Non-equilibrium thermal fluctuations of flow in thermal systems

2021 ◽  
pp. 1-13
Author(s):  
Wei Li
Keyword(s):  
Brownian Motion ◽  
Experimental Evidence ◽  
Temperature Difference ◽  
Cooling Tower ◽  
Fluid Motion ◽  
Thermal Fluctuations ◽  
Space And Time ◽  
Wave Element ◽  
Scientific Testing ◽  
Non Equilibrium

Abstract Fouling is detrimental to the heat transfer performance of concentrated solar power (CSP) plant components where heat exchange takes place with the cooling tower water. Wave elements cause an expression of deep insight of the fouling formation. A wave element is the wave interface between two molecule groups with different temperatures in flow; it is generated by density difference, which results from temperature difference. Tiny temperature differences always exist everywhere in a fluid. When a fluid is in motion, wave elements are generated among molecule groups. Wave motion and Brownian motion can be the two basic forms of motion of the molecules in flow. Temperature controls Brownian motion. Temperature differences and the fluid's motion cause the wave elements. Non-equilibrium thermal fluctuations present as wave elements in a flow. A wave element appears as wave behavior along the space and time dimensions that are based on the continuity relation. The direct experimental evidence for wave elements cannot be directly established at the present scientific testing capability because the temperature difference of two molecule groups adjoining each other in a flow is infinitesimal. A series of “enlarged size” experiments are conducted involving the cooling tower water fouling to show the wave elements' behaviors by tracing the molecules' movement. The experimental study presents that the wave interface along the space and time dimensions simultaneously exists between two densities due to fluid motion. The experimental evidence and theoretical analysis support each other.

Non-Equilibrium Thermal Fluctuation in Flow

2020 ◽  
Author(s):  
Wei Li
Keyword(s):  
Brownian Motion ◽  
Temperature Difference ◽  
Wave Motion ◽  
Thermal Fluctuation ◽  
Thermal Fluctuations ◽  
Oscillatory Behavior ◽  
Space And Time ◽  
Wave Element ◽  
Scientific Testing ◽  
Non Equilibrium

Abstract Non-equilibrium thermal fluctuations present as wave elements in a flow. A wave element is the wave interface between two molecule groups with different temperature; it is generated by density difference which results from temperature difference. Tiny temperature differences always exist everywhere in a fluid. When the fluid is in motion, wave elements are generated among molecule groups. Wave motion and Brownian motion may be the two basic forms of motion of molecules in flow. Brownian motion is controlled by temperature. Wave elements are caused by temperature differences and the motion of the fluid. Wave motion maybe the physical mechanism of convective heat transfer. Non-equilibrium thermal fluctuations exist everywhere among molecule groups in a flow. The theoretical analysis presents that a wave element presents oscillatory behavior along the space and time dimensions simultaneously. The experimental evidence for wave elements can not be directly established at present scientific testing capability because the temperature difference of two molecule groups adjoining to each other in a flow is very small. A series of “enlarged size” experiments of fouling to show the behaviors of wave elements by tracing the movement of molecules are conducted. The experimental study of fouling presents that oscillatory interface along the space and time dimensions simultaneously exists between two densities due to motion of the fluids. The experimental and theoretical analyses are supported to each other.

The Fluctuating Lattice Boltzmann

2018 ◽  
Author(s):  
Sauro Succi
Keyword(s):  
Brownian Motion ◽  
Fluid Flow ◽  
Lattice Boltzmann ◽  
Thermal Fluctuations ◽  
Directed Motion ◽  
Statistical Fluctuations ◽  
Lattice Boltzmann Models ◽  
Motion Versus ◽  
The Way

Fluid flow at nanoscopic scales is characterized by the dominance of thermal fluctuations (Brownian motion) versus directed motion. Thus, at variance with Lattice Boltzmann models for macroscopic flows, where statistical fluctuations had to be eliminated as a major cause of inefficiency, at the nanoscale they have to be summoned back. This Chapter illustrates the “nemesis of the fluctuations” and describe the way they have been inserted back within the LB formalism. The result is one of the most active sectors of current Lattice Boltzmann research.

