Where, Q is the discharge, C, n is the flume coefficients which vary with the size of the flume, and H is the measuring head.
Concrete flume calculator free#
However in case of free flow conditions, the discharge is measured by the following formula: Generally, Parshall flumes are calibrated empirically in laboratory conditions before installing in the field. Dimensions and capacities of Parshall flume of various sizes (Letter, refer Fig. Free flow condition prevails if the submergence ratio (H b/H a) remains within 0.5, 0.6 and 0.7 for width of throat varying from 2.5 to 7.5 cm, 1.5 to 22.5 cm and 3.0 to 24.0 cm, respectively. However, downstream head (H b) is also measured for submerged flow condition. To determine discharge through the flume under free flow condition, head is measured at upstream section (H a). Flow is submerged when the down-stream water elevation retards the rate of discharge. Discharge through the flume can occur under either free or submerged flow condition. Standard dimensions of Parshall flumes with discharge values are presented in Table 8.1 and 8.2, respectively. On the basis of the throat width, Parshall flumes have been classified into three main groups. Care must be taken while constructing the flumes exactly in accordance with structural dimensions. Parshall flumes are available in various sizes. The size ranges from 7.5 cm to several m in throat width. The size of flume is determined by the width of its throat. The flume consists a converging section with a level floor and walls converges towards the throat section, a throat section with a downward sloping floor and parallel walls, and a diverging section with an upward sloping floor and diverging walls towards the outlet.
Parshall flumes are devices for the measurement of flow of water in open channels when depth of flow is less i.e., head drop is very small, the volume of flow is less and channel bed slope is less. Installation requires extremely careful work.įlow at the entrance must be evenly distributed, with little turbulence, to produce accurate measurements. Provides a reliable measurement in free flow and submerged flow conditions. The flow-rate in flumes is usually high enough to prevent sedimentation they are therefore self-cleaning.
Enables measurement in a large range of flow.
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