Bassam Abu-Hijleh

Enhanced solar still performance using water film cooling of the glass cover

The effect of water film cooling of the glass cover on the efficiency of a single basin still is theoretically investigated. The effectiveness of film cooling under different operating conditions is reported. Part of the cooling water is recycled as makeup water to the still to further enhance its efficiency. The results of this investigation indicate that proper use of film cooling parameters can increase the still efficiency by as much as 6 percent, but poor combinations of film cooling parameters can lead to significant reductions in still efficiency. The presence of the cooling film neutralized the effect of wind speed on the still efficiency. The actual gain in still efficiency due to the use of a cooling film is further amplified when the practical considerations of where and how such a still is used are taken into account.

Entropy generation due to laminar natural convection over a heated rotating cylinder

Abstract Entropy generation due to laminar mixed convection from an isothermal rotating cylinder was calculated numerically. The study was conducted for three cylinder radii and covered wide ranges of Reynolds number and buoyancy parameter. Entropy generation increased as the Reynolds number and buoyancy parameter increased. Entropy generation decreased as the cylinder radius increased. For the same combination of Reynolds number and buoyancy parameter, entropy generation was mainly due to thermal effects at small cylinder radii and due to viscous effects at large cylinder radii.

The effect of the local inertial term on the fluid flow in channels partially filled with porous material

The transient hydrodynamics behavior of the fluid flow in parallel-plate channels partially filled with porous material is investigated numerically. The role of the local macroscopic inertial term in the porous domain momentum equation is studied. It is found that the effect of the local inertial term on the channel hydrodynamics behavior is insignificant when Da<1×10−6, over the entire range of 0.1<μR<10, 0<A<104, and for all porous substrate thicknesses. Also, it is found that the deviation between the predictions of the transient and the quasi-steady models is more significant in the porous domain and the deviation decreases as the time proceeds.

Enhanced Forced Convection Heat Transfer From a Cylinder Using Permeable Fins

the problem of cross-flow forced convection heat transfer from a horizontal cylinder with multiple, equally spliced, high conductivity permeable fins on its outer surface was investigated numerically. The heat transfer characteristics of a cylinder will permeable versus solid fins were studied for several combinations of number of fins and fin height over the range of Reynolds number (5-200). Permeable fins provided much higher heat transfer rates compared to the more traditional solid fins for a similar cylinder configuration. The ratio between the permeable to solid Nusselt numbers increased with Reynolds number and fin height but tended to decrease with number of fins. This ratio was as high as 4.35 at Reynolds number of 150 and a single fin with a nondimensional height of 3.0. The use of 1-2 permeable fins resulted in much higher Nusselt number values than when using up to 18 solid fins. Such an arrangement has other benefits such as a considerable reduction in weight and cost.

Natural Convection Heat Transfer From a Cylinder With High Conductivity Permeable Fins

The problem of laminar natural convection from a horizontal cylinder with multiple equally spaced high conductivity permeable fins on its outer surface was investigated numerically. The effect of several combinations of number of fins and fin height on the average Nusselt number was studied over a wide range of Rayleigh number. Permeable fins provided much higher heat transfer rates compared to the more traditional solid fins for a similar cylinder configuration. The ratio between the permeable to solid Nusselt numbers increased with Rayleigh number, number of fins, and fin height. This ratio was as high as 8.4 at Rayleigh number of 10 6 , non-dimensional fin height of 2.0, and with 11 equally spaced fins. The use of permeable fins is very advantageous when high heat transfer rates are needed such as in todays high power density electronic components.

CONVECTION HEAT TRANSFER FROM A LAMINAR FLOW OVER A 2-D BACKWARD FACING STEP WITH ASYMMETRIC AND ORTHOTROPIC POROUS FLOOR SEGMENTS

The fluid and energy equations for the incompressible laminar reattaching flow over a 2-D backward facing step with a porous floor segment were solved numerically using the finite element method. The focus of this study was the change in the forced convection heat transfer characteristics of the flow field due to the addition of a porous floor segment. Several porous flow segment configurations with different lengths and depths were studied. The effect of orthotropicity of the porous segments was also studied. The porosity of the segments was varied over a wide range by changing the value of the pressure loss coefficients in either or both of the x and y directions. The changes in the local and overall Nusselt numbers were reported and discussed. Depending on the configuration, the overall Nusselt number increased or decreased relative to the case of a solid floor. For all configurations, the maximum local Nusselt number increased.

An experimental study of a reattaching supersonic shear layer

A Mach 1.83 fully developed turbulent boundary layer was separated at a 25.4 mm backward step and formed a free shear layer. The incoming boundary layer thickness, momentum thickness, and Reynolds number were approximately 8 mm, 0.5 mm, and 52x10 to the 6th/m, respectively. A two-component coincident LDV system was used to take velocity measurements of the incoming boundary layer, the free shear layer, and the reattached shear layer. The results confirmed the existence of organized structures in both the free and the reattached shear layer which was reported earlier based on the authors dynamic pressure measurements and Schlieren photographs.

Validation of Thermal Equilibrium Assumption in Transient Forced Convection Flow in Porous Channel

The validity of the local thermal equilibrium assumption in the transient forced convection channel flow is investigated analytically. Closed form expressions are presented for the temperatures of the fluid and solid domains and for the criterion which insures the validity of the local thermal equilibrium assumption. It is found that four dimensionless parameters control the local thermal equilibrium assumption. These parameters are the porosity ∈, the volumetric Biot number Bi, the dimensionless channel length ξmax and the solid to fluid total thermal capacity ratio CR. The qualitative and quantitative aspects of the effects of these four parameters on the channel thermal equilibrium relaxation time are investigated.

ENTROPY GENERATION IN LAMINAR CONVECTION FROM AN ISOTHERMAL CYLINDER IN CROSS FLOW

Entropy generation due to laminar mixed heat convection from an isothermal heated cylinder in an air cross flow has been evaluated numerically for different values of the Reynolds number, buoyancy parameter, and cylinder diameter. Large cylinder diameters resulted in lower entropy generation. A guide is given to cylinder-diameter selection based on the value of the Reynolds number and the buoyancy parameter.

Optimized use of baffles for reduced natural convection heat transfer from a horizontal cylinder

Abstract The problem of laminar natural convection from a horizontal cylinder with one or more low conductivity fins (baffles) on its outer surface was investigated numerically. The aim was to optimize the number, size, and location of the baffle(s) for maximum natural convection heat convection, i.e., Nusselt number, over a wide range of Rayleigh number. The percentage reduction in heat transfer per baffle(s) unit length “cost-efficiency” was also studied. Changes in the thermodynamic efficiency was studied by calculating the entropy generation associated with each baffle configuration. It was found that the proper placement of a single or dual baffles has a significant effect on the heat transfer and entropy generatuion reduction. The optimal single and dual baffle locations is reported for different values of Rayleigh number and baffle height.