$3\mathrm{.}9.$ The calculation of flow rate given diameter, or of diameter given flow rate,

for a specified pressure gradient is iterative with a friction factor$-$Reynolds

number plot. Describe a way of replotting f$-$Re data so that the following cal$-$

culations can be carried out without iteration:

a$)$ Calculate the flow rate when pressure drop and pipe diameter are specified.

b$)$ Calculate the pipe diameter required to provide a specified mass flow rate

under a given pressure drop.