Large fluctuations during the Boiling Crisis
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1 Urbana Champaign, May 2011 Large fluctuations during the Boiling Crisis Eduard Vives (1), Francesc Salvat-Pujol (2), Pol Lloveras (1,3), & Lev Truskinovsky (3) 1 Dept. Estructura i Constituents de la Matèria Facultat de Física, Universitat de Barcelona Barcelona, Catalonia 2 Institut für Angewandte Physik Technische Universität Wien Wien Austria 3 LMS, CNRS UMR 7649, École Polytechnique, Palaiseau, France 1
2 Outline: Urbana Champaign, May Introduction Thermodynamics: pool boiling Classical dimensional analysis Recent advances 2-AE experiments Experimental Setup Avalanche counting Avalanche energy distributions 3-Modelling 4-Conclusions Introductory references the to boiling crisis problem -J.H.Lienhard Snares of pool boiling research (1995). -V.K.Dhir Boiling Heat Transfer, Annu. Rev. Fluid Mech (1998). -V.K.Dhir, H.S.Abarajith & G.R.Warrier From Nano to micro to macro scales in boiling, Microscale Heat transfer (2005). -V.K.Dhir Mechanistic prediction achievable or a hopeless task? Journal of heat Transfer 128, 1 (2006). 2
3 Urbana Champaign, May Introduction 3
4 Thermodynamics of boiling: Urbana Champaign, May 2011 Boiling is a first-order phase transition with a scalar OP: molar volume v Equilibrium phase diagram: Phases with different v coexist exactly at T eq P liquid v low simple fluid But: as many first-order phase transitions it hardly occurs in equilibrium, v high vapour T It requires the creation of interfaces bubble growth fluid motion T eq 4
5 Pool boiling Urbana Champaign, May 2011 There are many ways of boiling a liquid. The simplest case is pool boiling (kitchen), in which convection is natural (no imposed flow) And gravity is vertical, pointing down Control variable: heat flux Φ = ε / SS T Measured variable: temperature TOther mechanism: external flow boiling ε,i internal flow boiling immersion 5
6 Nukiyama curve S. Nukiyama J. Soc. Mech. Eng. Jpn 37, 53 & 367 (1934) Log Φ CHF Φ max Φ min Log (T-T eq ) Urbana Champaign, May 2011 V.K.Dhir, Journal of heat transfer 128, 1 (2006) 6
7 Boiling regimes Urbana Champaign, May 2011 Log Φ CHF Φ max Natural convection Nucleate boiling Crisis Transition Film boiling Log (T-T eq ) 10
8 Driving parameter Control variable: heat flux Urbana Champaign, May 2011 Hysteresis Enormous increase of T when crisis is reached BOILING CRISIS Log Φ Log (T-T eq ) 11
9 Driving parameter Control variable: temperature (difficult to perform) Urbana Champaign, May 2011 Hysteresis? Claims that no hysteresis in well wetted conditions Log Φ? Log (T-T eq ) 12
10 Urbana Champaign, May V.K.Dhir, Journal of heat transfer 128, 1 (2006) Complexity of the problem transitionradiationconvectionconductionφ + + Φ + Φ Φ = Φ
11 ()Dimensional analysis (1) Urbana Champaign, May 2011 When approaching the crisis from low T, the main = xvcontribution to Φ: Φ = Gρ Length & time scales in the problem? three energetic contributions: 42energy for creating a bubble: 4/-Excess R3-Potential energy (buoyancy force): LG143π ρ ρ R3V 2-Kinetic energy: 23π Gρ One can construct two equalities from these 3 terms and determine: 1σ ( ) gv= ( )4ρ L ρ Gρ GRπσ gvrrδ RR=Lgσ ρ L ρ G14
12 Dimensional analysis (2) The heat flux is then given by Φ = xlurbana Champaign, May 2011 ρ G( )4gσ ρ L ρ GScales: Kutetaladze 1948 P= Pa N 2 H 2 O Boiling T eq (K) ρ LIQUID (Kg/m 3 ) ρ VAPOUR (Kg/m 3 ) σ (N/m) L (kj/kg) R (mm) V (m/s) Φ/X (W/cm 2 ) Φ max (X=0.16)
13 Urbana Champaign, May 2011 Far-field models Almost identical formulas can be obtained from the study of far-field models (hydrodynamics, instability of a vapor jet, etc..) Zuber 1959 The parameter X contains, besides the fraction of surface covered by vapour, all the other adimensional dependences, geometrical factors and other correction coefficients (wettability, aging of the heater surface, etc ) Experimentally, critical heat flux Φ max in flat surfaces, corresponds to X=
![approaching the critical point L KZ1/4 [ σ ( ρ ρ )]](/docs-images/88/114793249/images/14-3.jpg "α( ) L Geq ϖ xv( ) 'TTNikolayexTα eqt ϖ smaller")
14 mamarecent advances: near surface models Recoil force mechanism Urbana Champaign, May 2011 Nikolayev et al. PRL 97, (2006) Recoil force increases with the evaporation rate and is opposed to bubble detaching. When this force wins, the gas film spreads and produces the crisis Φ Φ Dependence of Φ max when approaching the critical point L KZ1/4 [ σ ( ρ ρ )] α( ) L Geq ϖ xv( ) 'TTNikolayexTα eqt ϖ smaller scales play a role 17
