Buletinul Ştiinţific al Universităţii "POLITEHNICA" din Timişoara Seria HIDROTEHNICA TRANSACTIONS on HYDROTECHNICS

Transcription

1 Buletinul Ştiinţific al Universităţii "POLITEHNICA" din Tiişoara Seria HIDROTEHNICA TRANSACTIONS on HYDROTECHNICS To 55(69), Fascicola, 010 Experiental Stand for the Study of Unsteady Water Flow through s and Pipe Networks Stănescu Mădălina 1, Constantin Anca 1, Bucur Cosin, Stănescu Adrian 3, Roşu Lucica 1 Abstract - This paper presents the physical odel developed by authors for the study of hydraulic shock in a ring type distribution network. Using hydraulic siilarity criteria, the ring shaped stand odels the Aara village, Ialoita County, water supply network. In order to analyze the network behaviour in different types of consuption variation, the network is connected to a coputerized easuring unit, developed on a LabVIEW platfor (National Instruents) that provides easureent, real-tie display (graphical and / or tabular) of physical quantities collected fro the sensors attached to the network. Keywords: pipeline network, water distribution, transient, physical odelling. 1. INTRODUCTION The coplexity of the transients in water supply systes, the assuptions and liitations of various equations that govern otion soeties raise doubts on the scope of applicability and the liits of these equations. Transient analysis using specialized software packages carried out in parallel with physical odelling ay iprove understanding of the hydraulic shock physical phenoena and the ability to predict and control this phenoenon in pressurized hydraulic systes engineering design and operation. noinal diaeter (with e n =,30 pipe wall thickness and D int =35,40 inner diaeter) and D n 0 (with e n =1,60 and D int =16,80), according to the schee in Fig. 1 and Fig. 3. The rectangular supply basin is located on a,40 high support (Fig. 4). Inside the basin, the water colun has a height of 30c, resulting in a water volue of approxiately 160 liters. The water level in the tank is aintained constant by the use of a valve with float, which closes the water supply when the axiu height is reached. Basin water supply is assured fro the internal water supply network of the laboratory through a Ø0 diaeter HDPE pipe. The experiental odel is suppled with water by a HDPE Ø40 pipe, connected to the botto of the reservoir.. PHYSICAL MODEL DESCRIPTION Hydraulic experiental facility, in which deterinations were ade, is a loop fro an existing ring network, reduced proportionally, 0 ties, on the basis of hydraulic siilarity principles. The trial stand has the following coponents: - rectangular supply basin, with the diensions L = 90c, l = 60c, h = 40c; - HDPE (high density polyethylene) supply pipeline of Ø40 in diaeter,.30 in length; - HDPE network ring (PE80, SDR17, 5 PN6) coposed of tubes of two diaeter values: D n 40 For a good water oveent control, each node of the loop is equipped with flow and pressure easuring devices, as follows (Fig. ): - tap, with a axiu opening at 90 o (angle between the tap lever and the pipe axis); Fig Ring network schee pressure transducer, connected to the coputer; - water eter for deterining the quantity of water discharged in a given unit of tie. 1 Ovidius University of Constantza, Civil Engineering Faculty, B Unirii, 90054, ada_x_dobre@yahoo.co Ovidius University of Constantza, The Faculty of Industrial, Mechanical and Maritie Engineering Departent, 14 Blvd. Maaia, 90057, bcircea@univ-ovidius.ro 41 3 S. C, I.F.C.O. S.A., 4 Zburatorului, , Contantza, Roania, stanescuadrian78@yahoo.co

2 - Fig.. - Details of ounting the network nodes 1 transducer; tap; 3 watereter - geoetrical, with respect to the reduction of the diaeters and lengths of pipes; - kineatic, with respect to the proportional reduction of pipe flow rate; - dynaic, with respect to the network nodes pressure proportional reduction. Knowing that both odel and in nature water oveent are subjected to Newton's law. F a (1) where: F - force, - ass, a - acceleration ; the analyze of particle otion in an arbitrarily chosen X direction, will be ade such as the forces that produce oveent are expressed by correspondent relationships: - nature d X Fn n dt n n (1.a) - odel F d X dt (1.b) Fig Top view of the experiental stand where: F n and F - relevant forces; n and - corresponding asses; X n and x - proper distances; T n and T - fraction of tie. According to Froude law of siilarity, in ost cases of odeling, the ain force deterining the otion is the force of gravity. Thus, geoetric siilarity is required to report all relevant lengths are one and the sae: X L () X n where: (L) λ - coefficient of siilarity. Given the analyzed paraeters, the corresponding siilarity coefficients have the for presented in Table 1. Fig View during the experients Network loop water intake is by the node no. 1, D n 40 and distribution to consuers is by the other three nodes, which have the following features: node no. and node no. 3 have D n 40 and node no. 4 D n 0. The four sides of the loop consist of HDPE pipes of different diaeters, as follows: the -3 side has D n 0 in diaeter, and the other sides, 1-, 3-4, and 4-1 have D n 40 in diaeter. 3. HYDRAULIC SIMILARITY CRITERIA The design of the physical odel was achieved by hydraulic siilarity with the real situation, on the basis of the following criteria: Table 1 - Siilarity coefficients Type assiilation physics kineatics Feature length / diaeter flow Siilarity coefficients 5 L L dynaics pressure L where: - voluetric weight of water, - density of water. The laboratory stand reproduces, on the basis of the ain hydraulic principles, an existing water supply network, reduced by the siilarity coefficient L = 0. The results are presented in Table Table 5. 4

