Bourhan Tashtoush

Magnetic field effect on heat and fluid flow over a wavy surface with a variable heat flux

Abstract The effect of magnetic field on forced heat and fluid flow over a wavy surface subjected to a heat flux proportional to (1+ x 2 ) n (where n is constant) is investigated. The governing equations transformed into a non-dimensional form by using appropriate dimensionless variables that eliminate the wavy surface effect from the boundary conditions. A finite difference scheme is used to solve the governing equations. The numerical results are presented for different magnitudes of magnetic field parameter, M, power law index, n, surface wavy amplitude, a and Prandtl numbers, Pr . It was found that the magnetic parameter has a significant effect on the velocity flow field and pressure gradient. Increasing the magnetic parameter will increase the temperature and reduce the heat transfer rate.

Analytical Solution for the Effect of Viscous Dissipation on Mixed Convection in Saturated Porous Media

A new analytical solution is introduced for the effect of viscous dissipation on mixed convection flow and heat transfer about an isothermal vertical wall embedded in Darcy and non-Darcy porous media with uniform free stream velocity. The effect of viscous dissipation on mixed convection in both regimes has been analyzed for both the aiding and opposing flows using Gebhart number, Gex = gβx/cp. The governing parameters are Re, Ra, Pe and Gex. The case of Re = 0 corresponds to Darcy mixed convection region and Re/Pe is identified as the mixed convection governing parameter, Ra = 0 leading to pure forced convection. A good agreement was found between the numerical and analytical solutions. It was found from the Nusselt number results that viscous dissipation lowers the heat transfer rate in both Darcy and Forchheimer flow regimes for aiding as well as opposing flows.

Thermodynamic behaviour of an air-conditioning system employing combined evaporative-water and air coolers

The performance of an open absorption-system, energized by low-grade heat such as insolation and/or waste heat, has been investigated. This combined evaporative cooler (CEC) [i.e. an indirect evaporative cooler (IEC) together with a direct evaporative-cooler (DEC)] was used to cool the air. A computer simulation of the cooling cycle was devised, so that the performance characteristics of the system could be predicted for a range of operating conditions: the influences of various design-parameters on the coefficient of performance (COP) were also evaluated. The COP of the CEC system was at least 20% greater than those achieved when employing either the IEC or DEC systems alone.

Heat transfers and radial flows via a viscous fluid squeezed between two parallel disks

For the physical system (shown in Fig. 1 in the paper), the convective effect in the axial direction is considered and an analytical solution of the governing equations achieved. Good agreement is found between the analytical and numerical solutions so corroborating the approach adopted. For a small gap between the disks, heat actually flows into the upper disk, even though the imposed temperature difference would initially have been considered to cause the heat flux to be out of the upper disk. The radial pressure-distribution in the viscous liquid is presented as a function of the Reynolds number and R0/d ratio. Axial bulk convection rises as the separation between the two disks increases. Fig. 1. (a) Schematic section orthogonal to the two identical parallel disks; approach velocity u; (b) three-dimensional view of the two identical parallel disks.

TRANSIENT MIXED CONVECTION ALONG A VERTICAL PLATE EMBEDDED IN POROUS MEDIA WITH INTERNAL HEAT GENERATION AND OSCILLATING TEMPERATURE

The effects of oscillating plate temperature on transient mixed convection heat transfer from a porous vertical surface embedded in a saturated porous medium with internal heat generation or absorption are studied. The governing equations are transformed into dimenionless form by a set of variables and solved using the Galerkine finite element method. As the energy generation increases, the temperature near the wall will be higher than the wall temperature, thus increasing buoyancy forces inside the boundary layer and consequently increasing the velocity. The increase of energy absorption term for either space or temperature dependence will decrease the velocity inside the boundary layer and increase heat transfer rates. Different temperature and velocity profiles are drawn for different dimensionless groups. Numerical values for Nusselt numbers as well as local skin friction coefficient are also tabulated.

Natural losses from vegetable and fruit products in cold storage

Abstract Natural losses from fruit and vegetable products stored in cold conditions are investigated. A mathematical model describing heat and mass transfer processes taking place during storage time is presented and the resulting governing equations are solved using Software Mathcad7. The relative humidity of the ventilating air and the temperature field of an apple bulk are found for different cold storage conditions; namely the initial air relative humidity and air flow rate. It was found that the relative humidity of the ventilating air approaches a limiting value as the apple bulk depth increases up to 4.2 m. In addition, when the relative humidity is larger than the equilibrium relative humidity value, an increase in the ventilating air rate reduces the losses of the product during the period of its storage while larger losses occur when the relative humidity values are lower than the equilibrium one.

Computational Modeling of Non-Newtonian Blood Flow Through Stenosed Arteries in the Presence of Magnetic Field

Steady flow simulations of blood flow in an axisymmetric stenosed artery, subjected to a static magnetic field, are performed to investigate the influence of artery size, magnetic field strength, and non-Newtonian behavior on artery wall shear stress and pressure drop in the stenosed section. It is found that wall shear stress and pressure drop increase by decreasing artery size, assuming non-Newtonian fluid, and increasing magnetic field strength. In the computations, the shear thinning behavior of blood is accounted for by the Carreau-Yasuda model. Computational results are compared and found to be inline with available experimental data.

Heat transfer analysis of a non‐Newtonian fluid on a power‐law stretched surface with suction or injection for uniform and cooled surface temperature

Heat transfer characteristics of a non‐Newtonian fluid on a power‐law stretched surface with suction or injection were investigated. Similarity solutions of the laminar boundary layer equations describing heat transfer flow in a quiescent fluid were obtained and solved numerically. Temperature profiles as well as the Nusselt number Nu, were obtained for two thermal boundary conditions; namely, uniform surface temperature (b=0) and cooled surface temperature (b=–1), for different governing parameters such as Prandtl number Pr, injection parameter d and power‐law index n. It was found that decreasing injection parameter d and power‐law index n and increasing Prandtl number Pr enhanced the heat transfer coefficient.

Simulations of Magnetohemodynamics in Stenosed Arteries in Diabetic or Anemic Models.

Pulsatile flow simulations of non-Newtonian blood flow in an axisymmetric multistenosed artery, subjected to a static magnetic field, are performed using FLUENT. The influence of artery size and magnetic field intensity on transient wall shear stress, mean shear stress, and pressure drop is investigated. Three different types of blood, namely, healthy, diabetic, and anemic are considered. It is found that using Newtonian viscosity model of blood in contrast to Carreau model underestimates the pressure drop and wall shear stress by nearly 34% and 40%, respectively. In addition, it is found that using a magnetic field increases the pressure drop by 15%. Generally, doubling the artery diameter reduces the wall shear stress approximately by 1.6 times. Also increasing the stenosis level from moderate to severe results in reduction of the shear stress by 1.6 times. Furthermore, doubling the diameter of moderately stenosed artery results in nearly 3-fold decrease in pressure drop. It is also found that diabetic blood results in higher shear stress and greater pressure drop in comparison to healthy blood, whereas anemic blood has a decreasing effect on both wall shear stress and pressure drop in comparison to healthy blood.