This article deals with the in-mold cake baking process. The methodology relies on numerical and experimental investigations to validate a multiphysics developed model. This numerical model is next ...exploited to enhance the comprehension of the physical processes that occur during a typical cake baking phase. Based on the governing equations for heat and mass transport and under few assumptions (deformable porous medium, local thermodynamic equilibrium, ideal gas mixture …), the problem consists in solving a system of five coupled partial derivative equations. Temperature, moisture content, total gas pressure, porosity and displacement are used as state variables in this study. The swelling of the dough caused by the increase in total gas pressure is predicted by a viscoelastic model. This thermo-hydro-mechanical model is implemented in a finite element code. Moreover, an experimental laboratory set-up was developed to continually acquire temperatures, water losses and gas pressure inside the product. The browning kinetic is also studied. Furthermore, the cake deformation is tracked by camera. The numerical model is validated based on the conducted experiments. Different operating conditions are tested to verify the robustness of the model. Finally, a sensitivity analysis is performed to understand the impact of estimated parameters on the outputs of the developed model.
•A multiphysics model is developed to predict the kinetics of in-mold cake baking.•Heat and mass transfer, mechanical behavior and product coloration are considered.•Numerical sensitivity of the model is investigated.•The numerical model is experimentally validated at two different temperatures.•Instrumented product, mold and oven are used to investigate the cake baking.
•A method for controlling the reforming reaction based on Da number is summarized.•Modulation of the Da number distribution can increase the conversion rate by 10%.•Two-stage scheme increased the ...methanol conversion rate from 82% to 88.52%, USAER is 7.7.•The USAER of “4mm-2 mm-6 mm” is 8.342, and the USAER of “2mm-4 mm-2 mm” is 9.11.
In the amplification mode, microscale reforming reactions are controlled by the transfer rate. To avoid the amplification effect, the process coupling mechanism in the microchannel reactor must be studied to take full advantage of its precise control. This paper studies the coupling effect between the flow process and the reforming process in the microchannel and constructs a computational model of the flow coupling. A study was conducted on the influence of the coupling effect on the conversion rate, based on a combination of reliability verification and experiments. The following conclusions were obtained: the coupling effect in the reactive flow field was quantified based on the characteristic time of the flow process and the reaction process (Da number), and the microchannel was divided into three parts. The methanol conversion rate of the burst-expansion scheme was increased to more than 6%, and the USAER (unit surface area enhancement rate) reached 7.7. The USAER of the protrusion-expansion scheme can reach 8.342, with a potential for an 10% increase in conversion rate. The distribution of the three-segmented variable cross-section has the most effective regulation effect. The USAER of the protrusion-expansion scheme reaches 9.11, with a conversion rate that can be increased by 7%.
A Lagrangian tracking method is introduced, which uses a prediction of the particle distribution for the subsequent time-step as a mean to seize the temporal domain. Errors introduced by the ...prediction process are corrected by an image matching technique (‘shaking’ the particle in space), followed by an iterative triangulation of particles newly entering the measurement domain. The scheme was termed ‘Shake-The-Box’ and previously characterized as ‘4D-PTV’ due to the strong interaction with the temporal dimension. Trajectories of tracer particles are identified at high spatial accuracy due to a nearly complete suppression of ghost particles; a temporal filtering scheme further improves on accuracy and allows for the extraction of local velocity and acceleration as derivatives of a continuous function. Exploiting the temporal information enables the processing of densely seeded flows (beyond 0.1 particles per pixel, ppp), which were previously reserved for tomographic PIV evaluations. While TOMO-PIV uses statistical means to evaluate the flow (building an ‘anonymous’ voxel space with subsequent spatial averaging of the velocity information using correlation), the Shake-The-Box approach is able to identify and track individual particles at numbers of tens or even hundreds of thousands per time-step. The method is outlined in detail, followed by descriptions of applications to synthetic and experimental data. The synthetic data evaluation reveals that STB is able to capture virtually all true particles, while effectively suppressing the formation of ghost particles. For the examined four-camera set-up particle image densities
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up to 0.125 ppp could be processed. For noise-free images, the attained accuracy is very high. The addition of synthetic noise reduces usable particle image density (
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≤ 0.075 ppp for highly noisy images) and accuracy (still being significantly higher compared to tomographic reconstruction). The solutions remain virtually free of ghost particles. Processing an experimental data set on a transitional jet in water demonstrates the benefits of advanced Lagrangian evaluation in describing flow details—both on small scales (by the individual tracks) and on larger structures (using an interpolation onto an Eulerian grid). Comparisons to standard TOMO-PIV processing for synthetic and experimental evaluations show distinct benefits in local accuracy, completeness of the solution, ghost particle occurrence, spatial resolution, temporal coherence and computational effort.
