8/3/2019 m.uzair Shaikh--electronic Stability Control

http://slidepdf.com/reader/full/muzair-shaikh-electronic-stability-control 1/2

EXPERIMENT DEMONSTRATING THE INFLUENCE OF REYNOLD’S NUMBER IN PIPEFLOWS

Mohammad Uzair Shaikh

Dept. of Mechanical Engineering,College of Electrical and Mechanical Engineering,

National University of Science and Technology, Pakistan

Abstract

This paper reviews and presents the experiment and its procedure to determine the influence of Reynold’s Number in pipeflows. The experiment is similar to the one that Oswald Reynold carried out to determine the influence of Reynold’s Number on  a fluid flowing in a pipe. The main parameters impelling the behavior of the fluid are the flow rate of the fluid and the Headpress ure. A different technique involving a colored die is used to study the behavior of the fluid.

Keywords

Reynolds’s number, Head, Turbulence, Laminar

1.INTRODUCTION

In fluid mechanics, the Reynolds number Re is adimensionless number that gives a measure of the ratio ofinertial forces to viscous forces and consequently quantifiesthe relative importance of these two types of forces for givenflow conditions. Reynolds numbers frequently arise whenperforming dimensional analysis of fluid dynamics problems,and as such can be used to determine dynamic similitudebetween different experimental cases .They are also used tocharacterize different flow regimes, such as laminar or

turbulent flow: lam inar flow occurs at low Reynolds numbers,where viscous forces are dominant, and is characterized bysmooth, constant fluid motion; turbulent flow occurs at highReynolds numbers and is dominated by inertial forces, whichtend to produce chaotic eddies, vortices and other flowinstabilities.

2. EXPERIMENTAL MODEL

2.1 Purpose:

The purpose of this experiment is to illustrate the influenceof Reynolds number on pipe flows. Reynolds number is avery useful dimensionless quantity (the ratio of dynamicforces to viscous forces) that aids in classifying certain flows.

For incompressible flow in a pipe, Reynolds number basedon the pipe diameter, ReD = VaveDρ/μ, serves well. Generally,laminar flows correspond to ReD < 2100, transitional flowsoccur in the range 2100 < Re D < 4000, and turbulent flowsexist for ReD > 4000. However, disturbances in the flow fromvarious sources may cause the flow to deviate from thispattern. This experiment will illustrate laminar, transitional,and turbulent flows in a pipe.

2.2 Apparatus

The apparatus used in this experiment provides a means ofvisually observing the different pipe-flow regimes ofincompressible fluid, water in this case. A diagram of theapparatus is shown in Fig. 1. Water is supplied to the tank on

the left through the water supply line and valve. A constantwater level is maintained in the tank by overflow into thestandpipe. The water in the tank flows through a section of"fill", a collection of small spheres held in place by screens.The purpose of this arrangement is to produce a low

turbulence flow downstream of the fill. The water enters thetransparent observation tube through a rounded entrance.Blue dye is injected into the stream to provide the visualeffect. A pump is used to force the dye into the injection tubeand to control the rate at which it is injected. The pump hascontrols with a digital dial that can be set (on an arbitraryscale) to deliver dye from a very slow to a relatively fast rate.It also has a button (max) that when pressed delivers themaximum dye injection rate the pum p is capable of delivering.It is us eful for some flows to press and quickly release themax button to inject a spurt of dye and then observe themotion of the dye in the flow.

Fig. 1 Ap paratus for studyi ng laminar, transitional, and turbulent pipe flow  

Fig. 3 Schematic diagram of the head-orifice water f low meter. 

8/3/2019 m.uzair Shaikh--electronic Stability Control

http://slidepdf.com/reader/full/muzair-shaikh-electronic-stability-control 2/2

The apparatus includes the head-orifice flow meter shownin Fig. 1 and in more detail in Fig. 2. This allows rapiddetermination of the Reynolds number for the flow in theobservation tube. The meter consis ts of a closed -end tubein which flow from the observation tube is collected. Threeorifices that meter the flow are located in the bottom of theclosed end. These can be used selectively by insertingrubber stoppers in orifices not used. As the head ,h,

increases, the flow rate through an orifice (or acombination of orifices) increases. When the flow rate outof an orifice (or a combination of orifices) equals the flowrate into the meter from the observation tube, the head hwill be established at a fixed value. The flow rate is relatedto the h and the size of the orifice (or orifices) selected.This flow rate can then in turn be used to determine theReynolds number in the observation section of theapparatus. Thus, for a given orifice or (a selection oforifices), the observation tube Reynolds number based onins ide diameter D (= 0.750 inches) is directly related to thehead h. Table 1 gives information on the orifices of thehead-orifice flow meter. The velocity coefficient defined inthe table, accounts for non-ideal flow through an orifice.Videal = (2gh)

1/2. Figure 4 is a graph of ReD vs. head for the

head-orifice meter for each orifice and certaincombinations of orifices. The curves incorporate thevelocity coefficients

Fig.4 Observ ation tube Rey nolds number v ersus head. TH2O

=60F

2.3:Procedure

1. Prepare a data spreadsheet to record all of thepertinent information.

2. Conduct a series of runs. Use a digital camera (ifavailable) to record the patterns made by the dye inthe observation tube or sketch the pattern if thecamera is not available. Start with a very low flow rate(and Reynolds No.) by closing the flow control valveand using the small bypass control valve to regulatethe flow. Increase the flow rate gradually andeventually reach the fully turbulent regime. Selectorifices as necessary to cover the three flow regimes .Make sure the equilibrium value of h is establishedbefore using Fig. 4 to obtain Reynolds number. Besure to identify as closely as possible the Reynoldsnumber for transi tion from laminar to turbulent flow.

3. DISCUSSION:

Disturbances in the flow from several sources mayalter the Reynolds number at which transition from

laminar to turbulent flow takes place. To minimize flowdis turbances, a sm ooth properly-contoured entrancesection to the observation tube is required. This m aynot be the cas e in the apparatus used in thisexperiment. The presence of the dye injection tubemay cause flow disturbances that may affect transi tion.Injection of the dye at a velocity different from thewater velocity may unduly disturb the flow. In some

cases , disturbances related to dye injection will die outwith dis tance along the observation tube and laminarflow will clearly exist.

4. ACKNOWLEDEGMENT

I extend a s incere thanks to all m y fami ly and friends whosupported me throughout this venture.

5.References

[1] http://hyunitech.blogspot.com/2010/08l

[2] FREEPATENTSONLINE.COM

[3] HOWSTUFFWORKS.COM