利用TASC进行换热器振动分析.ppt

Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,*,Click to edit Master title style,Using the TASC Vibration Analysis,Why Worry About Vibration?,Cost if plant has to be replaced,Safety and reliability of operating plant,Mechanical damage,joint failure,fatigue failure,fretting(wear),impact,Introduction,The methods in TASC are designed to avoid problems at the design stage,All,geometries,allowed in TASC except G,H and K shells and,unbaffled,cases,(K shells in TASC v4.10 Performance modes),Single phase liquid,single phase gas and two phase,Options,Input data which affect the vibration analysis,Impingement protection,Tube material,Youngs,Modulus,Cross flow stream fraction,End zone lengths,U-bend blanking plate,Intermediate baffle supports(no tube in window cases only)and U-bend supports,Inlet and outlet exit heights,Tubes Considered,General approach:analyze a set of representative tubes,Factors which influence vibration characteristics:,velocity-use estimate of,crossflow,but allow for jetting at inlet nozzle,and increased flow at outlet nozzle,tube support-take account of baffle window,Tubes Considered,Baffles-Window and overlap regions:,Window Region-Tube supported at every,second baffle,Baffle overlap-Tube supported at every baffle,Baffles-Consider vertical or horizontal cut,Tubes Considered,Consider number of tube supports and their spacing-determines tube rows examined,Key locations are:,Top tube row:affected by inlet effects,Row just outside baffle overlap-in window region,but experiences the,crossflow,velocity,Row inside baffle overlap,Bottom tube row:experiences total,flowrate,above outlet nozzle,Tubes Considered,Tube rows for considered for single segmental baffles,tubes in window,1=Top tube row,2=Row outside baffle overlap,4=Row in baffle overlap,5=Bottom tube row,1,2,4,5,Tube Rows Considered,Tube rows for considered for single segmental baffles,NTIW,3,4,3=Top tube row,4=Row in baffle overlap,Tube Rows Considered,Summary,Vibration Phenomena,Two types -RESONANCE and INSTABILITY,Resonance occurs when the natural frequency coincides with a resonant frequency,Fluid elastic instability,TASC Velocity Calculations,These are based on the minimum flow area and allow for:,bundle by-passing and baffle leakage,change in density along the unit,changes in flow direction,crossflow,penetration into the window,jetting at the inlet nozzle,Problem Areas,What velocity should be used in calculations?,Flow is complicated by,Bypass and leakage flows,Flow around baffles,Nozzles and impingement plates,Natural Frequency-Straight Tubes,Increasing number of spans,Note:TASC considers the fundamental frequency only,E,=Youngs modulus,l,B,=span length,I,=second moment of area,m,e,=effective mass per unit length,Effect of,endspan,length,l,E,different from mid-span length,Natural frequency of U-bends,Graphs are available for,C,u,value depends on straight tube leg length and configuration,U-bend with blanking baffle,U-bend with unequal leg lengths,Turbulent Buffeting,Resonance Problem,Random spectrum of frequencies in turbulent flow modified if there is cross flow over a tube bundle,Only normally a problem if gas is on,shellside,and“triple coincidence”:,Vortex Shedding,Resonance Problem,S=,Strouhal,number(measured),Caused by breakdown of boundary layer,S is a function of tube layout and pitch/diameter,Only normally a problem if,triple coincidence,Acoustic Resonance,Acoustic wave set up,f,a,=,N,mn,C,/,D,s,N,mn,=constant(0.5861 for fundamental mode),C,=velocity of sound in fluid,D,s,=shell diameter,45 degree layouts prone to this problem,normally only occurs if gas/,vapour,on the shell side,Fluid Elastic Instability,Slight movement of tubes causes changes in pressure field,Acts as+,ve,feedback,Pitch of tubes only limit on amplitude,System becomes unstable when,energy absorbed energy dissipated,Energy is dissipated by,Damping,FLOW,Fluid Elastic Instability,Equation for critical velocity,u,crit,d,=,log-decrement,-a measure of damping,f,n,=natural frequency,D,o,=tube o.d.,m,e,=effective tube mass,K=instability constant,Experimental work by HTFS and other has established,d,and,K,TASC integrates along tubes,Results from TASC,Listed for each exchanger in turn(up to 12),Summary or detailed results,Possible problems indicated by,*,warnings given when,TASC Summary Output,TASC Output(continued),TASC Detailed Output,*,TABLE OF VIBRATION PREDICTIONS,*,-,I TUBE I DESCRIPTION I LOCATION I SPAN I FLOW MOM.FLUX I -VORTEX SHEDDING -I-TURBULENT BUFF-I,I POSN I I I LENGTH I VEL.RV,*,2 I STRN FV/FN FV/FA I FT/FN FT/FA I,-,I 1 I TOP TUBE ROW I INLET I 626.58 I 2.78 6788.61 I 0.80 0.66 0.11 I 0.53 0.09 I,I I IN BUNDLE I MIDSPACE I 179.55 I 0.40 145.82 I 0.40 0.05 0.01 I 0.01 0.00 I,I I I OUTLET I 626.58 I 0.11 11.78 I 0.80 0.01 0.00 I 0.00 0.00 I,-,I 2 I FIRST TUBE ROW I INLET I 806.13 I 0.19 33.16 I 0.80 0.04 0.00 I 0.01 0.00 I,I I OUTSIDE BAFFLE OVERLAP I MIDSPACE I 359.11 I 0.67 396.99 I 0.40 0.14 0.01 I 0.03 0.00 I,I I I OUTLET I 626.58 I 0.19 32.06 I 0.80 0.04 0.00 I 0.01 0.00 I,-,I 4 I FIRST TUBE ROW I INLET I 626.58 I 0.16 23.02 I 0.80 0.02 0.00 I 0.00 0.00 I,I I INSIDE BAFFLE OVERLAP I MIDSPACE I 179.55 I 0.56 275.69 I 0.40 0.07 0.01 I 0.01 0.00 I,I I I OUTLET I 626.58 I 0.16 22.27 I 0.80 0.02 0.00 I 0.00 0.00 I,-,I 5 I BOTTOM TUBE ROW I INLET I 626.58 I 0.12 12.18 I 0.80 0.01 0.00 I 0.00 0.00 I,I I IN BUNDLE I MIDSPACE I 179.55 I 0.40 145.82 I 0.40 0.05 0.01 I 0.01 0.00 I,I I I OUTLET I 626.58 I 1.25 1410.63 I 0.80 0.30 0.05 I 0.24 0.04 I,-,*,TABLES OF FLUID ELASTIC INSTABILITY ASSESSMENT,*,-DAMPING-ESTIMATED-,I TUBE I DESCR:HEAVY TYPICAL LIGHT I I TUBE I DAMPING I RATIO I,I POSN I L DEC:0.1 0.03 0.01 I I POSN I L DEC I W/WC I,-,I 1 I W/WC:0.08 0.14 0.25 I I 1 I 0.038 I 0.127 I,I 2 I 0.16 0.28 0.49 I I 2 I 0.044 I 0.233 I,I 4 I 0.07 0.12 0.21 I I 4 I 0.038 I 0.106 I,I 5 I 0.11 0.20 0.34 I I 5 I 0.038 I 0.177 I,-,