3 Table Pipe diaeters of the ring network, the odel and field Model pipe diaeters Real pipe diaeters Diaeter (HDPE tube) [] (etal pipe) [] reducing section wall D D n D thickness int coefficient int D int wall D calculated standard thickness n intake 40,3 35, ,9 734,8 1-40,3 35, ,9 734, ,6 16, ,9 7,9 339, ,3 35, ,9 734,8 0, ,3 35, ,9 734,8 output 40,3 35, ,9 734,8 output 3 40,3 35, ,9 734,8 output 4 0 1,6 16, ,9 7,9 339,7 Table 3 Flow rate in pipe sections section Model flow rate [l/s] Flow rate reduction factor Real pipeline flow rate [l/s] intake 0, , ,55 456, ,0 35, ,16 89, , ,85 347,038 output 0,35 40,381 output 3 0,18 35,571 output 4 0,03 Table 4 Lengths of pipe network Length of Length pipeline design reduction section [] factor 57,43 lenght field [] , 84 0,00 3-4, ,8 76 Table 5 Pressures in the ring network nodes Node Model node pressure [CA] Pressure reduction factor Real node pressure [CA] 1 1,949 38,97 1,83 36,45 0,00 3 1,80 36,39 4 1,898 37,96 The pressure transducer MBS 33 is designed for use in alost all industrial applications and provides a reliable easureent of pressure, even in difficult environental conditions. The flexible sensor covers an output signal 4 0 A and a gap easuring pressures fro 0 1 bar to bar at operating teperatures of o C. The pressure transducer MBS 33 has an excellent vibration stability, robust construction and a high conversion EMC / EMI to eet the ost stringent industrial requireents. Coputerized easureent syste can provide easureent, real-tie display (graphical and / or tabular) of physical quantities collected fro sensors attached to the network. Given the acadeic use of the easureent syste (in the Ovidius University), the solution chosen is based on the use of hardware and software for the acquisition of data contained within a particular starter-kit. Measureent and control syste consists of the following coponents: a) Local application developed in LabVIEW prograing environent; b) Data acquisition card NI PCI MIO 16XE-50, 16bit resolution; c) NI SCB-block connections 68LP (Fig. 6). d) Excitation syste consists of pressure transducers: - instruentation power source 0-30Vdc; - instruentation 55Ω resistors. 4. MEASUREMENT AND CONTROL SYSTEM Each node of the loop is equipped with a pressure transducer type MBS-1AB (Danfoss product) (Fig. 5). Fig. 6 - Block connections NI SCB-68LP Fig. 5 - pressure transducer 33 MBS The signal fro each sensor is collected as a voltage at the ends of the instruentation resistance. Fig. 7 and Fig. 8 present, for exaple, " Block Diagra", and respectively "Front Panel" of the progra Pressure Measureent.vi. 43

4 Fig. 7 - Block Diagra of the Pressure Measureent.vi Fig. 8 - Front Panel LabVIEW Platfor for the Pressure Measureent.vi 5. EXPERIMENTAL METHOD Experiental easureents, ade on the physical odel presented above, aied the analysis of the transient flow regie, taking as reference regie the steady flow of water through a ring shaped pipeline network. The occurrence and deployent of the hydraulic shock phenoenon due to disturbances induced in the network loop by valves anoeuvres were investigated according to: - valve opening angle, ; - ode of the valve operation ; - valve opening duration. 44 The following cases of network operation and handling of valves were siulated: - sudden anoeuvre of a single valve; - sudden anoeuvre and siultaneous operation of two valves; - sudden anoeuvre and siultaneous operation of three valves. The type of valves allowed easureents to be ade at various angles of opening, : 30, 45, 60 and 90. Our investigations were conducted on two ain directions: - the deterination of the flow rates in each node, in steady state operation, at different variants of