Brownian Motion

2018 ◽  
pp. 1-24
Author(s):  
Giovanni Zocchi
Keyword(s):  
Brownian Motion ◽  
Statistical Mechanics ◽  
Concentration Gradient ◽  
Nonequilibrium Statistical Mechanics ◽  
Thermal Fluctuations ◽  
Nonequilibrium System ◽  
Individual Particle ◽  
Equilibrium Concept ◽  
Self Diffusion ◽  
Main Ideas

This chapter provides an introduction to the main ideas of Brownian motion. Brownian motion connects equilibrium and nonequilibrium statistical mechanics. It connects diffusion—a nonequilibrium phenomenon—with thermal fluctuations—an equilibrium concept. More precisely, diffusion with a net flow of particles, driven by a concentration gradient, pertains to a nonequilibrium system, since there is a net current. Without a concentration gradient, the system is macroscopically in equilibrium, but each individual particle undergoes self-diffusion just the same. In this sense, Brownian motion is at the border of equilibrium and nonequilibrium statistical mechanics.

scholarly journals Thermal Fluctuations in Electric Circuits and the Brownian Motion

2010 ◽  
Vol 61 (4) ◽  
pp. 252-256 ◽  
Author(s):  
Gabriela Vasziová ◽  
Jana Tóthová ◽  
Lukáš Glod ◽  
Vladimír Lisý
Keyword(s):  
Brownian Motion ◽  
Brownian Particle ◽  
Mean Square Displacement ◽  
Thermal Fluctuations ◽  
Stochastic Equations ◽  
Thermal Bath ◽  
Current Fluctuations ◽  
Electric Circuits ◽  
The Mean ◽  
Optically Trapped

Thermal Fluctuations in Electric Circuits and the Brownian MotionIn this work we explore the mathematical correspondence between the Langevin equation that describes the motion of a Brownian particle (BP) and the equations for the time evolution of the charge in electric circuits, which are in contact with the thermal bath. The mean quadrate of the fluctuating electric charge in simple circuits and the mean square displacement of the optically trapped BP are governed by the same equations. We solve these equations using an efficient approach that allows us converting the stochastic equations to ordinary differential equations. From the obtained solutions the autocorrelation function of the current and the spectral density of the current fluctuations are found. As distinct from previous works, the inertial and memory effects are taken into account.

Micromachined Linear Brownian Motor: A Nanosystem Exploting Brownian Motion of Nanobeads for Uni-directional Transport

2008 ◽  
Vol 1096 ◽  
Author(s):  
Ersin Altintas ◽  
Edin Sarajlic ◽  
Karl F. Bohringer ◽  
Hiroyuki Fujita
Keyword(s):  
Brownian Motion ◽  
Three Dimensional ◽  
Thermal Fluctuations ◽  
Random Motion ◽  
Microfluidic Channels ◽  
Switching Sequence ◽  
Brownian Motor ◽  
Speed Performance ◽  
Random Fluctuations ◽  
Directional Transport

AbstractNanosystems operating in liquid media may suffer from random thermal fluctuations. Some natural nanosystems, e.g. biomolecular motors, which survive in an environment where the energy required for bio-processes is comparable to thermal energy, exploit these random fluctuations to generate a controllable unidirectional movement. Inspired by the nature, a transportation system of nanobeads achieved by exploiting Brownian motion were proposed and realized. This decreases energy consumption and saves the energy compared to ordinal pure electric or magnetic drive. In this paper we present a linear Brownian motor with a 3-phase electrostatic rectification aimed for unidirectional transport of nanobeads in microfluidic channels. The transport of the beads is performed in 1 μm deep, 2 μm wide PDMS microchannels, which constrain three-dimensional random motion of nanobeads into 1D fluctuation, so-called tamed Brownian motion. We have experimentally traced the rectified motion of nanobeads and observed the shift in the beam distribution as a function of applied voltage. The detailed computational analysis on the importance of switching sequence on the speed performance of motor is performed and compared with the experimental results showing a good agreement.

Hydrodynamic diffusion in active microrheology of non-colloidal suspensions: the role of interparticle forces

2015 ◽  
Vol 785 ◽  
pp. 189-218 ◽  
Author(s):  
N. J. Hoh ◽  
R. N. Zia
Keyword(s):  
Brownian Motion ◽  
External Force ◽  
Hydrodynamic Limit ◽  
Thermal Fluctuations ◽  
Longitudinal Force ◽  
Experimental Measurements ◽  
Interparticle Forces ◽  
Pair Density ◽  
Far From Equilibrium

