A pressure drop correlation for low Reynolds number Newtonian flows through a rectangular orifice in a similarly shaped micro-channel

► Developed correlation for pressure drop of a rectangular orifice at low Re numbers. ► The excess pressure drop is a strong function of an orifice aspect ratio. ► Two-dimensional approximation is valid only for aspect ratio bigger than 30. ► Contraction ratio is also important parameter especially when greater than 0.1. Current microfabrication methods mean that rectangular orifices in similarly shaped micro-channels are often found in microfluidic devices. The power required to overcome the pressure drop across such orifices is often of importance. In the contribution reported here, numerical results for low Reynolds number incompressible Newtonian fluid flow through rectangular orifice in similarly shaped micro-channel have been used to develop a correlation for pressure drop arising from the orifice. The correlation, which was motivated by theoretical developments, indicates that the pressure drop is proportional to the average velocity through the orifice, and a function of the orifice contraction ratio, length-to-width ratio and, most particularly, aspect ratio.