Duct flow velocity field

The previous methods are mainly used to measure duct flow. When measuring flows on supply or exhaust terminals, different methods are used. The measurement on exhaust terminals is simple to carry out, as the velocity field near the terminal is relatively constant, with no steep gradients or swirls. In the case of a grill, traversing across the terminal surface using a suitable velocity instrument is a good alternative. A suitable instrument for most cases is the vane anemometer. 

Duct flows, like steady two-dimensional flows, are poor mixers. This class of flows is defined by the velocity field... 

Steady parallel flow can be realized in ducts of essentially arbitrary cross section. A linear elliptic partial differential equation must be solved to determine the velocity field and the shear stresses on the walls. For an incompressible, constant-viscosity fluid, the axial momentum equation states that... 

The previous section was concerned with a flow in which only the temperature field was developing, the velocity field having reached the fully developed state before the heating began. In general, however, both the velocity and temperature fields develop simultaneously [24],[25]. In order to illustrate the nature of such flows, developing two-dimensional flow in a plane duct will be considered here. The flow situation considered is shown in Fig. 7.11. 

Attention was then turned to developing duct flows. A numerical solution for thermally developing flow in a pipe was first considered. Attention was then turned to plane duct flow when both the velocity and temperature fields are simultaneously developing. An approximate solution based on the use of the boundary layer integral equations was discussed. 

Figure 1.6 Geometry of ducts, impact of cross-sectional shape (a-c) and impactofbends (d-f). (a) Relevant geometries in segmented flows, including the shape of the menisci between the channel wall and dispersed phase. The graph shows what fraction of the cross-sectional area the menisci fill for round and square channels, as a function of Co [104]. (b) Evolution of meniscus shape in square channels [97]. The shape at the frontofthe bubble is markedly different from that at the tailing end. The numerical grid and computed film shape and velocity field were...

ABSTRACT The characteristic of turbulent flow in jackets with triangular helical ducts was simulated and the velocity fields of fully developed turbulent fluid flow in the jackets were obtained. The features of the local coefficient of resistance C/Reiocai) on outer walls and inner wall were summed up and the effects of dimensionless curvature ratio and Reynolds number on the flow field and the flow resistance were analyzed. The results indicate that the structure of secondary flow is with two steady vortices at turbulent flow conditions. The distribution of/ eiocai on the outer walls differs from that of/ eiocai on the inner wall. The mean coefficient of resistance (/Rem) on the outer walls is about 1.41 1.5 7 times as much as that on the iimer wall. With the increase of dimensionless curvature ratio or Reynolds number,/Rem on the boundary walls increases. 

In fact, the pitch of triangular flow channels is very small compared to the reactor radius, that is, the torsion tends to zero. (Liu, 1994) and (Bolinder, 1996) predicted a much weaker effect of a relatively small torsion on fluid flow in hehcal ducts. Then in this work, a deeply study of turbulent flow in the jacket with triangular hehcal duct based on the simplified physical model is presented. With numerical simulation method, velocity fields and turbulence kinetic energy of fully developed flow for different curvature ratio are obtained. The local coefficient of resistance on outer walls are... 

The flow field is symmetric over the period, with velocities in both directions at different times. Because of the symmetry there is no net flow through the duct, and thus the mean velocity profile is exactly zero. The average root-mean-square velocity, however, does have a radial dependence as shown in Fig. 4.11. The root-mean-square velocity is defined as... 

In some situations it is possible to find the heat transfer rate with adequate accuracy by assuming that the velocity is constant across the duct. Le to assume that so-called slug flow exists. Find the temperature distribution and the Nusselt number in sllug flow in a plane duct when the thermal field is fully developed and when there is a uniform wall heat flux. 

Sheldon started his Ph.D. studies at a time when the field of aerosol science was in its early stages of development. Working with H.F. Johnstone, he focused on how particles in turbulent airflow are deposited on the walls of pipes and ducts. Sheldon made important contributions right from the start he introduced the notion of a stopping distance of a particle injected into stagnant air, and then used this concept to predict particle motion through the viscous boundary layer to the surface. His thesis work laid the foundation for much of the later work on deposition of particles in industrial systems as well as dry deposition from the ambient atmosphere, where turbulent eddies impart velocities normal to the mean flow and enable particles to reach the surface. 

Simultaneously Developing Flow. The local Nusselt numbers obtained theoretically by Deissler [92] for simultaneously developing velocity and temperature fields in a smooth circular duct subject to uniform wall temperature and the uniform heat flux for Pr = 0.73 are plotted in Fig. 5.12. It can be seen from this figure that the Nusselt numbers for two different thermal boundary conditions are identical for xlDh > 8. 

The fundamental concept of the new methodologies developed by TAMU and LANL is that a representative sample can be obtained from a single point in a flow field provided the fluid momentum and any contaminants are both well mixed across the cross section of the flow. Criteria are placed on the performance of the sampling system however, the system design is at the discretion of the user. For aerosol sampling, this requirement is fulfilled if it can be demonstrated that the velocity, tracer gas, and 10-mm aerodynamic diameter (AD) aerosol particle profiles are relatively flat at the sampling location. It must also be shown that the sampling probe will acquire a representative sample from the undisturbed flow stream in the stack or duct, and that at least 50% of 10-mm AD aerosol particles will be transported from the undisturbed free stream to a collector or analyser. 

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