Applicable methodologies for modelling of heat and mass transfer phenomena in tumble dryers: A review

Theoretical and Analytical Methods for Determining Heat Transfer Coefficients in Evaporation Processes

In open-surface evaporation systems, the simultaneous transfer of heat and mass is vital for establishing the interrelated exchange of energy and mass between liquid and gas phases. This research offers a comprehensive examination of the physical mechanisms that control evaporation in both natural and forced convection scenarios. It also assesses different theoretical and empirical approaches for calculating the heat transfer coefficient. It has been shown through experiments and numerical analyses conducted in the past that the precision of predictions regarding heat and mass transfer is greatly influenced by factors such as geometrical configurations, convection regimes, and measurement accuracy. Various analytical methods are examined, such as the heat balance equation method that connects heat flux to temperature difference and evaporation rate through interfacial energy balance, and the dimensional analysis method that formulates general correlations based on important dimensionless numbers like Nusselt, Prandtl, Reynolds, and Rayleigh. Moreover, the heat–mass transfer analogy offers a practical framework for estimating one coefficient based on the other by taking advantage of the similarity between temperature and concentration fields. Furthermore, the Ackermann correction factor is implemented to consider the effect of vapor flow on the heat transfer, thereby improving estimations of the heat transfer coefficient during evaporation and diffusion. This research creates an extensive framework for the analysis of open-surface evaporation and the enhancement of heat and mass transfer coefficient predictions. This is achieved through a combination of theoretical, experimental, and analogy-based methods, leading to improvements in the design and functioning of thermal and evaporative systems.

Numerical investigation of coupled heat and mass transfer in deformable granular beds during humid-air and superheated-steam drying

Experimental Investigation and CFD Modeling of Heat and Mass Transfer During Drying of Alfalfa Leaf Fraction in a Rotary Drum Dryer

The convective drying of agricultural materials is an energy-intensive process, and optimizing dryer design is critical for improving efficiency and product quality. This study presents a comprehensive heat and mass transfer model for the convective drying of alfalfa leaves in a rotary drum dryer. Freshly harvested leaves with an initial moisture content of approximately 70% (w.b.) were used as the test material. The proposed system features a simplified drum design aimed at enhancing process efficiency while reducing equipment complexity. The primary objective was to reduce the moisture content of alfalfa leaves to below 50% to ensure their quality during subsequent storage and transportation. To determine the optimal operating conditions, the kinematics of leaf motion inside the rotating drum and the associated heat and mass transfer phenomena were investigated through analytical modeling, numerical simulation, and experimental studies on a laboratory-scale physical model. An analytical model was developed to establish relationships between transverse kinematic characteristics (detachment condition, Froude number, drum inclination angle), average longitudinal velocity, and residence time. Numerical simulations based on the Navier–Stokes equations (continuity, momentum, and energy) provided detailed moisture content distributions within individual leaves under varying airflow orientations and drying durations. The novelty of this work lies in the integrated determination of optimized operating parameters through combined analytical, numerical, and experimental approaches. A regression model relating final moisture content to key process variables (air velocity, temperature of 60 °C, drum rotation frequency and mass of loaded material) was developed from experimental data, yielding practical recommendations for the design and operation of rotary drum dryers for alfalfa and similar agricultural materials.

