Lattice Boltzmann simulation of nucleate boiling in micro-pillar structured surface

Transcription

1 Proceedngs of the Asan Conference on Thermal Scences 017, 1st ACTS March 6-30, 017, Jeju Island, Korea ACTS-P00545 Lattce Boltzmann smulaton of nucleate bolng n mcro-pllar structured surface Png Zhou, Zhchun Lu*, We Lu *Correspondng Author s Emal: zclu@hust.edu.cn a School of Energy and Power Engneerng, Huazhong Unversty of Scence and Technology, , Wuhan, Chna ABSTRACT A lattce Boltzmann method of two partcle dstrbuton functons, namely the densty dstrbuton functon and the temperature dstrbuton functon, s used to smulate perodc bubble nucleaton, growth and departure from a mcro-pllar structured surface. Pseudo-potental model and Peng-Robnson equatons of state are selected n our smulatons. Constant temperature boundary condton s appled n the bottom sold. It s fund that bubble generated n the vcnty of the mcro-pllars, whch ndcates that mcro-structure can contrbute to the nucleaton of the flud. Results mpled that characterstc scales of mcro-pllars have obvous effects on the growth of the bubble. Specfcally, we nvestgated the nfluence of the dstance between two pllars on the bubble growth. Results show that, to some extent, bubble departure perod and bubble departure dameter are decrease wth the ncrease of the dstance of two mcro-pllars. Dfferent mcro-pllar characterstc scales, manly nclude the heght of the pllar, the dstance of two pllars and the sde length of the pllar, also have varous effects n bubble growth, and a crtcal characterstc scale exsts for hgh bubble departure frequency and bg bubble departure dameter respectvely. KEYWORDS: lattce Boltzmann method, bubble departure dameter, bubble departure frequency, mcro-pllar structured surface 1. INTRODUCTION Heat dsperson of mcro-electron devces s of mportant sgnfcance for the development of aerospace engneerng and ntegrated chps. Loop heat ppe and mcro-channel are confrmed to be effectve means for heat dsperson n hgh heatng flux mcro-electron devces[1-4]. Nevertheless, mprove thermal dsspaton performance s a bg challenge n relate to fast-developng hgh ntegrated crcut. Nucleate bolng s an mportant phase change heat transfer process, whch can sgnfcantly enhance heat transfer n mcro-channel, a great deal of research has been made to enhance nucleate bolng, manly focused on mcro- or nano-structured surface[5]. KH Chu et al. [6, 7] and Jnsub Km et al.[8] ran a seres of experments about the effectve of mcro-structured surface roughness to nucleate bolng, especally to crtcal heat flux(chf). They found that CHF has an obvous mprove when the roughness mproved, up to 50W/cm at t s maxmum. Y Zhu et al. [9] and HJ Cho et al. [10] carred out experments n mcro-channel wth structured surface, they thnk mcro-structure decrease the surface tenson between lqud and vapor thereby ncrease the bubble departure frequency, mcro-structure also ncreases nucleate ste of the surface, these all conduce to nucleate bolng heat transfer. In addton, Cho attrbutes bolng enhancement manly to adsorpton to the sold-lqud nterface. Seol Ha Km et al. [11] conducted a set of experments show that bolng heat transfer(bht) ncreases wth the surface roughness, defned as the rato of the rough surface area to the projected area, but ths enhancement gradually slows, the heat transfer coeffcent of the structured surface s more than 300% that of the bare surface, the structured surface shows a 350% mprovement n CHF over the bare surface. Smulaton studes about nucleate bolng on structured surface are scanty n contrary wth consderable experment research. Recently, Gong and Chen nvestgated bubble nucleaton, growth and departure from a sngle cavty on the 1

2 top of a unformly hydrophlc heater and a unformly hydrophobc heater at low superheats numercally based on a two partcle dstrbuton functons lqud vapor phase-change lattce Boltzmann method [1, 13]. Utlzng ths method, we smulated nucleate bolng n a structured surface wth mcro-pllars, and part of our results wll be shown n the followng part.. SIMULATIONS AND RESULTS A lattce Boltzmann method of two partcle dstrbuton functons, namely the densty dstrbuton functon and the temperature dstrbuton functon, s used to smulate perodc bubble nucleaton, growth and departure from a mcro-pllar structured surface..1 LATTICE BOLTZMANN METHOD Lattce Boltzmann method conssts of three mportant parts: namely the evoluton equaton of dstrbuton functon, equlbrum dstrbuton functon and the lattce. Dscrete Boltzmann equaton and dscrete passve-scalar equaton are used as the evoluton equaton of densty dstrbuton functon and temperature dstrbuton functon, respectvely. f, f eq, g, and g eq 1 eq (1) f(x+ e δt, t + δt) f(x, t) = ( f(x, t) f (x, t)) + f(x, t) τ ( ) 1 () g(, ) (, ) (, ) (, ) eq x+ eδtt+ δt g xt = g xt g xt + δω t Φ τ f g e u ( e u ) u (3) [1 ] eq = ωρ cs cs cs (4) eq e U ( e U) U = ωt[1 + + ] 4 cs cs cs are densty dstrbuton functon and t s equlbrum dstrbuton and temperature dstrbuton and t s equlbrum dstrbuton, respectvely. D3Q19 lattce are used for our smulaton, as shown n Fg.1, t has nneteen veloctes n one lattce ste n a three degree space.. RESULTS We now smulate the 3D problem of bubble growth and departure from a heated horzontal sothermal surface wth mcro-pllar structure. A 85*85*95 lattce structure s chosen for computaton purposes, the mcro-pllar structure n the bottom s **10, shown as Fg.. Intally, the computaton doman s occuped by the lqud phase at a temperature of Tbulk = 0.93T. Pressure at the top boundary s kept constant and equal to the correspondng c saturaton pressure of T. A constant temperature at bulk Twall = 0.94T s specfed at the bottom wall. Perodc c boundary condtons are mposed on the lateral drecton for a 3D problem.

