Thermoviscous Liquid Research Articles

Experimental setup for researching the stability of fluid flow

The problem of studying the stability of the flow of a thermoviscous liquid is relevant in connection with the need to develop methods for controlling flow regimes in industrial condensers and heat exchange devices. These devices play an important role in a variety of technological processes, from food production to materials processing, and their effectiveness is directly dependent on the flow regime they establish. Awareness of the importance of both laminar and turbulent flow regimes leads to the need to balance between energy efficiency, which is often preferable to laminar flow, and heat and mass transfer efficiency, which is characteristic of turbulent flow. This makes it important to study and control the stability of the flow. As the speed of fluid flow increases, laminar flow loses stability and disturbances arise, which can lead to the formation of a secondary nonlinear regime that preserves the main characteristics of laminar flow, or to flow turbulization, which in turn can have a significant impact on the efficiency of technical devices. Although a lot of work has been done to study the stability of the flow of homogeneous liquids in channels and their spectral characteristics, the importance of taking temperature differences into account is often overlooked. However, it is the dependence of liquid viscosity on temperature that plays a significant role in determining flow patterns and requires additional study. Despite the ongoing numerical studies of the stability of fluid flow, there remains a need to compare experimental data with the results of numerical modeling to obtain a more complete understanding of the processes occurring in the system. In this regard, within the framework of this work, an experimental setup of an annular channel was developed and assembled in order to conduct a detailed experimental study of the stability of fluid flow and subsequently compare the results obtained with numerical simulations, which will provide more accurate data for further improving the design and operation of industrial devices.

Stability of traveling waves of a thermoviscous liquid film down the outer surface of a cylinder

Stability of traveling waves of a thermoviscous liquid film down the outer surface of a cylinder

Thermoviscous liquid conjugate heat exchange simulation in cylindrical channel

The article is concerned with the flow of a thermoviscous fluid in a cylindrical channel for various types of viscosity functions in the joint solution of the problem of conjugate heat exchange between the channel and the surrounding material. A model of a cylindrical channel with a thermoviscous liquid flowing inside at a given velocity and viscosity is considered. The methodology of the process consists in applying a system of model equations that describes the dynamics of thermoviscous fluid flow processes based on the laws of phase energy conservation, the continuity equation, the Navier-Stokes momentum conservation equation taking into account conjugate heat transfer and the heat transfer equation for a solid. Numerical implementation of model representations was carried out using the Comsol Multiphysics digital package. Velocity and temperature profiles were obtained in the cross section of the channel. The influence of the viscosity function on the flow profile is shown, as well as the quantitative characteristics of the flow and heat transfer. An analysis was made of the dependence of the nature of the velocity and temperature profiles on the viscosity of the liquid and the type of dependence of viscosity on temperature. The result of the work done is the found features and regularities that arise in the process of conjugate heat transfer of a thermoviscous liquid in a cylindrical channel when comparing the linear and exponential dependences of viscosity on temperature. The analysis of the obtained dependences of viscosity and temperature in the flow profile, the value of the maximum flow rate was carried out. It is shown that viscous friction causes a local increase in temperature near the pipe walls, followed by an increase in fluid velocity due to a decrease in viscosity. The results obtained are basic for the further development of this topic and will be used to solve new problems in the field of modeling the thermoviscous fluid flow and conjugate heat transfer.

Role of suction pressure in the stability of a gravity-driven thermoviscous liquid film flow down the interior surface of a cylinder.

This study aims to analyze the stability of a gravity-driven thin film flow in the heated/cooled interior surface of a vertical hollow cylinder. The model development involves simplifying the flow and energy equations using the usual thin-film approximation, where the average film thickness is considered to be much smaller than the radius of cylinder. A dispersion relation is then derived to study the temporal stability of the system in order to quantify the effect of various non-dimensional parameters present in the model, such as the thermoviscous number, Marangoni number, Biot number, and Bond number. Another non-dimensional parameter is introduced by considering an opposing suction pressure in the annulus region. The thermocapillary stress and the thermoviscous effect are shown to strongly affect the temporal stability of the flow. It is shown that although the suction pressure affects the velocity profile of the flow, it does not affect the temporal stability results. The suction pressure is then shown to have some effect on the spatiotemporal stability. Critical condition is presented for the transition between absolutely and convectively unstable systems, and parameter regimes are presented to quantify the effect of the above-mentioned parameters.

Gravity-driven thermoviscous liquid film down a heated or cooled vertical cylinder

Gravity-driven flow of a liquid over an isothermal cylinder is unconditionally unstable. The flow of a thermoviscous fluid over a heated or cooled substrate shows interesting stability behavior. The relevant parameters in the model affect the spatiotemporal nature of the instability.

