Liquid Dissipation Research Articles

How Does Heat Propagate in Liquids?

In this paper, we proceed to illustrate the consequences and implications of the Dual Model of Liquids (DML) by applying it to the heat propagation. Within the frame of the DML, propagation of thermal (elastic) energy in liquids is due to wave-packet propagation and to the wave-packets’ interaction with the material particles of the liquid, meant in the DML as aggregates of molecules swimming in an ocean of amorphous liquid. The liquid particles interact with the lattice particles, a population of elastic wave-packets, by means of an inertial force, exchanging energy and momentum with them. The hit particle relaxes at the end of the interaction, releasing the energy and momentum back to the system a step forward and a time lapse later, like in a tunnel effect. The tunnel effect and the duality of liquids are the new elements that suggest on a physical basis for the first time, using a hyperbolic equation to describe the propagation of energy associated to the dynamics of wave-packet interaction with liquid particles. Although quantitatively relevant only in the transient phase, the additional term characterizing the hyperbolic equation, usually named the “memory term”, is physically present also once the stationary state is attained; it is responsible for dissipation in liquids and provides a finite propagation velocity for wave-packet avalanches responsible in the DML for the heat conduction. The consequences of this physical interpretation of the “memory” term added to the Fourier law for the phononic contribution are discussed and compiled with numerical prediction for the value of the memory term and with the conclusions of other works on the same topic.

Stick-slip contact line motion on Kelvin-Voigt model substrates

The capillary traction of a liquid contact line causes highly localized deformations in soft solids, tremendously slowing down wetting and dewetting dynamics by viscoelastic braking. Enforcing nonetheless large velocities leads to the so-called stick-slip instability, during which the contact line periodically depins from its own wetting ridge. The mechanism of this periodic motion and, especially, the role of the dynamics in the fluid have remained elusive, partly because a theoretical description of the unsteady soft wetting problem is not available so far. Here we present the first numerical simulations of the full unsteady soft wetting problem, with a full coupling between the liquid and the solid dynamics. We observe three regimes of soft wetting dynamics: steady viscoelastic braking at slow speeds, stick-slip motion at intermediate speeds, followed by a region of viscoelastic braking where stick-slip is suppressed by liquid damping, which ultimately gives way to classical wetting dynamics, dominated by liquid dissipation.

Viscosity of fused silica and thermal noise from the standard linear solid model

The fluctuation-dissipation theorem states that each source of dissipation yields corresponding fluctuations. The most obvious source of dissipation in liquids is viscosity---internal friction between layers of matter. However, this property also exists in solid materials in a glass state, i.e., an amorphous substance that cannot become a crystal due to high viscosity. Fused silica is a low-loss glass material used in many interferometric applications demanding high stability, such as Fabry-Perot etalons and gravitational-wave detector mirrors and suspensions. Very high viscosity (from $1{0}^{17}$ to $1{0}^{40}\text{ }\mathrm{Pa}\text{ }\mathrm{s}$ in the literature) can be the source of additional noise and can influence the performance of such devices. We show that fused silica may be described with the standard linear solid model of viscoelastisity and present a method to estimate this type of noise.

High-frequency nano-optomechanical disk resonators in liquids.

Nano- and micromechanical resonators are the subject of research that aims to develop ultrasensitive mass sensors for spectrometry, chemical analysis and biomedical diagnosis. Unfortunately, their merits generally diminish in liquids because of an increased dissipation. The development of faster and lighter miniaturized devices would enable improved performances, provided the dissipation was controlled and novel techniques were available to drive and readout their minute displacement. Here we report a nano-optomechanical approach to this problem using miniature semiconductor disks. These devices combine a mechanical motion at high frequencies (gigahertz and above) with an ultralow mass (picograms) and a moderate dissipation in liquids. We show that high-sensitivity optical measurements allow their Brownian vibrations to be resolved directly, even in the most-dissipative liquids. We investigate their interaction with liquids of arbitrary properties, and analyse measurements in light of new models. Nano-optomechanical disks emerge as probes of rheological information of unprecedented sensitivity and speed, which opens up applications in sensing and fundamental science.

The origin of persistent shear stress in supercooled liquids

The persistence of shear stress fluctuations in viscous liquids is a direct consequence of the non-zero shear stress of the local potential minima which couples stress relaxation to transitions between inherent structures. In simulations of 2D and 3D glass forming mixtures, we calculate the distribution of this inherent shear stress and demonstrate that the variance is independent of temperature and obeys a power law in density. The inherent stress is shown to involve only long wavelength fluctuations, evidence of the central role of the static boundary conditions in determining the residual stress left after the minimization of the potential energy. A temperature T(η) is defined to characterise the crossover from stress relaxation governed by binary collisions at high temperatures to low temperature relaxation dominated by the relaxation of the inherent stress. T(η) is found to coincide with the breakdown of the Stokes-Einstein scaling of diffusion and viscosity.