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•An Al-based MIC (EF@EMOF) was prepared via electrospinning combining with in situ growth technique.•Obtained MIC has significantly increased heat release and burning rate.•The ...etching reaction avoids the sintering and improves combustion efficiency.
Combustion is a kind of reacting process involves fluid mechanics and chemical reactions at the same time. In the past decades, little attention has been paid to the improvement on the heat and mass transfer rate of EMs, especially for metastable intermixed composites (MICs). In this paper, an Al-based MIC (EF@EMOF) with modified chemical kinetics as well as improved heat and mass transfer rate was prepared by precisely designing the reaction process and introducing energetic metal organic frameworks (EMOF) with high specific surface area as the reactants. The overall reaction process includes the activation of n-Al by eliminating Al2O3, decomposition of EMOF producing metal oxide, followed by exothermic reactions between the activated n-Al with metal oxide and PVDF. Results show that obtained MIC has significantly increased heat release (3464 J g−1), burning rate (more than 5 times faster than that of mechanically mixed one), and improved combustion efficiency. Furthermore, it is found that the decomposition of EMOF as well as the etching reaction generates massive gas products on the interface layer which avoid the sintering and form lots of holes. Those holes, in return, provide new channels for the further reaction, thus significantly improving the energy output and chemical reaction kinetics.
•Particle behaviors in biomass gasification are studied via reactive CFD-DEM.•Higher temperature and S/B promote the solid vertical dispersion coefficient.•The contribution of different heat transfer ...modes during gasification is revealed.•Increasing temperature and S/B promotes all heat transfer modes.•The middle region of the reactor has the highest pyrolysis rate.
Biomass gasification in a bubbling fluidized bed (BFB) reactor is numerically studied based on a particle-scale computational fluid dynamics-discrete element method (CFD-DEM), with thermochemical and polydispersity effects featuring. After model validation, the particle-scale information (e.g., particle motions, particle mixing, solid dispersion, and heat transfer contribution) are thoroughly explored with the discussion of the effects of several critical operating parameters on particle behaviours. The results show that the middle dense region has the highest biomass pyrolysis reaction rate due to the vigorous particle motion. Sand and biomass particles show synchronous horizontal motions, and the solid vertical dispersion coefficients are much higher than the solid horizontal ones, denoting that the vertically introduced gas flow dominates bed hydrodynamics. A higher operating temperature causes a higher solid dispersion coefficient. Elevating temperature and steam to biomass ratio (S/B) first increases and then decreases the particle mixing index. Convection plays a dominant role during the biomass gasification process, followed by the radiation and heat of reaction. The conduction accounts for the smallest proportion and can be neglected. Increasing operating temperature promotes chemical reactions, biomass temperature, and all heat transfer modes. Increasing S/B promotes biomass motions and gasification reactions, leading to more heat consumed and biomass temperature decrease. Decreasing biomass temperature results in a larger temperature difference between biomass particles and bed material, which enhances the conduction, convection, and radiation.
In this work, a numerical simulation model of an industrial-scale magnesite flash calciner (MFC) was established based on computational fluid dynamics (CFD) method. The discrete phase model (DPM) was ...employed, and the results of kinetic analysis for magnesite decomposition were taken into consideration. Then, the influence of swirling gas inlet design on particle motion and decomposition in MFC was analyzed, thereby providing suggestions for production. The results indicate that incorporating a swirling design can attenuate the particle deposition at the feeding port and increase particle residence time in furnace. However, the conversion degree of magnesite is decreased. This phenomenon can be attributed to the particle accumulation near the wall, resulting in a localized lower gas temperature and subsequently leading to a gas-solid heat transfer degradation. By elevating the gas temperature and reducing its flow rate, the enhancement of magnesite decomposition and reduction in energy consumption are achieved. The gas-solid water equivalent ratio, determined by heat of reaction and sensible heat of flue gas, needs to be higher than 1.8 to maintain a mass fraction of MgO above 0.9.
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•Effect of swirling gas inlet on magnesite flash calciner performance is studied.•The particle motion and reaction behavior in furnace are analyzed using CFD method.•The particle motion is improved while the mass fraction of MgO is reduced.•The gas-solid equivalent ratio is introduced and a practical range is obtained.
