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Combustion of iron powder is a promising option for clean and sustainable generation of heat and power. However, a fundamental understanding of the flame propagation mode is missing, especially under strong convection effects. In part I of this work, we analyzed the modes of flame propagation under weak convection effects and estimated the discreteness parameter as a ratio of the particle burn time to the conduction timescale. We found that both, the selection of temperature at which thermal properties are evaluated, and the selected length scale, are critical for a reliable prediction of the transitional particle spacing indicating the transition from the continuous to the discrete mode. In this paper, we extend our previous work by studying the effect of convection on inter-particle heat and mass transfer using boundary layer resolved numerical simulations. It is shown that for increasing convection, iron flames transition from the continuous to the discrete mode at higher particle distances. Taking into account both diffusion and convection-dominated heat transfer, an extension for the scaling of transitional particle spacing of part I is proposed. Furthermore, since iron flames could experience varying ranges of particle distances at different velocities in a practical flame, a regime diagram is constructed which is based on the Péclet number and the particle spacing with a boundary separating the two modes of flame propagation. The regime diagram offers orientation for simulations of large-scale flames using Euler–Lagrange methods where boundary layers around the particles are not resolved. [ABSTRACT FROM AUTHOR]

This review paper presents an overview of transpired solar collectors (TSCs) - a clean energy technology that has gained considerable attention due to its potential to minimise building energy demand and contribute to achieving net zero emissions. The review is mainly focused on scrutinising the disparities in heat and mass transfer mechanisms, specifically the impact of homogeneous and inhomogeneous suction flow distributions on the TSC, encompassing performance improvement methods, performance assessment, and optimisation strategies for TSCs. The inconsistency between the theoretical and real-world performance of TSCs was observed, attributed to the high turbulence wind with non-uniform speed distribution and suction flow interactions with the main flow in the plenum. Corrugations on the absorber improved thermal performance but increased wind heat loss on the exterior surface, which could be mitigated by adding glazing to corrugated TSCs. The review highlighted the flexibility of integrating TSCs with other technologies, including coupling with separate phase change material (PCM) thermal energy storage units, which outperformed those placing the PCM plate into the plenum. Moreover, integrating TSCs with desiccant wheel cooling systems showed some interesting results in terms of cost and payback period, while integration with heat pump systems could reduce electricity consumption, but it was not recommended in cold climates. Exergetic analysis has been frequently used to determine thermodynamic losses of TSCs and it could provide a more accurate performance assessment when integrating TSCs with power generation systems. The review identified several research gaps in related study fields and provided recommendations, encompassing dimensionless analysis of the relationships between wind effect and heat transfer of TSC absorbers, the development of convective heat transfer correlations for TSC's absorber, and the exploration of cost-effective design and optimisation strategies for hybrid TSCs. • Heat and mass transfer mechanisms of transpired solar collectors (TSCs) were analysed. • TSCs can be integrated with different energy technologies to improve flexibility. • Various designs of TSC systems and their main design parameters were discussed. • It provides some insights into developing convective heat transfer correlations. [ABSTRACT FROM AUTHOR]

Pulsed Surface Arc Discharge (PSAD) actuators can improve the aerodynamic performance of aircraft due to their fast response speed and wide frequency band. Understanding the flow structure induced by arc discharge and its transfer process is the key to the sensible use of plasma excitation for flow control. This paper has investigated the dynamic heat and mass transfer process of charged particle clusters generated by arc discharge theoretically and experimentally. The results show that the clusters are composed of charged particles, and the thermal effect is the macroscopic manifestation of the thermal motion of charged particles. The heat and mass transfer processes of charged particle clusters can be expressed as a function of temperature. During heat and mass transfer, the transfer mode of the plasma cluster composed of charged particles will change. The plasma cluster will change from forced convection in the initial stage to natural convection in the final stage, and the Richardson number is different in different stages. The heat released by the gas discharge and the heat released by the plasma mass transfer will form accumulated heat in the space and change the temperature difference, thereby affecting the process of heat and mass transfer. This paper has constructed a model describing pulsed plasma clusters' dynamic heat and mass transfer. Furthermore, the dynamic mode decomposition results of the theoretical model function show that plasma clusters mainly conduct the mass transfer through low-frequency and heat transfer through high-frequency modes. [ABSTRACT FROM AUTHOR]

