CEBU INSTITUTE OF TECHNOLOGYN. Bacalso Avenue, Cebu City

Chemical Engineeing Department

FINAL REPORTChE Lab 1

Title of Experiment

Juphil A. LamanilaoBSChE-5

Engr. Lyda P. Abellanosa

Instructor

Abstract:

The flow of real fluids can basically occur under two very different regimes namely laminar and turbulent flow. The laminar flow is characterized by fluid particles moving in the form of lamina sliding over each other, such that at any instant the velocity at all the points in particular lamina is the same. The lamina near the flow boundary moves at a slower rate as compared to those near the center of the flow passage. This type of flow occurs in viscous fluids, fluids moving at slow velocity and fluids flowing through narrow passages. The turbulent flow is characterized by constant agitation and intermixing of fluid particles such that their velocity changes from point to point and even at the same point from time to time. This type of flow occurs in low density. A fine filament of dye is introduced in to the flow of water through the glass tube where different types of flow are seen at its entrance. At low velocities the dye filament appeared as straight line through the length of the tube and parallel to its axis, characterizing laminar flow. As the velocity is increased the dye filament becomes wavy throughout indicating transition flow. On further increasing the velocity the filament breaks up and diffuses completely in the water in the glass tube indicating the turbulent flow.

Objectives:

1.) To experimentally determine the values of the upper and lower critical Reynold’s Number and compare these values with those found in literature.

2.) To tabulate observations on the behavior of the film of dye as a function of water velocity.

Materials & Equipment:

Reynold’s Apparatus, KMnO4 solution, stopwatch, beaker, funnel, stirring rod, thermometer.

Sketch of the Set-up:

Procedure:

A. The equipment used was consisted of a horizontal glass tube immersed in a rectangular tank with water. A controlled flow of water was drawn through the tube by opening the valve. The entrance of the tube was flared and provision was made to introduce a fine filament of dye from as overhead flask into the water stream at the tube entrance. Initially, a thin film of dye is injected into the water stream at very slow water flow rate. Without turning off the flow of dye, the water flow rate was increased and with each incremental increase, quantity

of water was collected for flow rate measurements observation as to the behavior of the film of the dye was recorded as water flow varies from laminar to turbulent region.

B. Procedure was repeated this time going from turbulent to laminar region.

Tabulated Data & Result:

TRIALS

LAMINAR FLOWVolume, ml Time, s Discharge,

Q (m3/s)

Velocity , (m/s)

NRE

1 175 33.94 5.156 x10-6 0.025645 491.052 150 33.98 4.41436x10-6 0.02196 421.093 141 34.72 4.0611x10-6 0.0202 387.3074 150 34.64 4.33025x10-6 0.02154 412.9765 150 34.18 4.3885x10-6 02183 418.5346 150 33.44 4.4856 x10-6 0.02231 427.796

TRIALS

TURBULENT FLOWVolume, ml Time, s Discharge,

Q (m 3 /s) Velocity ,

(m/s)NRE

1 64.5 0.63 1.02381 x10-4 0.5092 9764.0672 48.5 0.44 1.10227 x10-4 0.5482 10512.373 52.5 0.53 8.9286 x10-5 0.49267 9447.0244 62.5 0.70 8.9286 x10-5 0.44407 8515.1755 45 0.57 7.8947x10-5 0.3927 7529.2076 59 0.59 1x10-4 0.49736 9537

Computations:

Given:T = 298.15 KUH2O = 0.8937x10-3 Pa-spH2O= 997.08 kg/m3

From Perry’s ChE Handbook:Sp. grav(KMnO4) = 2.703

pKMnO4= (2.703)(997.08 kg/m3)

(LAMINAR FLOW)Trial 1:Q = 175 ml/33.94 s = 5.156 x10-6 m3/s

V= Q/A = (5.156 x10 -3 m 3 /s) 2.01062x10-4 m2

= 0.025645 m/s

NRE = (0.016)( 0.02196 ) (2895.107) 2.4157x10-3 = 421.09

Trial 3:Q = 141 ml/34.72 s = 4.0611x10-6 m3/s

= 2895.107 kg/m3

by interpolation:U KMnO4 = 2.4157x10-3 Pa-sDi =0.016 mA = [3.1416(0.016m)2]/4 = 2.01062x10-4 m2