Hydrodynamic diffusion in the absence of Brownian motion is studied via active microrheology in the ‘pure-hydrodynamic’ limit, with a view towards elucidating the transition from colloidal microrheology to the non-colloidal limit, falling-ball rheometry. The phenomenon of non-Brownian force-induced diffusion in falling-ball rheometry is strictly hydrodynamic in nature; in contrast, analogous force-induced diffusion in colloids is deeply connected to the presence of a diffusive boundary layer even when Brownian motion is very weak compared with the external force driving the ‘probe’ particle. To connect these two limits, we derive an expression for the force-induced diffusion in active microrheology of hydrodynamically interacting particles via the Smoluchowski equation, where thermal fluctuations play no role. While it is well known that the microstructure is spherically symmetric about the probe in this limit, fluctuations in the microstructure need not be – and indeed lead to a diffusive spread of the probe trajectory. The force-induced diffusion is anisotropic, with components along and transverse to the line of external force. The latter is identically zero owing to the fore–aft symmetry of pair trajectories in Stokes flow. In a naïve first approach, the vanishing relative hydrodynamic mobility at contact between the probe and an interacting bath particle was assumed to eliminate all physical contribution from interparticle forces, whereby advection alone drove structural evolution in pair density and microstructural fluctuations. With such an approach, longitudinal force-induced diffusion vanishes in the absence of Brownian motion, a result that contradicts well-known experimental measurements of such diffusion in falling-ball rheometry. To resolve this contradiction, the probe–bath-particle interaction at contact was carefully modelled via an excluded annulus. We find that interparticle forces play a crucial role in encounters between particles in the hydrodynamic limit – as they must, to balance the advective flux. Accounting for this force results in a longitudinal force-induced diffusion $D_{\Vert }=1.26aU_{S}{\it\phi}$, where $a$ is the probe size, $U_{S}$ is the Stokes velocity and ${\it\phi}$ is the volume fraction of bath particles, in excellent qualitative and quantitative agreement with experimental measurements in, and theoretical predictions for, macroscopic falling-ball rheometry. This new model thus provides a continuous connection between micro- and macroscale rheology, as well as providing important insight into the role of interparticle forces for diffusion and rheology even in the limit of pure hydrodynamics: interparticle forces give rise to non-Newtonian rheology in strongly forced suspensions. A connection is made between the flow-induced diffusivity and the intrinsic hydrodynamic microviscosity which recovers a precise balance between fluctuation and dissipation in far from equilibrium suspensions; that is, diffusion and drag arise from a common microstructural origin even far from equilibrium.

scholarly journals Experimental evidence of thermal fluctuations on the x-ray absorption near-edge structure at the aluminumKedge

2012 ◽  
Vol 85 (22) ◽  
Author(s):  
D. Manuel ◽  
D. Cabaret ◽  
Ch. Brouder ◽  
Ph. Sainctavit ◽  
A. Bordage ◽  
...  
Keyword(s):  
Experimental Evidence ◽  
Thermal Fluctuations ◽  
Edge Structure ◽  
X Ray ◽  
X Ray Absorption

scholarly journals The Effect of Air Parameters on the Evaporation Loss in a Natural Draft Counter-Flow Wet Cooling Tower

Energies ◽  
2020 ◽  
Vol 13 (23) ◽  
pp. 6174
Author(s):  
Wei Yuan ◽  
Fengzhong Sun ◽  
Ruqing Liu ◽  
Xuehong Chen ◽  
Ying Li
Keyword(s):  
Temperature Difference ◽  
Heat Dissipation ◽  
Cooling Tower ◽  
Air Humidity ◽  
Counter Flow ◽  
Natural Draft ◽  
Evaporation Loss ◽  
Relative Air Humidity ◽  
Evaporation Heat ◽  
Rate Of Evaporation

The measures to reduce the impact of evaporation loss in a natural draft counter-flow wet cooling tower (NDWCT) have important implications for water conservation and emissions reduction. A mathematical model of evaporation loss in the NDWCT was established by using a modified Merkel method. The NDWCTs in the 300 MW and 600 MW power plant were taken as the research objects. Comparing experimental values with calculated values, the relative error was less than 3%. Then, the effect of air parameters on evaporation loss of NDWCT was analyzed. The results showed that, with the increase of dry bulb temperature, the evaporation heat dissipation and the evaporation loss decreased, while the rate of evaporation loss caused by unit temperature difference increased. The ambient temperature increased by 1 °C and the evaporation loss was reduced by nearly 26.65 t/h. When the relative air humidity increased, the evaporation heat dissipation and evaporation loss decreased, and the rate of evaporation loss caused by unit temperature difference decreased. When relative air humidity increased by 1%, the outlet water temperature rose by about 0.08 °C, and the evaporation loss decreased by about 5.63 t/h.

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