Showing papers by "Arun S. Mujumdar published in 2009"

Low-Rank Coal Drying Technologies—Current Status and New Developments

Abstract: Despite their vast reserves, low-rank coals are considered undesirable because their high moisture content entails high transportation costs, potential safety hazards in transportation and storage, and the low thermal efficiency obtained in combustion of such coals. Their high moisture content, greater tendency to combust spontaneously, high degree of weathering, and the dusting characteristics restrict widespread use of such coals. The price of coal sold to utilities depends upon the heating value of the coal. Thus, removal of moisture from low-rank coals (LRC) is an important operation. Furthermore, LRC can be used cost effectively for pyrolysis, gasification, and liquefaction processes. This article provides an overview the diverse processes—both those that utilize conventional drying technologies and those that is not yet commercialized and hence in need of R&D. Relative merits and limitations of the various technologies and the current state of their development are presented. Drying characteristics ...

Studies on Decreasing Energy Consumption for a Freeze-Drying Process of Apple Slices

Abstract: The shape, color, flavor, and rehydration capacity of freeze-dried (FD) products are all better than other dried products. However, the energy consumption during FD is very high, which limits the application of this drying method for common materials. In this article, microwave vacuum drying (MWVD) was applied before or after FD to decrease the energy consumption during FD. Moreover, energy consumption was divided into two parts: valid and invalid energy consumption. Apple slices were used as an example to calculate the saving percentage of invalid energy consumption by comparing combination drying with FD. Apple slices freeze dried for 8.28 h first and then dried by MWVD have the best appearance, with a savings of 39.20% in invalid energy consumption. But apple slices freeze dried for 6 h first followed by MWVD have the highest savings of invalid energy consumption, 54.02%, while still maintaining an acceptable appearance.

Drying-Induced Cracks in Thin Film Fabricated from Colloidal Dispersions

Abstract: As a colloidal dispersion is coated and dried on a nonporous rigid substrate, the enormous stresses developing during the drying process can fracture the thin film. The drying-induced cracks can produce serous technological consequences and even destroy the efficacy of coatings, which is not desirable in most industrial cases. Therefore, as the first step of controlling cracks in thin film, understanding of crack properties and cracking mechanisms leading to fracture is of vital significance. Although numerous experiments and models have been proposed for cracking during drying of colloidal dispersions, there is little consensus on even the most basic mechanisms, and the effect of heat transfer on cracks as well as optimization of drying process are rarely taken into account. Additional, the broad employments of nanosuspensions bring both opportunities and challenges for this area. This review will give a comprehensive physical picture of thin film fabrication by drying of colloidal dispersions and cracking phenomenon, present current investigations for drying-induced cracks, and point out some prospects for cracking researches especially for industrial R&D, as well as propose combination of thin film preparation with drying technique for exploring crack-free thin film.

Microwave Freeze–Drying Characteristics and Sensory Quality of Instant Vegetable Soup

Abstract: Instant vegetable soup mix was dehydrated in a microwave freeze dryer to study the drying characteristics and sensory properties of the dried product. The mix was dried at different microwave power levels, material thicknesses, and material loads. As expected, microwave power significantly influenced the total drying time and sensory quality of the final product. The total drying time increased with the increase of material thickness and load. A material layer that is too thin causes the product quality to deteriorate.

Drying Characteristics and Kinetics of Vacuum Microwave–Dried Potato Slices

Abstract: Vacuum microwave dehydration characteristics and drying kinetics of potato slices were evaluated using a laboratory-scale dryer. The test materials were placed on a rotating tray to allow uniform exposure to the microwave field. The effect of drying conditions on the drying characteristics was investigated. As expected, higher drying rates were obtained with higher microwave power and lower vacuum levels. The effect of vacuum pressure on drying rate was not as significant as that of microwave power. The Henderson & Pabis model provided better simulation of the drying curves for potato slices. Empirical models are presented for the drying rate constant as a function of the microwave power and vacuum pressure for potato slices under the range of operating conditions tested.

Innovative Hydrocyclone Inlet Designs to Reduce Erosion-Induced Wear in Mineral Dewatering Processes

Abstract: The hydrocyclone is a mechanical separation device that is used widely in mineral processing. The solid particles in mineral slurries are separated according to their density, size, and shape by the centrifugal force generated by an induced vortex motion in a cylinder-on-cone vessel. The larger and denser particles move closer to the wall region due to their greater inertia and descend by gravity; a higher concentration suspension is thus collected at the bottom of the hydrocyclone. The cleaned liquid and hydrodynamically smaller particles exit through an overflow outlet at the top of the hydrocyclone. Higher velocities, within limit, generally yield higher collection efficiency. However, higher stream velocities cause severe erosion of the internal wall of hydrocyclones as mineral slurries generally are abrasive. The objective of this study is to use the computational fluid dynamic (CFD) technique to model the turbulent swirling flow and predict regions of significant wear and how they are influenced by ...

