Hussein Togun

INVESTIGATION OF HEAT TRANSFER ENHANCEMENT IN A FORWARD-FACING CONTRACTING CHANNEL USING FMWCNT NANOFLUIDS

The turbulent forced convection heat transfer of water/functionalized multi-walled carbon nanotube (FMWCNT) nanofluids over a forward-facing step was studied in this work. Turbulence was modeled using the shear stress transport K-ω model. Simulations were performed for Reynolds numbers ranging from 10,000 to 40,000, heat fluxes from 1,000 to 10,000 W/m2, and nanoparticle volume fractions of 0.00% to 0.25%. The two-dimensional governing equations were discretized with the finite volume method. The effects of nanoparticle concentration, shear force, heat flux, contraction, and turbulence on the hydraulics and thermal behavior of nanofluid flow were studied. The model predictions were found to be in good agreement with previous experimental and numerical studies. The results indicate that the Reynolds number and FMWCNT volume fraction considerably affect the heat transfer coefficient; a rise in local heat transfer coefficient was noted when both Reynolds number and FMWCNT volume fraction were increased for all cases. Moreover, the contraction of the channel passage leads to the formation of two recirculation regions with augmented local heat transfer coefficient value.

Numerical simulation of laminar to turbulent nanofluid flow and heat transfer over a backward-facing step

This paper presents a numerical study of heat transfer to turbulent and laminar Cu/water flow over a backward-facing step. Mathematical model based on finite volume method with a FORTRAN code is used to solve the continuity, momentum, energy and turbulence equations. Turbulence was modeled by the shear stress transport (SST) K-ω Model. In this simulation, three volume fractions of nanofluid (0%, 2% and 4%), a varying Reynolds number from 50 to 200 for the laminar range and 5000 to 20,000 for the turbulent range, an expansion ratio of 2 and constant heat flux of 4000 W/m2 were considered. The results show the effect of nanofluid volume fraction on enhancing the Nusselt number in the laminar and turbulent ranges. The effect of expansion ratio was clearly observed at the downstream inlet region where the peak of the Nusselt number profile was referred to as enhanced heat transfer due to the generated recirculation flow. An increase of pressure drop was evident with an increasing Reynolds number and decreasing nanofluid volume fraction, while the maximum pressure drop was detected in the downstream inlet region. A rising Reynolds number caused an increasing Nusselt number, and the highest heat transfer augmentation in the present investigation was about 26% and 36% for turbulent and laminar range, respectively compared with pure water.

CFD Simulation of Heat Transfer and Turbulent Fluid Flow over a Double Forward-Facing Step

Heat transfer and turbulent water flow over a double forward-facing step were investigated numerically. The finite volume method was used to solve the corresponding continuity, momentum, and energy equations using the -e model. Three cases, corresponding to three different step heights, were investigated for Reynolds numbers ranging from 30,000 to 100,000 and temperatures ranging from 313 to 343 K. The bottom of the wall was heated, whereas the top was insulated. The results show that the Nusselt number increased with the Reynolds number and step height. The maximum Nusselt number was observed for case 3, with a Reynolds number of 100,000 and temperature of 343 K, occurring at the second step. The behavior of the Nusselt number was similar for all cases at a given Reynolds number and temperature. A recirculation zone was observed before and after the first and second steps in the contour maps of the velocity field. In addition, the results indicate that the coefficient pressure increased with increasing Reynolds number and step height. ANSYS FLUENT 14 (CFD) software was employed to run the simulations.

Sustainability and environmental impact of ethanol as a biofuel

Abstract Biofuels are acting as a renewable replacement for petroleum fuels due to some environmental and economic benefits. They are prepared by blending a major portion of diesel fuel and a certain minor percentage of bio-oils, which provides less greenhouse gas (GHG) compared to pure diesel. Recently, bioethanol has been the most widely used biofuel for transportation. Bioethanol can be produced from different kinds of agricultural raw materials classified into three categories: simple sugars, starch, and lignocellulose. Use of bioethanol-blended gasoline fuel for automobiles can significantly reduce petroleum use and exhaust GHG emission. Bioethanol from sugar cane, produced under the proper conditions, is essentially a clean fuel and has several clear advantages over petroleum-derived gasoline in reducing GHG emissions and improving air quality in metropolitan areas. However, there remains a compromise between GHG emission and saving of fossil fuel energy by introducing bioethanol either totally or as a blending component of engine fuel. Thus, considering biofuel as a replenishable energy source, the future pathway of energy management could be planned.

