Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Duct flow hydraulic diameter

Microfluidics is concerned with the flow of fluids in micromachined ducts whose hydraulic diameter, Dh, is defined in the conventional fashion as [1]... [Pg.320]

For a circular duct, the hydraulic diameter is equal to its physical diameter. For a noncircular duct, it is convenient to use the hydraulic diameter to substitute for the characteristic physical dimension. However, for ducts with very sharp corners (e.g., triangular and cusped ducts), the use of the hydraulic diameter results in unacceptably large errors in the turbulent flow friction and heat transfer coefficients determined from the circular duct correlation. Other dimensions have been proposed as substitutes for hydraulic diameter. These equivalent diameters, provided for specific ducts only, will be presented elsewhere in this chapter. [Pg.304]

Fully Developed Flow. For a parallel plate duct with hydraulic diameter Dh = 4b (b being the half-distance between the plates) and the origin at the duct axis, the velocity distribution and friction factor are given by the following expression ... [Pg.360]

Noncircular Channels Calciilation of fric tional pressure drop in noncircular channels depends on whether the flow is laminar or tumu-lent, and on whether the channel is full or open. For turbulent flow in ducts running full, the hydraulic diameter shoiild be substituted for D in the friction factor and Reynolds number definitions, Eqs. (6-32) and (6-33). The hydraiilic diameter is defined as four times the channel cross-sectional area divided by the wetted perimeter. For example, the hydraiilic diameter for a circiilar pipe is = D, for an annulus of inner diameter d and outer diameter D, = D — d, for a rectangiilar duct of sides 7, h, Dij = ah/[2(a + h)].T ie hydraulic radius Rii is defined as one-fourth of the hydraiilic diameter. [Pg.638]

The hydraulic diameter is four times the flow area divided by the duct perimeter. [Pg.784]

Al = Cross-secdonal area allocated to lighL phase, sq ft Ap = Area of particle projected on plane normal to direction of flow or motion, sq ft A, = Cross-sectional area at top of vessel occupied by continuous hydrocarbon phase, sq ft ACFS = Actual flow al conditions, cu ft/sec bi = Constant given in table c = Volume fraction solids C = Overall drag coefficient, dimensionless D = Diameter of vessel, ft Db = See Dp, min Dc = Cyclone diameter, ft Dc = Cyclone gas exit duct diameter, ft Dh = Hydraulic diameter, ft = 4 (flow area for phase in question/wetted perimeter) also, DH in decanter design represents diameter for heavy phase, ft... [Pg.284]

Figure 4.7 represents nondimensional axial-velocity contours for two ducts, one with an aspect ratio a = 1 and the other with aspect ratio a = 0.25. The figure shows how the product /Re varies as a function of aspect ratio. For a given channel geometry, fluid properties, and flow conditions, the hydraulic diameter and the aspect ratio can be determined easily. The friction factor / follows easily, which in turn provides the mean wall shear stress. [Pg.173]

When the inlet length is expressed in terms of number of gap widths , the difference between the flow in a tube and the flow in an annulus of narrow gap differs only by 25% [(0.05 - 0.04)/0.05]. This situation is an indication that the growth of the laminar boundary layers from the wall to the center of the channel is similar in both cases. Because duct friction coefficients, a measure of momentum transfer, do not vary by more than a factor of 2 for ducts of regular cross sections when expressed in terms of hydraulic diameters, the use of the inlet length for tubes or parallel plates can be expected to be a reasonable approximation for the inlet lengths of other cross sections under laminar flow conditions. In the annular denuder, the dimensionless inlet length for laminar flow development, L, can be expressed as... [Pg.57]

The convective heat-transfer coefficient and friction factor for laminar flow in noncircular ducts can be calculated from empirically or analytically determined Nusselt numbers, as given in Table 5. For turbulent flow, the circular duct data with the use of the hydraulic diameter, defined in equation 10, may be used. [Pg.484]

Now for a circular duct, i.e., a pipe with a uniform heat flux at the wall, the analysis discussed in the previous section gave Nup = 4.364. Therefore, for fully developed flow in a plane duct with a uniform heat flux at the wall, this would indicate using the hydraulic diameter concept, that ... [Pg.178]

Effect of wall thermal boundary condition oh the Nusselt number for hilly developed flow in a rectangular duct (Nusselt number based on hydraulic diameter)... [Pg.188]

Flow in Noncircular Ducts The length scale in the Nusselt and Reynolds numbers for noncircular ducts is the hydraulic diameter, D), = 4AJp, where A, is the cross-sectional area for flow and p is the wetted perimeter. Nusselt numbers for fully developed laminar flow in a variety of noncircular ducts are given by Mills (Heat Transfer, 2d ed., Prentice-Hall, 1999, p. 307). For turbulent flows, correlations for round tubes can be used with D replaced by l. ... [Pg.9]

