HiTRAN® Wire Matrix Inserts in Fouling Applications

The effects of the outflow of aortic blood through the celiac and renal arteries on the flow field in the external iliac arteries were studied under steady and physiologically realistic pulsatile flow conditions. Laser Doppler velocimetry (LDV) measurements were made close to the medial, lateral, ventral, and dorsal walls of the external iliac branches of a clear, flow-through replica of a porcine aorta and its daughter vessels. The outflow from each branch of the replica was controlled so that the infrarenal aortic flow rate and the flow partition at the aortic trifurcation were the same for all experiments. LDV measurements were made with flow exiting through both the renal and celiac artery ostia, only the celiac ostium, and neither ostium. The steady flow results indicate that while the outflow through the renal arteries did not have a significant effect on near wall shear rate in the external iliac arteries, the flow through the celiac artery did. However, in pulsatile flow, three indices of near wall velocity in the iliac arteries were unaffected by celiac artery outflow, while a fourth showed a small effect that can be attributed to differences in minimum velocity. These results indicate that reliable simulations of blood flow in the external iliac arteries can be carried out without including the renal and celiac vessels, provided that the correct infrarenal flow wave is used. They also demonstrate that the flow field downstream of a region, such as a branch, that strongly alters the flow, can be nearly independent of the velocity field entering the region.

Fouling of surfaces exposed to a flowing gas stream, occurs due to both physical and chemical processes. The main fouling mechanisms are particulate, corrosion and chemical reaction fouling. Particulate fouling is a physical process, involving both mass and heat transfer to the surface. It also depends on the physical properties of gas, its velocity and the particle size distribution.

Interaction between particulate fouling and precipitation fouling: Sticking probability and deposit bond strength

A computational algorithm for calculating the unsteady compressible and turbulent hydrodynamic and thermal boundary layers over a porous flat plate with uniform suction or injection is developed in the present work. The mathematical modeling involves the derivation of the governing partial differential equations of the problem. These are the continuity, the momentum, the ( κ −ε ) turbulence model and the energy equations. Besides, the perfect gas law and the Sutherland' s law of molecular viscosity are also used. A proper initial and boundary conditions are specified to be used in the solution of the governing equations. A numerical solution of the governing equations is made by using the control volume approach, with non-staggered grid technique and modified SIMPLE algorithm. The numerical solution is capable of calculating the velocity and temperature distributions of the calculation domain, the kinetic energy and dissipation of turbulence, the local and average skin-friction and heat transfer coefficients and Nusselt number, and the hydrodynamic and thermal boundary layers thicknesses. All these parameters are calculated at the transient and steady states. The numerical results show that the developed algorithm is capable of calculating the flow field, properly and accurately. The results show that injection causess light decrease in the temperature inside the thermal boundary layer, a decrease in skin – friction coefficient, a slight increase in the Nusselt number, a decrease in hydrodynamic boundary layer thickness, an increase in thermal boundary layer thickness and an increase in the time required to reach the steady state. Suction almost causes reverse effects.

The influence of Prandtl number on laminar mixed convective flow through a smooth, horizontal tube was investigated using ANSYS Fluent 22 to improve the understanding of the interaction between buoyancy and fluid viscosity on the thermohydraulic behaviour. Different propylene glycol concentrations (0%, 30%, 50%, 70%, 80%, and 90%) were considered for heat fluxes of 200-10 000 W/m 2 and Reynolds numbers of 250-2000. The tube had an inner diameter of 5.1 mm and a length of 10 m. It was found that as the Prandtl number increased, the buoyancy force increased up to 74% for the 90% propylene glycol concentration compared to pure water, resulting in higher vorticity and circulation strength. However, this was confined near the tube wall and when quantifying the buoyancy effects using the secondary flow strength, viscosity-induced damping was found to decrease buoyancy effects by up to 95%. Conversely, for low-Prandtl number mixtures such as 0% and 30% propylene glycol concentrations, increased secondary flow thinned the thermal boundary layer and enhanced heat transfer by 40% and 28%, respectively, compared to forced convective flow, despite a lower buoyancy force. Furthermore, secondary flow strength was quantified and grouped into three distinct regions: (1) developing region, (2) suppression region, and (3) enhancement region. When viscous effects dominated at higher Prandtl numbers (70% and 90%), the velocity profile became skewed above the tube's centre, and the merging position of the hydrodynamic boundary layers shifted upwards, which is the opposite of the trend seen in fluids with lower Prandtl number (0%, and 30%). Furthermore, as the Prandtl number increased, the hydrodynamic boundary layers along the axis merge closer to the tube inlet, while the thermal boundary layers merge further downstream. Hydrodynamic/thermal boundary layers and cross-sectional velocity/temperature profiles during forced/mixed convection for low/high Prandtl number fluids. • An increase in Prandtl number increased the buoyancy force but decreased buoyancy effects due to higher viscosities. • The vorticity magnitude increased with Prandtl number but was confined near the tube wall. • At high Prandtl numbers, the mixed convective velocity profile was skewed upward, shifting the peak velocity above the tube centre, while the opposite occurred at low Prandtl numbers. • The mixed convective temperature profile was skewed downward, causing the upper thermal boundary layer thickness to be greater than the bottom. • The hydrodynamic boundary layer merged earlier along the tube for increasing Prandtl number.

