Duct flow characteristics

In some instances the fan has a free discharge. Typical is the axial fan installed in a wall opening (wall fan). In most cases the fan is connected to a duct run in this instance the total pressure difference and volume flow are determined from both the fan and duct network characteristics. 

Figure 15. Example of flow characteristics in the measurement duct of the ClO-BrO instrument during a flight over Norway on January 6, 1989. The lowest solid line in each panel is the ambient temperature, pressure, and potential temperature as measured by the MMS instrument (9). In the top panel, temperatures 1, 2, and 3 (bottom to top) are taken inside the 5-cm-square measurement duct 0.0, 1.0, and 1.5 cm from the center of the duct. The velocity of the flow was roughly 22 m/s in the measurement duct.

TABLE 5.48 Flow Characteristics for the Entrance Problem in an Internally Finned Circular Duct... 

TABLE 5.56 Fully Developed Laminar Flow Characteristics of Regular Polygonal Ducts [1]... 

E. M. Sparrow, and M. Charmchi, Heat Transfer and Fluid Flow Characteristics of Spanwise-Periodic Corrugated Ducts, Int. J. Heat Mass Transfer, (23) 471-481,1980. 

Duct flows of nonnewtonian fluids are described by the governing equations (Eq. 10.24-10.26), by the constitutive equation (Eq. 10.27) with the viscosity defined by one of the models in Table 10.1, or by a linear or nonlinear viscoelastic constitutive equation. To compare the available analytical and experimental results, it is necessary to nondimensionalize the governing equations and the constitutive equations. In the case of newtonian flows, a uniquely defined nondimensional parameter, the Reynolds number, is found. However, a comparable nondimensional parameter for nonnewtonian flow is not uniquely defined because of the different choice of the characteristic viscosity. 

The aerodynamic valves have a specially designed inlet (e.g., a profiled orifice in the inlet pipe, contoured diffuser, or a shrouding duct) in which the fluid flow characteristics act as a physical barrier (fluid diode) to the backflow of combustion products. Such pulse combustors are termed the valveless combustors. Example of valveless pulse combustor is shown in Figure 23.4 (Putnam et al., 1986). 

The water flow within a rectangular duct is used for investigations on the effect of near wall injected polymer solution on development and cnaracte-ristics of boundary layer, comprising both bulk mean flow characteristics and turbulence structure. The author of the study had in mind possible... 

The device should be suitable whenever large quantities of bulk solids have to be measured downstream of mechanical conveyor systems and should be accurate even in case of large flows and high ambient temperatures. It should be possible to install the instmment on round pipes or ducts and should operate with the latest microprocessor technology. It should be dustproof and can be installed at an angle if required. The mass flow measurement should be independent of flow characteristics, and with no moving parts in the system, maintenance is not required. 

Wang, C. H. Tang, M. 2012. Laminar Flow Characteristics in Helical Duct with Right-angled Isosceles Triangle Cross Section. The Chin. J. of Process Eng. 12(5) 754-759. 

Flow, transition (vacuum technology) Gas flow conditions intermediate between viscous flow and molecular flow where the flow characteristics are determined by molecular collisions and collisions with the walls of the duct. 

Entrance flow is also accompanied by the growth of a boundary layer (Fig. 5b). As the boundary layer grows to fill the duct, the initially flat velocity profile is altered to yield the profile characteristic of steady-state flow in the downstream duct. For laminar flow in a tube, the distance required for the velocity at the center line to reach 99% of its asymptotic values is given by... 

The fan volume flow q, and its corresponding Ap,g, can be found when a Ap,o( - chart is drawn the duct parabola and experimental Ap, t both equal f(q ) (Eig. 9.47). The experimental curve Apj j = f q ) is called the fan characteristic curve, and the duct static pressure drop dependency on the duct volume flow is the characteristic curve. The characteristic curve intersection point is called fan operating point. 

Solution. Draw into the iv diagram the characteristic curve of the fan and the duct-pressure-drop volume flow dependency. The latter is a parabola passing through the origin with the following equation ... 

In a Ap-q, chart, the characteristic curve of the ducts is drawn. In the same chart is drawn the characteristic curve of both fans. At each volume flow q, the total pressure of each fan is added. In this w ay, we get a new - q ... 

For an existing process plant, the designer has the opportunity to take measurements of the fume or plume flow rates in the field. There are two basic approaches which can be adopted. For the first approach, the fume source can be totally enclosed, and a temporary duct and fan system installed to capture the contaminant. For this approach, standard techniques can be used to measure gas flow rates, gas compositions, gas temperatures, and fume loadings. From the collected fume samples, the physical and chemical characteristics can be established using standard techniques. For most applications, this approach is not practical and not very cost effec tive. For the second approach, one of three field measurement techniques, described next, can be used to evaluate plume flow rates and source heat fl uxes. 

Chapter 4 is devoted to single-phase heat transfer. Data on heat transfer in circular micro-tubes and in rectangular, trapezoidal and triangular ducts are presented. Attention is drawn to the effect of energy dissipation, axial conduction and wall roughness on the thermal characteristics of flow. Specific problems connected with electro-osmotic heat transfer in micro-channels, three-dimensional heat transfer in micro-channel heat sinks and optimization of micro-heat exchangers are also discussed. 

However, a change in the flight speed and/or the flight alhtude alters the airflow rate. Then, the air-to-fuel ratio in the combushon chamber is also altered, and the thrust produced by the ducted rocket is altered. Consequenhy the flight envelope of the projechle becomes highly limited. These operahonal characteristics of the fixed fuel-flow ducted rocket reshict its application as a propulsion system. 

The basic characteristics of a one-dimensional shock wave are described in Chapter 1 of this text. However, the shock waves in supersonic flow propagate not only one-dimensionally but also two- or three-dimensionally in space. For example, the shock waves formed at the air-intake of a ducted rocket are two- or three-dimensional in shape. Expansion waves are also formed in supersonic flow. The pressure downstream of an expansion wave is reduced and the flow velocity is increased. With reference to Chapter 1, brief descriptions of the characteristics of a two-dimensional shock wave and of an expansion wave are given here.Ii-5]... 

External flows involve a flow, that is essentially infinite in extent, over the outer surface of a body. Internal flows involve the flow through a duct or channel. It is not always possible to clearly place a convective heat transfer problem into one of these categories since some problems have several of the characteristics of both an internal and an external flow. An example of such a case is shown in Fig. 1.7. 

This chapter has been concerned with the analysis of laminar flows in ducts with various cross-sectional shapes. If the flow is far from the inlet to the duct or from anything else causing a disturbance in the flow, a fully developed state is reached in many situations, the basic characteristics of the flow in this state not changing with distance along the duct. If the diffusion of heat down the duct can be neglected, which is true in most practical situations, it was shown that in such fully developed flows, the Nusselt number based on the difference between the local wall and bulk mean temperatures is constant. Values of the Nusselt number for fully developed flow in ducts of various cross-sectional shape were discussed. 

Each of these techniques may be used with numerous cell designs. The design of cell will depend upon the characteristics of the system to be simulated. Commonly, the flow of electrolyte is important and must be known and in such cases, rotating-disc or ring-disc, flow-in-duct, or rotating-cylinder [36, 37] electrodes would be used. 

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