Ashrae Duct Fitting Databasel
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The CFD model for pressure drop along a common flat-oval fitting was appliedto a fitting with the same shape and length, but with a larger diameter. TheCFD model accurately predicted the ASHRAE database results from anorthogonal flow angle of 10-20[degrees] (Figure 2a) and decreasing angular flowspeeds from left to right (Figure 2b).
A common flat-oval fitting with a sharply decreasing diameter was chosen as an example of an elbow fitting where the eliminationspot is an ellipse at the transition point, similar to that of a hipped roundfilling (Figure 4). The CFD model results were not as accurate as that for the previous fittings. The CFDmodel did not replicate the shape of the real fitting well, and it showed poor conformance withthe ASHRAE database data for small flow velocities (Figure 5).
In this experiment, the calculations for pressuredrop across an inline straight-shaped fitting were again compared to the ASHRAEdatabase results. The inline straight fitting design with a 50[degrees] angle was chosen (Figure 6) as an example of a fitting with available published data. This fitting had a loss coefficient of 0.10. Both the CFD model and the experimental results were within30% of each other over a range of velocities from 10-21 m/s (1378-2560 fpm) (Figure 7).
The CFD model for pressure drop along a 90[degrees] miter fitting was applied to a90[degrees] mitered round fitting. The CFD model results closely matched theASHRAE database results (Figure 3a).
With a poorly designed duct system, return air airflow through the system will be too muchor too little and may in turn have adverse effects on other system componentsas, for example, the infiltration of cold or hot air into the conditioned space.
If you have tested your duct fitting using a flow development section andor using a Lab Pressure Loss measurement (see: read here )method, it is possible to add the below form to the report so users canenter the specifications, and calculations can be done on the fly. 7211a4ac4a