• Study the Buoyancy-Marangoni convection in a porous cubic cavity with complex surface. • The Weierstrass–Mandelbrot (W-M) function is applied to simulate the shape of the complex upper surface. • Find the effects of fractal dimension on fluid flow, heat and mass transfer. • Simulate the 3D convection with the high order accurate compact finite volume method. In this paper, a convection and heat transfer problem of power-law fluid in a three-dimensional porous media with complex surface is studied. The Buoyancy-Marangoni convection for non-Newtonian power-law fluids in porous media is solved using a compact high-order finite volume method. For this single-phase model, the left wall is kept at high temperature and high concentration, the right wall is affected by lower temperature and lower concentration, the upper wall is a complex surface, and the remaining walls are considered to be adiabatic and impermeable. The Weierstrass–Mandelbrot function is used to simulate the shape of the upper surface. The fluid in the porous cavity is a power-law nanofluids containing copper oxide nanoparticles. The solid material of the porous medium is aluminum foam. Numerical simulations can be used to determine the power law exponent, Marangoni number, Rayleigh number, and aspect ratio on the flow, heat transfer, and mass transfer rate. [ABSTRACT FROM AUTHOR]

Nanorefrigerants are a special type of nanofluids which are mixtures of nanoparticles and refrigerants and have a broad range of applications in diverse fields for instance refrigeration, air conditioning systems, and heat pumps. In this paper thermal–physical properties of nanoparticles suspended in refrigerant and lubricating oils of refrigerating systems were reviewed. The effects of nanolubricants on boiling and two phase flow phenomena are presented as well. Based on results available in the literatures, it has been found that nanorefrigerants have a much higher and strongly temperature-dependent thermal conductivity at very low particle concentrations than conventional refrigerant. This can be considered as one of the key parameters for enhanced performance for refrigeration and air conditioning systems. Because of its superior thermal performances, latest up to date literatures on this property have been summarized and presented in this paper as well. The results indicate that HFC134a and mineral oil with TiO 2 nanoparticles work normally and safely in the refrigerator with better performance. The energy consumption of the HFC134a refrigerant using mineral oil and nanoparticles mixture as lubricant saved 26.1% energy with 0.1% mass fraction TiO 2 nanoparticles compared to the HFC134a and POE oil system. [ABSTRACT FROM AUTHOR]

The brake disc of a high-speed train can produce huge heat in the process of steep brake or parking brake. Thus the heat transfer characteristics of the high-speed train brake discs are the basic information needed to design them. The main works of the present paper are to establish a flow model that is similar to the actual brake disc working conditions, and to obtain the local and average convective heat transfer characteristics of the outside surface of vehicle break disc experimentally. The naphthalene sublimation technique of heat/mass transfer analogy method is used. The significant result is that the diameter ratio of the brake disc to the wheel determines the convective heat transfer characteristics on the vehicle's brake disc outside surface. Due to the influence of the ground, the average Nusselt number on the surface of a break disc is larger than that of a rotating disc in crossflow at the same Reynolds number. The local Nusselt number on the surface of a break disc decreases along the radius direction. The correlations of the local and average Nusselt numbers, Reynolds number, and the diameter ratio of brake disc to wheel are established. The average Nusselt number is larger than that on the surface of a rolling wheel at the same Reynolds number. [ABSTRACT FROM AUTHOR]

• A deep reinforcement learning based forced convection control method is proposed. • A novel deep Q-network (DQN) integrating with three advanced techniques is used. • The method shows efficiency and robustness on learning nonlinear control strategy. • The trained agent has generalization ability on geometric configuration. In this paper, deep reinforcement learning (DRL) is applied on forced convection control of conjugate heat transfer systems governed by the coupled Navier-Stokes and heat transport equations. A novel value-based deep Q-network (DQN) integrating with three advanced techniques is utilized for identifying underlying heat and mass transfer mechanism in the interaction of close-loop active control. The effectiveness and feasibility of DRL based forced convection control is firstly demonstrated by studying a two-dimensional cooling problem, where a single heat source immersed in an open cavity. A more complex testbed with multiple immersed heat source and multiple degree-of-freedom control is investigated further, which shows outstanding capability of DRL algorithm to learn strong nonlinear control strategy, and compared to conventional control method, the novel DRL approach has ability to obtain better cooling effect of about 8 degrees lower. Then the robustness of the method is verified by applying trained agent on several situations with unknown physical conditions and adding additional customized control requirements/aims. Moreover, sensitivity analysis confirms that the trained agent has a certain generalization ability on geometric configuration, which strengthens the confidence of applying the DRL-based active heat transfer control method on practical applications. Current research demonstrates the efficiency and applicability of the DRL based active thermal control on strong-nonlinearity system, and also encourages further investigations on more complex and practical problems. [ABSTRACT FROM AUTHOR]

