Wan Ramli Wan Daud

CFD Evaluation of Droplet Drying Models in a Spray Dryer Fitted with a Rotary Atomizer

Computational fluid dynamics (CFD) modeling of spray dryers requires a simple but sufficiently realistic drying model. This work evaluates two such models that are currently in discussion; reaction engineering approach (REA) and characteristic drying curve (CDC). Two versions of the CDC, linear and convex, drop in drying rate were included. Simulation results were compared to the overall outlet conditions obtained from our pilot-scale experiments. The REA and CDC with a linear drop in drying rate predicted the outlet conditions reasonably well. This is contrary to the kinetics determined previously. Analysis shows that the models exhibit different responses to changes in the initial feed moisture content. Utilizing different models did not result in significantly different particle trajectories. This is due to the low relaxation time of the particles. Despite the slight differences in the drying curves, both models predicted similar particle rigidity depositing the wall. For the first time in a CFD simulation, the REA model was extended to calculate the particle surface moisture, which showed promising results for wet particles. Room for improvement was identified when applying this concept for relatively dry particles.

Thermal performance of the double-pass solar collector with and without porous media

This paper presents the thermal performance of a double-pass solar collector with and without porous media in the second or lower channel of the collector. The experimental setup has been designed to study the thermal performance over a range of design and operating conditions. Several important relationships between the design and operating conditions have been obtained. These relationships effect the thermal performance of the double-pass solar collector. The relationships include the effect of changes in upper and lower channel depth on the thermal efficiency with and without porous media. Moreover, the effects of mass flow rate, solar radiation, and temperature rises on the thermal efficiency of the double-pass solar collector have been studied. The study concluded that the presence of porous media in the second channel increases the outlet temperature, therefore increases the thermal efficiency of the systems.

Fluidized Bed Dryers — Recent Advances

Although industrial fluidized bed dryers have been used successfully for the drying of wet solid particles for many years, the development of industrial fluidized bed dryers for any particular application is fraught with difficulties such as scaling-up, poor fluidization and non-uniform product quality. Scaling-up is the major problem and there are very few good, reliable theoretical models that can replace the expensive laboratory work and pilot-plant trials. This problem is mainly due to the different behavior of bubbles and mixing regimes in fluidized bed dryers of different size. Simple transformation of laboratory batch drying data to continuous back-mixed dryers using the residence time distribution of the solids is insufficient to account for the complex flow and heat and mass transfer phenomena occurring in the bed. Although time scaling using temperature driving forces and solids mass flux for the same change in moisture content in the batch and continuous dryers has been successful in predicting moisture content profiles in the continuous dryer at the constant rate period, it does not take into account solid mixing. Two-phase Davidson–Harrison models have been used in modeling of the continuous back-mixed dryer with various degrees of success. On the other hand, the three-phase Kunii–Levenspiel model is seldom used in modeling fluidized bed dryers because it is too complex to handle. A combination of multi-phase models and residence time distribution could improve predicting power for back-mixed dryers because this combination takes into account both the bubbles and solid mixing phenomena. Incremental models were widely used to model continuous plug flow fluidized bed dryers, but the cross-flow of drying medium has not been sufficiently modeled except by the author. In some incremental models, axial dispersion is modeled using the Peclet number, Pe. A combination of an incremental model with an axial dispersion and cross-flow model of drying medium would improve predicting power. Poor fluidization of Geldart group C particles could be improved by the assistance of external means such as vibration, agitation, rotation and centrifugation. Both vibrated and agitated fluidized bed dryers have been successfully used in industry, but rotating or centrifugal fluidized bed dryers are still not available for industrial use.

Synthesis and characterization of Cu-Al layered double hydroxides

Abstract A series of Cu–Al hydrotalcite-like layered compounds has been synthesized by coprecipitation using metal nitrate precursors and sodium carbonate. The Cu/Al atomic ratio was varied between 0.5 and 4. The dried precipitates were characterized by powder X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The crystalline hydrotalcite-like phase was present as major component in all precipitates, the first time such crystalline phase was observed in the precipitates of the constituent metals ratio as low as 0.5. The malachite phase was also observed in variable amounts, and it became amorphous at low copper content.

Gas chromatographic determination of eugenol in ethanol extract of cloves

An ethanolic extract of cloves was analyzed by gas chromatography directly to identify eugenol and other major phenolic compounds without previous separation of other components. Separation was performed on a fused-silica capillary column of 30 m x 0.53 mm I.D., 0.53 microns film thickness. The detector was a flame ionization detector. Helium gas at a flow-rate of 3 ml/min was used as a carrier gas. The analysis were performed with linear temperature programming. Nine components were detected and special attention was given to the major phenolic compound, eugenol.