NRE = (DVp)/u

NRE = (0.016)(0.02565)(2895.107) 2.4157x10-3 = 491.05

Trial 2:Q = 150 ml/33.98 s = 4.41436x10-6 m3/sV= Q/A

= (4.41436x10 -6 m 3 /s) 2.01062x10-4 m2

= 0.02196 m/sV= Q/A = (4.0611x10 -6 m 3 /s) 2.01062x10-4 m2

= 0.0202 m/sNRE = (0.016)( 0.0202 ) (2895.107) 2.4157x10-3 = 387.307

Trial 4:Q = 150 ml/34.64 s = 4.33025x10-6 m3/s

V= Q/A = (4.33025x10 -6 m 3 /s) 2.01062x10-4 m2

= 0.02154 m/s

NRE = (0.016)( 0.02154 ) (2895.107) 2.4157x10-3 = 412.976

Trial 5:Q = 150 ml/34.18 s = 4.3885x10-6 m3/s

V= Q/A = (4.3885x10 -6 m 3 /s) 2.01062x10-4 m2

= 0.02183 m/s

NRE = (0.016)(0.02183)(2895.107) 2.4157x10-3 = 418.534

Trial 6:Q = 150 ml/33.44 s = 4.4856 x10-6 m3/s

V= Q/A

= (4.4856x10 -6 m 3 /s) 2.01062x10-4 m2

= 0.02231 m/s

NRE = (0.016)(0.02231)(2895.107) 2.4157x10-3 = 427.796

(TURBULENT FLOW)

Trial 1:Q = 64.5 ml/0.63 s = 1.02381 x10-4 m3/s

V= Q/A = (1.02381x10 -4 m 3 /s) 2.01062x10-4 m2

= 0.5092 m/s

NRE = (0.016)(0.509*2)(2895.107) 2.4157x10-3 = 9764.067

Trial 2:Q = 48.5ml/0.44 s = 1.10227 x10-4 m3/s

V= Q/A = (1.10227x10 -4 m 3 /s) 2.01062x10-4 m2

= 0.5482 m/s

NRE = (0.016)(0.5482)(2895.107) 2.4157x10-3 = 10512.37

Trial 3:Q = 52.5ml/0.53 s = 9.90567 x10-5 m3/s

V= Q/A = (9.90567 x10-5 m3/s) 2.01062x10-4 m2

= 0.49267 m/s

NRE = (0.016)(0.49267)(2895.107) 2.4157x10-3 = 9447.024

Trial 4:Q = 62.5ml/0.70 s = 8.9286 x10-5 m3/s

V= Q/A = (8.9286 x10 -5 m3/s) 2.01062x10-4 m2

= 0.44407 m/s

NRE = (0.016)(0.44407)(2895.107) 2.4157x10-3 = 8515.175

Trial 5:Q = 45ml/0.57 s = 7.8947x10-5 m3/s

V= Q/A = (7.8947x10 -5 m3/s) 2.01062x10-4 m2

= 0.3927 m/s

NRE = (0.016)(0.3927)(2895.107) 2.4157x10-3 = 7529.207

Data Analysis :

When discharge and Re having a small dye line was seen almost straight. This was clearly seen from stretches, until Re = 2000 i.e. from trial 1-6 (refer to the first table). This indicates laminar flow. When the discharge was further increased, the dye line moved towards pipe walls and still remains in a single line. This was seen in between the lower Re & upper Re when Re = 4000. Such flow indicates transition state and when the discharge is further increased, the straight streak line of the dye was seen for a small distance less than one third length of the pipe and then dye is thoroughly mixed in the flow this was turbulent flow. Re is more than 4000.

Recommendation:

In this experiment, the tank is of sufficient capacity to store water. So as to recommend, there should be a cock provided at the end of the glass tube to control the flow. The use of potassium permanganate is to give a brightly visible reddish streak such that it will be easy to determine what type of flow. Also, there should be proper materials when collecting the actual discharged water into the graduated cylinder where flow rate is further increased and since flow features are becoming different.

Application to ChE:

Aside from the application to fluid mechanics as to characterize different flow regimes, it is also an important quantity used in aerodynamics and hydraulics. Turbulent flow models of low Reynold’s number may be used to predict the electronic component heat transfer. This could ultimately help reduce the current dependency on experimental prototyping. With the new MEMS-based optical shear stress sensor, it is now possible to extend wall shear stress measurements to high Reynold’s number flows which can be obtained in the same manner using other techniques such as the oil film interferometry technique.