Heat and mass diffusion fluxes on a permeable wall with foreign-gas blowing

Volchkov, É. P.; Makarov, M. S.; Makarova, S. N.

doi:10.1016/j.ijheatmasstransfer.2011.11.041

Cited by 8 publications

(8 citation statements)

References 15 publications

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“…Even at evaporation of a water drop with large radius r without heating a wall, there is a significant effect of natural convection on the droplet evaporation law 44 . In the presence of a transverse gas flow from a permeable wall, the similarity of the laws of heat transfer, friction and mass transfer St = C f /2 = St d may be significantly violated ( St is the Stanton number, St d is the diffusion Stanton number, and C f /2 is the dimensionless friction coefficient) 45 . The analogous situation is observed in the problems of a permeable plate and foreign gas blowing into the boundary gas layer.…”

Section: Introductionmentioning

confidence: 99%

Evaporation of a sessile water drop and a drop of aqueous salt solution

Misyura

2017

Sci Rep

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The influence of various factors on the evaporation of drops of water and aqueous salt solution has been experimentally studied. Typically, in the studies of drop evaporation, only the diffusive vapor transfer, radiation and the molecular heat conduction are taken into account. However, vapor-gas convection plays an important role at droplet evaporation. In the absence of droplet boiling, the influence of gas convection turns out to be the prevailing factor. At nucleate boiling, a prevailing role is played by bubbles generation and vapor jet discharge at a bubble collapse. The gas convection behavior for water and aqueous salt solution is substantially different. With a growth of salt concentration over time, the influence of the convective component first increases, reaches an extremum and then significantly decreases. At nucleate boiling in a salt solution it is incorrect to simulate the droplet evaporation and the heat transfer in quasi-stationary approximation. The evaporation at nucleate boiling in a liquid drop is divided into several characteristic time intervals. Each of these intervals is characterized by a noticeable change in both the evaporation rate and the convection role.

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Section: Introductionmentioning

confidence: 99%

Evaporation of a sessile water drop and a drop of aqueous salt solution

Misyura

2017

Sci Rep

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“…The blowing parameter can be estimated as b = 3ρCH4VCH4(Rex) 0.5 /(ρ0U0) = 0.2. This value is much lower than the critical bcr = 1.86 [41][42][43][44], which corresponds to the separation of the wall layer. Thus, the injected methane from the powder can only partially deform the dynamic layer of air.…”

Section: Heterogeneous Character Of Methane Hydrate Combustion Velocmentioning

confidence: 95%

“…It is rather difficult to analytically connect the methane transfer with heat transfer, since they are described by different equations. However, it is possible to use a triple analogy and similarity between the transfer of heat, momentum, and diffusion [41][42][43][44]. In fact, this similarity is not performed even when there is gas injection through the wall [42,44].…”

Section: The Connection Of Dissociation Rate and Heat Transfermentioning

confidence: 99%

“…However, it is possible to use a triple analogy and similarity between the transfer of heat, momentum, and diffusion [41][42][43][44]. In fact, this similarity is not performed even when there is gas injection through the wall [42,44]. In our case, blowing is associated with dissociation, which depends on the heat flux and temperature, i.e., the velocity of the injected air cannot be constant.…”

Section: The Connection Of Dissociation Rate and Heat Transfermentioning

confidence: 99%

“…This deviation is probably due to the presence of both a forced air-flow and a free-convective flow due to high temperature gradient and gas density in the diffusion layer of the mixture. The degree n = 0.5 corresponds only to the plane laminar boundary layer when the buoyancy is neglected, i.e., when St~1/(Re) 0.5 and q~(U 0 ) 0.5 [41][42][43][44], where St and Re are the Stanton number and the Reynolds number, St = q/(ρ 0 U 0 c p ∆T), Re = ρ 0 U 0 x/µ, x is the longitudinal coordinate, µ is the dynamic viscosity, and c p is the heat capacity of the gas mixture. If the characteristic velocities caused by forced flow and buoyancy are comparable (of the same order), their ratio can be estimated using the Richardson number Ri = Gr/Re 2 (Gr is the Grashof number).…”

Section: The Dissociation Rate In the Combustion Of Methane Hydratementioning

confidence: 99%

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An Experimental Study of Combustion of a Methane Hydrate Layer Using Thermal Imaging and Particle Tracking Velocimetry Methods

et al. 2018

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In this paper, the combustion of methane hydrate over a powder layer is experimentally studied using thermal imaging and Particle Tracking Velocimetry (PTV) methods. The experiments are carried out at different velocities of the external laminar air-flow from zero to 0.6 m/s. Usually, simulation of methane hydrate combustion is carried out without taking into account free convection. A standard laminar boundary layer is often considered for simplification, and the temperature measurements are carried out only on the axis of the powder tank. Measurements of the powder temperature field have shown that there is a highly uneven temperature field on the layer surface, and inside the layer the transverse temperature profiles are nonlinear. The maximum temperature always corresponds to the powder near the side-walls, which is more than 10 • C higher than the average volumetric temperature in the layer. Thermal imager measurements have shown the inhomogeneous nature of combustion over the powder surface and the highly variable velocity of methane above the surface layer. The novelty of the research follows from the measurement of the velocity field using the PTV method and the measurement of methane velocity, which show that the nature of velocity at combustion is determined by the gas buoyancy rather than by the forced convection. The maximum gas velocity in the combustion region exceeds 3 m/s, and the excess of the oxidizer over the fuel leads to more than tenfold violation of the stoichiometric ratio. Despite that, the velocity profile in the combustion region is formed mainly due to free convection, it is also necessary to take into account the external flow of the forced gas U 0 . Even at low velocities U 0 , the velocity direction lines significantly deviate under the forced air-flow. combustion is associated with the presence of three interrelated processes: The dissociation of solid particles of methane hydrate; gas filtration through a multicomponent medium (methane-water-water vapor); and diffusion combustion of methane in the mixing layer (methane-air-water vapor), which is usually implemented over the powder layer. Therefore, it is necessary to consider the features of these processes.The gas hydrate dissociation rate is determined by the following driving forces: Deviation of temperature and pressure from the equilibrium states, size of particles, and structural characteristics of ice crust [4,5]. Dissociation at positive temperatures has a thin film of water formed on the surface of solid particles. The dissociation rate is quasi-constant for most of the dissociation time. The case of negative temperatures is significantly more difficult to describe due to the emergence of the phenomenon of self-preservation [6]. In the temperature range of 230-268 K, the dissociation rate of methane hydrate decreases by several orders of magnitude and strongly depends on temperature. This annealing temperature region was called the self-preservation region. The lowest dissociation rate of methane hydrate is achieved at th...

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Free convection and vapor diffusion of droplet aqueous solutions

Misyura

2017

Chemical Engineering Research and Design

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Heat and mass diffusion fluxes on a permeable wall with foreign-gas blowing

Cited by 8 publications

References 15 publications

Evaporation of a sessile water drop and a drop of aqueous salt solution

Evaporation of a sessile water drop and a drop of aqueous salt solution

An Experimental Study of Combustion of a Methane Hydrate Layer Using Thermal Imaging and Particle Tracking Velocimetry Methods

Free convection and vapor diffusion of droplet aqueous solutions

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