In this paper we present the numerical solution of the problem 2-D unsteady free convective heat and mass transfer flow over a moving semi-infinite vertical porous plate with thermal diffusion in presence of magnetic field, dissipative heat and Soret effects taking into account the induced magnetic field. The steady-state numerical solutions for the velocity field, induced magnetic field, temperature distribution and concentration distribution are obtained by the explicit finite difference method and the network simulation method. The obtained results have been shown graphically. The obtained numerical results were compared with other author data to demonstrate the efficiency of the method used, moreover all the cases the convergence is always quickly reached. An increase in Soret or Eckert number is found to strongly enhance the fluid velocity and temperature values, and this effect is reversed for the induced magnetic field. It is found that the flow velocity decreases with the increase in Hartmann and magnetic Prandtl number, and an opposite behaviour is observed for the fluid temperature. Applications of the study arise in the thermal plasma reactor modelling, the electromagnetic induction, MHD transport phenomena in chromatographic systems, and the magnetic field control of materials processing. The results show that both methods provide excellent approximations to the solution of this nonlinear system with high accuracy. [ABSTRACT FROM AUTHOR]

In this paper, a generalized formulation of stiffness and mass using modified integration rules (MIR) with flexible integration points is developed to improve the stability of transient heat transfer problems. With adjustment of integration points in the stiffness, the softening or stiffening properties of discretized model for heat transfer problems can be altered. In addition, it is found that the integration points in the mass have a great effect on the critical time step for the explicit formulation of transient heat transfer problems. With a proper selection of integration points in the mass, a much larger time step can be applied in the analysis of transient heat transfer problems. Furthermore, it is observed that the final steady solutions of transient heat transfer problems are identical regardless of locations of integration points in the mass model. Numerical experiments including 2D heat transfer problems with different boundary conditions including heat conduction, heat convection and radiation are studied to verify the properties of flexible integration points in the stiffness and mass. [ABSTRACT FROM AUTHOR]

In this paper bioconvection flow with heat and mass transfer of a water-based nanofluid containing gyrotactic microorganisms over a vertical wavy surface is investigated. The coupled nonlinear set of equations comprised of velocity, temperature, nanoparticle concentration and density of microorganisms is solved numerically by using implicit finite difference method. Flow characteristics are obtained in terms of skin friction coefficient, Nusselt number, Sherwood number and density number of microorganisms coefficient and are presented graphically by varying several controlling parameters. Interesting observations are recorded for the parameters: a , Nr , Lb and Rb . It is observed that the amplitude of the wavy surface has pronounced influence on the rates of heat and mass transfer, skin friction coefficient and density number of the microorganisms coefficient and all these quantities get augmented as the amplitude increases. [ABSTRACT FROM AUTHOR]

This paper experimentally investigates the heat transfer performance and characteristics of a heat sink with bio-mimetic oscillating foil. The oscillating foil is driven by a novel mechanism of grooved cam with linkage. The air flow is drawn into a rectangular duct through the motion of the bio-mimetic oscillating foil. Various heat sinks were set at the outlet of the duct to study the thermal performance. Two types of grooved cams were designed to obtain different angular velocity profiles for the oscillating foils. The angular velocity was specified as fast forward/slow backward and sinusoidal patterns. Foils with three flexural stiffness values were utilized in the study. The averaged velocity at the inlet was measured to estimate the Reynolds number and Strouhal number. The effects of configuration of heat sink design with oscillating foil were also under investigation. The junction temperature of the heat sink was measured to obtain the effective thermal resistance. Results show that the angular velocity profile and flexural stiffness of the oscillating foil have a significant effect on the thermal performance of the heat sink. [ABSTRACT FROM AUTHOR]

This paper focuses on designing an artificial neural network which can predict thermal conductivity and dynamic viscosity of ferromagnetic nanofluids from input experimental data including temperature, diameter of particles, and solid volume fraction. The experimental data were extracted and they were used as learning dataset to train the neural network. To find a proper architecture for network, an iteration method was used. Based on the results, there was no over-fitting in designed neural network and the neural network was able to track the data. ANN outputs showed that the maximum errors in predicting thermal conductivity and dynamic viscosity are 2% and 2.5%, respectively. Based on the ANN outputs, two sets of correlations for estimating the thermal conductivity and dynamic viscosity were presented. The comparisons between experimental data and the proposed correlations showed that the presented correlations were in an excellent agreement with experimental data. [ABSTRACT FROM AUTHOR]

