# Orifice Area

Written by Jerry Ratzlaff on . Posted in Flow Instrument

• Geometric Orifice Area (GOA)  -  The orifice opening
• Effective Orifice Area (EOA)  -  The minimal cross-section area of the downstream jet.
• Contraction Coefficient ($$C_c$$)  -  The ratio of the area measured at the vena contracta (EOA), to the area of the orifice (GOA) or $$C_c = \frac{EOA}{GOA}$$
• Discharge Coefficient ($$C_d$$)  -  The ratio of actual flow to ideal flow or $$C_d = \frac{Q_a}{Q_i}$$

## Orifice Area formula

 $$\large{ A_0 = \frac{ Q }{ C_d \; \sqrt{ 2 \; g \; H } } }$$

### Where:

 Units English Metric $$\large{ A_o }$$ = orifice area $$\large{ in^2 }$$ $$\large{ mm^2 }$$ $$\large{ h }$$ = orifice center of head $$\large{ in }$$ $$\large{ mm }$$ $$\large{ C_d }$$ = orifice discharge coefficient $$\large{ dimensionless }$$ $$\large{ Q }$$ = orifice flow rate $$\large{\frac{ft^3}{sec}}$$ $$\large{\frac{m^3}{s}}$$ $$\large{ G }$$ = orifice gravitational constant $$\large{\frac{lbf-ft^2}{lbm^2}}$$ $$\large{\frac{N - m^2}{kg^2}}$$

### Solve for:

 $$\large{ C_d = \frac { Q } { A_o \; \sqrt { 2 \; G \; h } } }$$