This paper presents two experimental investigations for cavitation characteristics of restriction orifices. The first experiment is about the spatial distribution of cavitation shock pressure in a pipe at the downstream of restriction orifices.
  The second experiment is the investigation of butterfly valve throttling to the cavitation in a multiperforated
orifice installed piping. From the results of the experiment for the cavitation shock pressure, it is concluded the maximum shock pressure remarkably increases with the decrease of cavitation number regardless of the orifice types. The maximum shock pressure becomes smallest on cone type orifice, and largest on single hole orifice. Multiperforated orifice is between this two.
  The results of the experiment for occurrence of cavitation due to the interference of butterfly valve show that the
cavitation occurs at a relatively high cavitation number when the multiperforated orifice is placed at 1D downstream
of the butterfly valve. The butterfly valve throttling accelerates the cavitation at the multiperforated orifice because of the closed orifice installation

Matsuda, Hiroyuki

Miyamoto, Hirofumi

Takahashi, Kei

English

CaltechCONF

CAV2001:sessionA9.006          1CAVITATION CHARACTERISTICS OF RESTRICTION ORIFICES(Experiment for Shock Pressure Distribution by Cavitation onRestriction Orifices and Occurrence of Cavitation atMultiperforated Orifices due to Interference of Butterfly Valve)Kei Takahashi and Hiroyuki MatsudaChiyoda Corporation, Yokohama, JAPANHirofumi MiyamotoChitose Institute of Science and Technology, Hokkaido, JAPANAbstractThis paper presents two experimental investigations for cavitation characteristics of restriction orifices. The firstexperiment is about the spatial distribution of cavitation shock pressure in a pipe at the downstream of restrictionorifices. The second experiment is the investigation of butterfly valve throttling to the cavitation in a multiperforatedorifice installed piping.  From the results of the experiment for the cavitation shock pressure, it is concluded the maximum shock pressureremarkably increases with the decrease of cavitation number regardless of the orifice types. The maximum shockpressure becomes smallest on cone type orifice, and largest on single hole orifice. Multiperforated orifice is betweenthis two.  The results of the experiment for occurrence of cavitation due to the interference of butterfly valve show that thecavitation occurs at a relatively high cavitation number when the multiperforated orifice is placed at 1D downstreamof the butterfly valve. The butterfly valve throttling accelerates the cavitation at the multiperforated orifice becauseof the closed orifice installation.1  IntroductionIn the process / chemical plants, restriction orifices, such assingle hole orifice, multiperforated orifice and cone type orificeare used to restrict the flow in the piping system. Figure 1shows three types of orifices. It is known that if severecavitation occurs at piping in which the restriction orifice isinstalled, the trouble such as pipe vibration, noise and pipeerosion may occur. For the restriction orifices, there are someinvestigations concerning the cavitation characteristics on thepipe vibration and noise for above three types of orifice (Tullis(1973), Numachi (1960), Fruman (1985), Kugou (1996)).Those investigation results can be used to design the restrictionorifices avoiding the pipe vibration and noise induced bycavitation. But there are few investigations concerning the pipeerosion due to cavitation. It could be considered that the pipeerosion is caused by the impact or fatigue destruction due tothe shock pressure that produced by the collapse of cavitationbubbles. Therefore, the spatial distribution of cavitation shockpressure inside the pipe at the downstream of restrictionorifices is examined by using the pressure detecting film that isfixed in pipe with film holder. Using the looped water pipingsystem where the restriction orifice is installed, the experimentis carried out.Severe cavitation at a restriction orifice can be avoided by appropriate design using the investigation results for thecavitation characteristics of restriction orifices. However, at the restriction orifice which is designed