Browsing by Subject "Compressor"
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Item Analytical and experimental evaluation of the leakage and stiffness characteristics of high pressure pocket damper seals(Texas A&M University, 2004-09-30) Gamal Eldin, Ahmed MohamedThis thesis presents numerical predictions for the leakage and direct stiffness coefficients of pocket damper seals. Modifications made to earlier flow-prediction models are discussed. Leakage and static pressure measurements on straight-through and diverging configurations of eight-bladed and twelve-bladed seals were used for code validation and for calculation of seal discharge coefficients. Higher than expected leakage rates were measured in the case of the twelve-bladed seal, while the leakage rates for the eight-bladed seals were predicted reasonably accurately. Results are presented for shake tests conducted on the seals at pressures of up to 1000 Psi (6.90 MPa). Test variables included pressure drop across the seals and rotor speed. The experimentally obtained stiffness coefficients are compared to results of a rotordynamic damper seal code, which uses the corrected mass flow-rate calculation method. Results show that the code under-predicts the magnitude of the seal's stiffness for most test cases. However, general trends in the frequency dependency of the direct stiffness are more accurately predicted. The expectation of high values of negative stiffness in diverging seals is confirmed by the results, but the frequency at which the sign of the stiffness becomes positive is considerably lower than is predicted. In addition to presenting high-pressure test data, this thesis also attempts to provide some insight into how seal parameters can be modified to obtain desired changes in seal stiffness.Item Bulk-Flow analysis for force and moment coefficients of a shrouded centrifugal compressor impeller(Texas A&M University, 2005-08-29) Gupta, Manoj KumarAn analysis is developed for a compressible bulk-flow model of the leakage path between a centrifugal compressor's impeller shroud and housing along the front and back side of the impeller. This is an extension of analysis performed first by Childs (1989) for a shrouded pump impeller and its housing considering an incompressible fluid, and then later by Cao (1993) using a compressible bulk flow model for the shroud of a cryogenic fluid pump. The bulk-flow model is used to develop a reaction force and moment model for the shroud of a centrifugal compressor by solving the derived governing equations and integrating the pressure and shear stress distribution. Validation is done by comparing the results to published measured moment coefficients by Yoshida et al. (1996). The comparison shows that the shroud casing clearance flow and the fluid force moment can be simulated by the bulk flow model fairly well. An Iwatsubo-based labyrinth seal code developed by Childs and Scharrer (1986) is used to calculate the rotordynamic coefficients developed by the labyrinth seals in the compressor. Tangential force and transverse moment components acting on the rotor are found to have a destabilizing influence on the rotor for a range of precession frequencies. Rotordynamic coefficients are derived for a single stage of a multistage centrifugal compressor, and a comparison is made to stability predictions using Wachel's coefficient using the XLTRC (rotordynamic FEA code). For the model employed, Wachel's model predicts a slightly lower onset speed of instability. The results also show that leakage that flows radially inwards on the back shroud has a greater destabilizing influence than leakage flow that is radially outwards. Seal rub conditions are simulated by increasing the clearance and simultaneously decreasing the tooth height, which increased the leakage and the swirl tothe eye seal inlet; and therefore reduced stability. Calculated results are provided for different seal clearances and tooth height, for seal and shroud forces and moments.Item Thermodynamic Modeling and Optimization of a Screw Compressor Chiller and Cooling Tower System(Texas A&M University, 2004-09-30) Graves, Rhett DavidThis thesis presents a thermodynamic model for a screw chiller and cooling tower system for the purpose of developing an optimized control algorithm for the chiller plant. The thermodynamic chiller model is drawn from the thermodynamic models developed by Gordon and Ng (1996). However, the entropy production in the compressor is empirically related to the pressure difference measured across the compressor. The thermodynamic cooling tower model is the Baker & Shryock cooling tower model that is presented in ASHRAE Handbook - HVAC Systems and Equipment (1992). The models are coupled to form a chiller plant model which can be used to determine the optimal performance. Two correlations are then required to optimize the system: a wet-bulb/setpoint correlation and a fan speed/pump speed correlation. Using these correlations, a "quasi-optimal" operation can be achieved which will save 17% of the energy consumed by the chiller plant.