Convection tube flow

Forced convection Tube flow Heat transfer Limits of validity... 

Table 3. Correlations for Convective Heat-Transfer and Friction Coefficients for Circular Tube Flow ...

Figure 9.21. Film coefficients of convection for flow of water through a tube at 289 K...

Forced convection outside tubes Flow across single cylinders... 

The dispersion in geometrically deformed tubes (squeezed, twisted and coiled ) has been extensively studied by Halasz (6, 7 and 8), and the effect of radial convection (secondary flow) on the dispersion introduced in tightly... 

Subscript a refers to the air portion, subscripts a + 1 and a - l refer to the upper and lower air portion, index k refers to the four cell slices. Qcv,a is the convective heat flow exchanged with the tube and with each cell slice, which can be calculated ... 

Laminar pulsatile flow in a tube Flow in a tube is in one direction, parallel to the electrode surface, (taken as the jr-direction). The time-dependent convective-diffusion equation for this geometry is given by equation (10.12). Mass transport to the surface of the electrode is thus determined both by the gradient perpendicular to the surface of the tangential flow, dujdy and the concentration gradient perpendicular to the surface ... 

It turns out that Eq. (5-56) can also be applied to turbulent flow over a flat plate and in a modified way to turbulent flow in a tube. It does not apply to laminar tube flow. In general, a more rigorous treatment of the governing equations is necessary when embarking on new applications of the heat-trans-fer-fluid-friction analogy, and the results do not always take the simple form of Eq. (5-56). The interested reader may consult the references at the end of the chapter for more information on this important subject. At this point, the simple analogy developed above has served to amplify ouf understanding of the physical processes in convection and to reinforce the notion that heat-transfer and viscous-transport processes are related at both the microscopic and macroscopic levels. 

In tube flow the convection heat-transfer coefficient is usually defined by... 

Churchill, S. W., and H. Ozoe Correlations for Laminar Forced Convection in Flow over an Isothermal Flat Plate and in Developing and Fully Developed Flow in an Isothermal Tube, J. Heat Transfer, vol. 95, p. 46, 1973. 

Fig. 7-13 Regimes of free forced and mixed convection for flow through vertical tubes according to Ref 10...

Often coal ash deposit effects are inter-related. For example, slagging will restrict waterwall heat absorption changing the temperature distribution in the boiler which in turn influences the nature and quantity of ash deposition in downstream convective sections. Ash deposits accumulated on convection tubes can reduce the cross-sectional flow area increasing fan requirements and also creating higher local gas velocities which accelerate fly ash erosion. In-situ deposit reactions can produce liquid phase components which are instrumental in tube corrosion. 

FIGURE 4J0 Regimes of forced and mixed convection for flow through horizontal tubes with uniform wall temperature, for 10 2 < (Pr DIL) < 1. From Metais and Eckert [190]. 

Vertical Tubes. The flow regime chart for vertical tube flow shown in Fig. 4.51 was prepared by Metais and Eckert [190] for either a uniform-heat-flux or uniform-wall-temperature boundary condition. The two boundaries of the mixed convection are defined in such a way... 

In regard to nonsteady tube flows. Mason et al. have observed both inward and outward radial migration of rigid, neutrally buoyant spheres in oscillatory (S9b, G9b) and pulsatile (Tl) flows in circular tubes at frequencies up to 3 cps, at which frequencies inertial effects are likely to be important. We refer here to inertial effects arising from the local acceleration terms in the Navier-Stokes equations, rather than from the convective acceleration terms. In the oscillatory case the spheres (a/R 0.10) attained equilibrium positions at about P = 0.85. Important Reynolds numbers here are those based upon mean tube velocity for one-half cycle and upon frequency. Nonneutrally buoyant spheres in oscillatory flow migrate permanently to the tube axis, irrespective of whether they are denser or lighter than the fluid (K4a). 

Gravitational settling of particle in fluid Flow of viscoelastic fluid Pressure and momentum in fluid Unsteady state heat transfer/mass transfer Fluid flow with free surface Gravitational settling of particle in fluid Heat transfer by natural convection Heat transfer to fluid in tube Flow of fluid exhibiting yield stress... 

Values of film transfer coefficients are usually obtained from correlations between dimensionless groups. For forced convection (turbulent flow) within circular tubes the relevant groups are ... 

Churchill SW, Ozoe H. Correlations for laminar forced convection in flow over an isothermal flat plate and in developing and fully developed flow in an isothermal tube. Journal of Heat Transfer 1973 95 Ser C 416-419. 

The remaining investigations [36, 37, 41-45] made measurements in tube flow under more controlled conditions. The earliest of these efforts [36] found that temperatures could be measured quite precisely at a given circumference (deviation of only 0.5 C or less). This result for (Gz < 5) and subsequent corroboration in later studies [37, 41-45] showed that natural or free convection was not a problem in heat transfer to flowing molten or thermally softened polymers. In addition, evidence was found for both cooling by expansion and viscous dissipation. 

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