taking theFlowConeMultiperforated OrificeA-A'AA'(B)  Multiperforated Orifice(A)  Single Hole Orifice(C)  Cone Type OrificeFigure 1  Restriction OrificesCAV2001:sessionA9.006          2cavitation into account, severe cavitation may occur due to the interference of valve throttling or elbow which isinstalled at upstream of a restriction orifice. In order to confirm the occurrence of cavitation due to interference of abutterfly valve by an experiment, and to investigate the countermeasure to avoid such cavitation, the pipingvibration is measured changing the location of the multiperforated orifice at 1D, 3D, and 5D downstream of thebutterfly valve (D : pipe inside diameter).  In these experiments, the spatial distributions of cavitation shock pressure and pipe vibrations are measuredagainst the cavitation number, K, defined by the following equation.20121vPPK vd⋅−=ρ      (1)where, K   : cavitation number [-]Pd1   : static pressure just at downstream of orifice [Pa]Pv   : vapor pressure of fluid [Pa]ρ       : density of fluid [kg/m3]v0     : mean velocity through orifice hole [m/s]2  Experimental FacilityBoth experiments are carried out using 3 inch looped water piping system. Figure 2 shows the experimental facility.Figure 3 and 4 show the test section for the experiment of shock pressure distribution (Experiment-1) and theinterference of butterfly valve (Experiment-2), respectively.Figure 2  Experimental Facility           Figure 3  Test Section for Experiment-1                 Figure 4  Test Section for Experiment-2A A'Pressure TransducerΦ80Test OrificeFilm HolderPressure Detecting FilmFlangeFlowxrTest Section (Acrylic Pipe)3inch Butterfly ValveTest OrificePressure TransducerTest Section (Acrylic Pipe)3inch3inch3inch Universal JointBypass LineTest OrificePressure TransducerMagnetic Flow MeterFrom PumpTo PondTo Pond3inch Gate ValveTo PondBypass Line3inch Gate ValveCAV2001:sessionA9.006          3The water which is pumped up from a test pond by a centrifugal pump (0.0278m3/s x 0.78 MPa), flows through the3 inch vinyl chloride piping, goes to the test section via a magnetic flow meter, and returns into the test pond.3  Experiment-13.1  Method of ExperimentFor Experiment-1 (experiment for cavitation shock pressure), the test section is 1.4m in length, 80mm in insidediameter and is made of the transparent acrylic pipe to observe the aspect of the cavitation. Table 1 shows thespecification of the test orifices used in this experiment. The test orifice is installed at the test section, and the holderfor pressure detecting film (hereinafter, referred as “film holder”) can be installed inside the pipe at 0.5D, 1.0D,1.5D, 2.0D and 2.5D downstream of the test orifice. Figure 5 shows the illustration of film holder. The film holder isthe device to fix the pressure detecting film inside the pipe. The spatial distributions of cavitation shock pressure aremeasured using the pressure detecting film changing the location of the film holder and the head of film holder. Thepressure detecting film can show the received pressure by density of red color.Figure 5  Illustration of Film HolderTable 1　Specification of Test OrificesType of Orifice Single Hole Multiperforated Cone TypePipe Size 3 inch 3 inch 3 inchRatio of equivalentorifice inside diameter topipe inside diameter0.37 0.37 0.37 ** : ratio of orifice area to pipe inside sectional area of cone = 0.4In this experiment, flow rates, pressures and spatial distributions of cavitation shock pressure are measured for 3types of orifice shown in Table 1. Table 2 shows the specification of measuring instruments. The pressures aremeasured at 1D upstream and 0.5D downstream of the orifice with the pressure transducers of strain gauge type andthe flow rate is measured with the magnetic flow meter.Table 2　Specification of InstrumentsInstrument Model No. Maker SpecificationsPressureTransducerPGM-2KC     -10KCKYOWA Rated Output: 0.2MPa（PGM-2KC）             1.0MPa（PGM-10KC）MagneticFlow MeterAM208 YOKOGAWAAccuracy : +-0.1% of Span (0-20%)         +-0.5% of Rate (20-100%)Flow Rate Range : 0-180m3 /hPressureDetectingFilmPRESCALE FUJIFILMPressure Range :0.5 - 2.5MPa（Super Low Pressure）1.0 - 10MPa（Low Pressure）7.0 - 25MPa（Middle Pressure）20 - 70MPa（High Pressure）3Φ7Φ169 6 4Front View Side View3D ViewFlow     