The foregoing arguments may be applied to turbulent flow in noncircular ducts by introducing a dimension equivalent to the diameter of a circular pipe. This is known as the mean hydraulic diameter, which is defined as four times the cross-sectional area divided by the wetted perimeter. The following examples are given ... [Pg.3866]

As with noncircular ducts the hydraulic mean diameter is employed in formulae that involve diameter. If a channel has a height of a and a width b, the flow area of the channel is ab. In the calculation of the wetted perimeter the free surface is not included so that the wetted perimeter is 2a - - b, and the hydraulic mean diameter... [Pg.981]

For flows through noncircular cross sections and ducts, the heat transfer correlations developed for pipes can be used based on a hydraulic diameter,... [Pg.300]

For fluid flow and heat transfer inside a duct, various dimensionless parameters are used. In these parameters, a characteristic length of the duct is commonly involved. The hydraulic diameter Dh of the duct serves this purpose. It is defined as follows ... [Pg.304]

Comparisons of precision using Eqs. 5.220 and 5.221 and Blasius s formula (Table 5.8) in which the diameter of circular duct 2a is replaced by hydraulic diameter 4b, b being the halfspace between two plates, have been conducted by Bhatti and Shah [45]. In the range of 5000 < Re < 3 x 104, Eq. 5.220 is recommended otherwise, Eq. 5.221 should be used to obtain the friction factor for fully developed turbulent flow in a parallel plate duct. However, use of the hydraulic diameter to substitute for the circular duct diameter in the Blasius equation is reasonable for the prediction of the fraction factor [45]. [Pg.366]

Fully developed fluid flow and heat transfer results for rough parallel plate ducts can be predicted using the results for rough circular ducts with the use of hydraulic diameter [45]. [Pg.367]

For most engineering calculations of friction factors and Nusselt numbers for fully developed flow in rectangular ducts, it is sufficiently accurate to use the circular duct correlations by replacing the circular duct diameter 2a with the hydraulic diameter Dh = 4abf(a + b) or with D/, defined by the following equations to consider the shape effect [168] ... [Pg.373]

For equilateral triangular ducts having rounded corners with a ratio of the corner radius of curvature to the hydraulic diameter of 0.15, Campbell and Perkins [180] have measured the local friction factor and heat transfer coefficients with the boundary condition on all three walls over the range 6000 < Re < 4 x 104. The results are reported in terms of the hydrodynamically developed flow friction factor in the thermal entrance region with the local wall (Tw) to fluid bulk mean (Tm) temperature ratio in the range 1.1 < TJTm < 2.11, 6000 < Re < 4 x 10 and 7.45 [Pg.382]

Three corrugated ducts are schematically shown in the insets of Fig. 5.59. Hu and Chang [265] have analyzed the / Re for fully developed laminar flow in circumferentially corrugated circular ducts with n sinusoidal corrugations over the circumference as shown in Fig. 5.59, inset a, for e = da = 0.06. The perimeter and hydraulic diameter of these ducts must be evaluated numerically. However, their free flow area Ac is given by Ac = m2(l + 0.5e2). [Pg.414]

It is generally accepted that the hydraulic diameter correlates Nu and /for fully developed turbulent flow in circular and noncircular ducts. This is true for the results accurate to within 15 percent for most noncircular ducts. Exceptions are for those having sharp-angled corners in the flow passage or concentric annuli with inner wall heating. In these cases, Nu and /could be lower than 15 percent compared to the circular tube values. Table 17.16 can be used for more accurate correlations of Nu and /for noncircular ducts. [Pg.1313]

A careful observation of accurate experimental friction factors for all noncircular smooth ducts reveals that ducts with laminar/Re < 16 have turbulent/factors lower than those for the circular tube, whereas ducts with laminar/Re > 16 have turbulent/factors higher than those for the circular tube [48], Similar trends are observed for the Nusselt numbers. If one is satisfied within 15 percent accuracy, Eqs. 17.87 and 17.88 for/and Nu can be used for noncircular passages with the hydraulic diameter as the characteristic length in / Nu, and Re otherwise, refer to Table 17.16 for more accurate results for turbulent flow. [Pg.1313]


See other pages where Duct flow hydraulic diameter is mentioned: [Pg.649]    [Pg.226]    [Pg.12]    [Pg.24]    [Pg.20]    [Pg.222]    [Pg.463]    [Pg.474]    [Pg.785]    [Pg.797]    [Pg.87]    [Pg.793]    [Pg.805]    [Pg.642]    [Pg.653]    [Pg.199]    [Pg.133]    [Pg.1142]   
See also in sourсe #XX -- [ Pg.170 ]




SEARCH



Duct flow

Ducting

Ducts

© 2024 chempedia.info