Interplay between particulate fouling and its flow disturbance: Numerical and experimental studies

Thermographic flow visualization is a contactless, non-invasive technique to visualize the boundary layer flow on wind turbine rotor blades, to assess the aerodynamic condition and consequently the efficiency of the entire wind turbine. In applications on wind turbines in operation, the distinguishability between the laminar and turbulent flow regime cannot be easily increased artificially and solely depends on the energy input from the sun. State-of-the-art image processing methods are able to increase the contrast slightly but are not able to reduce systematic gradients in the image or need excessive a priori knowledge. In order to cope with a low-contrast measurement condition and to increase the distinguishability between the flow regimes, an enhanced image processing by means of the feature extraction method, principal component analysis, is introduced. The image processing is applied to an image series of thermographic flow visualizations of a steady flow situation in a wind tunnel experiment on a cylinder and DU96W180 airfoil measurement object without artificially increasing the thermal contrast between the flow regimes. The resulting feature images, based on the temporal temperature fluctuations in the images, are evaluated with regard to the global distinguishability between the laminar and turbulent flow regime as well as the achievable measurement error of an automatic localization of the local flow transition between the flow regimes. By applying the principal component analysis, systematic temperature gradients within the flow regimes as well as image artefacts such as reflections are reduced, leading to an increased contrast-to-noise ratio by a factor of 7.5. Additionally, the gradient between the laminar and turbulent flow regime is increased, leading to a minimal measurement error of the laminar-turbulent transition localization. The systematic error was reduced by 4% and the random error by 5.3% of the chord length. As a result, the principal component analysis is proven to be a valuable complementary tool to the classical image processing method in flow visualizations. After noise-reducing methods such as the temporal averaging and subsequent assessment of the spatial expansion of the boundary layer flow surface, the PCA is able to increase the laminar-turbulent flow regime distinguishability and reduce the systematic and random error of the flow transition localization in applications where no artificial increase in the contrast is possible. The enhancement of contrast increases the independence from the amount of solar energy input required for a flow evaluation, and the reduced errors of the flow transition localization enables a more precise assessment of the aerodynamic condition of the rotor blade.

The problems of the simultaneous growth of the hydrodynamic and thermal boundary layers in the entrance region of a concentric annulus with a uniformly heated core are investigated using the momentum and energy integral equations, along with a modified Reichardt momentum eddy diffusivity variation. A radius ratio range of 0.2 to 0.8 was investigated over a Reynolds number range from 104 to 3 × 105 for a Prandtl number of 0.7. The analysis predicts velocity and temperature profiles and local variations of normalized pressure gradients and Nusselt numbers which are in satisfactory agreement with experimental data. The analysis also shows that the flow is hydrodynamically fully developed within 10 equivalent diameters of the annulus inlet, while a further 30 equivalent diameters are required for the thermal boundary layers to reach the outer insulated wall of the annulus.

Fouling mechanisms in anoxic-aerobic sequencing batch membrane bioreactor based on adapted Hermia models and main foulant characteristics

The effect of a novel ribbed wave tape on the augmentation of heat transfer in a solar air heater operating in a transitional flow regime is experimentally examined. Three different wave ratios are used, and the tube is uniformly heated using heat fluxes while the Reynolds number varied from 521 to 10,194. The transition for plain tube begins at 2810 and ends at 3724. For tube with ribbed wavy tapes, transition begins early and ends at higher Reynolds number than plain tube. For 2 kW/m2 of heat flux, the transition for wavy tape having wave ratio 3 begins at Reynolds number 2589 while at heat flux of 4 kW/m2, the transition begins at Reynolds number 2745. The end of transition takes place at Reynolds number 3969 and 4139 for wave ratio 3 at heat fluxes 2 and 4 kW/m2, respectively. The length of transition decreases with increase in the wave ratio at uniform heat flux. The average enhancement in Nusselt number for ribbed wavy tapes having wave ratio 3 at 4 kW/m2 heat flux was 262% and 85% for laminar and turbulent flow regime, respectively. Two empirical correlations were developed to predict the Nusselt number and friction factor for all the flow regimes.