First law analysis for viscous dissipation in liquid flows in micro-channels

This paper focuses on temperature rise due to the viscous dissipation in liquids flowing through micro-channels. In the past, equations for the prediction of the temperature rise have been obtained as a function of the friction factor, Reynolds number and Eckert number or a similar form, starting from Navier–Stokes equation and energy equation under the assumption of fully developed laminar flow by researchers. The temperature rises calculated from the equations have been compared with experimental data and the equations have been validated. However, in this paper, a new equation for the prediction of the temperature rise is simply obtained from the first law of thermodynamics without restriction of fully developed laminar flow.

Intercomparison of cloud model simulations of Arctic mixed-phase boundary layer clouds observed during SHEBA/FIRE-ACE

An intercomparison of six cloud-resolving and large-eddy simulation models is presented. This case study is based on observations of a persistent mixed-phase boundary layer cloud gathered on 7 May, 1998 from the Surface Heat Budget of Arctic Ocean (SHEBA) and First ISCCP Regional Experiment - Arctic Cloud Experiment (FIRE-ACE). Ice nucleation is constrained in the simulations in a way that holds the ice crystal concentration approximately fixed, with two sets of sensitivity runs in addition to the baseline simulations utilizing different specified ice nucleus (IN) concentrations. All of the baseline and sensitivity simulations group into two distinct quasi-steady states associated with either persistent mixed-phase clouds or all-ice clouds after the first few hours of integration, implying the existence of multiple states for this case. These two states are associated with distinctly different microphysical, thermodynamic, and radiative characteristics. Most but not all of the models produce a persistent mixed-phase cloud qualitatively similar to observations using the baseline IN/crystal concentration, while small increases in the IN/crystal concentration generally lead to rapid glaciation and conversion to the all-ice state. Budget analysis indicates that larger ice deposition rates associated with increased IN/crystal concentrations have a limited direct impact on dissipation of liquid in these simulations. However, the impact of increased ice deposition is greatly enhanced by several interaction pathways that lead to an increased surface precipitation flux, weaker cloud top radiative cooling and cloud dynamics, and reduced vertical mixing, promoting rapid glaciation of the mixed-phase cloud for deposition rates in the cloud layer greater than about 122610 –5 gk g –1 s –1 for this case. These results indicate the critical importance of precipitation-radiative-dynamical interactions in simulating cloud phase, which have been neglected in previous fixed-dynamical parcel studies of the cloud phase parameter space. Large sensitivity to the IN/crystal concentration also suggests the need for improved understanding of ice nucleation and its parameterization in models.

The Role of the Viscous Dissipation in Heated Microchannels

Many experimental works appeared in the last decade in the open literature dealing with forced convection through microchannels. The earliest experimental results on single-phase flows in microchannels evidenced that for channels having a hydraulic diameter less than 1mm the conventional continuum models can no longer be considered as able to accurately predict pressure drop and convective heat transfer coefficients. This conclusion seemed to be valid for both gas and liquid flows. Sometimes the authors justified this conclusion by invoking new micro-effects, e.g., electrostatic interaction between the fluid and the walls or scaling effects (axial heat conduction, viscous forces, conjugate heat transfer, wall roughness, and so on). In this paper the role of the viscous dissipation in liquids flowing through heated microchannels will be analyzed by using the conventional theory. We will present a correlation between the Brinkman number and the Nusselt number for silicon ⟨100⟩ and ⟨110⟩ microchannels. It will be demonstrated that the fluid is of importance in establishing the exact limit of significance of the viscous dissipation in microchannels; a criterion to analyze the significance of the viscous effects will be presented. The role of the cross-section aspect ratio on the viscous dissipation will be highlighted. The main goal of this work is to demonstrate that the problem of heat transfer enhancement in microdevices cannot be solved by indefinitely reducing the microchannel dimensions because the viscous dissipation effects shall offset the gains of high heat transfer coefficients associated with a reduction in the channel size.

Adhesion of a Soft Rubber on a Wet Solid

We study theoretically the dewetting of a liquid film intercalated between a flat solid and a weakly crosslinked rubber. The rubber is characterised by a static shear modulus, μ0, a high frequency modulus, μ∞ (≫ μ0) and a relaxation time, τ. The film dewets by nucleation and growth of a dry contact zone (radius R(t) at time t) surrounded by a liquid rim collecting the liquid. We expect three regimes: a. at short times (R < R c1), the rubber behaves like a hard elastic solid (μ = μ∞) and the dissipation is dominated by the liquid rim. We call this fast elastic dewetting. b. at intermediate times (R c1 < R < R c2), the rubber behaves like an ultra-viscous liquid. We call this “mixed viscous dewetting” because both components dissipate. c. at long times (R > R c2) the rubber behaves like a soft solid (μ = μ0) and the liquid dissipation is again dominant. We call this slow elastic dewetting.