Aaberg exhaust hoods design equations and

When dynamic simulation is used for process equipment and process safety design, it is necessary to ensure the model s assumptions are conservative. For example, if dynamic simulation is used to calculate the pressure rise in a heat exchanger after a tube rupture, the highest calculated pressure may be used as the design pressure. If all the assumptions are conservative, the actual heat exchanger pressure will not exceed the design pressure during a tube rupture. Despite this conservative approach, equipment design conditions calculated by dynamic simulation are often much less severe than the conditions determined by conventional calculation methods. This often leads to considerable cost savings. Dynamic simulation software should support the addition of user-written code for specialized equipment and control system models. For example, an unusual fractionator tray design or a correlation for an off-design heat transfer coefficient may have to be programmed into a user-written model. Dynamic simulation of "first-of-a-kind" plants often requires developing a dynamic model for a new equipment item. A control system vendor s DCS algorithm may also need to be programmed into a custom PID controller model. Users may need to add their own fluid property systems to increase computational efficiency and handle unusual systems. "Black box" models are too restrictive to provide realistic models for most dynamic simulation problems.  [c.46]

Fume velocity can be measured at the roof truss level by using several propeller-type anemometers mounted on a grid. The output from the anemometers can be connected to a recorder located at the operating floor level. Experience has shown that six to eight anemometers are usually sufficient to give a good description of the plume velocity. This approach has the advantage of obtaining both a velocity profile and an average velocity for the plume. The combined information of velocity distribution and observed plume size provides the necessary design parameters to ensure a satisfactory performance for the designed hood. Figure 13.29 is a plot of average plume flow rates measured at roof truss level as a function of time for a typical tapping operation on an electric steelmaking furnace. To carry out such velocity measurements as a standard method is not recommended because fume and dust tend to harm the propeller hearings, making the anemometer inoperative after a number of tests.  [c.1269]

The design of the axisymmetrical Aaberg exhaust hood is very similar to a traditional flanged hood. However, it is fitted with a flange through which air can be ejected radially from a narrow slot (see Fig. 10.77). The dramatic effect of the blowing jet on the hood s overall airflow can be explained as follows due to the friction developed at the radial jet/air interface an entrainment flow develops which, under the correct conditions, has the property of removing the clean air from in front of the hood (the recycled flow) as well as enhancing and concentrating the exhaust s suction in a zone along the hood s longitudinal axis (the efficient flow). The flow in front of the exhaust opening is now directional and the process is capable of creating a larger fluid flow toward the exhaust opening at greater distances along the axis of the exhaust hood. Further, although replacement air should still be supplied, the Aaberg exhaust works with sig-  [c.956]

Heat Kecope Steam Generators. Heat recovery steam generators, a special class of boilers where essentially all heat transfer takes place convectively, are used to extract energy from hot gas streams. One of the principal uses is extraction of heat from the exhaust gases of a combustion turbine. Turbine exhaust gas is typically 540°C (1004°F). Carehil design of the HRSG allows the gas leaving the HRSG to approach the feedwater temperature within 28°C (50°F). High heat-transfer rates in modem HRSGs are assisted by finned tubing.  [c.359]

See pages that mention the term Aaberg exhaust hoods design equations and : [c.2346]   
Industrial ventilation design guidebook (2001) -- [ c.0 ]