Ex .1: REYNOLD’S APPARATUS

Objective : To determine Reynold’s number for various type of flow pattern.

APPARATUS : Reynold’s apparatus.

Introduction to Reynold’s Number

The Reynolds ( Re ) number is a quantity which engineers use to estimate if a fluid flow is laminar or turbulent. This is important, because increased mixing and shearing occur in turbulent flow. This results in increased viscous losses which affects the efficiency of hydraulic machines.

RANGE 1: Laminar Flow
Generally, a fluid flow is laminar from Re = 0 to some critical value (2100) at which transition flow begins.

RANGE 2: Transition Flow (2100<NRe<4000)
Flows in this range may fluctuate between laminar and turbulent flow. The fluid flow is on the verge of becoming turbulent.

RANGE 3: Turbulent Flow (NRe>4000)
The fluid flow has become unstable. In turbulent flow, there is increased mixing that results in viscous losses which are generally much higher than in those in laminar flow.

re
Fig.1 Range of NRe for different flow of fluid through pipe

NOTE: The Re at which turbulent flow begins depends on the geometry of the fluid flow. The value is different for pipe flow and external flow (i.e. over/outside and object). Since we are studying fluid flow in hydraulic systems, WE WILL CONSIDER ONLY INTERNAL FLOWS (PIPE FLOWS).

EXPERIMENTAL PROCEDURE :
1) Allow the water to fill up the equipment and to flow at the lowest possible flow rate.

2) Adjust the flow of permanganate solution so that its velocity is about the same as the water.

3) Note that the colour filament appears as continuous thread without intermingling with water.
4) Determine the flow rate of water.

5) Repeat the experiment for different flow rate of water.(in increasing manner)

6) Observe the flow rate at which the continuous thread just breaks up and color gets gets diffused uniformly through out the tube.

7) For each run note down required readings.

Fig.1 Experimental Set Up.

OBSERVATION :
1) Temperature of water = _____oC

2) Density of water at oC, ρ= _______ kg/m3

3) Viscosity of water at oC, μ = _______ kg/m.sec

4) Inside Diameter of tube , D = 0.025 mt

5) Length of tube , L = 0.09 mt

6) Area of tube , (/4 D2) , A = _______ m2

OBSERVATION TABLE :

 

Sr. No. Water collected, m3 Time

in sec

Volumetric flowrate , Q m3/sec Velocity, v

Q/A m/s

NRe =ρVD/μ

 

         

Flow pattern

Obs.    Theo

 

MODEL CALCULATION :

(1) Area of tube , A =   Π/4 D2 = ______ m2

(2) Volumetric flow rate = Q =   Water collected,(m3 )/ Time, (sec)

(3) Velocity , v =    Volumetric flow rate (m3/sec)/ Area,(m2)

(4) Reynolds no.  NRe =ρVD/μ   (Dimensionless)

(5) Critical Reynolds no. = _________

(6) Critical Velocity = ________

 

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