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This paper reports on an experimental study of the airflow performance of a variable-area diffuser. The diffuser's performance was characterized by determination of the velocity decay coefficient, K, and the virtual origin, xp. The velocity decay profiles were measured for various diffuser outlet areas and flow rates. The results indicated that for this particular diffuser , the decay coefficient above a certain flow rate for a given outlet area is relatively independent of flow rate. At low flow rates, K decreases with decreasing flow rate. In addition, it was found that jets with the same momentum from a variable-area diffuser are not necessarily identical. At small diffuser openings, there exists nonsimilarity between the small opening and more standard openings. Similarity can be achieved between larger openings. Finally, analysis showed that K is inversely proportional to the square root of the tangent of the spread angle, beta.

KEYWORDS: Experiment, air flow, performance, diffusers, air jets, air flow rate.

Citation: Symposium, ASHRAE Trans., 1993, vol.99, part 2, paper number DE-93-1-1, 429-439, 7 figs, 2 tabs, refs.