Heat And Mass Transfer In Porous Media __HOT_

Drying in porous media involves complex processes of heat, mass and momentum transfer as well as phase change. Understanding these phenomena through mathematical models leads to considerable improvement in energy savings and cost reduction in industrial drying. This chapter provides an overview of the transport phenomena in porous media with specific application to drying. It reviews available drying models for porous media ranging from the liquid diffusion model to single phase to complex multiphase models along with the conjugate ambient model. The governing equations and their constitutive relations are discussed along with associated assumptions, approximations and limitations. Detailed discussion of the interphase mass, momentum, energy and species transfer is highlighted along with guidelines for future research direction. This provides an overview for the researcher as well as the drying practitioner to select the most suitable model depending on their need and purpose.

Phase change heat transfer in capillary porous media is of great relevance in diverse industrial applications. Heat pipes, vapor chambers, thermosyphons and cold plates are some of the phase change devices which employ microscopic porous media and are used in the thermal management of high-power electronics. These devices realize high heat transfer rates by exploiting latent heat exchange. The increasing power density of electronic chips requires that the performance of these devices be optimized so that heat can be efficiently removed from the electronic chip while limiting the temperature differential between the chip and ambient. The efficiency of heat spreading in heat pipes and vapor chambers relies on the capillary porous medium (wick structure) used in the device. The wick structure also determines the maximum heat transport capability. The study of phase change heat and mass transfer in wick structures can lead to the optimization of wick design and improved performance of the phase-change cooling devices. In the first part of this thesis, numerical models are developed to study the heat and mass transport in wick structures at the pore scale. The microstructures are characterized on the basis of their wicking and thin-film evaporation performance by modeling the rates of evaporation from the liquid menisci formed in common wick microstructures. Evaporation at the interface is modeled by using appropriate heat and mass transfer rates obtained from kinetic theory. At higher heat inputs, nucleate boiling occurs in the wick structure causing a decrease in the wick thermal resistance and improvement in the device performance. A volume-of-fluid-based model is developed to study the growth of vapor bubbles in wick microstructures. In the second part of this thesis, a transient three-dimensional heat pipe model is developed which is suitable for predicting the hydrodynamic and thermal performance of vapor chambers at high heat flux inputs and small length scales. The influence of the wick microstructure on evaporation and condensation mass fluxes at the liquid-vapor interface is accounted for by integrating a microstructure-level evaporation model (micromodel) with the device-level model (macromodel). The effect of boiling in the wick structure at higher heat inputs on the vapor chamber performance is modeled and the model predictions are validated with experiments performed on custom-fabricated vapor chambers. The model is further utilized to optimize the performance of an ultra-thin vapor chamber. The last part of this work focuses on the design of novel wick micro- and nano-structures for performance improvement of vapor chambers. The thermal and hydrodynamic performance of micro-pillared structures are first modeled and a ten-times improvement in the maximum heat transport capability of vapor chambers is revealed. The viability of utilizing nanostructures such as carbon nanotubes (CNTs) and metallic nanowires as wick structures for heat pipes is also assessed. Using theoretical models, it is concluded that the flow resistance of nanostructures poses a major bottleneck to their use as passive flow-conveying media. An alternative design which combines the micro- and nano-level wicks is proposed which leads to a 14% decrease in the wick thermal resistance.

Heat And Mass Transfer In Porous Media

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Heat and mass transfer processes in PM are part of our daily experience, and this general process is central to many environmental and engineering applications, from the evaporation of moisture from the soil to the drying of various products and building materials. The intensity of heat and mass transfer in porous media can exhibit complex dynamics, reflecting internal transport mechanisms and the motion of the phase transition front, which critically affect the distribution of surface energy [10,11,12,13,14,15,16].

One of the key thermophysical properties of porous media is effective heat and mass conduction. Identification and quantification of morphological features that correlate with thermal conductivity are vital to understanding the mechanism of thermal conductivity in porous media [17].

Thus, heat and mass transfer in porous media has been an important research topic for many decades because of its applicability. Despite numerous studies over more than a century, there are many new discoveries that are still improving the basic understanding of the subject.

