Showing papers by "Hussein A. Mohammed published in 2015"

Review of convection heat transfer and fluid flow in porous media with nanofluid

Abstract: There are two advantages of using porous media. First, its dissipation area is greater than the conventional fins that enhances the heat convection. Second is the irregular motion of the fluid flow around the individual beads which mixes the fluid more effectively. Nanofluids result from the mixtures of base fluid with nanoparticles having dimensions of (1–100) nm, with very high thermal conductivities; as a result, it would be the best convection heat transfer by using two applications together: porous media and nanofluids. This article aims to summarize the published articles in respect to porosity, permeability (K) and inertia coefficient (Cf) and effective thermal conductivity (keff) for porous media, also on the thermophysical properties of nanofluid and the studies on convection heat transfer in porous media with nanofluid.

Design characteristics of corrugated trapezoidal plate heat exchangers using nanofluids

Abstract: In this paper, fully developed turbulent flow and heat transfer behavior in trapezoidal channels using nanofluids are numerically studied. This study evaluates the effects of four different types of nanoparticles, Al2O3, CuO, SiO2 and ZnO, with different volume fractions (0–4%) and diameters (20–80 nm) under constant heat flux (6 kW/m2). The effects of geometrical parameters (wavy amplitudes, longitudinal pitch) of the trapezoidal channel on the thermal and flow fields are also examined. The results indicated that SiO2 has the highest Nusselt number among the nanofluids. Enhancement of heat transfer increases with particle volume concentration, but a slight increase in pressure loss with decreasing nanoparticle diameter is also observed. When nanofluids are used in a forced convection, 10% increase in average Nusselt number is observed for nanoparticles with a diameter of 20 nm and at 4 vol.%. Analysis of the flow and heat transfer in a corrugated trapezoidal channel is made based on the comprehensive evaluation factor J/f. The optimum (J/f) enhancement shows that the CuO nanofluid, lower concentration ratio of nanoparticles, trapezoidal height of 2.5 mm and a longitudinal pitch of 6 mm are the most desirable parameters for saving energy. Using nanofluids with a corrugated channel can improve the thermal performance because it can lead to more compact heat exchangers.

Three‐Dimensional Numerical Investigation of Nanofluids Flow in Microtube with Different Values of Heat Flux

Abstract: Forced convective laminar flow of different types of nanofluids such as Al2O3, CuO, SiO2, and ZnO, with different nanoparticle size 25, 45, 65, and 80 nm, and different volume fractions which ranged from 1% to 4% using ethylene glycol as base fluids were used. A three-dimensional microtube (MT) with 0.05 cm diameter and 10 cm in length with different values of heat fluxes at the wall is numerically investigated. This investigation covers Reynolds number (Re) in the range of 80 to 160. The results have shown that SiO2-EG nanofluid has the highest Nusselt number (Nu), followed by ZnO-EG, CuO-EG, Al2O3-EG, and finally pure EG. The Nu for all cases increases with the volume fraction but it decreases with the rise in the diameter of nanoparticles. In all configurations, the Nu increases with Re. In addition, no effect of heat flux values on the Nu was found.

Natural convection in a triangular top wall enclosure with a solid strip

Abstract: Natural convection inside a two-dimensional rectangular cavity with a triangular roof having an adiabatic solid strip inserted at a middle of the cavity is studied numerically using a finite volume method. Both of the triangular roof and the bottom wall are considered adiabatic while the vertical left side wall is maintained at constant temperature higher than that of inside fluid temperature. The right side wall is considered differentially heated by supplying a constant heat flux. The working fluid is chosen for analysis is air. The Computational Fluid dynamics (CFD) solution commercial package ANSYS FLUENT 14.0 is used for the numerical simulation purpose. The results are presented in the form of isotherms, streamlines, velocity vector and average Nusselt number (Nu) for Rayleigh numbers in the range of 103 to 106.Throughout this study, the aspect ratio is kept equal to 0.5.It is found that the solid adiabatic strip inside the cavity has a significant effect on the flow and thermal performance. The results indicated the usual fact that when the Rayleigh number increases the average Nusselt number also increases.

