Pipe/duct flow

As the air or gas flows through the blower system (piping/ ducts, filters, etc.), the movement causes friction between the flowing air/gas. This friction translates into resistance to flow, whether on the inlet (suction side) or outlet (discharge side) of the system in which the blower is a part and that creates the pressure drop (see Chapter 2, V. 1, 3 Ed., of this series) which the blower must overcome in order for the air/gas to move or flow. This resistance to flow becomes greater as the velocity of flow increases, and more energy or power is required to perform the required flow movement at the required pressures. 

Solar radiation may fall on outside walls or roofs, raising the skin temperature, and this must he taken into account. Most cold stores are huilt within an outer envelope which protects them from the elements and from direct sunshine. In cases where the insulation itself is subject to solar radiation, an allowance of 5 K higher outside temperature should he taken. Heat load must he estimated through all surfaces including piping, ducts, fan casings, tank walls, etc., where heat flows inwards towards the cooled system. 

Duct flows can be converted into efficient mixing flows (i.e., flows with an exponential stretch of material lines with time) by time- modulation or by spatial changes along the duct axis. One example of the spatially periodic class is the partitioned-pipe mixer (PPM). This flow consists of a pipe partitioned with a sequence of orthogonally placed rectangular plates (Fig. 5a). The cross-sectional motion is induced through rotation of the pipe with respect to the assembly of plates, whereas the axial flow is caused by... 

The most common application of flow measurement in process plants is flow in pipes, ducts, and tubing. Table 10-4 lists widely used... 

Using various test devices one can differentiate between two flow forms to detect the drag reduction phenomenon the so-called external flow which includes flow over flat plates as well as around submerged bodies such as ship hulls of submarine models. The second form, named the internal flow , includes flow situations in pipes, ducts, and pumps (Fig. 7). 

The nature of gas flow in pipes, ducts, etc. changes with gas pressure. The type of flow is defined by the Knudsen number (Kn) ... 

Internal flows of the type here being considered occur in heat exchangers, for example, where the fluid may flow through pipes or between closely spaced plates that effectively form a duct Although laminar duct flows do not occur as extensively as turbulent duct flows, they do occur in a number of important situations in which the size of the duct involved is small or in which the fluid involved has a relatively high viscosity. For example, in an oil cooler the flow is usually laminar. Conventionally, it is usual to assume that a higher heat transfer rate is achieved with turbulent flow than with laminar flow. However, when the restraints on possible solutions to a particular problem are carefully considered, it often turns out that a design that involves laminar flow is the most efficient from a heat transfer viewpoint. 

Therefore, as was the case with fully developed pipe flow, the velocity profile in fully developed plane duct flow is parabolic. 

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... 

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. 

The terms pipe, duct, and conduit are usually used interchangeably for flow sections. In general, flow sections of circular cro.ss section are referred to as pipes (especially when the fluid is a liquid), and flow sections of nnncircular cross section as ducts (especially when the fluid is a gas). Small-diameter pipes are usually referred to as tubes. Given this uncertainty, we will use more descriptive phrases (such as a circular pipe or a rectangular duct) whenever necessary to avoid any misunder.standings. 

Lee SL (1987) A unified theory on particle transport in turbulent dilute two-phase suspension flow-11. Int J Multiphase Flow 13(1) 137-144 Lee SL, Borner T (1987) Fluid flow structure in a dilute turbulent two-phase suspension flow in a vertical pipe. Int J Multiphase Flow 13(2) 233-246 Lee SL, Durst F (1982) On the motion of particles in turbulent duct flows. Int J Multiphase Flow 8(2) 125-146... 

The pipe head loss may be calculated by the well known Darcy- Weisbach equation [94], valid for duct flows of any cross section and for laminar and turbulent flow ... 

So far in this chapter and in the vast majority of problems in pipes, channels, ducts, etc., we assume that the velocity is practically uniform across the pipe, duct, or channel so that we may associate one velocity with the entire flow at one area perpendicular to the flow. In most flows of practical interest to chemical engineers, this simplification introduces negligible errors. However, there are somej very simple and common flows for which this is not the case. The simplest arid most illustrative example is the flow over a sharp-edged weir. 

If we choose as our system some pipe, duct, or channel with steady flow through it in one direction, e.g., the x direction, then Eq. 7.15 becomes... 

Many applications of Eq. 7,16 involve jets. A jet is a stream of fluid which is not confined within a pipe, duct, or channel examples are the stream of water issuing from a garden hose and the exhaust gas stream from a jet engine. If a jet is flowing at a subsonic velocity, its pressure will be the same as the pressure of the surrounding fluid. If a jet enters or leaves a system or device at subsonic speed, it will enter and leave at the pressure of the surrounding fluid, although its pressure may be different inside the device. 

The most common way for turbulent kinetic energy to enter flow is by a shear layer. When we stir the soup, often we use a circular motion and induce a circular flow and/or circular eddies. This is also common in vessels with rotating mixers. But for flows in pipes, ducts, around airplanes or ships, or in... 

If the above intuitive picture is correct, then no turbulence can be formed except by large-scale mechanical stirring or by some kind of shearing, analogous to that shown in Fig. 16.1(a). This is indeed observed. The turbulence in pipes, ducts, and channels is produced by the shear layers at the walls of the duct. Turbulence is steadily fed into the main flow in the duct and ultimately is consumed in viscous heating in the main flow. The turbulence in the wake of ships and airplanes is caused by the shear layer adjacent to the surface of the airplane or ship, and the turbulence decays with time, due to viscosity, after the airplane or ship passes. 

M2 For collectors with pipe ducts, the temperature nonuniformity of the absorber perpendicular to the flow direction of the medium is taken into account by an average temperature using the fin efficiency [43,56]. 

Fluid Flow The volume flow of a fluid, Q, or discharge, through some cross-section (pipe, duct or channel) is... 

Process flow diagram This document schematically shows all major equipment items within a plant and how they are linked together by piping, ducts, and... 

All manual valves and valve operators shall be located in areas readily accessible to operating personnel. If valves are installed in areas of high radiation or other hazards they should be provided with extended stems or equivalent devices allowing actuation from a lower radiation area. Handwheels and chain or extension handle operators should be located at a reasonable height above either the floor or a permanently installed platform to allow easy operation. Piping ducts and valves should be located and marked such that the operators can easily identify the flow paths. Pipes or ducts that cross the normal and safety pathways should be at least 2 m above the floor. 

Liu and Agarwal performed an experimental study on deposition of aerosol particles in turbulent pipe flows. McCoy and Hanratty, Wood, and Papaver-gos and Hedley reported several collections of available data on wall deposition rates. Kvasnak et al. reported their experimental data for the deposition rate of glass beads, various dust components, and glass fibers in a horizontal duct flow. Wood, Hidy, and Papavergos and Hedley reviewed the available methods for evaluating the deposition velocity in turbulent duct flows and discussed different deposition mechanisms. 

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