Rafat Al-Waked

Numerical study of heat transfer enhancement in the entrance region for low-pressure gaseous laminar pipe flows using Al2O3–air nanofluid

The gaseous low-pressure nanofluid flow of a steady-state two-dimensional laminar forced convection heat transfer in the entrance region of pipes is numerically investigated. Such flows are of interest for many engineering applications like the nuclear reactor and electronic equipment cooling, heat exchangers, and many others. Physical parameters considered in this study are Reynolds number (Re), Prandtl number (Pr), nanosolid particles volume fraction ( ϕ ) , Knudsen number (Kn), and the aspect ratio (AR). These parameters ranges are as follows: 500 ≤ Re ≤ 2000 , 0 . 76 ≤ Pr ≤ 0 . 95 , 0 ≤ ϕ ≤ 0 . 5 , 0 ≤ Kn ≤ 0 . 1 , and 1 ≤ AR ≤ 10 . The outcome of this study shows that by increasing Kn, velocity slip and temperature jump at the solid boundaries increase. In addition, heat transfer is enhanced by dispersing Al2O3 nanoparticles in the base low-pressure gaseous flow. Results show that there is no effect of the nanoparticles volume fraction with values below 0.03 on the average Nusselt number. The average Nusselt number increases ( Nu ¯ ) as the value of the nanoparticles volume fraction exceeds 0.03. For instance, at Re = 1000, results show that when dispersing Al2O3 nanosolid particles with volume fractions of 0.3 and 0.5; there is an enhancement in the average Nusselt number of 30.35% and 136.74%, respectively, when compared to the case of dispersing Al2O3 nanosolid particles of 0.03 volume fraction.. Moreover, it is concluded that the average Nusselt number ( Nu ¯ ) depends directly on Reynolds (Re), Prandtl (Pr) numbers, and the nanoparticles volume fraction ( ϕ ) and inversely on Knudsen number (Kn) and the aspect ratio (AR) for the investigated range of parameters considered in this study. Finally, a correlation of Nusselt number among all the investigated parameters in this study is proposed as Nu ¯ = 0 . 976 A R − 0 . 0536 P r 2 . 39 R e 0 . 22 K n − 0 . 378 ϕ 0 . 07 .

Computational fluid dynamics simulation of blood flow profile and shear stresses in bileaflet mechanical heart valve by using monolithic approach

Bileaflet mechanical heart valves (BMHVs) are widely used to replace diseased heart valves. However, patients may suffer from implant complications, such as platelet aggregation and damage to blood cells, which could lead to BMHV failure. These complications are related to the blood flow patterns in the BMHV. A three-dimensional computational fluid dynamic (CFD) model was developed to investigate blood hydrodynamics and shear stresses at different cardiac cycles. A user-defined function (UDF) code was developed to model the valve leaflet motion. This UDF updates the tetrahedral mesh according to the location of the valve leaflet, which enables modeling of complicated moving geometries and achieves solution convergence with ease without the need to adjust the relaxation factor values. The agreement between the experimental and numerical results indicates that the developed model could be used with confidence to simulate BMHV motion and blood flow. Furthermore, valve leaflet and valve pivot were found to be continuously exposed to shear stresses higher than 52.3 Pa which according to previous research findings may cause damage to blood platelets.

External flows on entry of a hybrid wind catcher-wind turbine system

A new concept in wind power harnessing is recently developed under INVELOX (Increasing VELocity) by the company Sheerwind in USA. It is claimed that the new concept can significantly outperforms traditional wind turbines in terms of reducing the diameter of wind turbine, improve aerodynamic characteristics under the same wind conditions, and delivers significantly higher output at reduced cost. The innovative feature of the wind turbine is the elimination of tower-mounted turbines. It is believed that the entry of such systems is crucially important because external flows over nozzle or diffuse devices are different from classically known internal flows. Shrouded wind turbines and wind catcher systems are normally use a diffuser shape at entry, however, the INVELOX concept suggest using a nozzle at entry. In this paper, two different simpler systems than INVELOX are designed with nozzle or diffuser at the entry using general methods in design of blower wind tunnels. In the first phase of this work, CFD (computational fluid dynamics) method is applied to solve external flows around nozzle and diffuser flows by solving the modelled RANS (Reynolds average Navier-Stokes) equations. The initial results indicate that the wind speed retarded at the entry of nozzle while wind speed accelerated at entry of a diffuser device.

Effect of Air to Air Fixed Plate Enthalpy Energy Recovery Heat Exchanger Flow Profile on Air Conditioning System Energy Recovery

Fixed plate enthalpy heat exchanger which utilizes permeable material as heat and moisture transfer surface has been used as an energy recovery system to recover sensible and latent heat in HVAC systems. The heat exchanger effectiveness is affected by the air flow profile. It is well known that counter flow configuration provides highest effectiveness, however, in real applications, it is not possible to implement a counter flow configuration, as both inlet and outlet ducts of the two flow streams are located on the same side of the heat exchanger. Therefore, several quasi-counter-flow heat exchanger designs including Z-shaped, L-shaped, Z-shaped opposite flow configurations are proposed in this research and their effect on energy consumed by an air conditioning cooling coil has been investigated, where each of the proposed heat exchanger is incorporated in an air conditioning cooling coil model. The modeled cooling coil energy consumption and energy recovered by the heat exchangers are evaluated under Kuala Lumpur weather conditions. It has been found that an air conditioner coupled with L-shaped heat exchanger recorded up to 20% increase in energy recovery in comparison with Z-shaped oposite and Z-shaped heat exchanger.

Using Computational Fluid Dynamics Simulation to Perform Fire Investigation

Fire occurred evening 10th July 1989 at Terwindle Rest Home Auckland. Incident report shows that this fire resulted in seven fatalities and extensive fire damage to the building. The primary cause of the death was carbon monoxide poising from smoke inhalation. The fire started at the lounge which contained ten upholstered couches with polyurethane foam padding. Sprinkler fire protection system was not installed and the building has no smoke detection system (based on the New Zealand Building code requirement that was imposed at that time). In this study, the fire is modeled using Computational Fluid Dynamics (CFD) software FDS (Fire Dynamic Simulator). The heat release rate of the fuel burned was obtained from lab measurement of a sofa. The results were validated against the approximate time scale of the progress of the fire as it was found from the fire investigation report. It has been found that FDS can provide accurate simulation to the fire which can be used to perform fire investigation provided that the correct heat release rate of the fire used in the model.

Numerical Investigation on the Effect of Down Stand Structure in Fire Compartment on Smoke Contamination Atrium Upper Balconies

Atrium is gaining popularity in the modern societies because of its special attraction. However, during fire incident it causes significant risk due to its open spaces between floors. In atriums smoke can move easily to upper floors through these open spaces and causes smoke contamination of the atrium upper floors. Moreover, presence of down stand structure at the fire compartment opening is required in any shop in atrium shopping mall to display the trade name of the shop. This study investigated the effect of down stand structure on smoke contamination of upper balconies of an atrium by using Fire Dynamic Simulator, CFD software. A correlation that predict the smoke contamination occurrence in the presence of fire compartment down stand structure is developed. The results shows that down stand structure resulted in increasing the effect of smoke contamination in upper floors of an atrium.