PressureDetecting FilmCAV2001:sessionA9.006          43.2  Results of Experiment(a) Single Hole OrificeFigures 6 and 7 show the spatial distributions of cavitation shock pressure inside the pipe at the cavitation number, K=1.4 and K=0.4, respectively. In these figures, the vertical axis shows the radial distance of shock pressuremeasuring point from orifice center, and the horizontal axis shows the axial distance of shock pressure measuringpoint form orifice center, and the distributions of cavitation shock pressure. Figure 6  Shock pressure distribution (single hole, K=1.4)      Figure 7  Shock pressure distribution (single hole, K=0.4)From Figures 6 and 7, the followings are observed.(1) There is a point where the cavitation shock pressure becomes maximum at the downstream of orifice edge (radialdistance of measuring point, r/R = 0.375). It could be considered that this phenomenon occurs because thecavitation bubbles generated near the orifice edge flows to downstream and collapses at the area in which thestatic pressure recovers. The large shock pressure is due to the collapse of the cavitation bubbles.(2) When the cavitation becomes severer (the cavitation number, K becomes smaller), the sphere in which the largeshock pressure is observed becomes wider in radial and axial direction, and the cavitation shock pressurebecomes larger. It could be considered that this phenomenon occurs because the amount of cavitation bubblesbecomes more and the sphere in which the static pressure recovers, extends to the downstream.(b) Multiperforated OrificeFigures 8 and 9 show the spatial distributions of cavitation shock pressure inside the pipe at the cavitation number, K=0.8 and K=0.4, respectively. For the multiperforated orifice, the shock pressure exceeding 0.5 MPa (lower limit ofpressure detecting film) is not observed at any point at the cavitation number, K > 0.8. Figure 8 Shock pressure distribution (multiperforated, K=0.8)    Figure 9 Shock pressure distribution (multiperforated, K=0.4)Shock Pressure  P [MPa]0.000.250.500.751.000 0.5 1 1.5 2 2.5 3Axial Distance  x/D [-]Radial Distance  r/R [-]0 2OrificeEdgePipe Wall4Pipe Center2.7MPa0 00 2 4 0 2 4 2 4 2 4PFlowShock Pressure  P [MPa]0.000.250.500.751.000 0.5 1 1.5 2 2.5 3Axial Distance  x/D [-]Radial Distance  r/R [-]0 20OrificeEdgePipe Wall40Pipe Center31.4MPa0 00 0P20 40 20 40 20 40 20 40FlowShock Pressure  P [MPa]0.000.250.500.751.000 0.5 1 1.5 2 2.5 3Axial Distance  x/D [-]Radial Distance  r/R [-]0 1OrificePipe Wall2Pipe Center1.4MPa0 00 0P1 2 1 2 1 2 1 2FlowShock Pressure  P [MPa]0.000.250.500.751.000 0.5 1 1.5 2 2.5 3Axial Distance  x/D [-]Radial Distance  r/R [-]0 10OrificePipe Wall20Pipe Center17.6MPa0 00 0P10 20 10 20 10 20 10 20FlowCAV2001:sessionA9.006          5From Figures 8 and 9, the followings are observed.(1) There is a point where the cavitation shock pressure becomes maximum near the pipe wall (radial distance ofmeasuring point, r/R = 0.875). It could be considered that the cavitation shock pressure becomes lower at thecenter of the flow because of the interference of the cavitation bubbles from orifice edges, and becomes largernear the pipe wall because of less interference of the cavitation bubbles.(2) When the cavitation becomes severer, the sphere in which the large shock pressure is observed becomes widerin radial direction, and the cavitation shock pressure becomes larger.(c) Cone Type OrificeFigures 10 and 11 show the spatial distributions of cavitation shock pressure inside the pipe at the cavitation number,K =0.6 and K=0.4, respectively. For the cone type orifice, the shock pressure exceeding 0.5 MPa is not observed atany point at the cavitation number, K > 0.6. Figure 10  Shock pressure distribution (cone type, K=0.6)         Figure 11  Shock pressure distribution (cone type, K=0.4)From Figures 10 and 11, the followings are observed.(1) There is a point where the cavitation shock pressure becomes maximum near the pipe wall (radial distance ofmeasuring point, r/R = 0.75). It could be considered that this phenomenon occurs because of same reason forthe multiperforated orifice. The maximum shock pressure is observed inner region in comparison with themultiperforated orifice because the flow has the vector to the pipe center due to the cone.