The influence of characteristic scales of convection on non-isothermal evaporation of a thin liquid layer

by:angelacrox     2020-06-08
Here, the convection in the liquid
The constant temperature evaporation of the horizontal thin layer on the thermal wall was studied.
It is believed that with the increase of salt concentration, the evaporation rate of salt is always reduced.
Depending on the nature of the evaporation rate, the aqueous solution can be divided into two different types :(1)
The equilibrium pressure of water vapor ps changes slightly with time; (2)
Ps decreased many times as the salt mass concentration increased, resulting in a sharp decrease in evaporation rate j.
The criteria for attribution of salt to characteristic types are proposed, and the relationship between the thermodynamic properties of j and salt solutions is determined.
Different modeling methods are proposed for each group.
For the first time, a simple calculation method linking Peclet and Marangoni criteria with convection in liquids and non-liquids
Static heat exchange is proposed.
The analysis shows that it is impossible to simulate heat transfer without knowing the local features of the velocity field in the liquid phase and the characteristic convection scale of the velocity field and temperature field.
So far, it has been thought that the surface Marangoni flow can be ignored due to the negative effects of the surface active agent.
However, the study in this paper shows that the significant increase in free convection is related to the flow of heat and solubility Marangoni.
The strong effect of Marangoni flow on liquid convection under high heat flow is extremely important for reliable simulation of layer evaporation in a wide range of modern technologies.
Aqueous solution represents an important area of research that links a variety of different disciplines: thermodynamics of solution, physical chemistry of the phase boundary, thermodynamics, crystalline dynamics, fluid dynamics of thin layers in solution and heat exchange.
Heat and Mass Transfer in solution cannot only take into account heat, momentum and energy transfer in the liquid body phase.
It is also important that the surface flow plays a role on the liquid boundarygas.
The small size of the film greatly limits the possibility of the experiment and makes the theoretical analysis complicated.
In the process of water evaporation
There may be salt solutions, local oversaturation areas, and different forms of crystal and crystal water may appear.
Absorption and evaporation of brine: LiCl/HO, LiBr/HO and CaCl/HO are effectively used by modern heat pumps.
The following factors determine the features of the salt water behavior: gas pressure, composition concentration and temperature on the surface of a free liquid, thermal physical properties of the liquid and wall, humidity, liquid and gas convection.
The degree of free convection and turbulence in the gas phase exacerbated the transfer process.
Since heat transfer depends on the thickness of the film, it is of interest to study the stability of the film.
Film instability is driven by a break from pressure.
The resonance interaction between the interface deformation and the substrate structure pattern leads to the continuity of the dispersion curve, similar to the occurrence of gaps in the energy spectrum seen in the application of Floquet theory in solid state physics.
When the liquid film spreads on the hot wall with uneven temperature distribution, three-
The dimensional circulation inside the liquid, the change in the direction of the liquid and the local rupture of the film.
This unstable behavior of the film is caused by the flow of hot Marangoni.
Local hot capillary flow and deformation of gas
When nanoparticles are deposited from the solution by laser radiation, the liquid interface occurs when laser cutting of the metal.
The features of the thermal capillary force in the film are also taken into account.
The heat exchange during film evaporation is considered.
Heat transfer during film evaporation is discussed.
The thermal transfer modeling of salt solutions is fundamentally different from the thermal transfer modeling of water layers.
Physical and thermodynamic properties of solution (
Latent heat of evaporation, diffusion coefficient, viscosity, surface tension)
With the increase of salt concentration in solution, the change is obvious.
The evaporation flux density of aqueous solution decreases many times over time.
In most numerical studies, the modeling of film evaporation rate does not take into account the free convection of gas and liquid.
The simulation of heat exchange in lubricating oil emulsion is introduced.
The physical properties of aqueous solution are introduced.
A membrane extractor and condenser containing brine were studied in experiments.
The behavior features of the heat transfer coefficient of the mixture falling film were considered.
Through the analysis of the existing literature, the following conclusions can be drawn.
Most of the experimental and theoretical work of absorption and evaporation is handled with LiCl, CaCl, and LiCl salts.
These salt are usually used for high
Heat pump temperature generator.
Scarce experimental data, right?
Constant temperature heat exchange of the film under multiple changes in layer height and salt concentration.
Our previous research work
Constant temperature evaporation of large water dropletssalt solutions.
Droplets of large diameter (>u200920–30u2009mm)have a quasi-
The plane shape, therefore, can partially reflect the behavior of the thin layer.
However, the simulation of large drops and thin liquid layers is mainly different.
When it drops, a high temperature gradient will appear on the interface.
In addition, there is a sharp change in the height of the solution near the contact line, and there is a high gradient.
For a layer, the liquid height is not dependent on longitudinal coordinates and it is difficult to simulate the surface temperature gradient.
In addition, the experimental dataHigh constant temperature
The temperature evaporation and heat exchange of thin layers are very rare.
Most of the works are carried out at a fixed salt concentration, viscosity, diffusion, and liquid film height.
These limitations do not allow accurate reproduction and high modeling processing
Temperature saline solution.
With regard to the above, one of the objectives of this work is to obtain experimental and theoretical dependence on evaporation rate and heat transfer coefficient, when the thermal physical properties of brine and the layer height in the evaporation process change many times.
So far, there is no
The constant temperature heat exchange of a large amount of salt has a significant difference in its thermal performance.
Generally, equilibrium curves and thermal physical parameters of salt are analyzed in the literature.
Another important goal of this work is to determine the key parameters that salt can be attributed to the feature group.
It is also crucial to determine how the evaporation rate and heat transfer coefficient relate to the properties of the salt;
Obtaining qualitative and quantitative dependencies for highly centralized behavior will help to further develop existing computational models.
Another purpose of this study is to determine the role of the Marangoni flow on the surface of the layer.
At present, it is generally believed that due to the influence of surface active substances, the effect of Marangoni number on liquid evaporation and the role of convection in thin layers is insignificant.
However, these approximations are not always fair.
Convection and Marangoni flow are not only in the descent, but also in the thin layer of the solution, which plays an important role in heat transfer and mass transfer.
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