Climate change and drying of agricultural products.

Abstract: Global warming is affecting the world and will continue to affect humans and the ecosystem in the future, in different regions of the earth in diverse ways: air temperature rise, modifications in the precipitation and snow/ice melting rates, sea level rise, changes in geographical distribution, and even extinction of some plants and animals. In particular, the predictions presented in the 2007 Report of the Intergovernmental Panel on Climate Change, Working Group 1 (available at www.ipcc.ch) for the mean temperature increase in the present century is about (3 ± 1)°C/century for a middle range scenario of human behavior. Mitigation measures need to be taken urgently in all aspects of activities in order to reduce the future impact of the temperature augmentation. In particular, the drying process (as well as the pre- and post-drying operations) needs to be reanalyzed, in order to try to participate in this world effort to reduce the impact of anthropogenic activities that introduce in the atmosphere an exc...

Investigation of Flow Behaviors and Bubble Characteristics of a Pulse Fluidized Bed via CFD Modeling

Abstract: The bubbling flow in a 2D pulsed fluidized bed is simulated using a developed Eulerian-Eulerian two-fluid modeling approach. Parametric studies are carried on for pulsed inflow of the gas phase with rectangular and sawtooth patterns where three pulsating frequencies of 0.4, 4, and 40 Hz are used. The flow instabilities are observed to develop in the pulsed fluidized bed and the mechanisms leading to the instabilities are discussed. The formation, coalescence, split-up of air bubbles, and their trailing wakes inside the bed are described and discussed in detail. Bubble rising velocity and size are obtained and analyzed. Bed expansion and fluctuation ratio are calculated to evaluate the pulsed fluidization quality. Numerical results improve the understanding of the pulsed fluidization.

Effect of Power Ultrasound Pretreatment on Edamame Prior to Freeze Drying

Abstract: Immersion freezing with the aid of power ultrasound prior to freeze drying of edamame was investigated. The effect of power ultrasound on the freezing rate was influenced by ultrasonic power, exposure time to ultrasound field, and the pulse duration of the ultrasound that was applied. The higher the ultrasound power and the longer the exposure time, the stronger the ultrasonication effect on edamame was. However, the ultrasound power, ultrasound intermittency, and exposure time need to be chosen with consideration of the thermal effect of ultrasound. Response surface methodology (RSM) was adopted for optimization. The hardness and the water-holding capacity of edamame after thawing were 6050 g and 92%, respectively, when 58-W ultrasound power was applied for 0.7 min, 50% pulsed at the coolant temperature of − 20°C.

Combined water and power plant (CWPP) — a novel desalination technology

Abstract: In recent years, an enormous increase of fuel cost and greater demand for fresh water have imposed tremendous challenges for researchers to pursue a drive towards more energy-efficient desalination technology. In the search for a more energy-efficient desalination process, the next generation plants will use a combination of membrane processes with multi-stage flash (MSF)/multi-effect distillation (MED) thermal processes to harness the maximum thermal energy that would otherwise be wasted from a power plant. The novelty of this proposed combined water and power plant (CWPP) concept lies in the usage of the power plant at rated conditions most of the time, where the power plant is most efficient, and when demand falls in one area (electricity), resources can be directed to another area (i.e. desalination). A detail thermoeconomic analysis of the proposed plant under different loads has been used to quantify the benefits of the CWPP. This study includes a combined cycle (CC) power plant with stand-alone MSF...

Non-Swirling Steady and Transient Flow Simulations in Short-Form Spray Dryers

Abstract: This paper numerically investigated the effect of chamber aspect ratio and operating conditions on flow stability within a short form spray dryer without the inclusion of droplet injection. Extensive analysis using different mesh configurations led to a new finding on the effect of expansion ratio on flow stability. A larger expansion ratio produces a more stable flow, which is due to the limitation of the jet fluctuation by the outlet geometry constriction. However, the flow might not be completely steady as fluctuations are magnified at higher inlet velocities, which can be explained by the confined jet feed-back mechanism. Fast Fourier Transform (FFT) analysis of the computed instantaneous velocity at selected spatial locations in the chamber revealed the effect of the chamber expansion ratio on periodicity of the flow structure. It is observed that changes in the expansion ratio primarily affect the amplitude of the 'noise' region in the frequency spectrum.

