It was in 1883 when Osborne Reynolds, a famous scientist and engineer tried to experiment on the relationship between the stability of fluid motion and the transition to turbulence. His final apparatus consisted of a glass-sided tank, 6 feet long, 18 inches deep and 18 inches wide. Inside it was a glass tube with `a trumpet mouth of varnished wood, great care being taken to make the surface of the wood continuous with that of the glass'. On the right-hand side, the tube was connected to an iron pipe equipped with a valve which could be controlled by means of a long lever. On the left-hand side is the device for introducing a streak of dye into the trumpet, while a float and dial indica ...view middle of the document...
If the value of NRe is below 2100, it is said to be laminar and if Nre is greater than or equal to 4000, it is turbulent. Between these phases is the transition state (2100 ≥ NRe ≥ 4000). At NRe ≥ 10, 000 the flow is also said to be completely turbulent.According to McCabe (1993) and Geankoplis (1993) laminar flow (Fig. 2.3a) is characterized by the absence of lateral or macroscopic mixing of adjacent fluid layers, cross currents nor eddies or swirls. The particles of the fluid are moving in definite and observable paths or streamlines (Daugherty, 1999). Meanwhile, the velocity profiles of laminar flow in pipe would indicate that the velocity increases from the wall to the center (White, 1999). Daugherty (1989) mentioned that Reynolds was able to observe that at a low flow rate or when the velocity of the water in the tube was small, the liquid dye was seen as a straight line throughout the length of the tube. Geankoplis (1993) declared that the dye pattern was regular. It formed one line of stream.The fluid has a fluctuating nature due to the presence of eddies, lateral or macroscopic mixing and cross currents (Geankoplis, 1993). Fluids in turbulent flow (Fig. 2.3c) consist of eddies of various sizes coexisting in the flowing stream. Large eddies continually flow, break into smaller ones then eventually disappears. McCabe (1993) pointed out that turbulent flow may also be generated either as wall turbulence or free turbulence. Wall turbulence results from contact of the flowing stream with solid boundaries while free turbulence results from the contact between two layers of fluids at different velocities. Daugherty (1989) described the pattern as a wavy and gradually disappearing as the dye spreads uniformly throughout the entire cross-section of the stream of water.When the flow is neither laminar nor turbulent, it is said to be in a transition flow (Fig. 2.3b). White (1999) stated that transition flow depends upon many effects such as wall roughness and fluctuations in the inlet stream (White, 1999). McCabe (1993) and Daugherty (1989) further declared that the transition flow is dependent on the entrance tube conditions, the apparatus details and the distance from the entrance.Fig. 2.3. Different Flow RegimesThis experiment aims to identify flow regimes at different flow rates following classical Reynolds' experiment; and to verify if visual observation of different flow regimes matches with the computed Reynolds' number.MATERIALS AND METHODSThe Reynolds' apparatus in the laboratory was used for this experiment. A water supply was secured to ensure that the water level was maintained. A hose was used to fill the water reservoir.The Reynolds' apparatus was tested for leaks and was thoroughly cleaned. Then, the water reservoir was filled to the overflow level. One to two liters of 0.4 M methylene blue was prepared and placed on the dye reservoir. Next, the bubbles in the glass tube were removed and the needle was adjusted. Tap wa...
