Q, Water flows at a speed of 6 cm/s thro a tube of radius 1 cm. Coeff. of voscosity of water at room temp. is 0.01 poise. Calculate the Reynold's no.

Ans : 120.

HCV , vol I, page 302 , q. 32

the velocity given must be critical vel ....

as we hve formula.. Vc = R (n/ rho D)

Vc= critical vel (max vel. fluid can have streamlined flow) , R= reynolds no., n= coef. of viscocity, D = 2r = diametr, and rho = density = 1 almost....

but i wonder why it isnt gven anythng abt critical vel.....

ANYWAYZ  this is the formula....

hope it helps...

Cheers!!!!!!!

does it come 120 ?

As given above Reynolds Number =  

It can be calculated for any velocity,not necessarily critical velocity.

It comes to 600.

Pls use the link http://www.efunda.com/formulae/fluids/calc_reynolds.cfm#calc

yes ans in that way comes 120 for sure...

bcos we hve ..

V= 0.06 m/sec

diametre = 0.02 m

and rho = 1000 kg/ m^3

and n = 0.01...

putting values we get 120....

but m still unsure.. cos i know well that R is a constant for a liquid and not variale and it is only possible to calc if V here is critical vel...

Cheers!!!!

and n = 0.01...it is poise

SI is  n = 0.001 decapoise or N-s/ m²

or, in calculating that no, n is to kept in poise while all others in SI ?

oh ok....

thn must be some mistake in printing..

forget that naa... it seems its not a big mistake...

but i hve a bigger prob...

how is it not gven that it is critical vel....  u sure of quest.?

cud u get it clarified.. cos i m damn sure Reynolds no is constant for a fluid....

mistake in printing..

it is hcv yaar !

From snails link I am getting Reynolds number = 1200.

A elder friend told me that this number can be calculated for any flow velocity in a pipe.

For Re below 2000 flow will be laminar, above this value flow becomes turbulant.

" .. For Re below 2000 flow will be laminar, above this value flow becomes turbulant. "

dats true.

But what is the no ? 120 or 1200 ?

When we take units in SI we get :

V = 0.06 m/s

d = 0.02 m

  = 1000 kg/m^3

 = 0.001 pascal sec (kg/m sec)

Reynolds No. = 1200

May be your units are not consistant.

In CGS units we get :

V = 6 cm/s

d = 2 cm

  = 1 g/cm^3

 = 0.01 poise (g/cm sec)

Reynolds No. = 1200