Advanced seal design for rotating machinery

Abstract

Labyrinth and more recently brush seals have been used extensively in high speed rotating machinery. Development is still in progress to reduce the leakage rate, and the frictional resistance of these seals beside the awareness of their stability characteristics. A seal very similar to the brush seal geometry is proposed here. It is composed of fine strips replacing the wires of the ordinary brush seal. A simple theoretical model for this strip seal is put forward here based on the assumption that the flow through it is steady laminar and incompressible. A Reynolds like equation is devised, governing the pressure inside the seal. Calculations of the leakage rate and the friction resistance are carried out for the various parameters considered and the results are presented and discussed in detail along with comparisons with previous work. It is shown in this work that the strip angle has a major effect on the performance of the seal as well as on the friction resistance. It is found that the larger the angle the lesser the leakage rate and the larger the friction force. The optimum value for minimum leakage is 90 but for mechanical stability and durability reasons it should be smaller. It is also found that the wider the strips the lesser the leakage rate for all values of the strip angle. The opposite holds for the friction resistance. The spacing between the strips has a minor effect on the leakage rate for small values of the strip angle but for larger values of the angle the increase in leakage becomes considerable when increasing the spacing for angles of order 70. Comparisons with previous works on different types of seals showed that the present seal model can satisfactorily be implemented in practice.