Dynamic mode decomposition (DMD) provides a practical means of extracting insightful dynamical information from fluids datasets. Like any data processing technique, DMD’s usefulness is limited by its ...ability to extract real and accurate dynamical features from noise-corrupted data. Here, we show analytically that DMD is biased to sensor noise, and quantify how this bias depends on the size and noise level of the data. We present three modifications to DMD that can be used to remove this bias: (1) a direct correction of the identified bias using known noise properties, (2) combining the results of performing DMD forwards and backwards in time, and (3) a total least-squares-inspired algorithm. We discuss the relative merits of each algorithm and demonstrate the performance of these modifications on a range of synthetic, numerical, and experimental datasets. We further compare our modified DMD algorithms with other variants proposed in the recent literature.
•Discussion on metal foam heat exchangers for various energy-intensive industries.•Comprehensive review of particulate fouling through porous metal foams.•Proposition of oscillatory fluids as a heat ...exchanger fouling mitigation technique.•Numerical and experimental methods to investigate heat exchanger fouling.
Curtailing the ever-increasing global energy demand remains an arduous challenge. The U.S. Energy Information Administration emphasized that the deployment of new heat exchanger technologies could revolutionize how industry uses energy. In this review, we highlight the significance of metal foam heat exchangers as an attractive alternative to traditional heat exchanger technologies. Research on metal foam heat exchangers is steadily gaining momentum. However, metal foam heat exchangers are highly susceptible to fouling which results in a myriad of issues such as low heat exchanger performance and high energy consumption. These issues are further compounded by the fact that the fundamental mechanisms governing particulate fouling in metal foam heat exchangers are poorly understood. As such, the overarching goal of reducing energy consumption and greenhouse gas emissions could be met by deploying energy-efficient heat exchanger technologies and also by gaining a solid comprehension of multiphase flows, heat transfer, and heat exchanger fouling mechanisms. The development of advanced numerical methods to unravel heat exchanger fouling mechanisms could pave the way for an optimized heat exchanger design with minimum energy consumption and greenhouse gas emissions. This paper provides researchers a review of the performance of metal foam heat exchangers for various industrial applications and the implications of particulate fouling on the thermal performance of metal foam heat exchangers.
Recently, the development of modern vehicles has brought about aggressive integration and miniaturization of on-board electrical and electronic devices. It will lead to exponential growth in both the ...overall waste heat and heat flux to be dissipated to maintain the devices within a safe temperature range. However, both the total heat sinks aboard and the cooling capacity of currently utilized thermal control strategy are severely limited, which threatens the lifetime of the on-board equipment and even the entire flight system and shrink the vehicle’s flight time and range. Facing these thermal challenges, the USA proposed the program of “INVENT” to maximize utilities of the available heat sinks and enhance the cooling ability of thermal control strategies. Following the efforts done by the USA researchers, scientists in China fought their ways to develop thermal management technologies for Chinese advanced energy-optimized airplanes and spacecraft. This paper elaborates the available on-board heat sinks and aerospace thermal management systems using both active and passive technologies not confined to the technology in China. Subsequently, active thermal management technologies in China including fuel thermal management system, environment control system, non-fuel liquid cooling strategy are reviewed. At last, space thermal control technologies used in Chinese Space Station and Chang’e-3 and to be used in Chang’e-5 are introduced. Key issues to be solved are also identified, which could facilitate the development of aerospace thermal control techniques across the world.
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•Heat and mass transfer behaviours of char combustion are studied at a particle scale.•Polydisperse drag model has to be used to accurately reproduce bed hydrodynamics.•Axial ...dispersion coefficient is one order of magnitude larger than horizontal one.•For reactive particles, the radiation and heat of reaction are dominated.•For inert particles, the radiation and convection are dominated simultaneously.•Particle concentration shows a weak influence on Nup and Shp.
In this study, the multiphase flow and thermochemical behaviours of char combustion in a bubbling fluidised bed (BFB) are simulated using CFD-DEM approach featuring particle size polydispersity and thermochemical sub-models. The model is first validated in terms of mixing index, particle temperature, and particle diameter. Then, it is applied to examine the contribution of each heat transfer mode and study particle-scale behaviours of char and sand comprehensively. The results show that the polydisperse drag model should be used to accurately reproduce bed hydrodynamics when simulating a BFB system with polydisperse particles. Under the simulation conditions, the particle-averaged heat fluxes to char particles through convection, conduction, radiation, and char reaction take 9.79%, 0.82%, 40.44%, and 48.95%, respectively; the particle-averaged heat fluxes to sand particles through convection, conduction, and radiation take 30.28%, 1.0%, and 68.72%, respectively. For reactive char particles, the radiation and heat of reaction are dominated, while for inert sand particles, the radiation and convection are dominated; and for both particle species, the conduction is negligible. Axial dispersion coefficient is one order of magnitude larger than the horizontal one, demonstrating the dominant role of the introduced gas flow in determining bed hydrodynamics.
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