Guyh Dituba Ngoma

Pressure gradient and electroosmotic effects on two immiscible fluids in a microchannel between two parallel plates

A model of the flow of two immiscible fluids in a microchannel between two parallel plates was made. The concept of pumping a nonconducting fluid using interfacial viscous shear stress was applied while taking into account the combined effect of the pressure gradient and electroosmosis. To determine the electric potential and flow parameters, the Poisson–Boltzmann equation and modified Navier–Stokes equations were solved for a steady fully-developed laminar flow. The results obtained demonstrate the influence of the pressure difference, the dynamic viscosity ratio, the wall and interfacial zeta potentials, the interface location and the interfacial shear stress on the flow characteristics of both fluids. A comparison of results was performed to validate the developed approach.

Numerical Identification of Key Design Parameters Enhancing the Centrifugal Pump Performance: Impeller, Impeller-Volute, and Impeller-Diffuser

This paper presents the numerical investigation of the effects that the pertinent design parameters, including the blade height, the blade number, the outlet blade angle, the blade width, and the impeller diameter, have on the steady state liquid flow in a three-dimensional centrifugal pump. Three cases were considered for this study: impeller, combined impeller and volute, and combined impeller and diffuser. The continuity and Navier-Stokes equations with the k-e turbulence model and the standard wall functions were used by means of ANSYS-CFX code. The results achieved reveal that the selected key design parameters have an impact on the centrifugal pump performance describing the pump head, the brake horsepower, and the overall efficiency. To valid the developed approach, the results of numerical simulation were compared with the experimental results considering the case of combined impeller and diffuser.

Numerical Investigation of a First Stage of a Multistage Centrifugal Pump: Impeller, Diffuser with Return Vanes, and Casing

This paper deals with the numerical investigation of a liquid flow in a first stage of a multistage centrifugal pump consisting of an impeller, diffuser with return vanes, and casing. The continuity and Navier-Stokes equations with the turbulence model and standard wall functions were used. To improve the design of the pumps first stage, the impacts of the impeller blade height and diffuser vane height, number of impeller blades, diffuser vanes and diffuser return vanes, and wall roughness height on the performances of the first stage of a multistage centrifugal pump were analyzed. The results achieved reveal that the selected parameters affect the pump head, brake horsepower, and efficiency in a strong yet different manner. To validate the model developed, the results of the numerical simulations were compared with the experimental results from the pump manufacturer.

Investigation of Three Immiscible Fluids in a Microchannel Accounting for the Pressure Gradient and the Electroosmotic Flow.

This study deals with the investigation of three immiscible fluids in a microchannel consisting of two parallel plates. These fluids were composed of two electric conducting fluids and one electric nonconducting fluid. The concept of pumping a nonconducting fluid using interfacial viscous shear stress was applied accounting for the effect of the electroosmosis and pressure gradient. The electric potential and the flow parameters were found resolving the Poisson-Boltzmann equation and the modified Navier-Stokes equations for a hydraulic steady fully-developed laminar flow of an incompressible fluid. The results achieved revealed the influence of the wall and interfacial zeta potentials, the pressure difference, and the dynamic fluid viscosity ratio on the flow characteristics of the three immiscible fluids. The developed approach was compared with a model of two immiscible flows to highlight the relevance of this work.

Design and numerical characterization of a first stage of a high capacity multistage centrifugal pump

In this paper, a numerical characterization of a first stage of a high capacity multistage centrifugal pump was performed for very high flow rates. A particular emphasis was placed on the diffuser design procedure. For this purpose, the equations of the continuity and the Navier-Stokes accounting for the boundary conditions were used by mean of ANSYS-CFX code to describe and to simulate the complex liquid flow in the multistage centrifugal pump. In order to identify the key parameters of the diffuser that can improve the pump stage performances, the effects of the inlet height of the diffuser vanes, the number of the diffuser vanes, the number of the diffuser return vanes, and the gap between the impeller and the diffuser on the pump stage head, brake horsepower and efficiency were analyzed. The validation of the developed model of a first pump stage was done comparing results of numerical simulations and experimental results obtained from a pump manufacturer.

Numerical investigation of liquid flow in two-, three- and four-stage centrifugal pumps

In this study, a liquid flow in two-, three- and four-stage centrifugal pumps was numerical investigated. The continuity and Navier-Stokes equations with the k-ε turbulence model and standard wall functions were used by means of the ANSYS-CFX code. To enhance the design of the multistage pump, the impacts of the number of impeller blades, diffuser return vanes and the number of stages on the performances of a multistage centrifugal pump were analyzed. The results obtained demonstrate that the selected parameters affect the pump head, brake horsepower and efficiency in a strong yet different manner. To validate the model developed, the results of the numerical simulations were compared with the experimental results from the pump manufacturer.

Parametric Study of a Transient Liquid Flow in a Microchannel of Square Cross-Section

Time-dependent laminar liquid flow and thermal characteristics in a square cross-section microchannel were numerically investigated using computational fluid dynamics code. In the numerical model developed the upper and bottom microchannel substrate properties, Joule heating caused by applying electric potential, pressure driven flow, electroosmosis, heat transfer coefficients on the microchannel bottom wall and variations in the liquid thermophysical properties were all taken into account. Liquid flow velocity distribution and temperature fields were calculated by solving both Navier-Stokes and energy equations, and electric field distribution was determined based on their electric potential. The results obtained demonstrate the impact that applied potential, pressure difference, heat transfer coefficient and microchannel dimensions have on liquid flow and thermal behaviors in a square microchannel. Finally, the results with the model developed were then compared with those of a liquid having constant thermophysical properties.Copyright

Transient Analysis of a Liquid Flow in Microchannel of Varying Cross-Section

In this study the transient analysis of a laminar liquid flow in a three-dimensional microchannel of varying rectangular cross-section was numerically investigated. The imposed heat fluxes on the microchannel upper and bottom wall, the Joule heating due to an applied electric potential at the microchannel inlet and outlet, the electroosmosis, the pressure-driven flow, and the liquid temperature-dependent thermophysical properties were accounted for. The time-dependent liquid flow velocity profile and the time-dependent liquid temperature distribution were obtained respectively solving the Navier-Stokes equations and the energy equations for a laminar incompressible liquid flow using a computational fluid dynamics code. The effects of the microchannel divergence angle and the microchannel dimensions on the liquid flow and the heat transfer in the microchannel were analyzed. Results obtained show significant influences of the pressure difference between the microchannel inlet and outlet, the imposed heat flux, and the microchannel inlet width on the transient and steady states of the liquid flow velocity and the liquid temperature distribution. A comparison of the results of the developed model with those achieved considering the liquid constant thermophysical properties and those obtained from a microchannel of a constant cross-section was made.Copyright

Development of a Thermal Approach to Optimize the Waste Heat Utilisation From an Existing Gas Turbine Station Without Heat Recovery System

The present work deals with a numerical simulation of a flow in finned tube banks arranged behind a gas turbine. Three models of dual-pressure tube systems are developed and analyzed in order to predict the static system performances by optimizing the utilization of the exhaust gas from an existing gas turbine without heat recovery system. For more precise modeling, the theoretical analysis of finned tube banks systems is based on the non-linear conservation equations of mass, momentum and energy. Simulations are accomplished to prove the effectiveness of the present work in performance prediction of the dual-pressure tube systems. The obtained results clearly show the necessity to take into account all relevant physical phenomena in the simulation of flows in and across finned tube banks installed behind a gas turbine. The results also reveal the different operating behavior of the developed models considering combined effects of the exhaust gas parameters and the tube geometries.© 2003 ASME