This project was conducted at Westinghouse's Savannah River Laboratories (SRL). The goal of SRL is to make certain that the modifications on the reactor are safe for those working at the plant as well as the general public. One of the steps needed to insure safety is the knowledge of the occurrences that result from a plenum pipe breakage. When a plenum pipe breaks, two things occur: air is sucked into the pipe and is trapped in the cooling water; and water used to cool the fuel rods is lost. As a result of these occurrences, the water is slowed down by both the loss in water pressure and the upward force of air bubbles pushing against the downward force of the water. The project required the conducting of tests to find the bubble velocity in an annular ribbed pipe filled with stagnant water. This document discusses the methodology and results of this testing

Burge, C.

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WSRC-MS--91-358DE92 0097 95CORRELATION OF BUBBLE RISE VELOCITY ANDVOLUME (U)byChris BurgeGreg Flach, Mentor/SpensorWestinghouse Savannah River Co.Savannah River SiteAiken, South CarolinaThis is a report to be sent toDr. Jeff Priest, Program DirectorSummer Science Res,, ProgramUSC- AikenAugust 21,1991 DISCLAIMERThis report was prepared as an account of work sponsored by an agency of the United StatesGovernment, Neither the United States Government nor any agency thereof, nor any of theiremployees, makes any warranty, express or implied, or assumes any legal liability or responsi-bility for the accuracy, completeness, or usefulness of any information, apparatus product, orprocess disclosed, or represents that its use would not infringe privately owned rights. Refer-ence herein to any specific commercial product, process, or service by trade name, trademark,manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recom-mendation, or favoring by the United States Government or any agency thereof, The viewsand opinions of authors expressed herein do not necessarily state or reflect those of theUnited States Government or any agency thereof.This report was prepared in connection with work done under Contract No. DE-AC09-89SR 18035witi', the U.S. Department of Energy. By acceptance of this paper, the publisher and/or recipientacknowledges the U.S. Government's right to retain a nonexclusive, royalty-free license in and toany copyright covering this paper, along with the right to reproduce and to authorize others toreproduce ali or part of the copyrighted paper.DtS[F_Ii.3I.JFtON OF. "lt..tiS tDOCLJN/I,'i]_I,,I] ;;'}. . , _:!:._.,t,NES-cD_- _lolz_Correlation of Bubble Rise Velocity and Volume ('_By: Chris BurgeClassification: UnclassifiedAuthorized Derivative Classifier:__.:'_¢4_-_ 7/_'/q!, , ]My project was conducted at Westinghouse's Savannah RiverLaboratories (SRL). The goal of SRL is to make certain that themodifications on the reactor are safe for those working at the plantas well as the general public.One of the steps needed to insure safety is the knowledge of theoccurrences that result from a plenum pipe breakage. When a plenumpipe breaks, two things occur:(1) air is sucked into the pipe and istrapped in the cooling water; and (2) water used to cool the fuel rodsis lost. As a result of these occurrences, the water is slowed downby both the loss in watew pressure and the upward force of airbubbles pushing against the downward force of the water, as Figure#1 illustrates.Figure #1 - Bubble rise in pipeTests using annular and regular pipes have been conducted at otherresearch facilities. Their research has shown that the larger thebubble the larger its terminal velocity. At a certain volume, the,,velocity of the bubble begins to level off and eventually hits amaximum velocity which an increase in volume of the bubble cannotchange.The tests show that the shape of the pipe also determines thebubble's velocity. Bubbles in annular pipes have a faster velocitythan those in regular pipes when correlated with the bubble'svolume. In these tests the areas of the pipes are the same thus itstands to reason that the geometry of the pipe helps to determinethe bubble rise velocity.Though research has been done on bubble rise rates in annular andregular pipes, no tests have been conducted with annular-ribbedpipes, to the best of our knowledge. Since the reactor at SRScontains annular-ribbed pipes, we at SRL find it important to knowthe correlation of bubble volume and its velocity in an annular-ribbed pipe. We need this information so that we can compare it toearlier tests using regular and annular pipes in other tests (Figures#2, #3, & #4 show different kinds of pipes).outerpipe(layer)cenlerofannulus p_pepipewithFigure#3Figure#2 ofp_Iroac_bet_oen_s andouterlayerbubOklupInpipebubblerising_np_ ,==gnantwaterInAnnular-Ribbed Roe Bligg]W..BJl_ p_out_'pipe(layer)inp_ jcentero_annulusP_' Figure#4Ixtobler_nginplpeAnnuluspl?eThe project that I have been given is in direct compliance with themission at SRL. it requires mo to conduct tests to find the bubblevelocity in an annular ribbed pipe filled with stagnant water. Thepipe that I work with is Rig C and is normally used to conduct tests, , 4that require flowing water in an annular pipe. Along the pipe, fourrings, with fittings, are placed thirty three inches apart of eachother. These rings have fittings that are used to introduce air in thesystem.Before I had been assigned this project, two engineers tried toconduct a similar test with an uncalibrated squeeze bottleconnected to a fitting on the ring at the bottom of Rig C. Since thesqueeze bottle was uncalibrated and did not show any volumemarkings, volume was estimated by the use of filming the bubble ona videocamera and recording its length and width. When a bubblewould break-up, the run was considered invalid and data was nottaken.. The run is invalid because the velocity of two bubbles areslower than one bubble of equal size. Their observations show thatas volume