Theo G. Keith

An Analysis of Cavitated Wave Journal Bearings

A numerical investigation of the two dimensional flow in cavitated wave journal bearings is presented in this paper. An algorithm based on an upwind differencing scheme combined with a Rosenbrock integrator was used to simulate bearing cavitation. The algorithm, which conserves mass throughout the bearing, automatically implements JFO boundary conditions at rupture and at reformation. The numerical predictions are compared with numerical results obtained with other algorithms.Copyright

A Numerical Study on Enhancement of Heat Exchanger Performance by Inserting Static Mixer Elements

In chemical processing industries, heating, cooling and other thermal processing of viscous fluids are an integral part of the unit operations. Static mixers are often used in continuous mixing, heat transfer, and chemical reactions applications. Generally, a static mixer consists of a number of equal stationary units, placed on the inside of a pipe or channel in order to promote mixing of flowing fluid streams. These mixers have low maintenance and operating costs, low space requirements, and no moving parts. A range of designs exists for a wide range of specific applications. The shape of the elements determines the character of the fluid motion and thus determines the effectiveness of the mixer. There are several key parameters in the design procedure of a static mixer. An ideal static mixer for heat transfer applications provides a higher rate of heat transfer and thermally homogenous fluid with low pressure drop and similar traveling history for all fluid elements. To choose a static mixer for a given application or in order to design a new static mixer, besides experimentation, it is possible to use powerful computational fluid dynamics (CFD) tools to study the performance of static mixers. This paper illustrates how static mixer can improve the performance of heat exchangers. Using different measuring tools, the global performance and costs of two popular commercial static mixers are studied in order to choose the most effective design for thermal applications.Copyright

A Numerical Study of Turbulent Flow in Helical Static Mixers

Many processing applications call for the addition of small quantities of chemicals to working fluid. Hence, fluid mixing plays a critical role in the success or failure of these processes. An optimal combination of turbulent dispersion down to eddies of the Kolmogoroff scale and molecular diffusion would yield fast mixing on a molecular scale which in turn favors the desired reactions. Helical static mixers can be used for those applications. The range of practical flow Reynolds numbers for these mixers in industry is usually from very small (Re ∼ 0) to moderate values (Re ∼ 5000). In this study, a helical static mixer is investigated numerically using Lagrangian methods to characterize mixer performance under turbulent flow regime conditions. A numerical simulation of turbulent flows in helical static mixers is employed. The model solves the three-dimensional, Reynolds-averaged Navier-Stokes equations, closed with the Spalart-Allmaras turbulence model, using a second-order-accurate finite-volume numerical method. Numerical simulations are carried out for a six-element mixer, and the computed results are analyzed to elucidate the complex, three-dimensional features of the flow. Using a variety of predictive tools, mixing results are obtained and the performance of static mixer under turbulent flow condition is studied.Copyright

The Robust Stability of a Wave Bearing

The purpose of this paper is to compare the stability of a three wave journal bearing with the stability of a hydrodynamic plain circular journal bearing. The study of the stability of a bearing can be reduced to the study of the stability of a fourth order linear system. In this paper, a perturbation method is used to compute the dynamic coefficients of the bearing. The critical mass is determined at every relative eccentricity, for both the circular hydrodynamic wave bearing and the three wave bearing. The influence of the amplitude of the wave on the stability of the wave bearing is also studied. However, not all the phenomena which affects the bearing’s operation can be taken into account, but it is important that the bearing preserves its stability in face of different types of uncertainty. This property is known as robust stability. In this paper, the robust stability of a bearing is evaluated by determining how great the perturbations of the dynamic coefficients could be so that the bearing remains stable. The robust stability is analyzed using the Kharitonov’s theorem.Copyright

Numerical Investigation of Choked Flow in Padded Finger Seals

The aim of the present work is to continue to improve the modeling of the high-pressure seal pads by two means. First, by using a set of governing equations that, unlike previous models, incorporates the inertial effects, including choking. This way, the additional approximations at the interface between two separate models are avoided. Second, since the flow may be choked, the equations are solved using a shock capturing numerical scheme. The method used in this case is the space-time conservation element and solution element (CE/SE) scheme, which can accurately predict flows in thin films with discontinuities. Special attention is given to the choked flow cases, for which the flow becomes discontinuous near the exit boundary. The analysis should prove useful in the design process, and also in the general level of understanding the phenomena that occur in more severe cases.Copyright

Dynamic Modeling of a Dual Clearance Squeeze Film Damper: Part III

Squeeze film dampers (SFD) are devices utilized to control vibrations of the shafts of high-speed rotating machinery. A dual squeeze film damper (DSFD) consists of two squeeze film bearings that are separated by a sleeve, which is released when the rotor experiences abnormal operating conditions. In this part of our study of DSFD we analyze the case when both the inner and the outer oil films are active and the separating sleeve is supported by a squirrel cage. Numerical results are compared with the experimental data.© 2005 ASME