Heat and Mass Transfer in Microwave Processing

1.46 - Microwave and Radiofrequency Processing of Plant-Related Food Products

Experimental mass and heat transfer at a serpentine tube heat exchanger located at the wall of a square stirred tank reactor

Film-inversion is an effective way recently developed to enhance heat and mass transfer in absorbers. However, only one-side of round or rectangular tube i.e. half of the total heat transfer area is used to form film-inverting configuration in the published literature. The paper presents a double-side film-inverting scheme, which consists of two plate bundles and a set of comb shaped conjunction guiders between them for leading solution film from both-sides of each couple of the upper plate bundle to the opposite sides of the bottom ones. A two-scale crosswise corrugation plate bundle, which has vertical large corrugations and horizontal small ones, is suggested instead of the plane plate bundle. The horizontal small corrugation can make the film turbulent and film distribution uniform before and after inversion with surface tension effect, thus increasing the heat and mass transfer coefficients of the absorption process. A mathematic model for heat and mass transfer in absorption process with aqueous Li-Br solution falling film-inverting on two sequential vertical plane plates was established and solved numerically. The distributions of dimensionless velocity, temperature and concentration of liquid film profile before and after film-inverting were obtained. The influence of the number of inversion on heat and mass transfer characteristics was analyzed. The calculation results show that the heat and mass transfer coefficients of the once-film-inverting scheme have about 58% and 73% increment respectively over these of the none film-inverting scheme.

The mixed Marangoni assisting/resisting flow of a nanofluid with thermal radiative heat flux is analyzed when thermal and solutal buoyant forces are significant. The heat and mass transfer rates are simultaneously optimized by utilizing the Response Surface Methodology (RSM). The face‐centered Central Composite Design (fc‐CCD) is used for the numerical experimental design involved in RSM. The sensitivities of the heat and mass transfer rates are evaluated to compare the impact of the thermal and solutal buoyant forces. Appropriate scaling and similarity transformations are utilized to simplify the problem and then numerical solutions are obtained. The nanoliquid flow, temperature, and concentration profiles are plotted for the buoyancy assisting and opposing Marangoni cases. The Marangoni flow with opposite buoyancy is found to have a greater magnitude of velocity while the flows assisted by the buoyancy have a greater magnitude of temperature and concentration profiles. Thermal buoyancy force has a predominant (0.6%) impact on both heat and mass transfer rates compared to solutal buoyancy force. Buoyancy forces are positively sensitive to heat and mass transfer rates. The thermal radiation aspect augments the temperature profile throughout the domain. The optimized mass and heat transfer rates ( and ) is achieved at the highest level of the buoyancy forces and ratio of Marangoni numbers.

Dew-point evaporative cooling (DPEC) is renowned for its great cooling effectiveness and energy savings. However, to improve its cooling performance by optimizing the cooler's common design parameters (e.g., operating conditions and channel dimensions) has reached a bottleneck where further breakthroughs are difficult to make. Although macro-roughened structures have been found effective to enhance the heat transfer in many devices, the lack of fundamental studies and understanding on the enhanced heat and mass transfer limits their utilization in DPEC. Therefore, this study aims to investigate the enhanced DPEC with rib-roughened dry channels. A dew-point evaporative cooler with seven pairs of dry-wet air channels was constructed and tested under varying supply air and operating conditions, which demonstrated excellent cooling performance particularly at high air velocities. Concurrently, a novel low-Reynolds number computational fluid dynamics (CFD) model was developed to capture the turbulent heat and mass transfer mechanism, validated with a maximum discrepancy of 8% by the experimental data. An in-depth theoretical investigation of the rib-roughened channels show that detached vortices found near the ribs can enhance the convective heat transfer in the dry channel, as well as heat and mass transfer in the wet channel. The average Nusselt number in the dry and wet channels can reach 4 and 1.13 times of that in flat channels, respectively, and the average Sherwood number in the wet channel can reach 1.14 times. More enhanced cooling effect is observed under high air velocity conditions, leading to a reduction of product air temperature by 2.3–3.0 °C and an increase in dew-point effectiveness by 0.14–0.18. The fundamentally enhanced heat and mass transfer in the macro-structured channels provides a new research direction for the development of DPEC.