Design of an Efficient Gas Distribution System for a Fluidized Bed Dryer

Abstract: Fluid bed dryers are commonly used to process granular solids. The design of the gas distributor has a significant impact on the performance of heat and mass transfer with or without chemical reactions in fluidized beds because it affects the quality of the fluidization obtained. In this work, an extensive study was carried out to design an optimal gas distribution system for a fluidized bed dryer. The air distribution chamber, also called a plenum chamber or gas chamber, was modified to obtain uniform air distribution across the bed cross section. Percentage maldistribution of the flow is considered as the basic evaluation parameter to quantify uniformity of the fluidizing gas distribution. Effects of various relevant design parameters such as the ratio of the orifice diameter to plate thickness (do/t), percentage free area, superficial gas velocity, etc., were examined experimentally and via modeling. The gas chamber was redesigned by inserting different types of packings in the chamber. In addition, th...

Baking of flat bread in an impingement oven: modeling and optimization.

Abstract: An artificial neural network (ANN) was developed to model the effect of baking parameters on the quality attributes of flat bread; i.e., crumb temperature, moisture content, surface color change and bread volume increase during baking process. As the hot air impinging jets were employed for baking, the baking control parameters were the jet temperature, the jet velocity, and the time elapsed from the beginning of the baking. The data used in the training of the network were acquired experimentally. In addition, using the data provided by ANN, a multi-objective optimization algorithm was employed to achieve the baking condition that provides the quality of the bread in all aspects simultaneously.

Effects of Predrying and Vacuum Impregnation with Nano-Calcium Carbonate Solution on Strawberries, Carrots, Corn, and Blueberries

Abstract: Predrying followed by vacuum impregnation using a solution of nanosized calcium carbonate was carried out for several products such as strawberries, blueberries, carrots, and corn. This process improved impregnation mass of the functional substance in the products tested. Though products like butter candy taste sweet, due to their high content of sugar and fat they face high consumer resistance. The objective of this study is to produce snack foods using fruits and vegetables that not only have sweet taste but that have the best retention of the original color, shape, and aroma of the fresh fruit or vegetable while retaining their vitamin, dietary fiber, and trace element contents.

Simulation of Drying Nonaqueous Systems—An Application of Simprosys Software

Abstract: Drying software, Simprosys (Simprotech Corp., California, USA), for nonaqueous systems is described briefly and applied to a case study. A closed-loop ethanol-nitrogen drying system is modeled with Simprosys 2.1. Simulation results including a parametric evaluation are presented and discussed.

Drying Kinetics of Magnesium Hydroxide of Different Morphological Micro Nanostructures

Abstract: Two kinds of Mg(OH)2 nanosheets were prepared using a precipitation conversion method, and Mg(OH)2 microparticles were synthesized by a direct precipitation method. Drying kinetics experiments of magnesium hydroxide of three morphological micro nanostructures were performed and their drying curves as well as drying rate curves were obtained at 80–140°C. The equilibrium moisture adsorption isotherms of magnesium hydroxide of three morphological micro nanostructures at 12°C were obtained. Results indicate that drying rate curves of magnesium hydroxide microparticles exhibit three stages: a setup period, a constant rate drying period, and a falling rate drying period. Drying rate curves of magnesium hydroxide nanosheets (nanosheets A and nanosheets B) show the same three stages with a small descending trend of constant rate drying period. It is also found that equilibrium moisture contents of Mg(OH)2 nanosheets are larger than those of Mg(OH)2 microparticles under the same drying conditions. The hydroscopici...

Mathematical Modeling of Hydrogels for Microfluidic Flow Control

Abstract: A mathematical model of a microfluidic controller comprising a hydrogel in a typical T- and Y-junction is derived and presented. The model takes into account conservation of momentum, mass and ions for laminar incompressible flow and the deformation/sensing of a pH-sensitive hydrogel. The response of the pH-responsive hydrogel is validated with experimental equilibrium swelling curves for which good agreement is found. The model is employed to study the behavior of the hydrogel and its impact on the overall fluid flow in different microfluidic flow channel/hydrogel configurations, e.g. in a T-junction, where the hydrogel can act autonomously and without external power supply to regulate the flow. Finally, we discuss how the model can be generalized for other types of stimuli-responsive hydrogels.