Turbulent kinetic energy transfer and dissipation in thermoviscous fluid flow

Turbulent flow of thermoviscous liquid is studied in a three-dimensional region with periodicity in two directions. Flow characteristics are described in the terms of equation for turbulent kinetic energy: this allows to differentiate contributions from different components related to generation, transport, and dissipation of turbulent kinetic energy. Those terms can be calculated from averaging the moments of different order. The previous studies demonstrated that thermoviscous liquid flow occurs through several stages of evolution, including the unsteady turbulence. This allows discussing the problem of mathematical rigorous statement and applicability of different methods for averaging. Existence of spatial periodicity allow using a combined spatial-time averaging for different values on the interval of steady turbulence. Results are presented as a set of Z—t-diagrams. Besides, the paper presents analysis of flow development on the basis of direct visualization of velocity and temperature.

Isolated Convection Modes for the Anomalous Thermoviscous Liquid in a Plane Cell

This work is devoted to the numerical research of free convection by a Newtonian anomalous thermoviscous fluid in a flat cell. The cell is heated from below, cooled from above; and the lateral boundaries are heat insulated. The viscosity anomaly of the fluid is modeled by the Gaussian function of temperature and is characterized by two parameters. A flow regime with isolated convective cells separated by a region of high viscosity, the so-called viscous barrier, was detected at a certain set of control parameters. For these flow regimes, current lines, heat fluxes, temperature fields, and contours of the components of the velocity vector of the fluid are given.

Stability analysis of a gravity-driven thermoviscous liquid film flowing over a heated flat substrate.

Two-dimensional steady-state solutions and their stability analysis are presented for a gravity-driven thin film of a thermoviscous liquid. The governing equations and boundary conditions are simplified using the lubrication approximation. The analytically obtained film thickness evolution equation consists of various dimensionless parameters such as the Marangoni number, Biot number and thermoviscosity number. The viscosity of the liquid is assumed as an exponential function of temperature. The viscosity decreases within the liquid film as the temperature increases. Due to localized heating interfacial temperature gradients generate surface tension gradient which results into thermocapillary or Marangoni stress. The Marangoni stress opposes the fluid flow at the leading edge of heater leading to an increase in the film thickness locally. This locally thick structure becomes unstable beyond critical values of the parameters that leads to formation of rivulets in the transverse direction. Using the linear stability analysis it is found that the Marangoni stress and the thermoviscous effect have a destabilizing effect on the thin-film flow. At much higher values of the thermoviscosity number another mode of instability appears which is known as thermocapillary instability which leads to oscillating film profiles. For streamwise perturbations, the destabilizing effect of the thermoviscosity number for localized and uniform heating remains consistent.

The hydraulic resistance of thermoviscous liquid flow in a plane channel with a variable cross-section

The problem of the possibility of adjusting the hydraulic resistance due to local thermal action is considered. The liquid flow with the temperature dependence of the viscosity in a plane channel with sudden contraction is investigated. The velocity profiles of the thermoviscous liquid flow and the dependence of the hydraulic resistance coefficient on various types of local action on the liquid flow with a temperature dependence of the viscosity in a plane channel are numerically obtained.

Hydrodynamic stability of thermoviscous liquid film inside a rotating horizontal cylinder: Heating and cooling effects

Steady two-dimensional solutions and their stability analysis are presented for thin film of a thermoviscous liquid flowing inside a cylinder rotating about its horizontal axis. The inner surface of the cylinder is either uniformly hotter or colder than the enveloping air. The mass, momentum, and energy equations are simplified using thin-film approximation. The analytically obtained film thickness evolution equation consists of various dimensionless parameters such as gravitational number, Bond number, Biot number, thermoviscosity number, and Marangoni number. The viscosity of the liquid is considered as an exponential function of temperature. The viscosity increases (decreases) within the film thickness away from the inner surface of the cylinder when the surface is uniformly hotter (colder) than the atmosphere. For hotter (colder) surface, the film thickness on the rising side decreases (increases) when convective heat transfer at the free surface is increased. The surface tension gradient at the free surface generates Marangoni stress that has a destabilizing (stabilizing) effect on the thin film flow in the case of a hotter (colder) cylinder. The thermoviscosity number stabilizes (destabilizes) the flow on a heating (cooling) surface and this effect increases with an increase in the heat transfer at the free surface. For a hotter surface and in the presence of Marangoni stress, the convective heat transfer at the interface has the destabilizing effect for small values of the Biot number and assumes a stabilizing role for larger values. Non-linear simulations show consistency with the linear stability analysis.

