What happensto the volume flow rate when the diameter of the tube decrease?

When the diameter of a tube decreases, the volume flow rate typically increases if the fluid is incompressible and the pressure driving the flow remains constant. This is due to the principle of conservation of mass, which states that the product of the cross-sectional area and flow velocity must remain constant in a steady flow. Therefore, as the diameter decreases, the flow velocity must increase to maintain the same volume flow rate, resulting in higher velocity through the narrower section of the tube.