Question

accomplish relation between critical velocity and Reynolds number

Answer 1

CRITICAL VELOCITY : The critical velocity is that velocity of liquid flow, up to which its flow is streamlined (laminar)& above which its flow becomes turbulent.It's denoted by Vc & it depends upon:
Coefficient of viscosity of liquid  (η)Density of liquid.Radius of the tube.Which brings us to the relation 
Vc = (K η)/ρr.
For the flow to be streamline, value of Vc should be as large as possible. For this, coefficient of viscosity should be large & ρ ,r should be small.
Which means Reynold's Number Nr must lie between 0 to 2000.