Luis M. López-Ochoa

NETWORK NUMERICAL ANALYSIS OF OPTICALLY THICK HYDROMAGNETIC SLIP FLOW FROM A POROUS SPINNING DISK WITH RADIATION FLUX, VARIABLE THERMOPHYSICAL PROPERTIES, AND SURFACE INJECTION EFFECTS

The steady, incompressible, laminar Newtonian magnetohydrodynamic slip flow with heat transfer from an impulsively started, spinning porous disk is investigated when strong injection (blowing) and significant thermal radiation heat transfer are present. The properties of the fluid, i.e., density, viscosity, and thermal conductivity, are assumed to vary with temperature. Using appropriate transformations, the axisymmetric flow conservation equations for mass, momentum, and energy in a cylindrical polar coordinate system (r, ϕ, z) are normalized to yield a series of highly nonlinear, coupled ordinary differential equations that are solved under appropriate boundary conditions with the network simulation method (NSM). Comparisons are made with an earlier study for the case of Prandtl number = 0.64 with suction present and found to be in excellent agreement. The effects of the radiation-conduction parameter (Nr), hydromagnetic parameter (Nm), slip factor (γ, which is related to Knudsen number), uniform injection parameter (W > 0), and temperature difference parameter (ϵ) on the axial, radial, and tangential velocity components, Nusselt number, and temperature function are investigated in detail. Applications of the study include turbine blade systems, magnetic field control of chemical engineering processes, and electronic computer disk drive cooling.

Delaunay variables approach to the elimination of the perigee in Artificial Satellite Theory

Analytical integration in Artificial Satellite Theory may benefit from different canonical simplification techniques, like the elimination of the parallax, the relegation of the nodes, or the elimination of the perigee. These techniques were originally devised in polar-nodal variables, an approach that requires expressing the geopotential as a Pfaffian function in certain invariants of the Kepler problem. However, it has been recently shown that such sophisticated mathematics are not needed if implementing both the relegation of the nodes and the parallax elimination directly in Delaunay variables. Proceeding analogously, it is shown here how the elimination of the perigee can be carried out also in Delaunay variables. In this way the construction of the simplification algorithm becomes elementary, on one hand, and the computation of the transformation series is achieved with considerable savings, on the other, reducing the total number of terms of the elimination of the perigee to about one third of the number of terms required in the classical approach.

Averaging Tesseral Effects: Closed Form Relegation versus Expansions of Elliptic Motion

Longitude-dependent terms of the geopotential cause nonnegligible short-period effects in orbit propagation of artificial satellites. Hence, accurate analytical and semianalytical theories must cope with tesseral harmonics. Modern algorithms for dealing analytically with them allow for closed form relegation. Nevertheless, current procedures for the relegation of tesseral effects from subsynchronous orbits are unavoidably related to orbit eccentricity, a key fact that is not enough emphasized and constrains application of this technique to small and moderate eccentricities. Comparisons with averaging procedures based on classical expansions of elliptic motion are carried out, and the pros and cons of each approach are discussed.

Non-linear transient hydromagnetic partially ionised dissipative Couette flow in a non-Darcian porous medium channel with Hall, ionslip and Joule heating effects

We study the transient magnetohydrodynamic (MHD) viscous laminar flow and heat transfer in a channel containing a Darcy-Forchheimer porous medium, under a constant pressure gradient with Hall current, ionslip, transpiration, viscous and Joule heating. The dimensionless momentum and heat conservation equations are solved using the Network Simulation Method (NSM). The effects of a number of thermophysical parameters on the transport phenomena are studied including Darcy number (Da), Forchheimer quadratic drag number (Fs), Hartmann number (Ha), Hall current parameter (βe), ionslip parameter (βi) and Eckert number (Ec). The model finds applications in geophysics and MHD energy generators.

