No abstract

The present study investigates the effect of fluid‐bed process parameters on the diffusion coefficient of nitrogen release and coating homogeneity of controlled‐release urea (CRU) produced in a rotary fluidized bed using polyvinyl‐alcohol‐modified starch as a coating material. An existing mathematical model was used to estimate the diffusion coefficient. The coefficient of variance of size distribution and coating mass variation are reported as a measure of coating homogeneity. Statistical analysis suggested that the most influential process variables that govern urea release characteristics and coating homogeneity were (a) fluidizing gas temperature and (b) coating time. A moderate spray rate combined with longer coating time yielded the lowest diffusion coefficient for nutrient release. Elutriation as the result of elevated fluidizing gas temperature allowed a higher diffusion coefficient due to lower coating thickness. Burst release patterns were observed for granules with coating imperfections. The augmented temperature of fluidizing gas had a negative effect on coating mass and size distribution of CRU granules but the influence of longer coating time was positive.

In bio-oil upgrading, the activity and stability of the catalyst are of great importance for the catalytic hydrodeoxygenation (HDO) process. The vapor-phase HDO of guaiacol was investigated to clarify the activity, stability, and regeneration ability of Al-MCM-41 supported Pd, Co, and Fe catalysts in a fixed-bed reactor. The HDO experiment was conducted at 400 °C and 1 atm, while the regeneration of the catalyst was performed with an air flow at 500 °C for 240 min. TGA and XPS techniques were applied to study the coke deposit and metal oxide bond energy of the catalysts before and after HDO reaction. The Co and Pd–Co simultaneously catalyzed the CArO–CH3, CAr–OH, and multiple C−C hydrogenolyses, while the Fe and Pd–Fe principally catalyzed the CAr–OCH3 hydrogenolysis. The bimetallic Pd–Co and Pd–Fe showed a higher HDO yield and stability than monometallic Co and Fe, since the coke formation was reduced. The Pd–Fe catalyst presented a higher stability and regeneration ability than the Pd–Co catalyst, with consistent activity during three HDO cycles.

Abstract-Droplet spreading on flat non-reactive surfaces is established; however, porous surfaces present a complicated case. Wetting of porous surface involves the simultaneous spreading and penetration of the droplet. The effect of low impact velocity (i.e <1 m/s) on dimensionless droplet diameter and dynamic contact angle has been experimentally observed in this study. Low impact velocity helps reducing the penetration of droplets into the droplets in case of porous substrates. In the low impact velocity range, the effect on contact angle is not significant. Dimensionless droplet diameter also shows similar behavior. I. INTRODUCTIONDroplet spreading has been studied for over a century [1]. surfaces with high Reynolds number and high Weber number, the droplet usually forms a radially spreading lamella and a circular rim around it due to capillary forces and viscosity effects [6].The droplet impact depends upon the impact parameters, properties of the liquid and also on the nature, topology and properties of the solid substrate. On dry surface some common outcomes of droplet impact may be droplet deposition, prompt splash, receding, partial or complete rebound [6]. Some new phenomena have also been observed like very thin gas layer in start of spreading, collision of two drops, bubble entrapment in spreading contacting line, lamella rupture in high velocity impacts, finger formation and periodic recoiling of droplet [6], [7].Phenomenological details of droplet spreading dynamics on flat solid surface below splashing threshold/ Initial phase of droplet impact are as follows:Rioboo et al. [8] described the droplet impact of Newtonian fluids on dry surfaces to be consisting of processes namely kinetic phase, spreading phase and relaxation phase. In the kinetic phase, liquid is compressed and shock wave is formed as shown in Fig. 1.. Increasing impact velocity and droplet diameter results in faster spreading while increasing surface tension and viscosity leads to slower spreading [9], [10]. The results suggest that at high Re no (>2000), and in the absence of splashing, Re no alone can represent the droplet deformation. This applies only if the surface roughness is very small in comparison to the film thickness. Otherwise film detachment will take place and hence splashing may occur. Increased roughness promotes splashing [7].During the spreading phase, the hemi-sphere changes into lamella which thickens and expands to obtain disk like shape and sometimes has a rim around it as shown in Fig. 2.The flow is directed from axial to radial direction. Generally, increasing the impact velocity and/or droplet diameter leads to faster spreading whereas increasing surface tension and/or viscosity results in slow expansion of droplet on the surface

No abstract

No abstract

No abstract

No abstract