A fan–duct system consists of a fan supplying air through a round duct with a diverging, round to round, transition (see Fig. 11.3b). The divergence angle of the transition is 30°. The lengths and...

A fan–duct system consists of a fan supplying air through a round duct with a diverging, round to round, transition (see Fig. 11.3b). The divergence angle of the transition is 30°. The lengths and diameters of the duct sections upstream and downstream of the transition are 7 m, 0.25 m and 16 m, 0.35 m respectively. The upstream section includes two 90° bends (see Fig. 11.3a). Assume the friction factor for the straight duct sections as 0.025. (i) Obtain the equation of the system curve for the duct network. (ii) Use the fan curves given in Fig. E11.8.1 to determine the air flow rates when the fan speeds are 250 rpm and 200 rpm.