(2) When the cavitation becomes severer, the sphere in which the large shock pressure is observed becomes widerin radial direction, and the cavitation shock pressure becomes larger.(d) Maximum Shock PressureFigure 12 shows the relation between the maximum shock pressure, PMAX and the cavitation number, K. Table 3shows the maximum shock pressure at the pipe wall, PWMAX at K = 0.4 (severest cavitation condition in theexperiment).Figure 12  Maximum shock pressure versus cavitation number0102030400 0.4 0.8 1.2 1.6 2Cavitation Number K [-]Maximum Shock Pressure PMAX [MPa]Single Hole OrificeMultiperforated OrificeCone Type OrificeOrifice TypeMaximum ShockPressure at PipeWall PWMAX[MPa]DetectedPositionon AxialDirectionCavitationNumber, K[-]Single Hole 2.5 1.5D 0.4Multiperforated 2.6 0.5D 0.4Cone Type 1.8 0.5D 0.4Table 3  Maximum Shock Pressure at Pipe WallShock Pressure  P [MPa]0.000.250.500.751.000 0.5 1 1.5 2 2.5 3Axial Distance  x/D [-]Radial Distance  r/R [-]0 1OrificePipe Wall 2Pipe Center1.9MPa0 00 0P1  2 1  2 1  2 1   2FlowShock Pressure  P [MPa]0.000.250.500.751.000 0.5 1 1.5 2 2.5 3Axial Distance  x/D [-]Radial Distance  r/R [-]0 5OrificePipe Wall10Pipe Center9.9MPa0 00 0P5 10 5 10 5 10 5 10FlowCAV2001:sessionA9.006          6From Figures 12 and Table 3, the followings are observed.(1) The maximum shock pressure remarkably increases with decrease of the cavitation number regardless of theorifice types.(2) The maximum shock pressure becomes smallest on the cone type orifice, and largest on single hole orifice. Themultiperforated orifice is between this two.(3) The maximum shock pressures at the pipe wall become almost same on single hole orifice and multiperforatedorifice, and the smallest on the cone type orifice. The maximum shock pressures at the pipe wall are muchlower than that at the inside of the pipe.4  Experiment-24.1  Method of ExperimentFor Experiment-2 (experiment for occurrence of cavitation due to interference of butterfly valve), the test section is1.3m in length, 80mm in inside diameter and is made of the transparent acrylic pipe to observe the aspect of thecavitation. The butterfly valve is installed at the test section and the test orifice is installed at 1D, 3D and 5Ddownstream of the butterfly valve. Table 4 shows the specification of butterfly valve. The test orifice is 3 inches 12holes multiperforated orifice, and the hole diameter is 8.5 mm.Table 4　Specification of Butterfly ValveType Wafer-Type Rubber Seated ButterflyValve (based on JIS B2032)Size 3 inch (80 mm)Rating Pressure 10 K (10 kgf/cm2G)In this experiment, flow rates, pressures and accelerations of piping vibration are measured changing the throttlingof the butterfly valve, and the length between the butterfly valve and the test orifice. The pressures are measured at1D upstream of the butterfly valve and 0.5D downstream of the orifice with the pressure transducers of strain gaugetype and the flow rate is measured with the magnetic flow meter. The accelerations of piping vibration are measuredat 0.5D downstream of the test orifice and treated using the FFT spectrum analyzer within the frequency range from1 Hz to 5 kHz, and the root mean square (r.m.s.) values “arms” are obtained.4.2  Results of ExperimentFigures 14 to 16 show the relation between the acceleration of piping vibration, α ’rms and the cavitation number, Kfor the 1D, 3D and 5D of length between butterfly valve and test orifice, respectively. In these figures, the verticalaxis shows the acceleration of piping vibration, α ’rms which is defined by the following formulae.   α ’rms = ratio between the r.m.s value of acceleration of piping vibration and total specific energy at upstream of orifice       = 22VPurms+ρα  [1/m]       (2)       where, α rms : r.m.s. value of the acceleration of piping vibration [m/s2]Pu : upstream pressure of the orifice [Pa]V : mean pipe velocity [m/s]CAV2001:sessionA9.006          7Figure 13  Acceleration of piping vibration versus cavitation number    Figure 14  Acceleration of piping vibration versus cavitation number   (Length between the butterfly valve and the test orifice = 1D)            (Length between the butterfly valve and the test orifice = 3D)Figure 15  Acceleration of piping vibration versus cavitation number   (Length between the butterfly valve and the test orifice = 5D)From Figure 13, the followings are observed for 1D length between the butterfly valve and the test orifice.