Editorial: Future of Engineering Education

Abstract: About 4 years ago I penned an editorial devoted to the future of engineering education by 2050. It was motivated by an interesting and thoughtful analysis of the issue as presented at http://www.newhorizons.org. As an engineering educator I have always been interested in the future of engineering education and research, because the engineering profession is intimately connected with wealth creation for every nation as opposed to wealth distribution. It can, if properly nurtured and channeled, increase the size of the economic pie and not simply cut the existing pie into pieces and redistribute it. The global situation in recent decades may give the naı̈ve onlooker the impression that indeed wealth creation is not that important if wealth can be accessed somehow without the hard work of generating it. Indeed, it seemed to have worked at the superficial level, with ‘‘soft’’ management or administrative work being rewarded better than ‘‘hard’’ engineering or technical work. This motivated an en masse switch from manufacturing to service industries. Indeed, globalization appears to have had an unanticipated negative effect of making global wealth available even to those who had the means to access it without actually producing it. The conservation law of wealth, which I am probably defining for the first time, requires that the total global wealth at any time shall diminish as significant parts of it are taken away for nonproductive (viz. non-wealth-creating) activities. This is probably an oversimplistic explanation for the current downturn in global economy but it does have a significant measure of truth in it. I believe that strong and rigorous engineering education is vital to a nation’s economy. It is also a key to innovative R&D, leading to enhancement of wealth. To attract the best talent to this ‘‘hard’’ profession the rewards must be commensurate with what the work entails. This has not been the case for decades where interest of young minds in science and technology has declined precipitously all over the world. Service-oriented professions have overtaken hardware-oriented professions to the detriment of wealth creation capabilities of most developed and appreciably developing countries. Talent has understandably migrated toward regions of higher financial returns than in their home countries and alleviated the problem in at least parts of the globe. However, flattening of the globe is making this process increasingly difficult and nonsustainable. Outsourcing of engineering services is a good but only a temporary solution for developed economies. Over the next four decades the globe will look very different, however, and reversal of talent flow directions is certainly likely and is already happening in some disciplines. In the following paragraphs I use the phrase engineering education to include education in applied sciences and technology as well. The current focus on pure sciences, though laudatory, is driven by the need of academic institutions to score high on various ranking exercises done by non-academic establishments. Each discipline has its optimum sustainable level but this is disturbed by the unfortunate ranking agencies around the world. Currently, basic sciences have already generated a huge gap between their state and its utilization for societal benefit. We need some catchup time in engineering and technology to justify the massive R&D expenses already incurred on basic research. Recall that it is engineering graduates who are still in greater demand for industrial work and R&D. Unfortunately, many major academic institutions that influence the emerging direction of engineering education and research are deviating seriously from fundamental strengths in engineering and migrating towards other ‘‘non-engineering’’ areas. The word engineering itself is being widely hijacked; e.g., we now have a ‘‘financial engineering’’ discipline as well. Of course, sciences are keys to engineering, as are humanities and management sciences. However, the focus should still be on engineering, which includes the ability to design, build, and operate engineering projects, which are becoming increasingly complex. Diluting engineering education to a point where engineering graduates cannot design or work effectively in an industrial setting is a serious matter that will affect a nation’s ability to excel. Maybe it will be necessary to stretch the duration of engineering programs; this will make engineering and applied sciences education even less attractive, however. A major challenge exists for those planning the future of engineering. It needs real visionaries with established track records of success. Also, institutions should ‘‘think global but act local’’. Thinking local and acting global has been a major problem with globalization in recent years! I do not have a solution to offer in a short editorial. Fortunately, the timescale of academic educational programs is long, so we have time to rectify weaknesses. I see current trends as disturbing and see them as at least a partial cause of problems we see today. Emphasis on ‘‘software’’ (read service) at the cost of ‘‘hardware’’ (read manufacturing or producing hard products) is a worrisome trend, especially if everyone around the world follows this trend. Remember, if there is no hardware, there is no need Drying Technology, 27: 627–628, 2009 Copyright # 2009 Taylor & Francis Group, LLC ISSN: 0737-3937 print=1532-2300 online DOI: 10.1080/07373930902820705

Enhanced Performance With an Impinging Jet Flow Configuration for PEMFC

Abstract: A flow structure which delivers the reactant transversely to the MEA using an impinging jet configuration at cathode side is proposed and modeled to examine its effectiveness for enhanced PEMFC performance, especially at high current densities. A two dimensional, non-isothermal, multi-phase model was developed to predict the performance of an impinging jet. The computational model was validated with published experimental data for a conventional PEMFC. For enhanced performance, a macro-porous gas diffusion layer with permeability in the order of 1e−09 m2 is required for the impinging jet design to be effective. Compared to standard channel flow, a single impinging jet design can improve fuel cell performance up to 80% at high current densities. A multiple impinging jet design is further suggested as an effective way to achieve flow and species uniformity with results in more uniform catalyst utilization. Compared to a single impinging jet, a multiple jet gives up to 14% predicted enhancement at a high current density at about 2A/cm2 . Experimental validation is needed for the proposed impinging jet configurations.Copyright © 2009 by ASME