This paper describes in detail the measurement of the overall heat transfer coefficient and phase transformation latent heat by modified pattern search method (PSM). By introducing the pattern search algorithm into finite element analysis, the measurement of heat transfer coefficients and phase transformation latent heat can be simplified as recording the temperature with time. Comparison of the measurements by PSM and temperature gradient method (TGM) shows that PSM can evaluate the overall heat transfer coefficient accurately. Experiments and simulations show that bainite transformation latent heat in 26NiCrMoV10-10 steel is about − 90.5 J/g, and the latent heat increases the surface temperature of a cylindrical specimen by a maximum of 76 °C. Error analysis shows that the highest difference between calculated temperature and measured temperature is 11.7 °C, which verifies that the heat transfer coefficient and phase transformation latent heat estimated by PSM are accurate, and that the pattern search method is reliable. [ABSTRACT FROM AUTHOR]

In this paper, the melting and solidification processes and the thermal conductivity enhancement of the phase change material (PCM) inside a sphere have been experimentally investigated to facilitate a greater understanding and improvement of the phase change heat transfer of PCM inside a sphere. The experiments are conducted by inserting a sphere filled with organic PCM into a constant temperature bath of hot/cold water. Through measuring and analyzing the temperature field inside the sphere under conditions of various initial and final temperatures, the thermal characteristics of melting and solidification processes of PCM are obtained. To determine the thermal conductivity enhancement effect of aluminum powder, the PCM-aluminum composite material in which the mass fractions of aluminum are 1% and 2%, respectively, is tested. And the experimental data of PCM-aluminum composite material are compared with those of pure PCM. Results indicate that the PCM in the upper part of the sphere melts faster than that in the lower part, and the PCM near the inner wall solidifies faster than that in the center of the sphere. The initial PCM temperature has little effect on the solidification process of the PCM inside the sphere when Stefan number ( Ste ) is small and Rayleigh number ( Ra ) is large. The thermal conductivity of the PCM inside the sphere is enhanced by adding aluminum powder. And the sedimentation of aluminum powder is more beneficial to accelerate the heat transfer of the whole sphere in the melting process, compared with the uniform diffusion of aluminum powder in the PCM. [ABSTRACT FROM AUTHOR]

In this paper, laminar forced convective heat transfer of water/alumina nanofluids in a straight microchannel is studied numerically using CFD modeling. In the first part, single-phase and two-phase mixture models have been used for prediction of hydrodynamics and heat transfer parameters of nanofluids in a simple microchannel heat sink. The CFD predictions were compared to the experimental data and it was concluded that the two-phase approach gives better predictions compared to the single-phase model. The effects of ribs turbulators on the fluid flow and heat transfer performance of microchannel were investigated in the second part. The effects of geometrical characteristics of the ribs were studied, and the results showed that the Nusselt number and friction coefficient of nanofluids in the ribbed microchannel are higher than those of simple microchannel, and this enhancement increased with increasing the width of the ribs. [ABSTRACT FROM AUTHOR]

Based on constructal theory, the construct of a three-dimensional cylindrical heat sources with convection heat transfer is investigated in this paper. The heat source model is composed of several cylindrical heat sources surrounded with a cylindrical fin or a conical fin. The heat source model not only exists in the heat generating electronic component surrounded with a fin to enhance heat transfer, but also in the heat generating fuel rod with zircaloy cladding. For the specified volumes of the fin and the heat sources, this construct is optimized by taking the minimization of the dimensionless hot spot temperature as optimization objective. The results show that the hot spot temperature of the model is effectively reduced after constructal optimization, which will provider some theoretical guidelines for the optimal design of heat source system. [ABSTRACT FROM AUTHOR]

In this paper, the characteristic variational multiscale (C-VMS) method is proposed to solve the nonstationary conduction–convection problems. The stability analysis is carried out using the energy estimate method. Compared with the standard variational multiscale (VMS) method, the C-VMS method does not need nonlinear iteration. Finally, some numerical examples are given, which show that the C-VMS method is efficient, reliable and can save a lot of CPU time for this problem, besides, it can deal with the high Rayleigh number. [ABSTRACT FROM AUTHOR]

This paper reviewed the application of nanofluids in vehicle engine cooling system. So far, nanoparticles have been used in engine oil, transmission oil, and radiator coolant to enhance heat transfer removal from vehicle engine. The heat transfer performance of nanofluids has been reported to perform better compared to pure fluid. This review focused on the experimental and numerical studies by previous researchers and their suggested amount of nanoparticles for optimum performance in vehicle engine cooling system. Finally, the conclusions and important summaries were presented according to the data collected. [ABSTRACT FROM AUTHOR]

