Showing papers by "Arun S. Mujumdar published in 2010"

Drying Technology: Trends and Applications in Postharvest Processing

Abstract: Thermal drying technologies have attracted significant RD conventional hot air drying can be detrimental to the retention of bioactive ingredients. High temperature tends to damage and denature the product, destroy active ingredients, cause case hardening and discoloration, etc. This article briefly summarizes some of the emerging drying methods and selected recent developments applicable to postharvest processing. These include: heat pump-assisted drying with multimode and time-varying heat input, low and atmospheric pressure superheated steam drying, modified atmosphere drying, intermittent batch drying, osmotic pretreatments, microwave-vacuum drying, etc.

Trends in Microwave-Assisted Freeze Drying of Foods

Abstract: Microwave-assisted freeze drying (MFD) can be accomplished in two distinct ways: freeze drying assisted concurrently with microwave application (MFD-1) and freeze drying and assisted microwave/vacu...

Drying of Woody Biomass for Bioenergy: Drying Technologies and Optimization for an Integrated Bioenergy Plant

Abstract: The heavy reliance of mankind on fossil fuels has caused serious consequences, such as global warming and potential energy crisis. Biomass originating from plants has been recognized as the most promising alternative source for energy and fuels in the future. The biomass, in the forms of wood chips, sawdust, bagasse, grass, and agricultural residues, contains moisture from 50 to over 150% and must be dried in order to increase energy efficiency, improve energy product quality, and reduce emissions during energy conversion. A number of dryer types and drying technologies can potentially be used for biomass drying. Selection of the dryer and optimization of drying conditions requires in-depth understanding and quantification of the biomass material, requirements of energy conversion, and the drying process. This review article focuses on woody biomass; it first discusses the characteristics of woody biomass and thermochemical energy conversion technologies in industrial applications. Then, promising drying ...

Studies on different combined microwave drying of carrot pieces

Abstract: Summary Three different combined microwave (MW) drying methods were compared, namely microwave-assisted vacuum drying (MWVD), microwave-assisted freeze drying (MWFD), microwave-enhanced spouted bed drying (MWSD), in terms of drying rate, drying uniformity, product colour, rehydration ratio, retention of β-carotene and vitamin C, and energy consumption. The drying rate of MWVD and MWSD were much faster than that of MWFD. The largest drying rate was obtained in MWSD with 3.5 W g−1. In general, the colour of MWSD products was very uniform. Rehydration ratio of MWFD carrot pieces was almost the same as the freeze-dried (FD) products and better than MWVD and MWSD products. In addition, the highest retention of carotene and vitamin C was observed in MWFD carrot pieces. No significant differences were observed in carotene and vitamin C between MWVD and MWSD products. However, the energy consumption in MWFD was the highest.

Effect of food ingredient on microwave freeze drying of instant vegetable soup

Abstract: The objective of this work was to study the effect of three different food ingredients viz. NaCl content (1–15 g/100 g water), sucrose content (5–25 g/100 g water) and sodium glutamate content (0.5–10 g/100 g water) on microwave freeze drying (MFD) of instant vegetable soup. Response surface methodology (RSM) was employed to optimize their addition levels in instant vegetable soup for MFD. Finally, a comparison of MFD for instant vegetable soup with and without added ingredients was carried out. The results showed that NaCl content and sucrose content had significant influence on drying time and sensory quality, while sodium glutamate content had insignificant effect. The optimum ingredients of the instant vegetable soup for MFD were: NaCl content of 3.2–5.3 g/100 g water, sucrose content of 2–6.8 g/100 g water and sodium glutamate content of below 4.5 g/100 g water. Comparing with MFD vegetable soup without ingredients, condiments addition could increase drying rate and shorten drying time.

Effects of Electric and Magnetic Field on Freezing and Possible Relevance in Freeze Drying

Abstract: Application of an electric or magnetic field can significantly affect the freezing characteristics of water. A DC electric field will tend to induce ice nucleation at a lower degree of supercooling, and there is evidence to show that an AC electric field delays the onset of ice nucleation. Industrial research has shown that a magnetic field can be used to delay nucleation and to induce small, unclustered ice. Smaller ice crystals are essential in the preservation of the structure or bioavailability of frozen materials, particularly biological or food products. On the other hand, larger ice crystals facilitate faster freeze drying because it results in less vapor mass transfer resistance. The end part of this review introduces another application of magnetic field in the form of magnetocaloric freezers. This technology is a potential alternative to heat pump drying for commercial freezing and refrigeration.