The biocathode of microbial electrochemical systems and microbially-influenced corrosion

The cathode reaction is one of the most important limiting factors in bioelectrochemical systems even with precious metal catalysts. Since aerobic bacteria have a much higher affinity for oxygen than any known abiotic cathode catalysts, the performance of a microbial fuel cell can be improved through the use of electrochemically-active oxygen-reducing bacteria acting as the cathode catalyst. These consume electrons available from the electrode to reduce the electron acceptors present, probably conserving energy for growth. Anaerobic bacteria reduce protons to hydrogen in microbial electrolysis cells (MECs). These aerobic and anaerobic bacterial activities resemble those catalyzing microbially-influenced corrosion (MIC). Sulfate-reducing bacteria and homoacetogens have been identified in MEC biocathodes. For sustainable operation, microbes in a biocathode should conserve energy during such electron-consuming reactions probably by similar mechanisms as those occurring in MIC. A novel hypothesis is proposed here which explains how energy can be conserved by microbes in MEC biocathodes.

Effect of Wall Surface Properties at Different Drying Kinetics on the Deposition Problem in Spray Drying

Current methods in alleviating the wall deposition problem in spray drying emphasize mainly controlling the stickiness of the drying particles and less attention is placed on the properties of the dryer wall. In this experimental study, the effect of wall surface properties on the deposition mechanism has been investigated. Properties considered in classifying different wall materials were surface energy, roughness, and dielectric properties. The model solution contained sucrose, representing low-molecular-weight sugars commonly encountered in spray drying of fruit and vegetable juices. The effect of wall properties on deposition was explored at different drying rates producing particles of different surface rigidity. Larger surface roughness produced higher deposition fluxes for particles with high impact velocity and moisture. Surface energy and surface roughness were found to have no significant effect for dry rigid particles at the middle and bottom elevation of the drying chamber. However, material with lower surface energy (Teflon) exhibited less deposition for rubbery particles at such elevations. Analysis shows that dielectric wall material (Teflon) tends to enhance deposition of dry particles because of attrition at the surface. Higher wall temperature was found to produce slightly more deposition. The results of this work give a general indication of the effect of wall material on the deposition problem and provide the fundamental understanding for further studies along this line. Proper selection of dryer wall material will provide potential alternatives for reducing the deposition problem.

Synthesis and application of polypyrrole/carrageenan nano-bio composite as a cathode catalyst in microbial fuel cells

A novel nano-bio composite polypyrrole (PPy)/kappa-carrageenan(KC) was fabricated and characterized for application as a cathode catalyst in a microbial fuel cell (MFC). High resolution SEM and TEM verified the bud-like shape and uniform distribution of the PPy in the KC matrix. X-ray diffraction (XRD) has approved the amorphous structure of the PPy/KC as well. The PPy/KC nano-bio composites were then studied as an electrode material, due to their oxygen reduction reaction (ORR) ability as the cathode catalyst in the MFC and the results were compared with platinum (Pt) as the most common cathode catalyst. The produced power density of the PPy/KC was 72.1 mW/m(2) while it was 46.8 mW/m(2) and 28.8 mW/m(2) for KC and PPy individually. The efficiency of the PPy/KC electrode system is slightly lower than a Pt electrode (79.9 mW/m(2)) but due to the high cost of Pt electrodes, the PPy/KC electrode system has potential to be an alternative electrode system for MFCs.

Drying Kinetics, Texture, Color, and Determination of Effective Diffusivities During Sun Drying of Chempedak

Sun drying of chempedak (Artocarpus integer) was carried out on different sample sizes to investigate the effects on product quality. Ficks second law model was used to determine the effective diffusivities of sun–dried chempedak slabs based on the drying rate versus moisture content plots. In addition, texture degradation and total color changes were investigated. The texture and color changes of dried chempedak were relatively significant (p < 0.05) compared to fresh chempedak. There was an increase in dried fruit hardness and chewiness but a decrease in springiness and cohesiveness during drying.

Optimization of the Spray Drying Operating Parameters—A Quick Trial-and-Error Method

This short communication reports an optimization approach to effectively determine suitable spray drying operating parameters for a pilot-scale dryer. The proposed optimization approach is essential, as pilot-scale investigations and medium-scale contract productions often involve usage of standard spray dryer units which is not specifically designed for the feed material used. This optimization approach was developed based on past studies on the effect and relationship of the many spray drying operating parameters and highlights two factors which has to be solved (or considered) chronologically: dripping problem, followed by product caking problem. Based on this proposed approach, an algorithm was developed in a case study to optimize an available spray dryer for our future experimental study on wall deposition. In this case, the operating parameters were determined under minimal experimental runs. This proposed optimization approach will be a useful tool for operators and experimenters utilizing spray dryers of similar type, particularly in exploring new feed materials. Depending on the optimization objectives and experimental limitations, different algorithms can be developed. Apart from that, interesting deposition pattern was also observed in the case study. This short communication also reported on the design of an internal rig for further studies on wall deposition.