The Effects of Air Preheating and Fuel/Air Inlet Diameter on the Characteristics of Vortex Flame

Abstract: The effects of fuel/air inlet diameter as well as air preheating on the flame stability, temperature distribution, pollutant formation, and combustion characteristics of a lab-scaled asymmetric vortex flame have been investigated. A three-dimensional steady-state finite volume solver has been used to solve the governing and energy equations. The solver uses a first-order upwind scheme to discretize the governing equations in the space. The semi-implicit method for pressure linked equations has been applied to couple the pressure to the velocity terms. Several turbulence models were applied to predict the flame temperature and it was found that RNG has given the best results in accordance with the experimental results. The results reveal that the inlet air diameter can enhance the thermal properties and reduce the emission while the inlet fuel diameter has less significant impact. Increasing diameters are accompanied with a pressure drop. It was found that preheating the air and fuel would significantly affect the flame temperature and emission with constant mass flow rate.

Experimental and Numerical Investigation of Combined Convection Heat Transfer and Fluid Flow around Circular Cylinder through Rectangular and Trapezoidal Open-Cell Aluminum Foams

Abstract: Combined convection heat transfer and fluid flow around a circular cylinder surface placed in open-cell aluminum foams and subjected to constant heat flux inside a rectangular, water-filled horizontal channel was numerically and experimentally studied. Two models (rectangular and trapezoidal open-cell aluminum foam shapes) made of 6101-T6 alloy with pore densities of 10 and 40 pores per linear inch (PPI) and 7–9% relative density were employed as test sections. The aluminum foam dimensions were 35.7 × 35.7 × 36.85 mm, the Reynolds number range was 60–2000, and the modified Grashof number range was 2 × 102–2.6 × 107. Governing equations (continuity, momentum, and energy) were solved using the finite-volume method (FVM). Effects of the porous characteristics of aluminum foams and mixed convection heat transfer parameters on buoyancy force, Nusselt number, friction factor, and pumping power values of the two models were investigated. The results show that high mixed convection occurred with the trapezoidal m...

Assisted and Opposed Mixed Convective Nanofluids Flow Over Vertical Backward Facing Step Having a Baffle

Abstract: Laminar mixed convection flow using nanofluids over backward facing step in a heated rectangular duct having a baffle mounted on its wall are numerically simulated. The continuity, momentum and energy equations are solved using finite volume method (FVM) and the SIMPLE algorithm scheme is applied to examine the effects of the baffle on heat transfer characteristics. In this study, several parameters such as different types of nanoparticles (Al2O3, CuO, SiO2 and ZnO), different volume fractions in the range of 1% to 4%, different nanoparticles diameter in the range of 25 to 80 nm, and wall flux in the range of 10 = qw = 70 W/m2 were used. The effects of the baffle height Hb, baffle thickness Wb, and distance between the backward-facing step and baffle D on Nusselt number variation are numerically investigated. The numerical results indicate that the nanofluid with SiO2 has the highest Nusselt number compared with other nanofluids types. The Nusselt number increases as the volume fraction of nanoparticles and the Reynolds number increase, while it decreases as the nanoparticles diameter increases. Effects of baffle distances baffle heights and baffle widths on heat transfer characteristics are significant, while, effects of wall flux are slightly insignificant.

The effect of geometrical parameters on enhancing the heat transfer inside a microtube

Abstract: In this paper, the effect of geometrical parameters of microtube on enhancing the heat transfer has been studied numerically. Single phase model was used to simulate the flow of sio2-ethlyen glycol nanofluids inside a microtube at different reynolds numbers ranged from 10 to 160 at constant heat flux boundary condition. The results show that the higher tube diameter and entrance size has the highest Nusselt number and lower pressure drop. Furthermore, no effect of inclination angles was found.