DESIGN AND FLOW MODELLING OF BALLAST TANK IN-LINE EJECTOR

Transcription

1 DESIGN AND FLOW MODELLING OF BALLAST TANK IN-LINE EJECTOR 1 Constntin DUMITRACHE, 2 Corneliu COMANDAR, 3 Bogdn HNATIUC 1,3 Mritime University of Constnt, Romni, 2 Ghe. Aschi Technicl University of Isi, Romni e-mil: ldumitr@yhoo.com ABSTRACT The purpose of this pper is to present the stges of designing wter in-line ejector used for llst tnks stripping opertion. The design opertion ws performed using NX Siemens CAD nd ANSYS 15 for computer fluid dynmic nlysis CFD. This ejector design ws sed on descriptive drwings of component prts, ll dimensions eing chosen from worldwide supplier of high qulity mrine products. Computer Fluid Dynmic nlysis is sed on the finite element method (FEM), meshing, oundry condition nd lods. Finlly, we reched importnt conclusions regrding velocities, pressure nd temperture of the fluid. KEYWORDS: in-line ejector, CAD NX Siemens, revolve, extrude, velocities, totl pressure, temperture, CFD 1. Introduction On ord of commercil ships there re lot of uxiliry devices, such s ejectors, emergency fire pumps, trnsfer pumps nd electricl control, which re most used in mritime industries [1]. An ejector is sttic piece of equipment with no moving prts (Figure 1). There re three mjor components of n ejector: the house with suction chmer (1), the motive nozzle (2) nd the diffuser (3). The operting principle of n ejector is to convert pressure energy of high pressure motive liquid into velocity. High velocity liquid emitted from motive nozzle is then used to work on the suction fluid. This work occurs in the suction chmer nd inlet diffuser. The remining velocity energy is then turned ck into pressure cross the diffuser. In simple terms, high pressure motive liquid is used to increse the pressure of fluid tht is t pressure well elow motive liquid pressure [2]. The ejectors re used in lrge rnge of pplictions in mritime industry: stripping of ilges from the ottom of the vessel; filling nd stripping of llst tnks; stripping of ll sorts of mediums from crgo holds includes oil, gs, wter nd sewge; stripping of ilge from chin lockers. In the engine room ejectors, cn oth e used for stripping of ilge nd for ventiltion of exhust or other gsses, nd removl of shes from incinertors. Multiple use portle ejectors re designed for multiple suction purposes. These ejectors cn e instlled with hoses, in order to utilize the ejector vrious plces on the ship. Portle ejectors re fvorle to use where vrious suction quntities re low or where corse vcuum clening re needed. Pek tnks re situted either in the front or the rer of the vessel. Ejectors cn oth e used for stripping nd filling these tnks. In the priming of centrifugl pumps the ejector cretes vcuum which will initite the function of pumps. 2. Construction of in-line ejector All dimensions for the in-line ejector were presented in the supplier s technicl documenttion [1]:

2 Fig. 1. Assemly NX cross section viewing prts of in-line ejector; 1- the house, centrl prt of ejector, contining suction nd motive inlet; 2 - the motive nozzle is mounted in the house with the purpose of regulting motive liquid; 3 - the diffuser, contins the process of mixing nd ejecting the motive nd sucked fluid D Design of house ejector The essentil feture of the ejector is the house (1) presented in Figure 2. pressure to velocity nd directs the flow of motive liquid into the diffuser. Fig. 3. Min view of motive nozzle Fig. 2. Section view of house ejector Achieving 3D house representtion strts with the sketch drwn with the yellow line in Figure 2 nd goes on with the use of the Revolve option tht gives the finl shpe with two flnges t the extremities. The third flnge, lso known s motive inlet, is done initilly in the form of sketch which is then extruded with the Extrude opertion. The dimeter pipe flnge is crossing the ejector ody nd mkes rounded ngle of 90 degrees tht ws done with the option Sweep long Guide D Design of motive nozzle The esiest 3D prt is motive nozzle constructed with 2D yellow sketch revolved with Revolve opertion (Figure 3). The nozzle is considered the hert of the ejector ecuse it converts the energy of D Design of diffuser The diffuser (Figure 4) is constituted of three prts: inlet diffuser; throt section; outlet diffuser. Inlet diffuser provides correctly shped introductory section nd converging diffuser section to hndle the high velocity flow of fluids. It is in this section tht entrinment nd mixing of the motive nd lod fluids is completed nd the energy of liquid velocity is converted to pressure. The throt section is the trnsition piece etween the converging inlet diffuser nd the diverging outlet diffuser. The outlet diffuser provides correctly shped diverging diffuser section for completing the conversion of velocity to pressure. The outlet diffuser

