Flow Advisor - Tank Empty Times

Time to empty a Tank The discharge from an orifice is dependant on various factors: The discharge coefficient (varies with the type of outlet fitting). The cross-sectional area of the orifice. The 'Head' of water above the orifice outlet.

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The Flow Advisor program offers a choice of outlet types: Rounded outlet - discharge coefficient 0.98 Square edge outlet - discharge coefficient 0.80 Sharp edge outlet - discharge coefficient 0.61 Borda outlet (projecting inside) - discharge coefficient 0.51 Discharge Flow Rate The discharge flow rate from an orifice is calculated as follows: Flow rate = Orifice discharge coefficient x Orifice cross-sectional area x square root (2gH) Where g = acceleration due to gravity Where H = head of fluid about outlet As the tank empties the fluid head will reduce and the discharge flow from the orifice will reduce.

Fluid Surface Area If the fluid surface area within the tank is not constant, the rate of change in the fluid head will not be constant. Initially the change in fluid head may be slow, but as the tank empties the fluid head will change more quickly. The example shows that the time to reduce the fluid level by 300 mm (12 inch) is initially 3m - 37s, where as the final 300 mm of fluid will empty in 1m - 33 s.

Effect of Discharge Pipe When a pipe is used to feed the tank discharge to some other point the pipe may restrict the discharge flow rate. When a 4 metre (13 ft) length of pipe is used, in this example, the time to empty is increased by almost 8 minutes.

Flow Advisor for Channels and Tanks can help you save time and money. Click here to download Flow Advisor for a FREE trial!