Lab Report

Title: Osborn Reynolds experiment Objectives  

To demonstrate the differences between laminar, turbulent, and transitional fluid flow. To calculate the Reynolds number at which each occurs.

Introduction Osborn Reynolds experiment is used to investigate the characteristic of the flow of the liquid in the pipe which is also used to determine the Reynolds number for each state of the flow. The design of the apparatus allowed studying the characteristic of the flow and calculate the range for the laminar and turbulent flow where the calculation is used to prove the Reynolds number is dimensionless by using the Reynolds number formula. This was demonstrated by Osborne Reynolds in 1883 through an experiment in which water was discharged from a tank through a glass tube. This experiment characterize Laminar, Transitional and Turbulent flow in terms of the Reynolds Number. The Reynolds apparatus allows to visualize the flow and determines whether it is Laminar, Transitional or Turbulent. An overflow tank maintains a constant pressure head on the flow tube while flow rate is controlled via the globe valve at the outlet. Dye is injected into the bell mouth at the flow tube in order to visualize the flow. Flow rates may be determined by collecting the liquid to a measuring cylinder at the outlet and recording the time it takes to fill a given volume. Moreover the apparatus should be leveled prior to beginning the experiment.

Theory The theory is named in honor of Osborne Reynolds, a British engineer who discovers the variables that can be used as a criterion to distinguish between laminar and turbulent flow. The Reynolds number Re is: 𝑅𝑒 = (𝑉𝑑) /v Where; V = flow velocity (m/s) d = inside diameter of pipe section (m) v = kinematic viscosity (m^2/s)

The Reynolds number is widely used dimensionless parameters in fluid mechanics, and Re is independent of pressure. Limiting values of Reynolds number to a quantitatively decide whether the flow is laminar or turbulent are as given below.   

Laminar flow Transition flow Turbulent flow

Re < 2300 2300 < Re < 4000 Re > 4000

For Reynolds number less than 2000, the pipe flow will be laminar. For Reynolds number from 2000 to 4000 the pipe flow will be considered a transitional flow. Turbulent occur when Reynolds number is above 4000. The viscosity of the fluid also determines the characteristic of the flow becoming laminar or turbulent. Fluid with higher viscosity is easier to achieve a turbulent flow condition. The viscosity of fluid is also dependent on the temperature.

Apparatus      

Osborne Reynolds demonstration apparatus Fabric dye Thermometer Stop watch Measuring cylinder Pipe line

Procedure 1. The Osborne Reynolds apparatus was set up and measured the inside diameter of the pipe section. The aluminum well was filled with fabric dye and the metering tap (dye flow control valve) and drain cock were closed. 2. Turned on the tap line, control valve was opened carefully and tap was adjusted to produce a constant water level in the reservoir. After a time the pipe section was completely filled. 3. The drain cock was slightly opened to produce a low rate of flow into the test pipe section. 4. The metering tap was opened and the dye was allowed to flow from the nozzle entrance of the channel until a colored stream was visible along the test pipe section. 5. The water flow was adjusted to a lowest rate until a laminar flow pattern which a straight thin line or streamline of dye was able to be seen along the whole pipe section. 6. 200ml volume of colored waste water that flow down at the outlet pipe was collected and noted down the time it took to fill the 200ml. the flow rate was calculated by using these data. 7. Above two steps were used with increasing rate of flow making a high water flow and an intermediate flow at the outlet pipe. The changing flow patterns were observed. 8. Two readings were taken from each flow pattern and calculated the Re for all six readings. 9. All the apparatus were cleaned after the experiment.

Results Run no

Volume V (m^3)

Time t (s)

1 2 3 4 5 6

0.001 0.001 0.001 0.002 0.002 0.001

10.47 10.07 67.34 132.68 145.42 73.70

Flow rate Q (x 10^-5 m^3/s) 9.55 9.93 1.49 1.51 1.37 1.35

Velocity V (m/s) 1.22 1.26 0.189 0.192 0.174 0.173

Reynolds number (Re) 15541.4 16050.96 2409.84 2446.16 2223.21 2201.88

Type of flow Turbulent Turbulent Transition Transition Laminar Laminar

Conclusion The laminar flow occurs when the fluid is flowing slowly and the turbulent flow occurs when it is flowing fast. In transitional flow, the flow switches between laminar and turbulent in a disorderly fashion. As the water flow rate increase, the Reynolds number calculated also increase and the dye line change from thin thread to swirling in shape Laminar flow occurs when the Reynolds number calculated is below than 2300; transitional flow occurs when Reynolds number calculated is between 2300 and 4000 while turbulent flow occurs when Reynolds number calculated is above 4000.It is proved that the Reynolds equation is dimensionless, no units left after the calculation. The objectives of the experiment was successfully completed.

References Bruce R Munson, D. F. Y. T. H. O., n.d. Fundamental Of Fluid Mechanics. fourth edition ed. s.l.:John Wiley & Sons, Inc..