3 section further reduces the fluid velocity to resonle level so s to convert prcticlly ll the velocity energy to pressure energy [3]. erosion is importnt. But stinless steel is little more resistnt to mechnicl-wer thn copper lloy due to the superior hrdness. 3. Computer fluid dynmics - CFD Fig. 4. Section view of diffuser 2.4. Assemly of component prts Our in-line ejector is F type (25 mm - inner dimeter of motive inlet, 50 mm - inner dimeter of suction inlet, 50 mm - inner dimeter of dischrge outlet) nd hs the est efficiency for llst tnks nd crgo tnks [1]. All three prts of the ssemly were dded using touching (on flnges), infer center xis (on holes), concentric constrints. The finl ssemly is creted when the component ojects re dded to the ssemly prt file, ech component oject eing mted with the corresponding ojects. The 3D Design of the ejector is presented in Figure 1. Copper lloy ws used for the house ejector nd the diffuser, nd stinless steel with mechnicl properties presented in Tle 1 ws used for the motive nozzle. Mteril Copper lloy Stinless Steel Tle 1. Mechnicl properties Yield Strength [N/mm 2 ] Ultimte Tensile Strength [N/mm 2 ] Both mterils show excellent resistnce to corrosion in se-wter ecuse of min constituents, copper nd nickel. This lloy hs excellent service under high-velocity conditions, where cvittions CFD hs ecome powerful tool tht cn e employed either for pure/pplied reserch or for industril pplictions. Computtionl simultions nd nlyses re incresingly performed in mny fluid-engineering pplictions, which include erospce engineering (irplnes, rocket engines), utomotive engineering, iomedicl engineering (lood flow in rtificil herts), chemicl engineering (fluid flow through pumps nd pipes), civil nd environmentl engineering [4]. The first step in our CFD nlysis is the cretion of the geometry of the flow region using NX Siemens softwre (Figure 1). This ssemly ws imported in ANSYS 15 to extrct the ejector flow region presented in section viewing in Figure 5. Fig. 5. Section view of flow meshed region The second step is meshing opertion (Figure 5) which genertes nodes nd elements Boundry conditions We considered tht the llst tnk in-line ejector is ssigned wter s the fluid, with 7 r pressure t the motive inlet nd temperture of 25 o C. It is clled in-line ejector ecuse the suction inlet nd outlet dischrge re plced on the sme line; oth suction inlet nd outlet hve the tmospheric pressure nd opening temperture 15 o C

4 Fig. 6. Velocity distriution: ) ejector section plne; ) centered stremlines vrition 1 (inlet) nd 2 (opening 1) Fig. 7. Totl pressure distriution: ) ejector section plne; ) centered stremlines vrition 1 (inlet) nd 2 (opening 1) Fig. 8. Temperture distriution: ) ejector section plne; ) centered stremlines vrition 1 (inlet) nd 2 (opening 1)

5 4. Conclusions As cn e seen in Figure 7, motive liquid pressure is very importnt ecuse it ensures the minimum pressure on the suction inlet. Generlly, it is recognized tht the mnufcturer hs designed the system to mintin stle opertion with liquid pressures t or ove minimum liquid pressure. In our exmple, the motive inlet pressure is 7 r nd for this vlue the pressure t the suction inlet is round 1 r. When the velocity of the fluid strts to increse t the motive nozzle, in the sme time the suction velocity t opening 1 is incresing (Figure 6). If the motive liquid supply pressure flls elow design, then motive nozzle will pss less liquid. When this hppens, the ejector is not provided with sufficient energy to compress the suction fluid to the design dischrge pressure. The sme prolem occurs when the supply motive liquid temperture rises ove its design vlue, resulting in incresed specific volume, nd consequently, less liquid psses through the motive nozzle [2]. An ejector my operte unstly if it is not supplied with sufficient energy to llow compression to its design dischrge pressure [5]. Unstle ejector opertion is chrcterized y drmtic fluctutions in operting pressure. If the ctul motive liquid pressure is elow design or its temperture ove design, then, within limits, n ejector nozzle cn e reored to lrger dimeter. The lrger nozzle dimeter llows more liquid to flow through nd expnd cross the nozzle. This increses the energy ville for compression. If the motive liquid supply pressure is more thn 20-30% ove design, then too much liquid expnds cross the nozzle. This tends to choke the diffuser. When this occurs, less suction lod is hndled y the ejector nd suction pressure tends to rise. If n increse in suction pressure is not desired, then ejector nozzles must e replced with ones hving smller throt dimeters or the motive liquid pressure corrected. In conclusion, n ejector is designed to operte t exct motive pressure nd motive cpcity, ny chnges in motive flow cn result in [1]: Vrying motive flow will decrese ejector performnce. Decresing motive flow from the specifictions might result in n insufficient or even non-performing ejector. Incresing motive flow might cuse the ejector to mlfunction. Ejectors re designed for mximum suction cpcity; therefore, incresing motive flow might not increse suction cpcity. References [1]. Mritime Diesel Electric, Mrine Consulting, Engineering & Technicl Purchsing, [2]. J. R. Lines, R. T. Smith, Ejector system trouleshooting, The Interntionl Journl of Hydrocron Engineering, UK, [3]. F. Duncn Berkeley, Ejectors, Grhm Mnufcturing Compny, Iinc., BATAVIA, N. Y., Reprinted from Petroleum Refiner, Decemer [4]. Jiyun Tu, Gun-Heng Yeoh, Choqun Liu, Computtionl Fluid Dynmics, A Prcticl Approch, Second Edition, Butterworth-Heinemnn is n imprint of Elsevier. [5]. Yveline Mrnier Antonio, Christelle Périlhon, et l., Thermodynmic Modelling of n Ejector with Compressile Flow y One-Dimensionl Approch, open ccess Entropy 2012, 14, p , ISSN