CFD Modeling of N2/H2 Gaseous Flow with Geometric Variations in a Monolithic Channel

AbstractGeometric variations by means of orientation of obstructions to the fluid flow can have a significant effect on the flow dynamics of gases in pursuit of maintaining required mixing in a low Reynolds number flow for a prospective reaction between the two gases. In this study, the effect of placing the obstructions parallel and perpendicular to the N2 and H2 flow was observed initially. Parallel placement resulted in favorable conditions in maintaining the desired ratio of the two components giving more than 90% mixing index throughout the channel length while perpendicular placement signaled better lateral movement on encountering the obstruction. Taking a cue from this, geometries having a combination of parallel and perpendicular obstructions were proposed based on results of parametric study on number of wires and spacing between them. Increasing perpendicular obstruction sets beyond 5 took the mixing index down to as low as 60%. Increasing spacing from 1.5mm to 2mm deteriorated mixing index further but reducing perpendicular sets from 5 to 3 with 2mm spacing resulted in 90% mixing index throughout the channel and benchmark observed in axial-only configuration was regained. Also, increasing number of axial wires on a given perpendicular set or reducing their spacing did not alter desired mixing index to a great extent

Quantitative Analysis of Interfacial Area on Liquid-liquid Multiphase Flow of Transesterification Process in Cross-junction Microchannel Reactor

Key advantage of microfluidic technology in chemical processing is the high interfacial area which is especially important factors in multiphase reaction. The multiphase reaction like transesterification of vegetable oil and methanol to produce biodiesel are largely dependent on interfacial area for better mass transfer. However, little attentions have been given to the hydrodynamic factor which affects the interfacial area in a microchannel. In this study, the interfacial area from the droplet flow regime was studied by varying the parameter of methanol to oil ratio (M/O), total flow rate (QTotal) and catalyst concentration. The droplet flow was created by a cross-junction channel and photos were made to measure the size of the droplets with help of microscope. The maximum M/O ratio of 23 and lowest flow rate of 10 μL/min exhibited the highest interfacial area, where increasing M/O by 67% could increase the interfacial area by 23%. By varying the KOH catalyst concentration, the change in the interfacial area was very small, hence showing the lowest impact on the interfacial area of the droplet. Therefore, further analysis must be performed to investigate the impact of interfacial area and mass transfer coefficient on the reaction performance to produce highest yield of biodiesel in microchannel reactor

Quantitative Analysis of Interfacial Area on Liquid-liquid Multiphase Flow of Transesterification Process in Cross-junction Microchannel Reactor

Key advantage of microfluidic technology in chemical processing is the high interfacial area which is especially important factors in multiphase reaction. The multiphase reaction like transesterification of vegetable oil and methanol to produce biodiesel are largely dependent on interfacial area for better mass transfer. However, little attentions have been given to the hydrodynamic factor which affects the interfacial area in a microchannel. In this study, the interfacial area from the droplet flow regime was studied by varying the parameter of methanol to oil ratio (M/O), total flow rate (QTotal) and catalyst concentration. The droplet flow was created by a cross-junction channel and photos were made to measure the size of the droplets with help of microscope. The maximum M/O ratio of 23 and lowest flow rate of 10 μL/min exhibited the highest interfacial area, where increasing M/O by 67% could increase the interfacial area by 23%. By varying the KOH catalyst concentration, the change in the interfacial area was very small, hence showing the lowest impact on the interfacial area of the droplet. Therefore, further analysis must be performed to investigate the impact of interfacial area and mass transfer coefficient on the reaction performance to produce highest yield of biodiesel in microchannel reactor

Reaction-Multi Diffusion Model for Nutrient Release and Autocatalytic Degradation of PLA-Coated Controlled-Release Fertilizer

A mathematical model for the reaction-diffusion equation is developed to describe the nutrient release profiles and degradation of poly(lactic acid) (PLA)-coated controlled-release fertilizer. A multi-diffusion model that consists of coupled partial differential equations is used to study the diffusion and chemical reaction (autocatalytic degradation) simultaneously. The model is solved using an analytical-numerical method. Firstly, the model equation is transformed using the Laplace transformation as the Laplace transform cannot be inverted analytically. Numerical inversion of the Laplace transform is used by employing the Zakian method. The solution is useful in predicting the nutrient release profiles at various diffusivity, concentration of extraction medium, and reaction rates. It also helps in explaining the transformation of autocatalytic concentration in the coating material for various reaction rates, times of reaction, and reaction-multi diffusion. The solution is also applicable to the other biodegradable polymer-coated controlled-release fertilizers

Modeling the Release of Nitrogen from Controlled-Release Fertilizer with Imperfect Coating in Soils and Water

Urea is vulnerable to losses from volatilization or leaching when applied to soils. This study proposes a porous model that couples the interfacial area ratio (IAR) equation for the diffusion of nitrogen with mass transport equation in porous medium (soil). The model presents the release of a single granule with an imperfect coating thickness in different environments. The model is validated with experiments in water and soil environments. In addition, it is compared to our previous model and shows an enhancement in its predictive ability because the imperfection of the coating layer has been integrated in the model. On the basis of the proposed model, the influence of coating variation and soil types also are investigated. In general, simulation results suggest that the coating layer imperfection leads to earlier and faster nitrogen release than an ideal one. Also, nitrogen release in soil depends on soil characteristics such as surface area, particle size, and density. The comparison with experimental observations taken from the literature has validated the model’s prediction of nitrogen release in different soil types. Finally, the model has an advantage that it can model the nitrogen release either in water or soil environments. By using the input from the experimental data for the release in water, the release in soil is extrapolated based on the specific soil properties, which can be obtained from experiments or the literature

Production and Characterization of Controlled Release Urea Using Biopolymer and Geopolymer as Coating Materials

Synthetic polymers-based controlled release urea (CRU) leaves non-biodegradable coating shells when applied in soil. Several alternative green materials are used to produce CRU, but most of these studies have issues pertaining to nitrogen release longevity, process viability, and the ease of application of the finished product. In this study, we utilized tapioca starch, modified by polyvinyl alcohol and citric acid, as coating material to produce controlled release coated urea granules in a rotary fluidized bed equipment. Response surface methodology is employed for studying the interactive effect of process parameters on urea release characteristics. Statistical analysis indicates that the fluidizing air temperature and spray rate are the most influential among all five process parameters studied. The optimum values of fluidizing air temperature (80 degrees C), spray rate (0.13 mL/s), atomizing pressure (3.98 bar), process time (110 min), and spray temperature (70 degrees C) were evaluated by multi-objective optimization while using genetic algorithms in MATLAB((R)). Urea coated by modified-starch was double coated by a geopolymer to enhance the controlled release characteristics that produced promising results with respect to the longevity of nitrogen release from the final product. This study provides leads for the design of a fluidized bed for the scaled-up production of CRU