Flow rectangular ducts

The solution flow is nomially maintained under laminar conditions and the velocity profile across the chaimel is therefore parabolic with a maximum velocity occurring at the chaimel centre. Thanks to the well defined hydrodynamic flow regime and to the accurately detemiinable dimensions of the cell, the system lends itself well to theoretical modelling. The convective-diffiision equation for mass transport within the rectangular duct may be described by... 

A significant heat-transfer enhancement can be obtained when a nonckcular tube is used together with a non-Newtonian fluid. This heat-transfer enhancement is attributed to both the secondary flow at the corner of the nonckcular tube (23,24) and to the temperature-dependent non-Newtonian viscosity (25). Using an aqueous solution of polyacrjiamide the laminar heat transfer can be increased by about 300% in a rectangular duct over the value of water (23). 

The critical Reynolds number for transition from laminar to turbulent flow in noncirciilar channels varies with channel shape. In rectangular ducts, 1,900 < Re < 2,800 (Hanks and Ruo, Ind. Eng. Chem. Fundam., 5, 558-561 [1966]). In triangular ducts, 1,600 < Re < 1,800 (Cope and Hanks, Ind. Eng. Chem. Fundam., II, 106-117 [1972] Bandopadhayay and Hinwood, j. Fluid Mech., 59, 775-783 [1973]). 

This also applies to circular pipes or ducts and oval and rectangular ducts not flowing full. The equivalent diameter is used in determining the Reynolds number for these cases, but does not apply to very narrow or slotted or annular flow cross-sections. 

The data for heating and cooling water in turbulent flow in rectangular ducts are reasonably well correlated by the use of equation 9.59 in the form ... 

Zhou, B., Sobiesiak, A., and Quan, P, Flame behavior and flame-induced flow in a closed rectangular duct with a 90 degrees bend. International Journal of Thermal Sciences, 45, 457-474, 2006. 

The volumetric flow rate Q (leakage rate) of a fluid in laminar flow through a high aspect ratio (h/w 1) rectangular duct (i.e., the seal volume) of width, w, height, h, and path length, z, in the flow direction is given by ... 

Channel techniques employ rectangular ducts through which the electrolyte flows. The electrode is embedded into the wall [33]. Under suitable geometrical conditions [2] a parabolic velocity profile develops. Potential-controlled steady state (diffusion limiting conditions) and transient experiments are possible [34]. Similar to the Levich equation at the RDE, the diffusion limiting current is... 

Middleman, S., Flow of Power Law Fluids in Rectangular Ducts, Trans. Soc. Rheol., 9, 83 (1965)... 

Wheeler, J. A. and Whissler, E.H., The friction factor-Reynolds Number Relation for the Steady Flow of Pseudoplastic Fluids through Rectangular Ducts. Part 1. Theory, Am. Inst. Chem. Eng. J., 11, 207 (1965)... 

Extrusion and extruder design are apparently almost entirely empirical at present. This field might well defy rigorous theoretical analyses until the simpler problems of flow in annular spaces and rectangular ducts and of nonisothermal fluid flow are understood. 

Noncircular Channels Calculation of frictional pressure drop in noncircular channels depends on whether the flow is laminar or turbulent, and on whether the channel is full or open. For turbulent flow in ducts running full, the hydraulic diameter DH should be substituted for D in the friction factor and Reynolds number definitions, Eqs. (6-32) and (6-33). The hydraulic diameter is defined as four times the channel cross-sectional area divided by the wetted perimeter. For example, the hydraulic diameter for a circular pipe is DH = D, for an annulus of inner diameter d and outer diameter D,DH = D-d, for a rectangular duct of sides a, b, DH=ab/[2(a+b)]. The hydraulic radius Rh is defined as one-fourth of the hydraulic diameter. 

In this section, we only discuss the case of stratified horizontal pipe flow in a rectangular duct. The expansion rate projected on the pipe axis for the gas phase (j = gas) is small (as... 

Jet deflection flow detectors can be considered for flow measurement in large, low-pressure, circular, or rectangular ducts. If they are used in stacks... 

Installation of area-averaging Pitot tube ensembles in rectangular duct for metering the flow rate of gases. (Courtesy of Air Monitor Corp.)... 

The Rectangular Duct Thermal-Entry Length, with Hydrodynamically Fully Developed Laminar Flow... 

The thermal entrance region in a hydrodynamically fully developed flow in a rectangular duct may be studied by the use of the integral method. In this section, the uniform wall temperature and the uniform wall heat flux cases are discussed. The physical model is based on the following assumptions ... 

Consideration will next be given to the solution for the temperature function, G. As with fully developed pipe and plane duct flows, the solution depends on the nature of the thermal boundary conditions at the wall. In the case of flow in a rectangular duct there are a variety of possible boundary conditions, some of these being shown in Fig. 4.11. Here, attention will be restricted to the case where the wall... 

Effect of wall thermal boundary condition oh the Nusselt number for hilly developed flow in a rectangular duct (Nusselt number based on hydraulic diameter)... 

Consider lamina fully developed flow through either a circular pipe or a rectangular duct whose cross-section has a length/width ratio of 8. Both of these ducts have the same cross-sectional area and the average velocity in them is the same. Determine the ratio of the (heat-transfer coefficient X surface area) product for these two flow situations. 

Using an alternative geometry Evans et al. [16] developed the channel stopped flow method (CSFM). This technique, to date, has been used to measure solution diffusion coefficients (independent of knowledge of the concentration of the electroactive species) and crystal dissolution kinetics. The channel flow cell consisted of a rectangular electrode, typical dimensions 2.5 mm long and 6.25 mm wide, situated in a rectangular duct, 10 mm wide and 0.25-1.0 mm high. The electrode was placed a suitable distance... 

Air at 1 atm and 15°C flows through a long rectangular duct 7.5 by 15 cm. A 1.8-m section of the duct is maintained at 120°C, and the average air temperature at exit from this section is 65°C. Calculate the air flow rate and the total heat transfer. 

Figure 22 shows a schematic diagram of a channel electrode (ChE), which consists of an electrode embedded in the wall of a rectangular duct through which solution is made to flow under well-defined laminar steady-state conditions (Compton and Unwin, 1986 Cooper and Compton, 1998). 

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