Oil and gas companies and research organizations developed and implemented in industry for new ways and processes of extraction and refining of oil and gas. For example, in today's world there is an enormous amount of research in the theory of filtration with a sufficient set of various mathematical models and different approaches to solve them, but unfortunately the reality of developments in the oil and gas fields, more complex processes of filtration options, taking into account the kinetics heat and mass transfer, etc., which of course directly affects the process flow operation of the facility and information systems requires a "fast" response (calculation) and forecasting. The latter implies the formation of an adequate IT systems, computer simulation and its early settlement for the shortest time that can not be achieved without the use of modern programming packages. Similary problems in using of surfactants. Injection of heat-carriers include mass and heat transfers in two different areas, combined transition interfaces through the moving front and accompanied by phase changes. The last two characteristics describe a general class of problems known as the Stefan and Verigin types of problem. We developed and studied a variety of mathematical models of filtration in a porous media with kinetic relations of heat and mass transfer. Created a computational algorithm of the task. In studying the process of pumping Surfactants in a productive oil reservoir must consider thermal effects that are more convenient to define a kinetic equation of heat and mass transfer characteristics for two different areas, combined transition interfaces through the moving front and accompanied by phase changes, which defines a single constructive approach solving a general class of problems like Stefan and Verigin or Darcy-Stefan. We offered mathematical model describing the mass transfer processes for nonisothermal filtration with conditions of formation boundaries of "transition" zones and computational parallel algorithm for 3D case based on Web oriented applications.

The performance of the absorber significantly affect the overall efficiency of any absorption refrigeration system. One of the major reasons for the poor design of the absorber for ammonia-water refrigeration systems is the neglect of mass transfer resistances in the vapour or liquid phase in favour of only heat transfer considerations. Heat removal is critical to the absorption process, however, the ammonia gas is constantly absorbed by the liquid ammonia-water solution. This means that two-phase mass and heat transfer operations take place during the absorption process. Therefore, this implies that, for any proper absorber design, both heat and mass transfer considerations are paramount. Accurate absorber design is further predicated on accurate properties correlations. The correlations required for the absorber design include liquid and vapour enthalpies, saturated vapour pressure, specific heat capacity of water and ammonia vapour, liquid solution dynamic viscosity, liquid solution density, surface tension, liquid solution thermal conductivity, liquid-liquid diffusivity and vapour-liquid diffusivity. Procedures for calculating these parameters have been presented in this paper and their accuracy with previous studies compared. Results showed relatively low percentage deviations and so can be applied for the design and simulation of the absorber. Designs of the absorber for various cooling capacities have been carried in this paper. The variation of ammonia vapour temperatures, liquid ammonia-water solution temperatures, cooling water temperatures, and flow rates of ammonia-water solution and ammonia vapour across the absorber is investigated for the four cooling capacities. For refrigeration systems with cooling capacities of 1 kW, 2 kW, 3 kW and 4 kW, the calculated lengths for a water-cooled coiled absorber are 4.484 m, 8.1467 m, 12.50459 m and 14.78329 m respectively. The calculated overall heat transfer coefficients for the absorption process for the four cooling capacities (1 kW, 2 kW, 3 kW and 4 kW) were 0.4427, 0.4376, 0.4208 and 0.4309 kWm-2K-1 while the mass transfer coefficients were 3.721 x10-9, 4.206 x10-9, 4.556 x10-9and 4.856 x10-9 m2s-1 respectively. Concurrent flow is considered in this study, but the procedure can also be applied to countercurrent flow. KEYWORDS: Absorption Refrigeration, Ammonia Water Heat and Mass Transfer, Design

Thermodynamic and Gasdynamic Aspects of a Boiling Liquid Expanding Vapour Explosion

Simultaneous mass and heat transfer with reactions in a multicomponent, laminar, falling liquid film