A special issue of this journal is devoted to the topical scientific problem of studying the processes of interconnected heat and mass transfer in porous media. This problem is one of the complex and important fundamental areas of modern science and is of significant applied importance. The results of studies of heat and mass transfer in porous materials can be used to intensify heat transfer in various power plants to increase their energy efficiency.

In [19], Kumierek K. and others developed the topic of research on highly porous carbon materials. The authors focused on carbon materials with different porosities: single-walled carbon nanotubes, heat-treated activated carbon, and reduced graphene oxide for studying adsorption processes. The dependence of the adsorption and electrochemical properties of these materials on their porosity has been established.

In [22], the results of studies of the capillary effect in porous structures with different pore sizes are presented in order to develop passive cooling systems based on the mechanisms of the liquid-vapor phase transition to remove large heat fluxes. The high intensity and density of energy flow in some industries require efficient and reliable heat transfer. In such technologies, heat pipes are actively used since they have the ability to transfer heat efficiently. This topic is developed by the authors of whose article [23], the results are related to the production of heat pipes. A new approach in their products is the use of high-tech additive manufacturing technologies, in which the most complex geometries are made layer by layer directly from a digital file. This technology produces efficient homogeneous structures with the desired porosity, uniform pore size, permeability, thickness, and uniform pore distribution.

The research work [26] presents modelling of the dynamics of a vapour-gas mixture and heat and mass transfer in the capillary structure of a porous medium. At the heart of the approach implemented in this article, the porous structure is represented by a system of linear microchannels in a three-dimensional coordinate system. The area of the channels is modelled by a set of cubic elements with a certain humidity, moisture content, pressure, and temperature. Such a modelling scheme includes a certain number of parameters, thermophysical properties, and characteristics of the porous material, depending on the moisture content. The authors of the article directly considered the effects of heat and mass transfer in the structure of the material and phase transition-evaporation or condensation in the elements of the porous structure.

Another important class of heat and mass transfer problems in porous media is determined by physical processes in the environment, for example, in soil, when low-grade heat is used to operate heat pumps [62,63,64].

Citation: Zhao Y, Wu H and Dang C (2023) Effect of mechanical vibration on heat and mass transfer performance of pool boiling process in porous media: a literature review. Front. Energy Res. 11:1288515. doi: 10.3389/fenrg.2023.1288515

In magnetic resonance imaging (MRI), this MRI is used for the diagnosis of the brain. The dynamic of these particles occurs under the action of the peristaltic waves generated on the flexible walls of the brain. Studying such fluid flow of a Fractional Second-Grade under this action is therefore useful in treating tissues of cancer. This paper deals with a theoretical investigation of the interaction of heat and mass transfer in the peristaltic flow of a magnetic field fractional second-grade fluid through a tube, under the assumption of low Reynolds number and long-wavelength. The analytical solution to a problem is obtained by using Caputo's definition. The effect of different physical parameters, the material constant, magnetic field, and fractional parameter on the temperature, concentration, axial velocity, pressure gradient, pressure rise, friction forces, and coefficient of heat and mass transfer are discussed with particular emphasis. The computed results are presented in graphical form. It is because the nature of heat and mass transfer coefficient is oscillatory which is following the physical expectation due to the oscillatory nature of the tube wall. It is perceived that with an increase in Hartmann number, the velocity decreases. A suitable comparison has been made with the prior results in the literature as a limiting case of the considered problem.

Drying is an essential step in many manufacturing processes, for it will have an important impact on the product quality. This is why many numerical models have been realized over decades, in order to predict the hygrothermal behavior of porous media during the drying process. In this paper, we present a model allowing to properly simulate the pressure, heat and mass transfer during the drying of moist plaster on dry concrete. We take advantage of the continuity of vapor pressure between two materials to use it as the main variable in the mass conservation equation, and calculate the moisture content separately through a partial differential equation. This model will also simulate the deformation of plaster using the Navier-Stokes equations. be457b7860