Effect of Osmotic Dehydration on Microwave Freeze-Drying Characteristics and Quality of Potato Chips

Abstract: In this study, the effects of osmotic pretreatment on microwave freeze-drying (MFD) characteristics and quality of potato chips were studied. Potato slices were pretreated by immersion in salt solution (5, 10, 15% w/w) or sucrose solution (30, 40, 50% w/w) at 20°C for 6 h prior to MFD. Results showed that osmotic pretreatment significantly improved the MFD drying rate compared with MFD of fresh samples under the same operating conditions. However, there is an optimal level of osmotic dehydration beyond which it has an adverse effect on product quality. Osmotic pretreatment with salt concentration below 5% and/or sucrose concentration below 30% prior to MFD drying resulted in dried products of good quality with shorter total drying times relative to MFD of untreated samples.

Microwave Freeze-Drying Characteristics of Banana Crisps

Abstract: This experimental study investigated the drying characteristics of microwave freeze drying (MFD) of banana slices of varying maturity. Results show that the drying time was shortened with increase of both microwave power and degree of maturity of the banana. In terms of the quality parameters such as hardness, fracturability, color, and rehydration ratio, high maturity samples with high sugar content displayed better performance. The best sensory scores were obtained for medium maturity bananas processed using 2.0 W/g microwave power.

Dewatering and Drying in Mineral Processing Industry: Potential for Innovation

Abstract: Wet beneficiation of minerals necessarily requires removal of large amounts of water—typically contaminated—before further processing of the concentrated ores can be carried out. Often such concentrates are transported over large instances by ground or sea transport. For economic reasons dewatering/drying are essential unit operations. Often the capacity requirements of the mining operations are very large, the product processed has low unit value, and the material is abrasive. The selection of dryers is often arbitrary. No clear guidelines can be found by noting current practices in different countries. This article provides a global view of the types of dewatering equipment and dryers currently used in the mineral processing industries, provides guidelines for selection of drying systems, and recommends emerging innovative technologies, such as superheated steam and pulse combustion drying for future applications in this industry. A few case studies are examined.

An overview of the recent advances in spray-drying

Abstract: A global overview is presented of recent developments in spray drying. Recent advances in computational fluid dynamics modeling have provided new insights into the flow processes occurring within the spray chamber. This is important since detailed experimental measurements within an operating spray dryer are almost impossible due to the hostile environment of high-temperature two-phase flow, which may be unsteady, and the high cost that would have to incur. Some recent predictive studies on predicted effects of innovative chamber geometry, reduced pressure operation, operation in low dew-point air and superheated steam are presented. Also, a comparison is made between steady and unsteady state computations to highlight the critical issues. Predicted results on a horizontal spray chamber configuration are also presented. Finally, a brief survey is made on the recent literature on spray freeze-drying as well as multi-stage drying processes.

Study of the optimisation of puffing characteristics of potato cubes by spouted bed drying enhanced with microwave.

Abstract: BACKGROUND: In commercial deep-fat frying of potato chips, the oil content of the final products ranges from 35 to 45 g 100 g−1 (wet basis). High-temperature frying may cause the formation of acrylamide, making the products unhealthy to the consumer. The aim of this research was to explore a new method, spouted bed microwave drying, to produce healthier puffed snack potato cubes as possible alternatives to oil-fried potato chips. The influence of drying conditions of the spouted bed microwave drying on puffing characteristics of potato cubes were studied and compared with the direct microwave and hot air drying method. RESULTS: Tandem combination drying of microwave-enhanced spouted bed drying (MWSB) could achieve a good expansion ratio, breaking force and rehydration ratio. The puffing characteristics of potato cubes were significantly affected (P < 0.05) by moisture content before starting microwave power in spouted bed microwave drying, by microwave (MW) power, and by the original size of potato cubes. CONCLUSION: The optimum processing parameters were the moisture content at the start of microwave power (60%), the size of potato cubes (10–12 mm), and microwave power (2–2.5 W g−1) Copyright © 2010 Society of Chemical Industry

Model for sludge cake drying accounting for developing cracks.

