Research on Face Fluid Field and Seal Performance of T-shape Groove Dry Gas Seal
To obtain more details about the fluid field and high stability of dry gas seal, according to Reynolds equation of compressible perfect gas, on isothermal condition, the controlling equation of gas between the T-shape groove dry gas seal faces is established, and the controlling equation is converted into a non-dimensional equation. The gas flow capacity of T-shape groove dry gas seal is reached with computer simulation in Fluent software, on the basis of numerical simulation, the working parameters (such as, rotating speed, pressure, viscosity of medium, etc.) and the geometric parameters (such as, groove number, groove deep, groove width ratio, balance clearance, etc.) which affect seal performance, are discussed in detail, and the affecting curves are gained. The parameters ( such as, groove deep, balance clearance) which affect seal performance mostly should be chosen correctly in design. The general principle for selecting geometric parameters and working parameters of T-shape groove dry gas seal are obtained, for example, the groove number should be chosen within 12¿16, the groove deep should be chosen within 4¿6 μm, the balance clearance should be chosen within 0.8¿1.4 μm. It offers theoretical support for engineering design and application of T-shape groove dry gas seal.
Numerical Simulation of Face Flow Field for Dry Gas Seal
Based on the Navier-Stokes equation,the laminar model and the SIMPLEC algorithm,the numerical simulation of face flow filed under different face clearances and rotational speeds was carried out to obtain more details about the fluid field and high stability of dry gas seal.The distribution of film pressure and the variety of opening force were investigated emphatically.The numerical result shows that there is a clear change in film pressure at the intersection of groove and dam.Hydrodynamic pressure produces at the outlet,and a negative pressure zone is formed at the inlet.Hydrodynamic pressure decreases rapidly with the increase of face clearance and changes acutely when the clearance is less than 3 μm.The difference pressure of inlet and outlet will raise opening force and film stiffness.Opening force and film stiffness can be raised through enlarging the positive pressure zone and reducing the negative zone,and as a result,the stability of dry gas seal is increased.
Practical, legal, and ethical issues in expanded access to investigational drugs.
The authors review the FDA policies and procedures that permit some patients with serious conditions to receive investigational drugs before formal product approval and examine the legal and ethical issues associated with expanded access.