This paper presents a transient model of internal catalytic combustion suitable for isolated channels and monolith reactors. Due to time-scales in the problem, the model considers a quasi-steady gas phase with a transient solid. The gas is described by axially varying bulk temperature and species. The gas includes lateral diffusion via transfer coefficients and the specification of a gas-phase species concentration at the wall; axial diffusion is neglected. The solid phase is a thermally thin shell with axially varying temperature, surface species, and surface species concentrations. The solid includes axial heat conduction and external heat loss by convection and radiation. The combustion process utilizes detailed gas and surface reaction models. The gas-phase model becomes a system of stiff ordinary differential equations with respect to axial position; the upstream (inlet) boundary conditions are specified and the axially varying solid properties are parameters in integration. The solid phase discretizes into a system of stiff ordinary differential-algebraic equations with respect to time. The time evolution of the system comes from alternating integrations of the quasi-steady gas phase and transient solid. The model is compared to two experimental cases using CO fuel: (1) steady-state conversion in an isothermal platinum tube and (2) transient propagation of a catalytic reaction inside a small platinum tube and includes external tube temperature measurements. This work presents sensitivity studies on important parameters including internal transfer coefficients, catalytic surface site density, external heat-loss, and others. Under mass-transfer limited conditions, global transfer coefficients are adequate to predict fuel conversion. Near light-off, the model predictions improve for the first case after adjusting the surface kinetics such that the net rate of CO adsorption increases compared to O 2 . For the second case, predictions of transient propagation speeds are good for equivalence ratios near unity and greater but require adjustment of external heat loss or kinetics to match under lean conditions. [ABSTRACT FROM AUTHOR]

• Energy performance in a building element filled with a phase change material is studied numerically. • Numerical simulation based on the enthalpy variable is performed. • Thermal nature of ambient temperature is described by the harmonic law. • PCM based block shows a higher thermal resistance in a horizontal position. Recent developments in the field of net zero energy buildings are related to energy savings and solar energy conservation systems. The use of new materials, such as phase change materials, is one of the most promising directions of energy storage. In this paper, building element made of layers of concrete and heat-insulating material with a cavity filled with RT-25 as a PCM was considered. The process of heat transfer in a building element under non-stationary external thermal effect is investigated. The influence of the inclination angle of the element from 0 to 90° on the melting process of the material and its ability to restrain the heating process under the condition of convective mixing of the melt are analyzed. The equations of heat and mass transfer are solved taking into account phase transitions and buoyancy forces in the melt. It is shown that the tilt angle of the block with the PCM insert determines the intensity of heat transfer due to convective mixing of the melt. Under the same external thermal conditions, PCM wall transmits more heat than PCM roof, the difference on the indoor surface at peak thermal conditions for different tilt angles can reach 4.5°. [ABSTRACT FROM AUTHOR]

• Intensity of heat and mass transfer between the flowing air and bed particles. • Determine the quantitative values ​​of the stored and supplied heat in real facilities. • Modeling heat and mass processes occurring in a rock-bed accumulator. The paper presents the results of the research concerning heat and mass transfer phenomena occurring in a porous bed of a rock-bed heat accumulator. The tests were carried out in a standardized semi-cylindrical foil tunnel, commonly used in horticulture farming, equipped with a rock-bed accumulator covering the area of 74.8 m2. Input data for the analysis were obtained from experimental studies carried out from April to October, including 435 charging and 409 discharging cycles. During the experiments, the process parameters, such as temperature, relative humidity and air flow velocity, in different measuring points of the system were recorded. Using modern mathematical modeling a multi-scale analysis was carried out to quantify the intensity of heat and mass transfer between the flowing air and bed particles, as well as the degree of humidification or drying of the air flowing out of the accumulator. The values of convective heat transfer coefficients and mass transfer coefficients for individual charging and discharging cycles were determined and correlation equations for them were found. The conducted analysis showed that the coefficients determined by measurements fit the proposed regression models with the following values of R2 (coefficient of determination): 0.83 and 0.86 for mass transfer coefficient (condensation and drying, respectively), and 0.85 for convective heat transfer coefficient. Using the similarity theory, the equations for calculating Nusselt and Sherwood numbers were found, from which the coefficients adopted for analysis can be derived. It was also analyzed to what extent the obtained results differ from the results presented by other authors describing similar issues. The originality of this research consists in determining the values of heat and mass transfer coefficients for the air flow through the porous bed and finding their functional dependencies on the input parameters. The research results fill the gaps in scientific knowledge; moreover, they can be applied in heat transfer engineering issues, such as modeling heat and mass processes occurring in a rock-bed accumulator in a greenhouse or in other facilities, thus enhancing the energy efficiency of the designed systems. [ABSTRACT FROM AUTHOR]