Abstract: This study analyzed convective drying of wastewater sludge cakes with three-dimensional cake structures probed using an X-ray microcomputerized tomography scanner (micro-CT). Crack development and surface skin layers were utilized in model development. The drying cake had an extremely heterogeneous structure, with detail presented by constructed three-dimensional, tetrahedral volumetric grids. Drying modeling was conducted numerically by solving the conservation equations with assigned boundary conditions at so-constructed complicated volumetric structural model.

Effect of calcium ion and microwave power on structural and quality changes in drying of apple slices.

Abstract: Effects of impregnated calcium ion and microwave (MW) power on texture, rehydration, shrinkage, color, and other selected indexes of freeze-dried apple slices were investigated. Apple slices were dried by freeze drying and microwave freeze drying (MFD) separately. Vacuum impregnated (VI) and non-vacuum-impregnated apple slices were dried at various microwave power levels. Non-vacuum-impregnated apple slices were found to preserve their mechanical structure better than the VI-treated ones. Microwave application resulted in decreased protopectin fraction as well as total pectin content. As microwave power varied from 1.2 to 2.0 W/g, the total pectin content decreased from 0.810 to 0.521 (expressed as g galacturonic acid/100 g fresh sample). The effect of microwave power in decreasing the drying time was significant. The color of MFD apple slices varied to a minor extent with MW power level over the range of parameters studied.

CFD simulation of solid–liquid flow in a two impinging streams cyclone reactor: Prediction of mean residence time and holdup of solid particles

Abstract: The hydrodynamic behavior of a two impinging streams cyclone reactor (TISCR) was simulated using the computational fluid dynamics (CFD) technique. An Eulerian multiphase model has been used to compute the unsteady flow of a solid–liquid suspension in a 3D geometric configuration. The mean residence time ( t m ) and holdup of solid particles were calculated from a number of simulated results obtained at different solid and liquid flow rates. The CFD simulation results were compared with the experimental data available in the literature and a fairly well agreement was observed. Such a correlation was gradually improved with increasing solid flow rate.

Water coagulation using electrostatic patch coagulation (EPC) mechanism

Abstract: Coagulation of fine particles to form large flocs is an essential step to reach efficient dewatering of wet materials. The electrostatic patch coagulation (EPC) mechanism was applied in this study to remove turbidity and natural organic matters in water using four different dosing-mixing schemes. Sufficient rapid mixing and slow mixing or applying two-stage coagulation benefit removal of turbidity. The EPC mechanism could only efficiently remove organic matters of molecular weight of 7500–10,000 Da. Only sufficient rapid mixing is relevant to organic matter removal. The mechanisms for natural organic matters (NOM) removal are proposed to be complexation of ions and NOM to form insoluble aggregates to be separated by membrane filtration.

Experimental and Numerical Investigation of Spray-Drying Parameters on the Dried Powder Properties of Ginkgo biloba Seeds

Abstract: The operating parameters for spray drying play a significant role in determining the properties of the dried product. Ginkgo biloba (GB) seeds are a popular food and additive in the food and medicine market; in this study we spray dried these seeds. According to the L1644 orthogonal experimental design, a total of 16 tests was performed in a compact spray dryer. Parameters, i.e., inlet air temperature, air flow rate, outlet air temperature, and feed concentration, were selected as affecting factors. The dried product was evaluated with respect to residual moisture content, color difference, mean particle size, and protein content. The effects of these four parameters on the product properties were investigated. The experimental results showed that operating air temperature, especially the outlet air temperature, significantly affected the residual moisture and protein content in the dried product. High outlet air temperature can reduce the product quality. On the other hand, the mean particle size of GB p...

