In completing my hw on mixing and flocculation tanks, I am having trouble unders

Question

In completing my hw on mixing and flocculation tanks, I am having trouble understanding when to use the viscosity of water in terms of Ns/m^2 versus in terms of kg/ms. I have pasted 2 different problems with the beginning of the solution. For each, you start by solving for the Renolds Number (a dimensionless value), Nr with the formula Nr = (n*p*d^2)/u where n= rotational speed (rps), p= density of water, d= diameter of impeller and u = fluid viscosity.

In the first problem, they use u = 1.139 Ns/m^2 and in the second they use u = 1.31 x 10^-3 kg/ms. Can you please explain how you know when to use which value of u? All of the other values in each formula have the same exact units in both problems so it is really not clear to me at all how these problems can possibly be correct or how you know when to use which value! thanks!!!

POWER REQUIREMENTS FOR MIXING Determine the power requirements for 3-m-diameer. six-blade flat-blade turbine impeller mixer running at 15 t/min in a 10-m-diameter mixing tank of standard configuration. Aiso compute the power per thousand cubic meters of volume. Assume the fuid being mixed is waer the water depth is 9.0 m. and the temperature is 15°C SOLUTION 1. Determine the Reynolds number (15/601/s) 999.1 kg/m' (3 m) 139 N s/m2 -1974

Explanation / Answer

Both units are same.

1 N-s/m2 = 1 kg/ (m-s)

1N = 1 kg (mass) * m/s2 ( acceleration)

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