Investigation of the thermoviscous liquid flow in a plane channel with a narrowing

In this paper, the problem of the possibility of regulating hydraulic resistance due to local thermal action is considered. The flow of an incompressible liquid with a temperature dependence of the viscosity in a plane channel with a variable cross section and an inhomogeneous temperature field is investigated. The flow velocities profiles of a thermoviscous liquid for a narrowed channel are obtained numerically. Using the example of a thermoviscous liquid flow in a plane channel with a sharp expansion, it is shown that the temperature factor exerts a significant influence on the value of the local resistance coefficient for the variable channel cross-section.

Regimes of stabilization of the flow of anomalous thermoviscous liquid depending on the heat exchange

In the paper the results of numerical modeling of the flow of an incompressible fluid with a non-monotonic dependence of the viscosity on the temperature in a channel are presented. On the channel’s walls the heat exchange is specified that are written mathematically in the form of the boundary conditions of the third kind on the basis of the Newton– Richman convective heat exchange law. The regimes of flow stabilization in the channel depending on the Nusselt numbers have been studied. Four different types of unsteady processes are discovered and it has been shown that they are determined by the different heat exchange intensity.

Numerical research of influence of viscosity–temperature relation on structure of Couette flow

In work results of a numerical research of influence of viscosity-temperature relation on structure of a convective Couette flow of thermoviscous liquid are presented in ring area between two coaxial cylinders under a condition when one of them has more high temperature. Comparison of a convective Couette flow of model liquid with non-monotone temperature dependence of viscosity and liquid with constant viscosity is carried out. Depending on parameters of viscosity anomaly the steady and oscillation flow regimes both with periodic and with not repeating fluctuations of vortex structures are found. The number of time-constant vortex structures also depends on parameters of viscosity anomaly.

Mathematical modeling of Couette flow in anomalous thermoviscous liquid

The steady flow of anomalous thermoviscous liquid between the coaxial cylinders is considered. The inner cylinder rotates at a constant angular velocity while the outer cylinder is at rest. On the basis of numerical experiment various flow regimes depending on the parameter of viscosity temperature dependence are found.

Single-phase filtration in the porous medium saturated with anomalous thermoviscous liquid

In work the single-phase filtration of anomalous thermoviscous liquid on an example of thermoreversible polymer gel, named МЕТКА, is simulated numerically. Features of a filtration liquid flow at her injection into porous medium are investigated. Characteristic distribution pictures of fields of temperature, viscosity and velocity vector components are constructed when using first-type and third-type boundary conditions.

Filtration of anomalous thermoviscous liquid in layered non-uniform formation

The mathematical model is developed and the numerical research of a filtration flow features of liquid with model nonmonotonic dependence of viscosity on temperature is conducted. Existence of the ”viscous barrier“ defining character of a filtration flow of anomalous thermoviscous liquid in the porous medium is established. Characteristic pictures of the steady distribution of viscosity and temperature in layered non-uniform formation are constructed. It is established that formation flow rate depends on a maximum of viscosity coefficient and pressure difference essentially.

Stability of thermoviscous Hele-Shaw flow

Viscous fingering can occur as a three-dimensional disturbance to plane flow of a hot thermoviscous liquid in a Hele-Shaw cell with cold isothermal walls. This work assumes the principle of exchange of stabilities, and uses a temporal stability analysis to find the critical viscosity ratio and finger spacing as functions of channel length, Lc. Viscous heating is taken as negligible, so the liquid cools with distance (x) downstream. Because the base flow is spatially developing, the disturbance equations are not fully separable. They admit, however, an exact solution for a liquid whose viscosity and specific heats are arbitrary functions of temperature. This solution describes the neutral disturbances in terms of the base flow and an amplitude, A(x). The stability of a given (computed) base flow is determined by solving an eigenvalue problem for A(x), and the critical finger spacing. The theory is illustrated by using it to map the instability for variable-viscosity flow with constant specific heat. Two fingering modes are predicted, one being a turning-point instability. The preferred mode depends on Lc. Finger spacing is comparable with the thermal entry length in a long channel, and is even larger in short channels. When applied to magmatic systems, the results suggest that fingering will occur on geological scales only if the system is about freeze.

NONUNIFORMITIES AND STABILITY IN THERMAL FLUID MECHANICS

In this paper we study the influence of temperature and velocity gradient nonuniformities on the stabilization of the adiabatic symmetric flow caused by a constant pressure gradient of a thermoviscous liquid with temperature-dependent viscosity. We show that the choice of the viscosity function permits the stabilizing effect of internal dissipation to prevail and deliver a stable large time response, without “shear band” formation.