3 Fg.1 D3Q19 lattce Fg. Mcro-pllar structure n the bottom (n s the dstance of two mcro-pllar n lattce unt). (a) n=6 (b) n=8 3

4 Fg.3 temperature dstrbuton (c) n=10 (a) n=6 (b) n=8 (c) n=10 Fg.4 bubble growth over the pllar (densty dstrbuton) 4

5 We can fnd n the temperature dstrbuton pcture that between the four mcro-pllars a hgh temperature core s formed, so a nucleate ste s actvated and bubble growth ensued. When the dstance of two pllars s 6 lattce unt, the central has the hghest temperature and can perodcally form obvous bubble, wth the ncrease of the dstance, although has a hgh departure frequency, t can t form obvous bubble. 3. CONCLUSIONS A two partcle dstrbuton functons lattce Boltzmann method s adopted to smulate the structured surface nucleate bolng. Results show that bubble generates near the mcro-pllars, and the mcro-structure can ncrease nucleate ste. The dstance of two mcro-pllars has an obvous effect on bubble growth, to some extent, the departure perod and the departure dameter decrease wth the ncrease of the dstance of two pllars. ACKNOWLEDGMENT The work s supported by the the Natonal Natural Scence Foundaton of Chna ( ) and Natonal Key Basc Research Program of Chna (973 Program) (013CB830) REFERENCE [1] He S, Lu Z, Wang D, Zhao J, Lu W, Yang J. Investgaton of the flat dsk-shaped LHP wth a shared compensaton chamber [J]. Appled Thermal Engneerng. 016, 104: [] He S, Lu Z, Zhao J, Jang C, Yang J, Lu W. Expermental study of an ammona loop heat ppe wth a flat plate evaporator[j]. Internatonal Journal of Heat and Mass Transfer, 016, 10: [3] L H, Lu Z C, Chen B B, Lu W, L C, Yang J. Development of bporous wcks for flat-plate loop heat ppe[j]. Expermental Thermal and Flud Scence, 01, 37: [4] Lu Z C, L H, Chen B B, Yang J G, Lu W. Operatonal characterstcs of flat type loop heat ppe wth bporous wck[j]. Internatonal Journal of Thermal Scences, 01, 58: [5] K. Nshkawa, T. Ito, Augmentaton of nucleate bolng heat transfer by prepared surfaces., n: Hemsphere Publ Corp, 1983: pp [6] Chu K H, Enrght R, Wang E N. Structured surfaces for enhanced pool bolng heat transfer[j]. Appled Physcs Letters, 01, 100(4): [7] Chu K H, Joung Y S, Enrght R, et al. Herarchcally structured surfaces for bolng crtcal heat flux enhancement[j]. Appled Physcs Letters, 013, 10(15): [8] Km J, Jun S, Laksnaran R, et al. Effect of surface roughness on pool bolng heat transfer at a heated surface havng moderate wettablty[j]. Internatonal Journal of Heat and Mass Transfer, 016, 101: [9] Zhu Y, Antao D S, Chu K H, et al. Enhanced Flow bolng heat transfer n mcrochannels wth structured surfaces[c]//15th Internatonal Heat Transfer Conference, Paper No. IHTC [10] Cho H J, Sresht V, Blankschten D, et al. Understandng Enhanced Bolng Wth Trton X Surfactants[C]//ASME 013 Heat Transfer Summer Conference collocated wth the ASME 013 7th Internatonal Conference on Energy Sustanablty and the ASME th Internatonal Conference on Fuel Cell Scence, Engneerng and Technology. Amercan Socety of Mechancal Engneers, 013: V00T07A047-V00T07A047. [11] Km S H, Lee G C, Kang J Y, et al. Bolng heat transfer and crtcal heat flux evaluaton of the pool bolng on mcro structured surface[j]. Internatonal Journal of Heat and Mass Transfer, 015, 91: [1] Gong S, Cheng P, Quan X. Two-dmensonal mesoscale smulatons of saturated pool bolng from rough surfaces. Part I: Bubble nucleaton n a sngle cavty at low superheats[j]. Internatonal Journal of Heat and Mass Transfer, 016, 100: [13] Gong S, Cheng P. Two-dmensonal mesoscale smulatons of saturated pool bolng from rough surfaces. Part II: Bubble nteractons above mult-cavtes[j]. Internatonal Journal of Heat and Mass Transfer, 016, 100: