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This study investigates the heat and mass transfer characteristics of a binary mixture (R134a/R245fa) evaporated in a porous medium. The Eulerian model coupled with the multiphase VOF model and species transport equations is employed to establish a multi-component evaporation model. The effects of heat flux ranging from 200 kW/m2 to 500 kW/m2, porosity ranging from 0.4 to 0.6, and mass fraction ratios (R134a/R245fa) of 3:7, 5:5, and 7:3 are explored. The results indicate that an increase in heat flux contributes to an increase in the evaporation rate. For the overall evaporation rate, the evaporation rates of R134a and R245fa improve by 11.3%, 6.9%, and 16.3%, respectively, while the maximum improvement in heat transfer coefficient is only 1.4%. The maximum evaporation rate is achieved at intermediate porosity in the porous medium, and the highest heat transfer coefficient is obtained at a porosity of 0.4. With the increase in mass fraction, the evaporation rate of the corresponding species also increases, while the overall evaporation rate and heat transfer coefficient remain almost unchanged. [ABSTRACT FROM AUTHOR]

Therefore, heat transfer during flow with a change of phase in mini-channels turned out to be a necessary solution to achieve high heat fluxes with reasonably miniature geometrical dimensions and a temperature at a not very high level within the heat exchanger device. The authors noted that there was an increase in the heat flux and the heat transfer coefficient for surfaces with microchannels. The transfer of large heat fluxes is one of the most significant issues in modern technology. The authors indicated that the construction of a compact heat exchanger with a group of rectangular mini- and microchannels with enhanced surfaces can improve the heat transfer process. [Extracted from the article]

The heat transfer performance of the evaporator significantly affects the heat transfer capacity of the loop heat pipe (LHP). The vapor blanket can be formed once the vapor penetrates the wick especially at high heat flux, resulting in an unsaturated state of the wick and deteriorating the evaporator performance. It is crucial to understand the liquid–vapor behavior for enhancing the LHP performance by investigating the fundamental heat and mass transfer in the wick with phase-change. However, previous modeling studies only considered a single-phase flow or complete saturation in the wick, and the capillary effect on the fluid states was rarely taken into account. The present work developed two mathematical models based on the assumptions of saturated and unsaturated wicks. The fluid states were analyzed at the liquid–vapor interface under the consideration of the capillary effect, and a pore-scale evaporation model was applied to study the phase change behavior and interfacial heat and mass transfer. The relative permeability was introduced to describe the two-phase flow in the porous wick, and the capillary force was modeled as a function of the local saturation in the two-phase region. The temperature results calculated by the models were compared with the experimental results, and the assumption that the vapor penetration leads to deterioration of evaporator performance at high heat flux was validated. Vapor blanket thickness can be estimated through the saturation profile, which provides a simple and effective method. It was also found that the capillary number ω was the key factor affecting the thickness of the vapor blanket. The greater the ω , the faster the vapor blanket thickness increases. [ABSTRACT FROM AUTHOR]

This research investigated the flow and heat mass transmission of a thermal Buongiorno nanofluid film caused by an unsteady stretched sheet. The movement of the nanoparticles through the thin film layer is caused by the strength of the heat flow and the stretching force of the sheet working together. The thermal thin-film flow and heat mechanism, and the properties of mass transfer along the film layer, were comprehensively investigated. The consequences of the heat generation, magnetic field, and dissipation phenomenon were also thoroughly examined. Using appropriate dimensionless variables, the fundamental time-dependent equations of thin film nanofluid flow and heat mass transfer were modeled and converted to the ordinary differential equations system. Mathematica version 12 is the software that was used to build the numerical code here. Next, the shooting technique was applied to numerically solve the transformed equations. The elegance of the shooting technique and evidence of the consistency, dependability, and precision of our acquired results is that the results are more effective than those for the thin film nanofluid equations that are now available. There is a significant degree of consistency between the recently calculated results and the results that have been published for a limiting condition. Investigations were conducted into the effects of a variety of parameters on the flow of nanoliquid films, including the Nusselt number, skin friction, and Sherwood number. In addition, a detailed overview of the physical embedded parameters is provided through graphs and tables. However, the important features of the most relevant outcomes are the effects of higher porous and unsteadiness parameters on minimizing the thickness of the thin film; and the viscoelastic parameter has the reverse effect. Additionally, it is seen that the temperature profile improves as a result of higher thermophoresis and Brownian motion parameter values. [ABSTRACT FROM AUTHOR]

Commonly based on the liquid diffusion theory, drying theoretical studies in porous materials has been directed to plate, cylinder, and sphere, and few works are applied to non-conventional geometries. In this sense, this work aims to study, theoretically, the drying of solids with oblate spheroidal geometry based on the thermodynamics of irreversible processes. Mathematical modeling is proposed to describe, simultaneously, the heat and mass transfer (liquid and vapor) during the drying process, considering the variability of the transport coefficients and the convective boundary conditions on the solid surface, with particular reference to convective drying of lentil grains at low temperature and moderate air relative humidity. All the governing equations were written in the oblate spheroidal coordinates system and solved numerically using the finite-volume technique and the iterative Gauss–Seidel method. Numerical results of moisture content, temperature, liquid, vapor, and heat fluxes during the drying process were obtained, analyzed, and compared with experimental data, with a suitable agreement. It was observed that the areas near the focal point of the lentil grain dry and heat up faster; consequently, these areas are more susceptible to the appearance of cracks that can compromise the quality of the product. In addition, it was found that the vapor flux was predominant during the drying process when compared to the liquid flux. [ABSTRACT FROM AUTHOR]

Current disquisition is presented to excogitate heat and mass transfer features of second grade fluid flow generated by an inclined cylinder under the appliance of diffusion, radiative heat flux, convective and Joule heating effects. Mathematical modelling containing constitutive expressions by obliging fundamental conservation laws are constructed in the form of partial differential equations. Afterwards, transformations are implemented to convert the attained partial differential system into ordinary differential equations. An implicit finite difference method known as the Keller Box was chosen to extract the solution. The impact of the flow-controlling variables on velocity, temperature and concentration profiles are evaluated through graphical visualizations. Variations in skin friction, heat transfer and mass flux coefficients against primitive variables are manipulated through numerical data. It is inferred from the analysis that velocity of fluid increases for incrementing magnitude of viscoelastic parameter and curvature parameter whereas it reduces for Darcy parameter whereas skin friction coefficient decreases against curvature parameter. Assurance of present work is manifested by constructing comparison with previous published literature. [ABSTRACT FROM AUTHOR]