COMPREHENSIVE ASSESSMENT OF TWO-PHASE FLOW DURING REFRIGERANT BOILING INSIDE PROFILED HORIZONTAL TUBES

This paper presents an evaluation of research results on hydrodynamics and heat transfer during the boiling of refrigerant R22 inside a heat exchange tube with internal longitudinal fins, based on models and correlations proposed by various authors in the available literature. The models demonstrate different approaches to representing correlations for heat transfer calculations, taking into account the influence of hydrodynamic forces such as surface tension, viscosity, and inertia, which affect the motion of two-phase flow in tubes and channels and contribute to the understanding of physical phenomena. The study describes the experimental setup, where heat transfer during refrigerant boiling was investigated under the following operating parameters: heat flux density q = 5, 10, and 20 kW/(m2⋅K), mass flux G = 70, 110, and 200 kg/(m2⋅s), local vapor quality x = 0.01–0.64, and refrigerant saturation temperature ts=15 °C. The influence of heat flux, mass flux, and vapor quality on heat transfer was analyzed, providing valuable insights into heat transfer processes during two-phase refrigerant boiling in tubes and channels. A manufacturing technique for longitudinal fins and unique mandrels for drawing inside copper tubes was developed. Flow visualization revealed stratified, wavy, wavy-slugs, and annular flow regimes. Verification of two-phase flow regimes was performed by comparing experimental results with calculations based on corresponding dependencies from existing flow regime maps. Experimental data were processed using an appropriate methodology for calculating heat transfer coefficients. Based on the obtained results, heat transfer during boiling of two-phase R22 flow inside the finned tube was calculated using 14 models and correlations. The analysis identified models and correlations that most accurately describe the experimental results and can be recommended for engineering practice. Bibl. 31, Tab. 4, Fig. 4.

Flow and Heat Transfer of a Rotary Regenerative Thermal Oxidizer

Thermal storage combustion technology is one of the most efficient methods for treating volatile organic compounds (VOCs), with the rotary regenerative thermal oxidizer (R-RTO) representing the latest generation. However, research on R-RTOs remains scarce and rarely considers the impact of rotation on the flow dynamics and heat transfer. This study employed simulations using the standard k-ε model with enhanced wall function, porous media model, species transport model, Finite-Rate/Eddy-Dissipation combustion model, and the Sliding Mesh method. After validating the simulation accuracy, the velocity and temperature distributions and heat transfer patterns within the channels of the regenerator were investigated. The following conclusions were drawn: The gas flow was uniform within the regenerative chamber but became nonuniform in the lower section of the chamber and within the oxidation chamber owing to the structural and flow directions. This nonuniformity also affected the uniformity of the temperature distribution. A small portion of the gas within the combustion chamber exhibited a short residence time. During rotary valve rotation, inlet gas flow short-circuiting occurred, causing severe fluctuations in the inlet/outlet pressure difference and flow rate, and reducing the VOC removal efficiency. An analysis of the thermal storage media channels revealed that the channel length and inlet air velocity significantly affected the heat transfer coefficient. However, the impacts of these two parameters (length and velocity) and the switching time on thermal efficiency were minor. Furthermore, the switching time had little impact on the heat transfer coefficient.

Comparative evaluation of three thermal conductivity model for AA7072-AA7075-ethylene glycol–water viscoelastic hybrid nanofluid with porous medium using Levenberg Marquardt technique

The purpose of this investigation is to assess the outcome of Soret and Dufour effects on viscoelastic hybrid nanofluid flow across a sheet with convective conditions. The Levenberg–Marquardt technique is notable for its novel approach and convergent stability in the field of artificial neural networks. Using regression plots, state transition measures, histogram representations, and mean squared errors, this proposed model generates a numerical approach. The thermal–solutal convective flow of viscoelastic hybrid nanofluid based on AA7072–AA7075-ethylene glycol–water that is appropriate for complex industrial heat transfer systems where simultaneous mass and heat transport is essential. Heat exchanger design and optimization, cooling systems for metallurgical and chemical processing facilities, polymer production, and energy systems needing improved thermal performance under intricate flow circumstances are all areas in which it is especially helpful. The model helps enhance thermal efficiency, regulate concentration gradients, and guarantee stable operation in high-performance industrial applications by taking into consideration Soret-Dufour effects in addition to viscoelastic behavior. This study investigates mass and heat transmission enhancement in a laminar, steady, and incompressible flow of AA7072–AA7075/EG–H₂O Boger hybrid nanofluid across a sheet. Dufour–Soret effects, convective boundary conditions, thermal radiation, magnetic fields, and Darcy–Forchheimer porous resistance all affect the flow.