Manzi_Roger_Dusabimana Reynolds Number and Transitional Flow

1. California Baptist University
Manzi Roger Dusab.
ID: 460234
Lab Partners: Danielle Lynch
Suhail Farah.
Linneah Gomez
Fluids Mechanics Lab: Reynolds Number and Transitional Flow
Prof: Helen Jung, Ph.D
Lab Submission Date: 04/04/2013

2. I.ABSTRACT
This activity focuses on making analysis regarding the Reynolds number. The idea behind
Reynolds discovery is that, when a fluid flows next to a solid boundary the nature of that flow
depends on its velocity relative to that boundary. This results into having flows classified in three
main categories: laminar: the layers of fluids move smoothly; mix-up: as the velocity is
increased, small disturbance causes eddies; and turbulent: when the flow patterns are very
turbulent. Reynolds, a famous scientist, proved that these behaviors depends on a balance
between inertia and viscous forces in a fluid, by coming up with a non-dimensional parameter
known as Reynolds number. His discoveries have a very important application in high speed
transportations apparatuses, fluids flow in pipes, hydroelectric dams, etc. The expression for
Reynolds number is as follow:
𝑹𝒆 =
𝜌𝑑𝑢
𝜇
Where Re: Reynolds number, ρ: fluid density, d: length, u: velocity and𝜇: viscosity. At the end
of the experiment the team was able to make clear distinctions between the above mentioned
types of flow behaviors based on Reynolds number. By timing the amount of time it took to fill
out a gallon of water, remarks were made on the effect of velocity change to the Reynolds
number, therefore to the flow behavior. The time measurements were 8 minutes 3.5 seconds for
the laminar flow, 3minutes and 24.3 seconds for the transitional flow, and only 56.3 seconds for
the turbulent flow.

3. II.INTRODUCTION
The objective of this lab was to demonstrate the dependence of fluids flow on the
Reynolds number. An assembly known as the Reynolds number and transitional was used
throughout this experiment. The idea is that, when a fluid flows next to a solid boundary the
nature of that flow depends on its velocity relative to that boundary. This results into having
flows classified in three main categories: laminar, mix-up, and turbulent. During this experiment
in particular, the apparatus enables the nature of the flow in a pipe to be studied by observing the
behavior of a filament of dye injected into fluid. The flow rate was varied and the transition from
laminar to turbulent flow could be clearly demonstrated. The flow rate variations were results of
changes in the fluid’s viscosity, which fallouts of temperature variations.

4. III. EXPERIMENTAL SETUP
Description of the apparatus
To effectively perform this experiment the sets of equipment’s are needed.
These are:
-The Reynolds number and transitional flow demonstration apparatus. [Fig. A]
-The temperature control module. [Fig. B]
Fig. A
 Verify that both apparatus are
well assembled, and connected
to the electric power supply.
Fig. B

5. IV. Experimental Procedure
Etape1: After checking that the apparatus is perfectly assembled, water supply was turned on
and had the discharge valve partially open.
Etape2: The water supply was adjusted until the level in the constant head tank is just above the
overflow pipe and is maintained at this level by a small flow down the overflow pipe.
Etape3: The dye injector was opened and adjusted to obtain a fine filament of dye in the flow
down the glass tube. It was a laminar flow is achieved at this stage. This condition is satisfied
when the filament of dye passes down the complete length of the tube without disturbance.
Etape4: The flow rate was then slowly increased by opening the discharge valve until
disturbances of the dye filament were noted. See Fig (b)
Etape5: The temperature of the water was recorded using a thermometer. The flow rate on the
other side was measured by timing the collection of a known quantity of water from the
discharge pipe.
Etape6: The flow was increased using the procedure described above until the disturbance
increase such that the dye filaments becomes rapidly diffused as shown in the Fig (c ) below.
The temperature and the flow rate were again recorded in this case.
Etape7: Afterwards, the flow rate was decreased slowly until the dye just returned to a steady
filament representing a laminar flow.
Note: for each of the flows, a picture was taken, and the flow rate was measured by timing the
collection of a gallon of water from the discharge pipe.

6. V. RESULTS AND DISCUSSION
After performing each of the above mentioned steps as described by the lab manual and with
help from the Instructor Dr. Jung; the following observations were made:
Laminar Flow
Time: 8 min 35 sec
With a close attention, we
remarked a slight twisting of
the dye filament with no
disturbance.
Transitional Flow
Time: 3min 24.3sec
We observed a
intermittent pulses of
turbulences.
Turbulent Flow
Time: 56.3 sec
The dye quickly mixed with
the fluid and became very
dispersed.

7. VI.CONCLUSION
This experiment was conducted to; to provide an advanced understanding of the principles
behind the famous Reynolds number, and various types of flows. The team performed
measurements of the flow rate of a fluid (water) and observations were made on the behavior
of a dye-substance mixed with the fluid. The experiment showed that in laminar flows, the
dye filament will appear slightly twisted, and it took about 8 minutes to collect a gallon of
water from the discharge pipe. For transitional flows, a gallon of water was collected after
3min 24.3 seconds, and the dye-filament had intermittent pulses. On the other side, the dye-
filament immediately mixed with the fluid and it took only 24.3 seconds to collect a gallon of
water. These results showed a direct relation between Reynolds number and the velocity
changes. When the velocity is increased the value of the Reynolds number increases, which
means more turbulences.