(1) The relations between the piping vibration and the cavitation number are almost same for over 60 degree of theopening of butterfly valve.(2) The incipient cavitation number (piping vibration starts to increase at this cavitation number) becomes larger asthe opening of the butterfly valve becomes smaller.(3) When the opening of the butterfly valve is 30 degree, the piping vibrations at around K = 3 to 4 become large incomparison with that for other larger valve openings.(4) The cavitation occurs at a relatively high cavitation number. The butterfly valve throttling accelerates thecavitation at the multiperforated orifice because of the closed orifice installation.From Figures 14 and 15, the followings are observed for 3D and 5D lengths between the butterfly valve and the testorifice.(1) The relations between the piping vibration and the cavitation number are almost same regardless of the openingof the butterfly valve.(2) The incipient cavitation number is about Ki = 3.5 regardless of the opening of the butterfly valve.0.00.51.01.52.02.53.00.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0Cavitation Number K (-)α'rms  (1/m)90de g .75de g .60de g .45de g .30de g .Valve Opening×10-1Straight Length at Downstream of Valve : 1D0.00.51.01.52.02.53.00.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0Cavitation Number K (-)α'rms  (1/m)90de g .75de g .60de g .45de g .30de g .Valve Opening×10-1Straight Length at Downstream of Valve : 3D0.00.51.01.52.02.53.00.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0Cavitation Number K (-)α'rms  (1/m)90de g .75de g .60de g .45de g .30de g .Valve Opening×10-1Straight Length at Downstream of Valve : 5DCAV2001:sessionA9.006          85  ConclusionFrom the results of the experiment for the cavitation shock pressure, it is concluded that : (1)The characteristics ofthe distribution of cavitation shock pressure vary with the orifice types at low cavitation number. The maximumshock pressure is observed at the downstream of orifice edge on single hole orifice and near the piping wall onmultiperforated and cone type orifice. (2)The maximum shock pressure remarkably increases with the decrease ofcavitation number regardless of the orifice types. The maximum shock pressure becomes smallest on cone typeorifice, and largest on single hole orifice. Multiperforated orifice is between this two.The results of the experiment for occurrence of cavitation due to the interference of butterfly valve show that thecavitation occurs at a relatively high cavitation number when the multiperforated orifice is placed at 1D downstreamof the butterfly valve. The butterfly valve throttling accelerates the cavitation at the multiperforated orifice becauseof the closed orifice installation.ReferencesFruman, D. H., Rousseau, A., and Nienaltowska, E., 1985, “Critical Cavitation Numbers of Multiperforated Plates”,ASME, Fluids Engineering Division, 153-160Kugou, N., Matsuda, H., Izuchi, H., Miyamoto, H., Yamazaki, A., Ogasawara, M., 1996, “Cavitation Characteristicsof Restriction Orifices (Experiment on Characteristics of Piping Vibration and Noise)”, ASME, FluidsEngineering Division Summer Meeting, Vol. 236, No. H01072-1996, 457-462Numachi, F., Yamabe, M., and Oba, R., 1960, “Cavitation Effect on the Discharge Coefficient of the Sharp-EdgedOrifice Plate”, ASME Journal of Basic Engineering, 1-11Tullis, J. P., Asce, M., and Govindarajan, R., 1973, “Cavitation and Size Scale Effects for Orifices”, ASCE Journalof the Hydraulic Division, Vol.99, No. HY3, 417-430

Critical Cavitation Numbers of Multiperforated Plates”, ASME, Fluids Engineering Division,

Cavitation Characteristics of Restriction Orifices (Experiment for Shock Pressure Distribution by Cavitation on Restriction Orifices and Occurrence of Cavitation at Multiperforated Orifices Due to Interference of Butterfly Valve)

Cavitation Characteristics of Restriction Orifices (Experiment for Shock Pressure Distribution by Cavitation on Restriction Orifices and Occurrence of Cavitation at Multiperforated Orifices Due to Interference of Butterfly Valve)

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