An off-shore oil platform uses desalinated seawater as its source for a freshwat
ID: 1498264 • Letter: A
Question
An off-shore oil platform uses desalinated seawater as its source for a freshwater delivery system. The delivery system has four stages and starts with a large intake pipe for the seawater, eventually desalinating the flowing seawater and delivering freshwater to a precise location using a small nozzle. The intake pipe diameter in stage one is 0.9m, and the seawater is flowing at 0.1 lm/s. The pipe diameter in stage two is 0.5 m. Desalination occurs between stage two and three. The pipe diameter for the fresh water in stage three is 0.2m, and the nozzle diameter for the final stage is 0.05m. Assuming that the volumetric flow rate for each stage remains constant and neglecting any gravitational effects, determine whether the flow is laminar or turbulent at each stage of the process. If you was now commissioned to design and deploy a similar four-stage delivery system in an environment where ensuring laminar flow at each stage was critical, what specific design recommendations would you have? Assume that the diameter of each subsequent stage is reduced, that that the overall size of the system can be changed and a different fluid can be used.Explanation / Answer
(a)
For first stage,
Intake velocity v = .11 m/s
Reynold number, R = rho*v*d /mu
=1026*0.11*0.9/1.2*10^-3
=84645
For the final stage,
speed
v' = A*v / A' = 0.9^2 *.11 /.05^2 =35.64
Reynolds number,
Re = 1026* 35.64*.05/1.2*10^-3 =1523610
which shows the current is continue to be turbulent for all other stages.
(b)
Addition to reduction in diameter and increases more viscous fluid, I would suggest to use much slower intake flow speed. If reduction in dinsity can be achieved, that option too can be deployed.