Advanced Studies in Theoretical Physics Vol. 9, 2015, no. 2, 57 - 61 HIKARI Ltd, www.m-hikari.com http://dx.doi.org/10.12988/astp.2015.412152
The Characteristics of Increased Pressure Drop in Pipes with Grooved Putu Wijaya Sunu Mechanical Engineering Department Bali State Polytechnic, Bali, Indonesia Copyright © 2014 Putu Wijaya Sunu. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract The aim of this study was to investigate the characteristic of increased pressure drop in grooved straight pipes. The observation has been done at number of groove of 9, 25 and smooth pipe used as comparison. The result shows that the instantaneous pressure drop signal of grooved pipe fluctuate in small time-scale as a result the overall pressure drop increase compare to the pressure drop of smooth pipe. Keywords: Pressure drop, signal characteristics, rectangular grooves
Introduction Over long distances materials flowing through pipes lose a lot of pressure from the presence of fluid turbulence. And in the field of piping such materials as oil, this increases costs considerably, thus the importance of finding methods of overcoming this pressure drop. One way to do this is to incise grooves into the internal surfaces of pipes, this is a passive method which is relatively cheap to install and requires little or no maintenance. Over the years, much study has looked into pressure drop and fluids flowing over grooves to those without. [1] In their investigation found that on low speed wind tunnel, grooves influence turbulence intensity and [4] discovered they were very effective in reducing vortex vibration in cross flows. One study looked into the effect of restructuring the internal surfaces of pipes on hydrogen flowing through them [3] and found that they were very effective in reducing pressure drop. [2] Found grooves lowered pressure drop by 4%. [5] discovered the relationship
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of fluid behavior to friction factors in internally grooved pipes. The objective of this study was the explain pressure drop based on the characteristics of pressure drop signals produced by grooves.
Experiment Set-up The set-up of the experiment equipment is shown schematically in Figure 1.
Fig.1 Schematic of experiment equipment Water was pumped by a centrifugal pump stabilized by an electric stabilizer. A valve was used to control water volume flow rate in order to achieve Reynold Number (Re) 24695, 22146, 20637, 18155, and 15038 respectively at 270 C (±10 C). The PVC pipe test section was 100 cm in length and 2.6 cm in diameter. Grooves were incised internally employing a conventional method, these grooves were longitudinal and rectangular in shape measuring 1 mm x 1 mm. The total number of grooves was 9 and 25, arranged by dividing 360° by 9 and 25 respectively. A plain pipe without grooves was used as control. In addition, a 70 cm long pipe entrance section was installed to ensure that the fluid entering the test section was fully developed. 3 mm Diameter of pressure taps were placed at both the entrance and exit of the test pipes and connected to a pressure transducer and a data logger to enable nominal pressures in the pipe to be read. Pressure data at both the entrance and exit were recorded for 1 minute and 7 times at a frequency of 250 Hz to improve accuracy.
Result and discussion The data from both pressure transducers at the pipe test section entrance and exit were converted into pressure differentials between the entrance and exit respectively.
The characteristics of increased pressure drop in pipes with grooved
Smooth pipe
9 groove
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25 groove
450
Pressure Drop (Pa)
400 350 300 250 200 150 100 1,5E+04
1,7E+04
1,9E+04
2,1E+04
2,3E+04
2,5E+04
Re
Fig.2 Pressure drop as a function of Re
Smooth pipe
9 groove
25 groove
% Change of Pressure Drop
10 8 6 4 2 0 1,5E+04
1,7E+04
1,9E+04
2,1E+04
2,3E+04
2,5E+04
Re
Fig.3 Change in Pressure drop as a function of Re
Fig. 2 Shows the correlation of the Reynold Numbers to both the pressure drop of 9 and 25-groove pipes. The dashes (line) indicate pressure drop from the smooth pipe without grooves. It can be seen that the pressure drops in the grooved pipes at various Reynold Numbers were greater than that of the smooth pipe. Fig. 3 Shows the change of pressure drop values for each Reynold Number. Positive values depict the increase in pressure drops compared to those of the smooth pipe. Increases in Reynold Number values tended to have higher pressure drops caused by the rise in turbulence in the fluid flows which, in turn, induced an increase in momentum convection in them thus raising energy pressure which was converted into heat. For further understanding, the pattern pressure drop signals were analyzed.
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Fig.4 Instantaneous pressure drop at Re= 24695. a) smooth pipe; b) 9 groove; c) 25 groove Fig. 4 demonstrates the pattern of the instantaneous pressure drop in the smooth (no groove) pipe, and the 9 and 25-groove pipes. The pattern of the pressure drop signal indicated a change in pressure drop at the small time scale. This phenomena showed that small scale energetic fluid motion had been formed and in order to prove this beyond doubt, it was necessary to determine the skewness factors of all the pipes.
0,10
15038
18155
20637
22146
24695
Skewness Factor
0,05 0,00 -0,05 0
10
20
-0,10 -0,15 -0,20 -0,25
Groove Number
Fig 5. Pressure drop skewness factor
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The characteristics of increased pressure drop in pipes with grooved
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The skewness factor describes the distributions of pressure drop, based on average levels, can give an initial understanding of concerning pressure drop as any increase in pressure drop can be correlated to the skewness factor value. Fig. 4 demonstrates that the skewness factors of both 9 and 25-groove pipes were negative. This shows that both periodic motion and angular speed increases pressure changes (Fig. 4) and any pressure change at small time scale raises shear stress at pipe walls and finally increasing overall pressure drop.
Conclusion It can be concluded that in the 9 and 25-groove pipes, pressure drop occurred at small time scale so that flows tended to raise shear stress at the pipe walls thereby increasing their pressure drop over all compared to that of the smooth (no groove) pipe.
References [1] Baron A. and Quadrio M., Some Preliminary Result on The Influence of Riblets on The Structure of a Turbulent Boundary Layer. Int. J. Heat and Fluid Flow, 14 (1993) No.3, 223-230. http://dx.doi.org/10.1016/0142-727x(93)90052-o [2] Nakao Shin – Ichi, Effect of Riblet Bend on Pipe Flow. Applied Scientific Research, 54 (1995), 237 – 247. http://dx.doi.org/10.1007/bf00863511 [3] Peet Y, P. Sagaut, Y. Charron, Pressure Loss Reduction in Hydrogen Pipelines by Surface Restructuring. International Journal of Hydrogen Energy, 34 (2009): 8964 – 8973. http://dx.doi.org/10.1016/j.ijhydene.2009.08.035 [4] Shan Huang, VIV Suppression of a Two-Degree-of-Freedom Circular Cylinder and Drag Reduction of a Fixed Circular Cylinder by The Use of Helical Grooves. Journal of Fluids and Structures, 27 (2011), 1124–1133. http://dx.doi.org/10.1016/j.jfluidstructs.2011.07.005 [5] Sunu P.W., ING Wardana, A.A. Sonief, Nurkholis Hamidi, Flow Behavior and Friction Factor in Internally Grooved Pipe Wall. Adv. Studies Theor. Phys., Vol. 8, 2014, no. 14, 643-647. http://dx.doi.org/10.12988/astp.2014.4573
Received: December 14, 2014; Published: January 23, 2015