The air gap membrane distillation (AGMD) process was applied for water desalination. The main objective of the present work was to study the heat and mass transfer mechanism of the process. The experiments were performed on a flat sheet module using aqueous NaCl solutions as a feed. The membrane employed was hydrophobic PTFE of pore size 0.22 . A mathematical model is proposed to evaluate the membrane mass transfer coefficient, thermal boundary layers` heat transfer coefficients, membrane / liquid interface temperatures and the temperature polarization coefficients. The mass transfer model was validated by the experimentally and fitted well with the combined Knudsen and molecular diffusion mechanism. The mass transfer coefficient increased with an increase in feed bulk temperature. The experimental parameters such as, feed temperature, 313 to 333 K, feed velocity, 0.8 to 1.8 m/s (turbulent flow region) were analyzed. The permeation fluxes increased with feed temperature and velocity. The effect of feed bulk temperature on the boundary layers` heat transfer coefficients was shown and fairly discussed. The temperature polarization coefficient increased with feed velocity and decreased with temperature. The values obtained were 0.56 to 0.82, indicating the effective heat transfer of the system. The fouling was observed during the 90 h experimental run in the application of natural ground water and seawater. The time dependent fouling resistance can be added in the total transport resistance.

From a subsurface physical point of view, this paper discusses the necessity of considering the two‐phase heat and mass transfer process in land surface models (LSMs). The potential‐based equations of coupled mass and heat transport under constant air pressure form the basis of the proposed model. The model is developed considering dry air as a single phase, and including mechanical dispersion in the water vapor and dry air transfer. The adsorbed liquid flux due to thermal gradient is also taken into account. The set of equations for the two‐phase heat and mass transfer is formulated fully considering diffusion, advection, and dispersion. The advantage of the proposed model over the traditional equation system is discussed. The accuracy of the proposed model is assessed through comparison with analytical work for coupled mass and heat transfer and experimental work for isothermal two‐phase flow (moisture/air transfer). The influence adding airflow has on the coupled moisture and heat transfer is further investigated, clearly identifying the importance of including airflow in the coupled mass and heat transfer. How the isothermal two‐phase flow is affected by considering heat flow is also evaluated, showing the influence of heat flow only to be significant if the air phase plays a significant role in solving the equations of the water phase. On the basis of a field experiment, the proposed model is compared with the measured soil moisture, temperature, and evaporation rate, the results showing clearly that it is necessary to consider the airflow mechanism in soil‐atmosphere interaction studies.

Professor Michael J. Pikal: Scientist, family man, educator, colleague and friend

The significant research has seen with nano fluid flow and heat transfer. But still there is a wide scope of research in mass transfer with nano fluids due to Brownian motion of particles. A theoretical investigation has attempted in this paper to study the chemical reaction effects during mass transfer. We have studied convective heat and mass transfer of MHD nano fluid flow past inclined, oscillating permeable flat plate with radiation and Abstract: The significant research has seen with nano fluid flow and heat transfer. But still there is a wide scope of research in mass transfer with nano fluids due to Brownian motion of particles. A theoretical investigation has attempted in this paper to study the chemical reaction effects during mass transfer. We have studied convective heat and mass transfer of MHD nano fluid flow past inclined, oscillating permeable flat plate with radiation and Abstract: The significant research has seen with nano fluid flow and heat transfer. But still there is a wide scope of research in mass transfer with nano fluids due to Brownian motion of particles. A theoretical investigation has attempted in this paper to study the chemical reaction effects during mass transfer. We have studied convective heat and mass transfer of MHD nano fluid flow past inclined, oscillating permeable flat plate with radiation and

Heat and mass transfer in a cylindrical grain silo submitted to a periodical wall heat flux

This study analyses the entropy and heat transfer characteristics of couple-stress Casson fluid in a porous vertical microchannel, incorporating the effects of isothermal cubic autocatalytic chemical reactions, variable thermal conductivity, uniform heat source/sink, and thermal radiation. The governing equations are transformed into dimensionless form and solved numerically using the fourth and fifth-order Runge-Kutta-Fehlberg method. Key findings reveal that the inverse couple-stress parameter and variable thermal conductivity, significantly influence temperature distribution and fluid flow, enhancing heat transfer efficiency throughout the microchannel system. The study also highlights that homogeneous-heterogeneous reactions reduce concentration levels, improving lubrication and optimizing thermal performance. Additionally, entropy generation increases with higher Biot number, variable thermal conductivity, radiation, and heat source/sink effects. The Nusselt number decreases with increasing thermal conductivity, while drag force minimizes as the inverse couple-stress parameter rises. These findings contribute to the optimization of microfluidic thermal systems, with practical applications in energy-efficient cooling technologies, microchannel heat exchangers, advanced chemical reactors, and biomedical engineering, where precise heat and mass transfer control is essential for improved performance and efficiency.