Spatial Reaction Engineering Approach Research Articles

Simulating the Moisture Diffusion and Evaporation of Sawdust during Convective Drying using the Spatial Reaction Engineering Approach

AbstractThe spatial reaction engineering approach (S‐REA) was used to simulate hot air drying of sawdust. The studies extended the previous work reported in literature where the sawdusts were dried using hot air at 70 °C, 80 °C, and 90 °C. The simulated results were found to agree well with the experimental moisture content (R2 > 0.98) and temperature (R2 > 0.82) profiles. In a further analysis using S‐REA, the spatial profiles of moisture content and vapor concentration were generated to understand better the physics behind. Simulation also revealed that the external mass transfer resistance was more dominant as compared to the internal diffusion resistance. The vapor concentrations were observed peaked at time range of about 10 800– 18 000 s and dropped thereafter upon further heating. This observation could be supported by the variation in the vapor effective diffusivities where peak diffusivity values typically occur after most of the moisture evaporates towards the end of drying.

Combined infrared and hot air drying (IR-HAD) of sweet potato explored using a multiphase model: application of reaction engineering approach

For better understanding of transport phenomena, local evaporation rate and water vapor concentration should be taken into consideration when predicting drying behavior. However, to the best of our knowledge, there is no model which explicitly represents this. Predictive modeling of combined infrared-heating and hot air drying (IR-HAD) is useful to assist in designing new dryer units and manufacturing the products with desirable quality. As the quality changes are basically local phenomena, the model should be able to capture the local evaporation rate. In this study, for the first, time, spatial reaction engineering approach (S-REA) was developed and used to describe infrared-heating drying of the food materials by using the reaction engineering approach (REA) to represent local evaporation rate. Benchmarks against the single-phase approach and the results showed that the S-REA gave high accuracy toward the experimental data (R2 = 0.978–0.999). The S-REA successfully provided reasonable predictions of two-dimensional (2 D) profiles of moisture content, concentration of water vapor and temperature. This highlights the accuracy of the REA framework to describe the local evaporation rate during the infrared-heating. The REA-based predicted variables can then be applied to project the local quality parameters for quality assurance in food processing. The model is also ready to be used to audit energy demands in drying systems.

A successful comparison between a non-invasive measurement of local profiles during drying of a highly shrinkable food material (eggplant) and the spatial reaction engineering approach

A reliable mathematical model is useful for predicting internal profiles inside materials during drying. In this study, for the first time, the spatial reaction engineering approach (S-REA) is employed to model the local profiles of food materials during drying. The REA is applied as the local rate of phase change and combined with a set of equations of conservation of heat and mass transfer to yield the spatial profiles of temperature and concentration during drying. The S-REA predictions are benchmarked against the Magnetic Resonance Imaging (MRI) data. The study indicates that the S-REA is applicable to model the internal profiles inside food materials during drying. The S-REA predictions also show closer agreement towards the experimental data than the effective diffusion model. While the S-REA predictions are accurate, it requires minimum number of experiments to generate the drying parameters. The S-REA has contributed to better analysis of transport phenomena inside food materials during drying through generation of local profiles. The S-REA predictions can potentially be implemented to interpret the sensory and quality matters during drying.

Miniature bread baking as a timesaving research approach and mathematical modeling of browning kinetics

Miniature bread baking is presented as an economical and timesaving laboratory approach to study the baking process in the present work. Results indicate that the miniature bread baking is essentially analogical to the baking process of regular-sized bread: quality-related properties of miniature breads, such as crumb formation, crust thickness, crust color and moisture content, behaved similarly to regular-sized breads (380g) during baking, albeit at a different time scale. This was explained as analogous for large breads, initially baking is externally limited and only later internal limitations play a dominant role with the crust being formed. After initial development of the crust, the lightness and the total color difference were found linearly correlated with the crust thickness. Moreover, the S-REA (spatial reaction engineering approach) was used here to model the moisture content and temperature during miniature bread baking whose results were implemented to describe the browning kinetics. The results indicate that the S-REA accurately models the browning kinetics during miniature bread baking.

S-REA (spatial reaction engineering approach): An effective approach to model drying, baking and water vapor sorption processes

An effective model of simultaneous heat and mass transfer processes is useful to assist in process design, optimization of existing processes and monitoring product quality. Previously, the lumped reaction engineering approach (L-REA) has been shown to model the global drying rate of several heat and mass transfer processes very well. Here, the REA (reaction engineering approach) framework is implemented to model the local evaporation/condensation rate in drying of non-food materials, baking and water vapor sorption. The REA is combined with a set of equations of conservation of heat and mass transfer to yield the S-REA (spatial reaction engineering approach) to model these processes. For modeling each process, the activation energy is generated from one accurate run and evaluated according to environmental temperature and humidity. The relative activation energy implemented in the L-REA is implemented in the S-REA by applying local variables. The results indicate that the S-REA is accurate to describe baking, drying and water vapor sorption process which shows the applicability of the REA to model the local evaporation/condensation rate of these processes. The S-REA is readily implemented to assist in process design, evaluation of existing processes and maintenance of product quality. In near future, by coupling with solid mechanics, the REA may be employed to predict material deformation and shape change during heat and mass transfer processes by coupling with solid mechanics. The development of the REA to describe migration of volatiles inside materials undergoing heat and mass transfer processes is also underway.

