groove. The opening performances of different groove bottoms of tipical spiral grooves were theoretical compared. Results showed that the load capability and stability of the gas film were enhanced by the optimized bottom structures compared with the equal depth groove under low-speed and low-pressure operating conditions. The opening performances of tapered bottom grooves are parallel to the ladder-like bottom grooves.Based on the theoretical and experimental investigations on the opening performances of the tipical spiral grooves, the design theory of DGS under low-speed and low-pressure operating conditions was improved. Therefore, the value of this paper is very important to enlarge the application field of the typical spiral grooves and also has great significance for theoretical and engineering applications.

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