Abstract
Little information is available on the nature of converging flow in bilateral junctions. Industrial Ventilation (American Conference of Governmental Industrial Hygienists) recommends against bilateral junctions without providing any justification. The American Society of Heating, Refrigerating and Air-Conditioning Engineers provides a table of coefficients for one type of bilateral junction, but it is of limited use in converging flow ventilation systems. The authors experimentally determined losses in one symmetrical bilateral junction designed to connect two 12.7 cm lateral ducts (both 45° entries) and one 17.8 cm collinear duct to a 25.4 cm main duct. Velocity ratios of the converging ducts were varied from 0–3.7 to produce 35 test conditions. The linear kinetic power model provided a good fit to the empirical data. As expected, power losses were lowest when velocity ratios were near unity. Compared for practical conditions to two single lateral junctions in an optimum layout, the power losses in the bilateral junction tested were 0–51% higher—a maximum increase equivalent to about 1.25 relatively smooth elbows. Those costs may be acceptable when weighed against the convenience of bilateral junctions in system layouts. Furthermore, under conditions where bilateral junctions would be convenient to use, actual losses for single-lateral junctions may be higher than those for bilateral junctions.