Bread baking and its color kinetics modeled by the spatial reaction engineering approach (S-REA)

Baking is a relatively complex process involving simultaneous heat and mass transfer coupled with reactions and structural changes. An accurate and physically-meaningful model of baking is useful to assist process design and product quality improvement. The reaction engineering approach (REA), which has been proven to accurately model the drying rate of porous foods, is implemented here to describe the local evaporation/condensation rate during bread baking for the first time. The REA is coupled with a set of equations of conservation of heat and mass transfer to yield the spatial reaction engineering approach (S-REA). The results of modeling match well with the experimental data. The S-REA can also model the browning kinetics during bread baking accurately. The S-REA is readily implemented for process design by implementing it in computational fluid dynamics (CFD)-environment. The S-REA can also be used for optimization to determine baking trajectories to achieve the desired product properties.

An assessment on modeling drying processes: Equilibrium multiphase model and the spatial reaction engineering approach (S-REA)

An accurate drying model is useful in assisting process design and product design when drying is involved. Generally, drying models can be classified into equilibrium and non-equilibrium multiphase models. Both models employ a similar set of equations of conservation of heat and mass transfer. For the equilibrium ones, the moisture sorption isotherm relationship is used to link the concentration of water vapor inside the pore space and moisture content in and on solid matrix. On the other hand, the non-equilibrium ones have an expression of local evaporation/condensation rate to relate these relationships. Here, both models are compared and assessed to model several cases of convective and intermittent drying. The reaction engineering approach (REA) is used to describe the local evaporation/condensation rate in non-equlibrium model (i.e. the spatial reaction engineering approach (S-REA)). The results of modeling indicate that for the cases investigated, the equilibrium model does not work well. The S-REA can accurately model both convective and intermittent drying cases. For the interest of probing the dynamics of drying process, it is suggested that a non-equilibrium model is more appropriate.

Examining the Suitability of the Reaction Engineering Approach (REA) to Modeling Local Evaporation/Condensation Rates of Materials with Various Thicknesses

The reaction engineering approach (REA) is examined here to investigate its suitability as the local evaporation rate to be used in multiphase drying. For this purpose, REA is first implemented to model the convective drying of materials with various thicknesses. The relative activation energy, as the fingerprint of REA, generated from one size of a material is used to model the convective drying of the same material with different thicknesses. Because the results indicate that REA parameters can model the drying of materials with various thicknesses, REA can be scaled down to describe the local evaporation rate (at the microscale as affected by local composition and temperature). The relative activation energy is used to describe the global drying rate in modeling the local evaporation rate. REA is combined with a system of equations of conservation of heat and mass transfer in order to yield the spatial reaction engineering approach (S-REA) as a nonequilibrium multiphase drying model. By using S-REA, the spatial profiles of moisture content, concentration of water vapor, temperature, and local evaporation rate can be generated, which can assist in comprehending the transport phenomena.

Spatial Reaction Engineering Approach (S-REA) as a Multiphase Drying Approach to Model the Heat Treatment of Wood under a Constant Heating Rate

Wood may contain several harmful chemicals which can be removed by high-temperature treatment. This is essentially a drying process under linearly increased gas temperature up to final gas temperat...

Multiphase modeling of intermittent drying using the spatial reaction engineering approach (S-REA)

Several schemes of energy minimization of drying process including intermittent drying have been attempted. Intermittent drying is conducted by applying different heat inputs in each drying period. An effective and physically meaningful drying model is useful for process design and product technology. The lumped reaction engineering approach (L-REA) has been shown previously to be accurate to model the intermittent drying In L-REA, the REA (reaction engineering approach) is used to describe the global drying rate. In this study, the REA is used to model the local evaporation/condensation rate and combined with the mechanistic drying models to yield the spatial reaction engineering approach (S-REA), a non-equilibrium multiphase drying model. The accuracy of the S-REA to model the intermittent drying under time-varying drying air temperature is evaluated here. In order to incorporate the effect of time-varying drying air temperature, the equilibrium activation energy and boundary condition of heat balance implement the corresponding drying settings in each drying period. The results of modeling using the S-REA match well with the experimental data. The S-REA can yield the spatial profiles of moisture content, concentration of water vapor, temperature and local evaporation/condensation rate so that better understanding of transport phenomena of intermittent drying can be obtained. It is argued here that the REA can describe the local evaporation rate under time-varying external conditions well. The S-REA is an effective non-equilibrium multiphase approach for modeling of intermittent drying process.

Spatial reaction engineering approach as an alternative for nonequilibrium multiphase mass‐transfer model for drying of food and biological materials

Drying is a complex process which involves simultaneous heat and mass transfer. Complicated structure and heterogeneity of food and biological materials add to the complexity of drying. Drying models are important for improving dryer design and for evaluating dryer performance. The lumped reaction engineering approach (L‐REA) has been shown to be an accurate and robust alternative for cost‐effective simulations of challenging drying systems. However, more insightful physics has to be shown spatially. In this study, the REA is coupled with the standard mechanistic drying models to yield the spatial‐REA (S‐REA) as nonequilibrium multiphase mass‐transfer model. The S‐REA consists of a system of equations of conservation with the REA representing the local evaporation and wetting rate. Results of the modeling using the S‐REA match well with the experimental data reported previously. This is the first comprehensive REA approach to model the profiles of water vapor concentration during drying of food and biological materials. This study indicates that the S‐REA can be an accurate nonequilibrium multiphase mass‐transfer model with appropriate account of the local evaporation rate. The overall REA concept is expected to contribute substantially for better and cost‐effective representation of transport phenomena of drying process. © 2012 American Institute of Chemical Engineers AIChE J, 59: 55–67, 2013