Aerodynamics is the top-level of fluid mechanics science which is deals with the flow of air over bodies like aircraft or any other solid surface. Boundary layer can be classified into hydrodynamics and thermal boundary layer and had wide range of applications in the Aerodynamics. The present work examines the hydrodynamics boundary layer theory over a flat plate. It is interested subject due to its wide range of applications in industry and nature like airplane, missiles, rocket etc. the three laws of physics (mass, momentum and energy) had been derived and then the governing equations of boundary layer had been derivded. The boundary layer is sub-divided into three regions or zones, which they are the laminar, transition and turbulent boundary layer. The Integral Momentum Von-Karman Equation is derived in-full details over the flat plate and then it is used to derived the main parameters in the laminar and turbulent regions like rate of growth of each layer, skin friction coefficient, shear stress and drag coefficient. It is worthy to mention that despite various velocity profiles for laminar region, there is only one profile for the turbulent region which is the seventh root law that suggested by Prandtle. Also, for laminar boundary layer, Blasius proposed a solution that can be used to obtain the drag. The transition zone us discussed also and it is worthy to mention that the analysis of this region is limited in the textbooks of fluid flows and heat transfer.

A visualization of thermal diffusion in a horizontal pipe flow is conducted to elucidate the axial diffusion characteristics of two fluids of differing temperatures, particularly those flows between the laminar and turbulent flow regimes. Tracer particles are used to detect the thermal diffusion interface as well as to measure streamwise velocity profiles. We found that the Hagen–Poiseuille parabolic velocity profile established a long axial diffusion length that drives thermal convection in the pipe cross-sectional plane. This situation results in a 3D interface at Reynolds number, Re = 600, and a vertically stratified interface at Re = 1900. In turbulent flows at Re = 5700, an anti-diffusion spot appears in the front section before undergoing rapid mixing under turbulence. From the visualized particle images, the apparent axial coefficients of diffusion were measured and compared with the friction properties of the pipe. Furthermore, particle image velocimetry (PIV) explored the two-way coupling mechanism of between the temperature and the velocity within the thermal diffusion process.

An improved prediction of frictional pressure drop using an accurate shear rate equation for high-yield stress drilling fluids at the surface and downhole conditions

Free flow above permeable domains is a common problem in both natural and industrial environments. The classical problem of turbulent flows above forests and urban areas, known as the canopy flow problem (Finnigan 2000), was addressed by hundreds of publications. A library search for the keywords ‘canopy and flow’ in the ISI database returned 1312 results in April 2007 and 1845 results in April 2009, about 40% increase in the last 2years alone. In fact, this search underestimates the actual number of publications since research of flow above permeable domains covers a much wider range of scenarios. Vegetated flows in rivers and wetlands, flow above gravel streambeds, and flow above coral reefs are a few environmental examples; industrial examples include flows in coating processes, chemical reactors, and electronic cooling; and examples of a much smaller length scale include flows above bio-films and inside bio-tissues. Studies of flows over permeable domains include both laminar and turbulent flow regimes. Where most of the porous media studies focus on laminar and creeping flows, terrestrial, ocean, and atmospheric flows are all turbulent. Combinations such as turbulent channel flows above laminar flow inside dense gravel beds are also common. Most of the past and present research activities are often classified by the following four disciplines: porous media flows (e.g., Whitaker 1999), atmospheric canopy flows (e.g., Finnigan 2000), vegetated flow (e.g., Nepf 1999), and fluvial flows. Studies of fluvial flows were recently addressed in a special issue on double averaging applications (Nikora and Rowinski 2008). The following special issue with its 13 publications covers both laminar and turbulent flow regimes while emphasizing on fundamental questions of formulating the transport conditions at the interface between the fluid and the porous domains. The most famous publication on laminar flows above porous interfaces is the study by Beavers and Joseph (1967) (cited 771 times, ISI, April 2009). By investigating the flow above porous domains, they developed a linear relationship between the velocity gradient above the interface and the interface slip velocity. However, numerous studies showed that the Beavers and Joseph condition is not general enough and a coupled solution of both the free flow and

The motion of quantized vortices is studied using a vibrating wire in superfluid 4He. A vortex filtering method provides a superfluid practically free of remanent vortices in which the vibration of a wire cannot generate turbulence. Vortex lines are produced by cooling through the superfluid transition and remain forming bridges between a wire and a surrounding wall. Bridged remanent vortices increase the resonance frequency of a vibrating wire: the rate of an increase due to the remanent vortices is constant in a laminar flow regime and steeply increases in a turbulent flow regime with increasing wire velocity. These results suggest that oscillation of the bridged vortices provides a linear contribution to the wire vibration in the laminar flow regime, until instability occurs in the oscillation of the vortices, causing turbulence.