超临界压力下二元混合物的湍流管道流动和传热:交叉扩散效应的影响

IF 4.1 2区 工程技术 Q1 MECHANICS Physics of Fluids Pub Date : 2024-09-10 DOI:10.1063/5.0221800
Yangjian Ren, Mingfei Xiao, Zhan-Chao Hu
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引用次数: 0

摘要

交叉扩散效应,包括索雷特效应和杜富尔效应,在二元混合物的伪临界温度(Tpc)附近会增强。目前还很少研究它们对超临界压力下传热的影响。为了弥补这一差距,我们进行了大涡流模拟(LES),研究了在超临界压力下,圆形管道中的二氧化碳-乙烷混合物在均匀热通量作用下的强制对流传热。模拟中包括加热和冷却条件,以及不同的初始浓度和热力学压力。LES 结果表明,索雷特效应会导致浓度分离,形成浓度边界层。热扩散因子(kT)和径向温度梯度的大小控制着分离的强度,在接近临界压力和高热通量时分离更为明显。由于 kT 仅在 Tpc 附近显著,当 T=Tpc 的位置远离壁面时,会观察到浓度分离的下游衰减,从而使局部径向温度梯度减小。影响传热的主要因素是浓度分离导致的热导率和等压比热的变化。相比之下,杜富尔效应和伴随的相互扩散作用可以忽略不计。在劣化情况下,体积努塞尔特数(Nub)的最大相对降幅为 8%,而在增强情况下,Nub 的最大相对升幅为 10%,劣化和增强都在下游衰减。交叉扩散效应对密度和流向速度的影响可以忽略不计,但会明显改变流向速度波动和湍流动能。
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Turbulent pipe flow and heat transfer of a binary mixture at supercritical pressure: Influences of cross-diffusion effects
Cross-diffusion effects, including Soret and Dufour effects, are enhanced around the pseudo-critical temperature (Tpc) of a binary mixture. Their influences on heat transfer at supercritical pressure have been scarcely studied. To bridge this gap, large-eddy simulations (LES) are conducted to investigate forced convective heat transfer of a CO2–ethane mixture at supercritical pressures in a circular pipe subject to a uniform heat flux. Both heating and cooling conditions, along with varying initial concentrations and thermodynamic pressures, are included in the simulations. The LES results reveal that the Soret effect causes concentration separation, resulting in a concentration boundary layer. The magnitudes of the thermodiffusion factor (kT) and the radial temperature gradient control the intensity of separation, which is more pronounced at near-critical pressure and high heat flux. Since kT is significant only around Tpc, downstream decay of the concentration separation is observed as the loci of T=Tpc migrate away from the wall so that the local radial temperature gradient diminishes. The primary factors affecting heat transfer are the variations in thermal conductivity and isobaric specific heat resulting from concentration separation. In contrast, the Dufour effect and the accompanying inter-diffusion play negligible roles. In deterioration scenarios, the bulk Nusselt number (Nub) shows a maximum relative drop of 8%, whereas in enhancement scenarios, Nub shows a maximum relative increase in 10%, with both deterioration and enhancement decaying downstream. Cross-diffusion effects have negligible impacts on density and streamwise velocity, but noticeably alter streamwise velocity fluctuation and turbulent kinetic energy.
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来源期刊
Physics of Fluids
Physics of Fluids 物理-力学
CiteScore
6.50
自引率
41.30%
发文量
2063
审稿时长
2.6 months
期刊介绍: Physics of Fluids (PoF) is a preeminent journal devoted to publishing original theoretical, computational, and experimental contributions to the understanding of the dynamics of gases, liquids, and complex or multiphase fluids. Topics published in PoF are diverse and reflect the most important subjects in fluid dynamics, including, but not limited to: -Acoustics -Aerospace and aeronautical flow -Astrophysical flow -Biofluid mechanics -Cavitation and cavitating flows -Combustion flows -Complex fluids -Compressible flow -Computational fluid dynamics -Contact lines -Continuum mechanics -Convection -Cryogenic flow -Droplets -Electrical and magnetic effects in fluid flow -Foam, bubble, and film mechanics -Flow control -Flow instability and transition -Flow orientation and anisotropy -Flows with other transport phenomena -Flows with complex boundary conditions -Flow visualization -Fluid mechanics -Fluid physical properties -Fluid–structure interactions -Free surface flows -Geophysical flow -Interfacial flow -Knudsen flow -Laminar flow -Liquid crystals -Mathematics of fluids -Micro- and nanofluid mechanics -Mixing -Molecular theory -Nanofluidics -Particulate, multiphase, and granular flow -Processing flows -Relativistic fluid mechanics -Rotating flows -Shock wave phenomena -Soft matter -Stratified flows -Supercritical fluids -Superfluidity -Thermodynamics of flow systems -Transonic flow -Turbulent flow -Viscous and non-Newtonian flow -Viscoelasticity -Vortex dynamics -Waves
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