title: Fractal aggregation kinetics contributions to thermal conductivity of nano-suspensions in unsteady thermal convection.
abstract: Nano-suspensions (NS) exhibit unusual thermophysical behaviors once interparticle aggregations and the shear flows are imposed, which occur ubiquitously in applications but remain poorly understood, because existing theories have not paid these attentions but focused mainly on stationary NS. Here we report the critical role of time-dependent fractal aggregation in the unsteady thermal convection of NS systematically. Interestingly, a time ratio λ = tp/tm(tpis the aggregate characteristic time, tmthe mean convection time) is introduced to characterize the slow and fast aggregations, which affect distinctly the thermal convection process over time. The increase of fractal dimension reduces both momentum and thermal boundary layers, meanwhile extends the time duration for the full development of thermal convection. We find a nonlinear growth relation of the momentum layer, but a linear one of the thermal layer, with the increase of primary volume fraction of nanoparticles for different fractal dimensions. We present two global fractal scaling formulas to describe these two distinct relations properly, respectively. Our theories and methods in this study provide new evidence for understanding shear-flow and anomalous heat transfer of NS associated non-equilibrium aggregation processes by fractal laws, moreover, applications in modern micro-flow technology in nanodevices.
authors.affiliation: School of Energy and Environmental Engineering, University of Science and Technology Beijing, Beijing 100083, China.|School of Mathematics and Physics, University of Science and Technology Beijing, Beijing 100083, China.
authors.forename: Jize
authors.initials: J
authors.lastname: Sui
authors.affiliation: School of Chemistry, Beijing Normal University, Beijing 100875, China.
authors.forename: Peng
authors.initials: P
authors.lastname: Zhao
authors.affiliation: Department of Mathematics, King Saud University, Riyadh, Saudi Arabia.
authors.forename: Bandar
authors.initials: B
authors.lastname: Bin-Mohsin
authors.affiliation: School of Mathematics and Physics, University of Science and Technology Beijing, Beijing 100083, China.
authors.forename: Liancun
authors.initials: L
authors.lastname: Zheng
authors.affiliation: School of Energy and Environmental Engineering, University of Science and Technology Beijing, Beijing 100083, China.
authors.forename: Xinxin
authors.initials: X
authors.lastname: Zhang
authors.affiliation: Artie McFerrin Department of Chemical Engineering, Texas A&M University, College Station, Texas 77843, USA.
authors.forename: Zhengdong
authors.initials: Z
authors.lastname: Cheng
authors.affiliation: Guangdong Provincial Key Laboratory of Functional Soft Condensed Matter, Materials and Energy School at Guangdong University of Technology, Guangzhou 510006, China.
authors.forename: Ying
authors.initials: Y
authors.lastname: Chen
authors.affiliation: Department of Mathematics and Institute for Quantum Science and Engineering, Texas A&M University, College Station, TX 77843, USA.|Science Program, Texas A &M University at Qatar, Education City, Doha, Qatar.
authors.forename: Goong
authors.initials: G
authors.lastname: Chen