Square duct

This formula is valid for square ducts. For the parallel extension part, one could calculate... 

An air ventilating system must be designed to deliver air at 20°F and atmospheric pressure at a rate of 150 ft3/s, through 4000 ft of square duct. If the air blower is 60% efficient and is driven by a 30 hp motor, what size duct is required if it is made of sheet metal ... 

Rowe and Henwood(26) made similar studies by supporting a spherical particle 12.7 mm diameter, in water, at the end of a 100 mm length of fine nichrome wire. The force exerted by the water when flowing in a 150 mm square duct was calculated from the measured deflection of the wire. The experiments were carried out at low Reynolds numbers with respect to the duct (< 1200), corresponding to between 32 and 96 relative to the particle. The experimental values of the drag force were about 10 per cent higher than those calculated from the Schiller and Naumann equation. The work was then extended to cover the measurement of the force on a particle surrounded by an assemblage of particles, as described in Chapter 5. 

The third factor that is important in determining the detection limit is the conversion efficiency of the kinetics. A conversion efficiency of 1.0 requires that the airstream have a velocity substantially less than 200 m/s because uniform mixing of NO is very difficult. At the same time, collisions of the sample airstream with wall surfaces in slower inlet systems may cause a chemical loss of CIO and BrO, because they are both reactive with wall surfaces. The solution to this problem was suggested by Soderman (83). Soderman s novel design consists of two nested ducts in which the air speed is decreased from 200 m/s to 60 m/s in a 14-cm-diameter outer duct that protrudes 60 cm in front of the left wing pod and is reduced to 20 m/s inside a smaller 5-cm-square duct in which the measurements are made. The entrance to the smaller measurement duct is 60 cm downstream of the entrance to the outer duct, and the NO injector tubes, the two CIO detection axes, and the one BrO axis are 25 cm, 37.5 cm, 55 cm, and 72.5 cm downstream of the entrance of the measurement duct. Ninety percent of the air that enters the outer duct bypasses the measurement duct through additional duct work, and only the center 10% of the airstream is captured and sampled by the measurement duct. These two flows are recombined downstream of the instrument and are vented out the side of the wing pod that houses the instrument. 

Figure 6. Visualization of mass transfer in monolith structures (flow from left to right). Top Corrugated packing bottom Square duct monolith [9],...

A square duct, 30 by 30 cm, is maintained at a constant temperature of 30°C and an airstream of 50°C and 1 atm is forced across it with a velocity of 6 m/s. Calculate the heat gained by the duct. How much would the heat flow be reduced if the flow velocity were reduced in half ... 

The analysis employed mass transfer coefficients for fully developed laminar flows in square ducts. 

Hot air at atmospheric pressure and SOX enters an 8-m-long uninsulated square duct of cross section 0.2 m x 0.2 m that passes through the attic of a house at a rate of 0.15 m /s (Fig. 8-31). The duct is observed to be nearly Isolhermal at 60°C. Determine the exit temperature of the air and the rale of heat loss from the duct to the attic space. 

SOLUTION Heat loss from uninsulated square ducts of a heating system in the attic Is considered. The exit temperature and the rate of heat loss are to be ] determined. 

Later, Tomiyama [156, 154] observed a defect in the original model by Antal et al, namely, that a bubble located far from the wall is attracted to the wall. Based on a best fit of model simulations to experimental data from a square duct with wall-distance H, a modified wall force was given as ... 

Set Ax = Ay (this does not imply a square duct with W = H). Then... 

Determine the axial velocity profile for laminar flow in a square duct. Also determine the pressure drop per unit length for water in a square duct with H = pm (each side is 2 pm)... 

Equation 16.10 is the counterpart for a square duct of Equation 3.18 for a circular duct. The units are consistent. Using SI units for p, u, and H will give the pressure gradient in pascals per meter. The pressure drop for the example case is 71,100 Pa m . A duct length of 1 cm would give f = 1000 s and a pressure drop of about 700 Pa or 0.25 psi. Thus pressure drops are small for the envisioned use as a reactor. 

Jwall = Iwall This makes it a square duct... 

For square ducts, a = 1, the Nusselt numbers for the , , and thermal boundary conditions have been obtained by Chandrupatla and Sastri [162]. As recommended by Shah and London [1], the results obtained by Chandrupatla and Sastri [162], shown in Table 5.34, are more accurate than those presented by Wibulswas [160]. 

TABLE 5.34 Local and Mean Nusselt Numbers in the Thermal Entrance Region of a Square Duct With the , , and Boundary Conditions [162]... 

Simultaneously Developing Flow Table 5.35 presents the results for simultaneously developing flow in rectangular ducts these were obtained by Wibulswas [160] for the and boundary conditions for air (Pr = 0.72). Transverse velocity is neglected in this analysis. However, Chandrupatla and Sastri [163] include transverse velocity in their analysis for a square duct with the boundary condition. 

TABLE 5.36 Local and Mean Nusselt Numbers for Simultaneously Developing Flow in a Square Duct (a = 1) With the Boundary Condition [163]... 

The following formulas are suggested by Shah and Joshi [195] to compute the friction factor for fully developed laminar flow in curved square ducts ... 

The following correlation, obtained by Cheng et al. [228], is recommended for curved square ducts ... 

Fully Developed Turbulent Flow in Curved Rectangular and Square Ducts... 

For curved rectangular ducts as well as square ducts, when Re < 8000, the fully developed friction factors can be computed from the following correlation obtained by Butuzov et al. [230] and Kadambi [231] ... 

Square Ducts With Thin Longitudinal Fins... 

Gangal and Aggarwala [268] have analytically obtained the/Re and NuHi for fully developed flow in a square duct with four equal internal fins, as that shown in Fig., 5.43. The fins were treated as having zero thickness and 100 percent efficiency. The results of /Re and NuHm for fully developed flow are provided in Table 5.50. 

FIGURE 5.43 A square duct with four equal longitudinal thin fins. 

TABLE 5.50 Longitudinal Four Thin Fins Within a Square Duct (/Re)d and NuHi.[Pg.402]

A. R. Chandrupatla, and V. M. K. Sastri, Laminar Forced Convection Heat Transfer of a Non-Newtonian Fluid in a Square Duct, Int. J. Heat Mass Transfer, (20) 1315-1324,1977. 

M. K. Gangal, and B. D. Aggarwala, Combined Free and Forced Convection in Laminar Internally Finned Square Ducts, Z. Angew. Math. Phys., (28) 85-96,1977. 

Equation 10.59 was solved by Schechter [49] using a variational principle and by Wheeler and Wissler [50] using a numerical method. Wheeler and Wissler also presented an approximate equation for the square duct geometry. Schechter reported approximate velocity profiles for a power law fluid flowing through rectangular ducts having aspect ratios 0.25, 0.50, 0.75, and 1.0. His results may be expressed as follows ... 

Wheeler and Wissler proposed an approximate equation for the fully developed friction factor for laminar flow of a power-law fluid through a square duct ... 

Here Re+ = pU2 "d /K and 0.4 < n < 1.0. Chandrupatla and Sastri also reported friction factor results for flow in a square duct [51]. 

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