A novel dielectric drying method of sea cucumber

Abstract: Summary The sea cucumber autolyses readily so it must be dehydrated for preservation. Traditional drying methods of sea cucumber need very long time and have adverse effect on quality. Hence, a novel microwave freeze drying technique was developed to dry sea cucumber. Because microwave heating is a function of dielectric properties of the material in microwave field, dielectric properties of sea cucumber were determined. As expected, the dielectric loss factor of sea cucumbers was very low in frozen state, and several pretreatments (nanoscale calcium carbonate impregnation and vacuum impregnation, salt impregnation, etc.) were analysed to improve the dielectric properties of sea cucumber. Vacuum impregnation with nanoscale calcium carbonate combined with microwave freeze drying was found to be an efficient drying method for sea cucumber by anova (P < 0.01). Compared with microwave freeze drying method without any treatments, this drying method could reduce the drying time by up to two hours.

Extracellular Polymeric Substances (EPS) and Extracellular Enzymes in Aerobic Granules

Abstract: This work highlighted the main cause of vacuole formation, which may contribute to the stability loss for stored granules, using extracellular polymeric substances (EPS) fractionation in conjunction with fluorescence staining approaches. The results showed that the stored granules had an integrated appearance after 30 days' storage. However, their interior was composed of large vacuoles at 30 μm cryomicrotome sections. After storage, protease activity was bound principally with tightly bound EPS (TB-EPS) fractions, whereas proteins were predominant in the loosely bound EPS fractions (i.e., supernatant and slime), few in the tightly bound EPS fractions (i.e., TB-EPS and pellet). About 74.5% of Mg2+ was present in the supernatant and slime fractions, and only 25.5% of Mg2+ was found in the LB-EPS, TB-EPS, and pellet fractions. The vacuoles were formed as a result of protease hydrolysis reaction at the core regime that breaks the bonds between proteins and cations (mainly Mg2+). This action leaks the protein...

Electroosmotic Flows in Sludge at Dewatering

Abstract: Electroosmotic dewatering of activated sludge is an important transport process playing a critical role in electroosmotic dewatering of sludge. In the present work, a comprehensive physical model considering both pressure-driven and electroosmosis-driven flows in an activated sludge floc was developed and numerically solved. Meshes were produced via scanning images based on real sludge flocs. The permeabilities of pressure and electroosmotic flows were evaluated, from which the total detwatering flow rate can be estimated.

Rheological Properties of Cabbage Pulp

Abstract: The rheological behavior of cabbage pulp was determined using a computer controlled rotational rheometer at a temperature range of 20, 30, 40, and 50°C. The flow behavior of pulp was pseudoplastic and fitted well to the Casson model. In all the cases, the effect of soluble solids on apparent viscosity was more pronounced than the effect of temperature. The combined effect of temperature and soluble solid content on viscosity was also given. The activation energy value of 3–6°Brix cabbage puree varied from 7 to 12.6 kJ/mol when shear rate increased from 1 to 10 s−1. The exponential model developed had an excellent fit (r2 > 0.87) and would be useful for the engineering applications.

Editorial on Industry–Academia Collaboration in R&D

Abstract: The high level of interest in drying R&D, particularly in the academic institutions around the globe, is evident from the series of successful conferences devoted to drying that were held in 2009. ...

Improving energy efficiency and sustainability of industrial thermal drying systems using simprosys software

Abstract: Industrial thermal drying plays a major role in many industries such as the food, pharmaceutical, chemical and mineral processing. Thermal drying process is highly energy intensive. In developed countries, up to one fifth of the rational industrial energy consumption goes into thermal drying operations. With industrial drying efficiencies ranging only from 30 to 60 percent, there is great potential for improvement. The aim of this work is to present different options for improving dryer energy efficiency for two cases, viz., coal drying and spray drying of sodium palconate using a new software package entitled "Simprosys" (http://www.simprotek.com). This is accomplished by recovering heat from exhaust streams from the dryer. Through Simprosys simulation, the use of recycling exhaust air from dryer or recycling a part of dried material back into the dryer enables one to improve the energy efficiency of a drying system. However, recovering heat from exhaust air to preheat the fresh air results in significant increase in the energy efficiency in case of a coal drying system. Another way of improving sustainability is the use of renewable sources of energy for air heating which is also analyzed using Simprosys. The analysis of spray drying flow sheet was carried out in the same fashion with similar conclusions. The main advantage of Simprosys is that it allows rapid evaluation of alternate flowsheets to evaluate and optimize overall energy efficiency and sustainability.