5 opening angle.. The flow rates in nodes, 3 and 4 stand for the real flow rates of the network consuers. Therefore, we aied to establish the valve opening angle corresponding to the real flow rate of these consuers. - the deterination of pressures and related instant water flow rates in each node, in unsteady regie operation. The unsteady oveent was provoked by sudden anoeuvres of valves, in different cobinations. The average water flow rate in each network node was deterined in the case of steady, siultaneous operation of the three valves in the nodes N, N3 and N4, at each following value of the opening angle, : 30, 45, 60 and 90. It was assued that the steady state regie is established 10s after the valves opening. The unsteady regie was induced by the valve obturator operating odes. The easureent was carried out following the sequence: - sudden opening of valves at a prior established angle; -water instant flow rate easureent at two oents: t 1 = 1 s; t = s - sudden closing of the valves; -continuous pressure variation recording. To ensure greater accuracy of experiental data, a set of three easureents has been ade for each opening angle,,. The discharge in node N1 is obtained by suing the flows deterined in the other three nodes. 6. RESULTS The experiental results with respect to the water flow rate in steady state regie are presented in Table 6, for each network node. A ore intuitive presentation of these data is graphically ade the Fig. 9. Table 6 Deterination of the flow rate, in the case of steady and siultaneous operation of the three valves Angle of tap Discharge [l/s] opening Node Node 3 Node 4 Node 1 [degrees] 30 0,40 0,30 0,087 0, ,75 0,607 0,148 1, ,939 0,759 0,189 1, ,100 0,808 0,08,116 Discharge, Q [l/s],5,0 1,5 1,0 0,5 0,0 N N3 N4 N Opening angle, α Fig. 9-Variation of average flow rate, in the case of steady and siultaneous operation of the three valves, for different opening angles,. Siultaneously with the flow easureents, pressure variation was recorded by each sensor installed in the ring network nodes during each entire experient.. Pressure values were collected and recorded using the progra MASURARE PRESIUNE.vi (Pressure Measureent.vi). The following siulated operating odes are presented bellow: - opening - closing after 10 sec. of the three valves: N, N3 and N4 (Fig. 10); - opening - closing after 10 sec. of two valves: N and N3 (Fig. 11); - opening - closing after 10 sec. of two valves: N and N4 (Fig. 1); - opening - closing after 10 sec. of two valves: N3 and N4 (Fig. 13). Pressure p [bari] 1 0,8 0,6 0,4 0, 0 5-0, Fig Changes in pressure when opening the three valves siultaneously, = 90 In Fig. 10, the notation,,, refers to the pressure transducers of the corresponding nodes of the network, naely, N1, N, N3, N4. The curves plotted in Fig. 9 represent the water flow rate in each node of the experiental network loop. The curve for node 1 depicts, in fact, the water intake variation. 45

6 Pressure p [bari] 1 0,8 0,6 0,4 0, , -0,4 Fig Pressure variation in the case of siultaneously opening of the valves in node and node3, = 90 Pressure p [bari] 0,7 0,5 0,3 0,1-0, ,3 Fig. 1 - Pressure variation in the case of siultaneously opening of the valves in node and node4, = 90 Pressure p [bari] 0,8 0,6 0,4 0, 0-0, ,4-0,6 Fig Pressure variation in the case of siultaneously opening of the valves in node3 and node4, = 90 Analyzing pressure variation graphs presented above (Fig. 10 Fig. 13) the iniu and axiu values of pressure at sudden valve closure and the transducers that are recording these values can be deterined (Table 7). Table 7 - Miniu and axiu pressure values Tap p in p ax handle [bari] Node [bari] Node N N3 N4-0,0 N3 0,81 N3 N-N3-0,30 N4 0,90 N N-N4-0,1 N3 0,68 N3 N3-N4-0,4 N3 0,80 N3 7. CONCLUSIONS The experiental deterination presented above lead to the following conclusions: 1. On the basis of the graphic representation of average flow rate variations, in the case the three water distributing valves are siultaneously open (Fig. 9), one can deterine the exact opening angle of each valve obturator, to ensure on the odel the correspondent flow rate requested by the consuer. Thus: - N distribution ensures the flow rate Q=0.35l/s by opening the valve at an angle =17 ; - N3 distribution ensures the flow rate Q=0.18l/s by opening the valve at an angle =18 ; - N4 distribution ensures the flow rate Q=0.03l/s by opening the valve at an angle =10.. Analyzing the results it was found that the worst situation is the case the valves deliver their axiu discharge that eans the valves are suddenly opened / closed to / fro 90, in any cobination. 3. The opening of a valve results in an iediate vacuu, followed by soe pressure oscillations. The steady state flowing regie is established after 3 4s. 4. According to Table 7 it ay be noticed that the N3 node of the ring network is considered the ost unstable, and also, the necessary tie for pressure oscillation attenuation in this node is axial. 5. The highest and lowest pressure values, in sudden closure cases, are obtained when the valve obturators are siultaneously acting in the nodes N-N3 or N3-N4. The difference between the highest and lowest recorded pressure is about 1.0 bars. REFERENCES [1] I. Bartha, V. Javgureanu, N. Marcoie, Hidraulică, vol.ii, Editura Perforantica, Iaşi, 004 [] H. Chaudhry, Applied hydraulic transients, Van Nostrand Reinhold Copany, New York, 1987 [3] Gh. Constantinescu, Contribution on Pressured Hydraulic Installation Protection, Doctoral thesis, Institutul Politehnic Tiişoara, 1983 [4] S. Hâncu, G. Marin, Hidraulică. Teorie şi aplicată, Vol. I, Editura Cartea Universitară, Bucureşti, 007 [5] M. Popescu, Hydropower plants and puping stations Transient hydraulic operation, Ed. Universitară, 008 [6] M. Popescu, D. I. Arsenie, P. Vlase, Applied Hydraulic Transients for Hydropower Plants and Puping Stations, Balkea Publishers, Lisse, Abington, Tokyo, 003,