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Queenie Gene Gadong Date Performed: September 12, 2011Groupmates: Date Submitted: September 26, 2011

Louise Alain ImbongMa. Lourdes MercolitaAngelo TugahanJoshua Revesencio

Experiment No. 4Reynolds Number

I. Introduction

The food industry offers a lot of products, be it hard solids or fluids. That said a FoodTechnologist must not only be familiar with solid raw materials and finished goods. An efficient foodtechnologist must also be knowledgeable of the principles and theories regarding fluid flow.

The word fluid does not only cover liquids it also includes the gases and fluidized solids. Theseare materials that have the tendency to behave as fluid that is they have the ability to flow. Fluids arefurther subdivided to consider their specific properties into thin liquids, thick liquids, gases and fluidizedsolids.

The study of fluids is also subdivided into two, fluid statics, and fluid dynamics, or fluids at rest,and fluids in motion. The principles of fluid statics are almost an exact science. (Geankoplis, 1995) Themost important property of a fluid at rest is its pressure. The pressure of the fluid it exerts in itssurroundings is measured as the amount of force exerted on an area. The fundamental equation usedto calculate the fluid pressure considers the acceleration due to gravity (g), the density of the fluid ( ),and the depth of the fluid (Z) as factors that give the pressure at a given depth of fluid. (Earle, 1983)

The study of fluid dynamics as compared to that of fluid statics is more complex. The overallbalance of mass and energy equation is used to create a design for the motion of fluid flow. The type of flow of fluids is an important fluid dynamics aspect. When watching a flowing open stream or river onewould notice two types of pattern in the waters flow. When the flow is slow the pattern of flow issmooth, but when the movement of water is rapid, eddies or swirls moving in all directions aredeveloped.

The two types of flow pattern are the Laminar flow, and the Turbulent flow . In the laminar flowvelocity of fluid is low and the fluid layers slide off smoothly without the appearance of eddies or swirls.Turbulent flow happen when the velocity is high and there is the presence of the eddies or swirls,showing a fluctuating nature. (Geankoplis, 1995) Although we have said that there are only two types of

fluid flow another term is added to denote the type of flow occurring between the laminar andturbulent flow, the Transitional flow.

The existence of the two types of fluid flow was initially visualized by British engineer, OsborneReynolds. He experimented by injecting a thin stream of dye to a transparent pipe with a smooth streamof water. Reynolds noted that when the flow is slow the flow of the dye is smooth, in a single line andfollows the direction of the flow, indicating a laminar or viscous flow. But when the velocity of the water

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is increased the smooth straight line of the dye is broken, and the pattern became very erratic. Fromthese observations Reynolds concluded that the instability of flow is not only a function of velocity but isalso due to the density and viscosity of the fluid. And so the term Reynolds Number became theparameter that establishes if a fluid flow is laminar or turbulent.

The (Re) is a dimensionless value that denotes the ratio of the inertial force, which maintains themovement of the fluid, and the viscous drag that retard the motion of fluid. When the calculated (Re) isless than 2100 the flow is laminar, if it is greater than 4000 the flow is turbulent, but when the (Re) isbetween 2100 and 4000 the flow is considered transitional.

II. Objectives:1. To characterize the flow of water in a pipe in terms of its Reynolds No. (Re)2. To determine the upper and lower critical Re3. To describe the flow behavior as function of velocity

III. Results:Table 1: Behavior of fluid flow from low to high flow.

Adjustment Case 1: From low to high flow

Velocity (m/s) Appearance of Filament of Dye1. 0.0229 788

2. 0.0261 898

3. 0.0386 1328

4. 0.0299 1029

5. 0.0462 1590

6. 0.0598 2058

7. 0.0988 3400

8. 0.1089 3748

9. 0.1327 4567

Critical Upper 3748

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Table 2: Behavior of fluid flow from low to high flow.

Table 3 : Critical Reynolds Number

TrialUpper Lower

Velocity (m/s) Velocity (m/s)

1. 0.1089 3748 0.0634 2182

Literature Value 4000 2100

% Difference 6.32% 3.91%

IV. Discussion

Taking in table 1, an initial glance on the appearance of the filament of dye column one wouldassume that the Upper would the seventh 7 th data collected. The Upper is the critical valueobtained just before the flow in the set-up turned turbulent. The initial hypothesis that the 7 th data iscritical number for the low to high flow is wrong, since it was just a guess coined out of the appearanceof the dye. As it turned out in calculating for the (Re) of all the data obtained the 8 th data was thecritical value. The Upper N Re is 8

th data with the (Re) of 3748, which is much closer to the >4000 range of turbulent flow, as compared to the 3400 of the 7 th data. The (Re) has no unit; this is because all of theunits in the equation are able to cancel each other out. Comparison of the Literature value, 4000, and

the critical number obtained by the group yielded a 6.32% difference, see table 3.

To find the lower N Re we had to find the critical value on our data just before the high to low flowset-up turned to laminar. Noting the table 2 values and depictions the researcher originally concludedthat the lower N Re would be the 3

rd data obtained. In calculating for the (Re) this hypothesis proved true,the lower N Re is 2182. Comparison of the literature value

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V. Conclusion and Recommendation

In conclusion we can see that the Upper is 3748 a value with just a 6.32% difference from the>4000 range for turbulent flow and the lower is 2182 with only a 3.91% difference from the