Editorial on Measurement of Outcome of R&D

Abstract: Most developed economies of the world tend to credit their advanced educational institutions and R&D activities in science and technology for their success. The strong historically proven correlation between the R&D effort and economic development is hard to dispute. However, I believe that there are many more factors affecting the outcome of R&D. Successful R&D may not necessarily result in economic returns; on the other hand, many nations have prospered with little or no R&D effort. Nevertheless, I favor strong support of ‘‘R’’ in academia and ‘‘D’’ in industry and policies that can forge a strong link between the two as a formula for success. Academia is where human talent can be nurtured and cultivated to carry out cutting-edge research; industry can then utilize such talent to develop new technologies that are economically beneficial and socially valuable for the general well-being. Many attempts to do both in academia have met with limited, if any, success. As I have noted in several of my earlier editorials, the underlying objectives and timescales of research and development activities are widely different, which lead to limited success. Science thrives on basic research; it is challenging, creative, and risky and can lead to game-changing technologies. The timescale required is typically long. It is carried out for its own sake with no limitations requiring specific applications and short-term return on funds invested. Academia is an ideal location to house such activity. The knowledge thus created is generally made available freely to whoever wants it and can digest it. High-level human talent is needed to utilize such basic advancements for engineering or technological applications. Applied or engineering R&D is motivated by real-life needs and opportunities; it is also constrained by shorter timescales and cost effectiveness. Science can propose new avenues that economics may deny. Not all basic research can be transformed into practical applications, but it is hard to predict which ones will be. Support of basic research is therefore expensive and perhaps more appropriate to the richer nations of the world. R&D should ideally be taken as an investment in the future health of an industrial state. However, it is easier to consider it as an operating expense for accounting and tax purposes; this is what most nations do. Because R&D outcomes need a long gestation period, it is nearly impossible to demonstrate returns on such expenses on a quarterly or even annual basis. R&D projects in industry thus become susceptible to frequent terminations and new startups. This can, although not necessarily, lead to wasted financial and human resources as many projects are left incomplete and nonconclusive. R&D policy therefore needs to be driven by highly technical and creative teams who can appreciate the intricacies involved and not focus only on the bottom line in the short term. It is important to be cautious in embarking on new R&D projects and even more careful and responsible in terminating such projects. One major problem that policy makers face is the inherently dynamic and local needs of R&D; yet this is affected by globalization. What competing nations or companies do does affect such policies. Clearly, a collaborative effort can save financial and human resources but often the proprietary nature of industrial R&D prohibits this option. On the other hand, major global issues affecting all nations, e.g., greenhouse gas emissions and climate change, can and have led to successful cooperation in R&D across geopolitical boundaries. Closely linked to the economic returns on R&D is the issue of intellectual property (IP) rights. There is scholarly work that shows that IP can decrease innovation by limiting use and enhancement of patented technologies. When Switzerland and The Netherlands stopped patent protection for some years, studies showed a rise in innovations measured by some metrics. I think the problem is too nonlinear and longer term to arrive at such definitive conclusions. However, it is true that IP issues have slowed down industrial interactions with academia due to the protracted nature of resulting negotiations and associated additional costs. If academia wishes to produce research outcomes of industrial interest, a simpler cost-effective IP regimen is clearly needed. I am not aware of universities that prospered as a result of their technological discoveries. It is impossible to do without industry participation and support. Finally, one must face the key issue of evaluation of R&D outcomes. This is truly a tough nut to crack. It is hard to place a dollar figure on the prior IP that human talent brings to any R&D project. The same is true of soft and hard knowledge that institutions bring to a given project. When a well-educated Ph.D. in science and technology moves from one country to another, several studies show that an equivalent of over a million dollars is transferred to the new (developed) economy. Yet, this is never taken into any R&D analysis. Without such human talent no R&D is possible. Also, without injection of financial resources, human talent cannot be utilized effectively; hence the need for both types of resources to succeed in Drying Technology, 28: 743–744, 2010 Copyright # 2010 Taylor & Francis Group, LLC ISSN: 0737-3937 print=1532-2300 online DOI: 10.1080/07373937.2010.485079