Development of lumped parameters models for aerostatic gas bearings

L'abstract è presente nell'allegato / the abstract is in the attachmen

The Aerostatic Seal: Analysis and Development of a New Dynamic Seal Concept for Steam Turbine Application

This thesis describes the development of a new seal concept for steam turbines called the Aerostatic Seal. The Aerostatic Seal is a dynamic seal, and so can respond to rotor radial movement to maintain a low clearance between the seal and the rotor. As the seal is dynamic, smaller clearances can be achieved without rotor contact compared to conventional static seals such as the labyrinth seal, hence increasing the efficiency of the turbine through reduced leakage. Furthermore, as the seal is dynamic it can tolerate larger radial transients typically found during start up and shut down of the steam turbine, and so also contributes to increasing the flexibility of the turbine plant. In this thesis an analytical design and analysis methodology was developed for the Aerostatic Seal. The methodology was used to generate a number of seal designs which were experimentally tested in a non-rotating test facility using room temperature air. The results confirmed that the seal would operate dynamically, and the experimental campaign provided valuable data on the operation of the seal. The non-rotating rig was also used to test a second generation seal design. The seal was then tested in a rotating test facility, which modelled high speed rotor radial transients with an adjustable eccentric rotor. The Aerostatic Seal demonstrated the ability to respond to high speed transients. A final test campaign was conducted in the high temperature steam rig at TU Braunschweig, Germany, enabling experimental demonstration of the Aerostatic Seal using realistic materials and represented realistic steam turbine conditions. Finally, based on the experimental and analytical work carried out within this thesis, a proposed Aerostatic Seal design for steam turbine implementation is presented

Design and Analysis of Aerostatic Bearings of Cryogenic Turbines for Helium Refrigerator/Liquefier

Aerostatic bearings are generally used in the field of high speed applications. The Helium Refrigerator/Liquefier (HRL) needs turbines as expansion machines to produce cooling effect which is further used for production of liquid helium. Cryogenic turbines are significantly smaller in size compared to those for room temperature applications but rotational speed is very high, about few hundred thousands of rpm and hence these have contact less gas bearings or magnetic bearings. This project involves the design and analysis of the aerostatic bearings with horizontal shaft configuration. In the aerostatic bearings, pressurized helium gas is passed through the bearings. Based on this pressure and temperature and the rotational speed of the turbines, the shaft of the turbine rotates without contact with bearing wall and the leakage between process gas and bearing gas is minimum. For different normal and offnormal operations, speeds will be different and hence the flow parameters for bearing gas flow will be controlled via control valves and the bearing should be designed to provide such contactless rotation. In this study, a theoretical analysis is presented for the load capacity, stiffness, flow rate of aerostatic journal bearing and thrust bearing with pocketed orifice. Effects of orifice diameter, radial clearance, inlet pressure and outlet pressure on load capacity, mass flow rate and stiffness have been analyzed. Dynamic unbalances like whirling of the shaft have also been covered in this study. Design considerations for limiting dispersion effect, and to avoid pneumatic hammer has also been taken into account. Validation of the analysis has been done by using ANSYS CFX with the numerical result

Gas Bearings: Modelling, Design and Applications

This book focuses on the modelling and the design process of gas bearings, on the experimental validation of such models, and on their applications. In particular, recent developments about foil bearings, aerostatic bearings, porous bearings, and non-contact precision positioning systems are shown

Development of porous ceramic air bearings

Porous air bearings enjoy some important advantages over conventional air bearing types such as increased load carrying capacity, higher stiffness and improved damping. However, these types of bearings have yet to find widespread acceptance due to problems with obtaining materials with consistent permeability, instability issues relating to the volume of gas trapped at the bearing surface in the pores, and manufacturing the bearing without altering the permeability. Using a series of fine grades of alumina powder to minimise surface pore volume it has been demonstrated that it is possible to consistently and reproducibly manufacture porous bearings by injection moulding and slip casting. The relationship between powder size, processing conditions, porosity, mechanical properties and fluid flow characteristics were experimentally determined. The temperature of processing and the green density were found to be the controlling parameters in the resulting fluid flow properties for a given powder size, Test bearings were produced from the range of processing conditions investigated. It was found that the fine powder size bearings were stable over the entire range of test conditions irrespective of their initial manufacturing route. The most important consideration for the bearing performance was the quality of manufacture. The bearings were found to be sensitive to the flatness of their working surface and quality of fit in their test holder. The bearings were compared with published theories for load capacity and stiffness. A reasonable agreement was found with load carrying capacity once a correction for surface roughness was incorporated. Stiffness predictions provided a useful tool for the analysis and prediction of properties such as optimum values of permeability for a given geometry, if certain allowances are made

Analytical Study of Non-Recessed Conical Hole Entry Hybrid/Hydrostatic Journal Bearing with Constant Flow Valve Restrictor

The present work studies the analysis of a non recessed hole entry conical hybrid/hydrostatic journal bearing adjusted for constant flow valve (CFV) restriction. The paper provides effectiveness between the conical bearings with hole entry operating in hybrid and hydrostatic mode. The Reynolds formulae, for the flow of fluid through the mating surfaces of a conical journal and bearing, are numerically worked out in both the modes considering the finite element analysis (FEA) and the necessary boundary preconditions. Holes in double row are marked on conical bearing circumference to accommodate the CFV restrictors, the angular distance between two holes are 30o apart from the apex. Qualitative features of the conical journal bearing system with hole entry have been elaborated to analyze bearing performance for radial load variation Wr = 0.25-2. Numerical results obtained from the present study indicate that load carrying capacity of conical bearing, operating in hydrostatic mode, is enhanced by the maximum pressure, direct fluid film damping and direct film stiffness coefficients vis-a-vis corresponding hybrid mode. &nbsp

A bibliography /with abstracts/ on gas-lubricated bearings Interim report

Gas lubricated bearings - annotated bibliograph