Question

During the filling process of a given sand mould cavity by molten metal through a horizontal runner of circular C.S, the frictional head loss of the molten metal in the runner will increase with the

• A. Increase in runner diameter
• B. Increase in average velocity of molten metal
• C. Decrease in length of runner
• D. Decrease internal surface roughness of the runner

Answer 1

The correct option is B Increase in average velocity of molten metal

Flow of molten metal inside the horizontal runner is similar to the flow of fluid through a pipe, hence from Darcy-Weisbach equation we get that head loss of molten metal will increase with velocity of metal inside the runner.

$h_f=\frac{fL{V}^2}{2gD}$

Moreover, high velocity also causes turbulence leading to increase in frictional head loss.