15 Gravity dependence 4Very important for space-crafts Urbana Champaign, May 2011 Some results do not agree with the dependence -Relative fluctuations Φ x1δφ maφ max 4x-Spatially resolved heat flux, But measurements at low g (large fluctuations) are rather stable g ma( ) ggδ shows that in the boiling regions the flux is independent of gravity The effect of gravity is on the dry surface x(g) Kim & Benton Int. J. Heat Fluid Flow 23, 497 (2002) 18
16 Burnout experiments (1) Urbana Champaign, May 2011 Theofanous et al. Experimental Thermal and Fluid Science 26, 775 & 793 (2002) Powerful imaging techniques (Optical microscopy, thermography, and X-rays) with spatial and temporal resolution - Cold, Hot & Dry spots -Strong temperature fluctuations: (larger than 10%) Water 122 W/cm 2 19
17 Burnout experiments (2) Urbana Champaign, May 2011 Theofanous, Tu, Dinh & Dinh Experimental Thermal and Fluid Science 26, 775 & 793 (2002) - Existence of a liquid microlayer Water 100 W/cm 2 Water 150 W/cm 2 20
18 Urbana Champaign, May 2011 Experiments 21
19 ()Acoustic Emission Urbana Champaign, May 2011 Scruby J.Phys.E: Sci Instr. 20 (1987) Sources of AE (detected on the metal): - Liquid flow Continuous signals - Nucleation of a bubbles (creation of interfaces) - Acceleration of liquid-gas interface Intermittent bursts Standard analysis: AE is used for monitoring industrial processes. Most studies focus on spectral analysis. Avalanche analysis -separate the continuous noise -identify pulses statistical analysis V E= 01t R t2d[ ] DVt22
20 ()Boiling by immersion Urbana Champaign, May 2011 Immersing a hot metal into a liquid is an easy way to access the boiling Φ(ΔT) curve T.W.Listerman et al. AJP 54, 554 (1986)dAl cylinder at room T in a liquid N 2 bath Φ = 1dQd= SmCSpTdT23
21 Experimental setup: piezoelectric transducer preamplifier Urbana Champaign, May 2011 Al PCI-2 EPAC neck Pt-100 resistor head (Sample) microscope N 2 Dewar flask 24
22 Optical images (Δt=1s) Urbana Champaign, May mm 25
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35 ()Experimental Nukiyama curve Φ = 1dQSd= mctdtpsdurbana Champaign, May 2011 The experiment is not designed for a pool-boiling Nukiyama curve -Dynamic experiment: Delay with respect to the stationary curve -Cylindrical geometry: Different regimes simultaneously for vertical and horizontal faces ΔT/T eq -Heat transfer through the neck: Pure natural convection regime and early stages of nucleate boiling regime are never reached 40
36 AE raw signal: typical result Urbana Champaign, May
37 Pulse counting (b) Transition and crisis Urbana Champaign, May 2011 (a) Film boiling (c) Nucleate boiling 42
38 )Energy distributions P(E) (b) (a) (c) one count EpdEEE 2.τ frequency frequency frequency1where(± τd 050.Urbana Champaign, May 2011 uniform power law power law (+ cutoff) 45
39 Urbana Champaign, May 2011 Simulations 46
40 Model Lattice model (Lx=50)x(Ly=50)x(Lz=20) Urbana Champaign, May 2011 Liquid reservoir Fixed temperature T eq Liquid/Vapor S i =-1,1 Initially T i =T eq, S i =-1 Heater Quenched Gaussian distribution of T around T M ±σ with T M >T eq 49
41 Simulation steps Urbana Champaign, May 2011 Initial condition: all sites liquid at T t 1 Thermal equilibration: A-Heat transfer (Fourier equation) B-Decision on transition/overcooling/overheating C-Phase transition + new T 2 Mechanical equilibration: Drift + filling the voids 50
42 Urbana Champaign, May 2011 Model parameters: N 2 at atmospheric pressure N 2 Boiling T eq (K) ρ LIQUID (Kg/m 3 ) ρ VAPOUR (Kg/m 3 ) 4.6 τ (N/m) K LIQUID (J/mKs) K VAPOUR (J/mKs) C LIQUID (J/Kg K) 2042 Free: T M σ= 0.1 a= 1mm Δt= 1ms C VAPOUR (J/Kg K) L (kj/kg)
43 Simulation results Urbana Champaign, May 2011 Convection and radiation not included We associate each acoustic signal to a single numerical bubble ΔT/T eq 52
44 Urbana Champaign, May 2011 Critical distribution of bubble sizes at the crisis 53
45 Urbana Champaign, May 2011 Conclusions 54
46 )Conclusions Urbana Champaign, May 2011 Experimental analysis of acoustic emission activity during the boiling crisis as an avalanche process (± Energy distribution of acoustic signals has no characteristic scale, approximating well to a power-law behavior with exponent1 τe τ This is indicative Ep of the existence of critical phenomena associated with the boiling crisis Simple near hot surface model describes well the lack of characteristic scale in the bubble size when approaching the crisis. It supports the origin of the boiling crisis to lie just close to the hot surface (percolation of bubbles) The agreement with experimental exponent suggests that energy of acoustic signals only depends on the contact area between bubble and hot surface 55
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