Numerical Study of Turbulent Heat Transfer in Annular Pipe with Sudden Contraction

Turbulent heat transfer to air flow in annular pipe with sudden contraction numerically studied in this paper. The k-ε model with finite volume method used to solve continuity, moment and energy equations. The boundary condition represented by uniform and constant heat flux on inner pipe with range of Reynolds number varied from 7500 to 30,000 and contraction ratio (CR) varied from 1.2 to 2. The numerical result shows increase in local heat transfer coefficient with increase of contraction ratio (CR) and Reynolds number. The maximum of heat transfer coefficient observed at contraction ratio of 2 and Reynolds number of 30,000 in compared with other cases. Also pressure drop coefficient noticed rises with increase contraction ratio due to increase of recirculation flow before and after the step height. In contour of velocity stream line can be seen that increase of recirculation region with increase contraction ratio (CR).

Heat transfer and fluid flow of pseudo-plastic nanofluid over a moving permeable plate with viscous dissipation and heat absorption/generation

The purpose of the present study is investigating the heat transfer of non-Newtonian pseudo-plastic nanofluid flow on a moving permeable flat plate with viscous dissipation and heat absorption/generation. The flow is uniform and parallel to the moving flat plate, and both flat plate and flow are moving on the same directions. The investigated parameters in this study are power-law index, permeability parameter, Eckert number, volume fraction of nanoparticles, nanoparticles type, velocity ratio and heat absorption/generation parameter. The nanoparticles used in this paper are Al2O3, TiO2, Cu and CuO dispersed in sodium carboxymethyl cellulose/water as the base fluid. By using suitable transformations, the governing partial differential equations are converted into the ordinary differential equations, and after that, the resulting ODEs are solved with Runge–Kutta-Fehlberg fourth–fifth-order numerical method. The results of this investigation showed that heat transfer of Newtonian and non-Newtonian nanofluids in the presence of viscous dissipation and generation/absorption of heat has an interesting behavior: For Newtonian fluid, by increasing the amounts of high-conductive nanoparticles to carrying fluid, a higher heat transfer is not obtained. For instance, copper nanoparticles, despite having highest thermal conductivity compared to other nanoparticles, show the lowest local Nusselt number. However, for pseudo-plastic non-Newtonian nanofluids the observed trend was reversed. Furthermore, in both Newtonian and non-Newtonian nanofluids, the local Nusselt number decreased, by increasing injection parameter, heat generation or volume fraction of nanoparticles (in high Eckert numbers). That is while, by enhancing the heat absorption, velocity ratio, suction parameter or volume fraction of nanoparticles (in low Eckert number), the local Nusselt number augments.

A CFD study of turbulent heat transfer and fluid flow through the channel with semicircle rib

In the present paper turbulent heat transfer and fluid flow through the channel with semicircle ribs numerically studied. The SST k-ω turbulence Model with finite volume method was employed in simulation. The adopted boundary condition considered step heights of ribs varied from 2.5mm to 10mm with pitch ratio different from 2.5 to 40 and flow Reynolds number between 10000 to 25000 at constant surface temperature. The computational results showed recirculation region after each ribs which effect on performance of heat transfer rate. Increase of Reynolds number and number of ribs leads to increase in heat transfer coefficient. Step height and pitch ratio of ribs increase local heat transfer coefficient along the channel. This simulation has been done by ANSYS 14 FLUENT.

Heat Transfer to Separation Flow in Heat Exchangers

Separation flow is appeared over and behind a body surface when it is separated from that surface. In separation flow the region is relatively small compared to the body and enclosed by the separating stream line and points of separation and reattachment. Separation flows are formed at the upstream of a forward facing step downstream of a rearward facing step, within a cutout in a body surface and also on the upper surface of an airfoil.