increased so do the chances of bubble break-up.Eventually, the chances of bubble breakup increases to a point that itbecomes impossible to take measurements on one whole bubble. Thetest done by the engineers ended with few valid points at a lowmeasurement of volume.After reviewing their test, I came up with a few ideas on how tolimit bubble break-up. The observations of Andrea Kielpinski showthat bubble break-up occurs at the entrance of the air bubbles. Basedon her observations, I decided that the bubble break-up occursbecause of buoyancy force becoming greater than the surface tensionof the bubble. Before I was able to run any tests of my own, I cameup with three ways of keeping the bubble from breaking up when itenters the pipe. One way is to add on a different kind of fitting tothe pipe which allows me to enter the bubble at a different angle. Myreason for supporting this hypothesis is the fact that this increasesthe surface area of the bubble thus increasing the surface tension toa desired size. My second idea is to build an apparatus at the bottomof the pipe which injects enter a certain volume of air in the pipe atone instant. This nullifies the effects of buoyancy force on thebubble. My third solution is that the effect of buoyancy force is lessif a heavy, viscous nonsoluble chlorinated hydrocarbon is used as theliquid in the lower portion of the pipe. Since the liquid that thebubble is formed in is more viscous than water, the buoyancy forceproves to be small enough to form large bubbles. After reviewing myoptions, I decided that my first two ideas did not fit with theoptions I had in solving this problem. This is because I was not givenenough time to modify or completely rebuild another rig. My thirdidea achieves the goal of forming a large single bubble but producesan error in the curve thus causing the bubble to rise slowly up thepipe.Before resigning myself to having a test with a known error, Idecided to conduct a few tests with the rig in a similar fashion tothe test with the two engineers. I modified the test I_y using asyringe with markings of designated volumes. I also calibrated thesyringe by us6ng the volume = mass/density equation. This is inhopes of having a more accurate knowledge of the volume of thebubble. Other than using a syringe instead of a squeeze bottle, thetest that I conducted is exactly like the one conducted by the twoengineers (As Figure #5 shows).Figure#5Sydnge TygonTubing_tlng SurfaceTension, FormingBubbleSvrinaeand FittingFor the first few bubbles that I inserted, no data is taken. This isbecause I wanted to observe what the bubble does while rising upthe pipe. I hoped to use my own observations as a tool towardssolving the problem. What I observed is that even at small volumas(i.e. 2 ml) the bubble fills the width of the channel in 'which it isinjected. Beginning at 4 ml, it seems that slugs begin to form in thechannel. At 4 ml, bubble break-up begins near the top of the pipe (i.e.100 inches). Later observations show that break-up caused by thebubble hitting a rib results in a seepage of air in the channel on theother side of the rib. As the bubble increased in volume, the seepageof air into another channel happens sooner and sooner.Based on my observations in my earlier test, I decided to take dataand correlate bubble volume to bubble velocity. Unlike the testi b, 0 7conducted by the two engineers, I decided to include data on bubblesthat break up. The data taken shows that at approximately 8 ml. thebubble velocity leveled out toa straight line (As Figure #6illustrates).Data from "Vol. vs Vel. (m/s).Data"y = 0.27514 + 0.26097*LOG(x) R^2 = 0.9451E>, l- / [] Velocity(m/s)_.- f00•"$ annularof same size> (.31 m/s)•I • • • • • • • • | • • • • • • • •1 10 100Volume (ml) ,This data is comparable to those found with regular and annularpipes except for the fact that the terminal velocity is higher in anannular-ribbed pipe. lt seemed as though the seepage was a naturaloccurrence in keeping the bubble at a terminal velocity•I reason that there are several factors for air seepage. One factor isthe size of the bubble. The length of the bubble increasessubstantially once the width of the chamber is filled. Based on thefilm taken of the bubbles, water enters the bubble in tiny waves asair seeps out. The longer length gives the waves a better chance toinvade the bubble. If the spacing is large enough, I believe that thespace between the ribs and the outer layer attracts bubble seepage .This explains why the bubbles tend to seep at one side rather thanthe other.Though the project seems to be complete there is uncertainty in thetests. Further tests should be conducted to determine if seepage didgive an acceptable curve by doing tests without seepage. Also, Othertests should be done with more accurate equipment so that the curvewill be more accurate.References1. Kelessidis, V.C., and Dukler, A.E., "Motion of Large Gas BubblesThrough Liquidsin Vertical Annuli" Int. Journal of Multiphase PhaseFlow, Vol. 16, No. 3, pp. 375-390, 1990.iiLii i, Jii* ot• i, oII• I6, ilis.....L ilm"lDI.__00L_o-F cmm•m ,ld i_ID • '-(1) > .., U) "U C:: .12 .--'- .... (/) (I:I"-- _".c:: (_ .c:: "_ 12. *-, £:: (_In lD i.. _ "lD ,- --m s. 0 C _ _ 0 _-_ > 0Ill ",-' (ll (II .,.,._ _ o_ 0 .C _" t_ ' I_ 0(I) t_ (I) 0 _ _ ._ _ "--0 _ 0 C: 0'-- _ E _ C:: ,- 0 _ 0• , 0 • _- _ C: "0 _ • .tC::0 0 m ._ _ .-- _ .--_, .c 0 • _13. c 0 = a) .o I_ _) "o _ "o•-- " (_ .I= .,-' 4)• " "-_ -_ .12 > .._m 0 [_ 0• " ._ 0 ., _ .. "- _.o o o = o) m 1C. .=_ o) F_. _) o o)I: 0 _ ..u n .u _- u. _ m _ m rr"t_ t_(n(_) ,'--•_-- 0iimo__ _:_:,i,d ,t.,8'-0(1)Q-_2. tn 0.,- ,- .c:I::::r" _..--_,_..0 0.__ _.__ eO° _L. I,-, •0 lmm oo d ___Ii___ _'_. _l}lmoo,,I-=dII° .,"" I=:3:p_ >+ r",__: 4-c5II(+/iu) XllOOleA

Correlation of bubble rise velocity and volume

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Correlation of bubble rise velocity and volume

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