Question

A Venturi meter with a throat diameter d = 2 cm measures the flow rate in a pipe of diameter D = 6 cm, as shown in the figure. A U-tube manometer is connected to measure the pressure drop. Assume the discharge coefficient is independent of the Reynolds number and geometric ratios. If the volumetric flow rate through the pipe is doubled, Q2 = 2Q1, the corresponding ratio of the manometer readings $\Delta h2/\Delta h1,$ rounded off to the nearest integer, is _______

Official answer: 4