NUMERICAL MODELING OF MHD CONVECTIVE HEAT AND MASS TRANSFER IN PRESENCE OF FIRST-ORDER CHEMICAL REACTION AND THERMAL RADIATION

An analysis was carried out numerically to study unsteady heat and mass transfer by free convection flow of a viscous, incompressible, electrically conducting Newtonian fluid along a vertical permeable plate under the action of transverse magnetic field taking into account thermal radiation as well as homogeneous chemical reaction of first order. The fluid considered here is an optically thin gray gas, absorbing-emitting radiation, but a non-scattering medium. The porous plate was subjected to a constant suction velocity with variable surface temperature and concentration. The dimensionless governing coupled, nonlinear boundary layer partial differential equations were solved by an efficient, accurate, extensively validated, and unconditionally stable finite difference scheme of the Crank-Nicolson type. The velocity, temperature, and concentration fields were studied for the effects of Hartmann number (M), radiation parameter (R), chemical reaction (K), and Schmidt number (Sc). The local skin friction, Nusselt number, and Sherwood number are also presented and analyzed graphically. It is found that velocity is reduced considerably with a rise in the magnetic body parameter (M), whereas the temperature and concentration are found to be markedly boosted with an increase in the magnetic body parameter (M). An increase in the conduction-radiation parameter (R) is found to escalate the local skin friction (τ), Nusselt number, and concentration, whereas an increase in the conduction-radiation parameter (R) is shown to exert the opposite effect on either velocity or temperature field. Similarly, the local skin friction and the Sherwood number are both considerably increased with an increase in the chemical reaction parameter. Possible applications of the present study include laminar magneto-aerodynamics, materials processing, and MHD propulsion thermo-fluid dynamics.

Precise Analytical Computation of Frozen-Eccentricity, Low Earth Orbits in a Tesseral Potential

Classical procedures for designing Earth’s mapping missions rely on a preliminary frozen-eccentricity orbit analysis. This initial exploration is based on the use of zonal gravitational models, which are frequently reduced to a simple analysis. However, the model may not be accurate enough for some applications. Furthermore, lower order truncations of the geopotential are known to fail in describing the behavior of elliptic frozen orbits properly. Inclusion of a higher degree geopotential, which also takes into account the short-period effects of tesseral harmonics, allows for the precise computation of frozen-eccentricity, low Earth orbits that show smaller long-period effects in long-term propagations than those obtained when using the zonal model design.

Study of the Technical Feasibility of Increasing the Amount of Recycled Concrete Waste Used in Ready-Mix Concrete Production

The construction industry generates a considerable amount of waste. Faced with this undesirable situation, the ready-mix concrete sector, in particular, has invested energy and resources into reusing its own waste in its production process as it works towards the goal of more sustainable construction. This study examines the feasibility of incorporating two types of concrete waste, which currently end up in landfill, into the production process of ready-mix concrete: the waste generated during the initial production stage (ready-mix concrete waste), and waste created when demolition waste is treated to obtain artificial aggregate. The first phase of the study’s methodology corroborates the suitability of the recycled aggregate through characterization tests. After this phase, the impact of incorporating different percentages of recycled coarse aggregate is evaluated by examining the performance of the produced concrete. The replacement rate varied between 15% and 50%. The results indicate that recycled aggregates are, indeed, suitable to be incorporated into ready-mix concrete production. The impact on the final product’s performance is different for the two cases examined herein. Incorporating aggregates from generic concrete blocks led to a 20% decrease in the produced concrete’s strength performance. On the other hand, using recycled aggregates made from the demolition waste led to a smaller decrease in the concrete’s performance: about 8%. The results indicate that with adequate management and prior treatment, the waste from these plants can be re-incorporated into their production processes. If concrete waste is re-used, concrete production, in general, becomes more sustainable for two reasons: less waste ends up as landfill and the consumption of natural aggregates is also reduced.

Combined Heat and Mass Transfer by Natural Convection from a Semi-Infinite Plate Submitted to a Magnetic Field with Hall Currents

Abstract: The present work is concerned with the MHD unsteady free convection flow from a vertical semi-infinite plate of an incompressible electrically conducting fluid. The effects of the viscous dissipation and the Hall currents are analyzed. The unsteady governing equations are reduced to a system of ordinary differential non-dimensional equations and the resulting equation system is solved numerically by using the Network Simulation Method. This numerical method is based on the electrical analogy, where only previous spatial discretization is necessary to obtain a stable and convergent solution with very low computational times. To solve the system of algebraic equations with time as continuous function, an electric circuit simulator is used. Numerical results for velocities, temperature, concentration and current terms are illustrated graphically. We have observed that the Grashof number for heat transfer (Gr) and mass transfer (G*) accelerate the velocity of the flow field at all points. But the increase in velocity of the flow field is more significant in presence of mass transfer. The effect of Schmidt number Sc on mass transfer process is a decrease of concentration distribution as a result of decrease of the concentration boundary layer thickness.