Is the mass flow rate the same upstream and down stream an orifice?

Yes, the mass flow rate is the same upstream and downstream of an orifice, assuming there are no leaks and the flow is steady. This principle is based on the conservation of mass, which states that mass cannot be created or destroyed in a closed system. However, the velocity and pressure of the fluid will change as it passes through the orifice, resulting in a drop in pressure and an increase in velocity downstream.