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Browning and a serious drop in anthocyanin level occur during microwave-assisted spouted bed drying (MWSB) of purple-flesh sweet potato (PFSP) cubes. Blanching pretreatment inhibits browning and also affects the drying behavior. Effects of microwave blanching (MWB), hot water blanching (HWB), and steam blanching (SB) were examined experimentally. The results showed that MWB leads to rapid peroxidase (POD) degradation, reduces the drying time, and yields highest anthocyanin level after MWSB drying. However, the color of the dried product was not as bright and purple as those obtained by HWB and SB treatments. Microwave blanching can improve the MWSB drying process to maintain the anthocyanin level in dried products while reducing the drying time. [ABSTRACT FROM AUTHOR]

Non-uniform heating is a major issue in microwave applications, mainly due to inherently uneven distribution of electromagnetic energy in the microwave applicator. In this work, our aim is to improve electric field distribution uniformity by utilizing microwave reflection from electrically conductive beads placed in the microwave oven. The effects of position, size, and number of electrically conductive beads on the electric field distribution were numerically investigated, and validated through water-load experiments in the cavity. It is found that uniform electric field distribution was realized to some extent by appropriate placement of electrically conductive beads; meanwhile, average electric field intensity in the microwave oven was increased. [ABSTRACT FROM PUBLISHER]

Purple-fleshed sweet potatos (PFSP) were loaded into a laboratory-scale, microwave-assisted spouted bed with a coating of sodium alginate (SA) of 0, 0.2%, 0.4%, 0.8% (w/w) for both steam-blanching pretreated and fresh-cut raw samples. The drying curves, rehydration ratio, and maximum penetrating forces were studied for final products; color changes and anthocyanin level were also taken into consideration. It was concluded that coating processing forms barriers to moisture content, which changes the dielectric properties of PFSP cubes and shortens the drying time; however, coating PFSP cubes with SA did not lead to a porous microstructure in the final products. The final hardness was high and rehydration ratio was low. Steam-blanching was helpful for color and anthocyanin-level retention compared with raw samples. In sum, microwave-assisted spouted bed (MWSB) drying of PFSP cubes is not an ideal processing method, even with coating treatment, but blanching is an approach to obtain products with high anthocyanin level and fine purple color. [ABSTRACT FROM AUTHOR]

Pretreatments of fruits before drying have been proposed as alternative way to improve the quality of dried fruits and reduce drying time. In the present study, the effects of different pretreatments (ultrasound and microwave) on apple cubes prior to spouted bed drying were investigated. Ultrasound pretreatment resulted in a great loss of sugars (25.7% for 15 min) compared to microwave pretreatment, where little rise in sugar content was observed (1.6% at 300 W). Ultrasound pretreatment improved the drying rate more than microwave pretreatment. Nevertheless, microwave-pretreated dried apples were harder and had lower water activity than ultrasound-pretreated ones. Low-frequency nuclear magnetic resonance (LF-NMR) analysis was used to study the water state and revealed that all pretreatments promoted redistribution of water among apple cell compartments and showed that most of the water lost was from the vacuoles. If dried low-calorie fruits are required then ultrasound pretreatment would be preferred. [ABSTRACT FROM AUTHOR]

Drying is one of the most common methods for processing and preserving squids. A novel forced convective dryer based on infrared heating was developed with an online temperature control. By setting the drying medium temperature of 50°C, we studied the effects of infrared wavelength and air velocity on drying characteristics of the shredded squid and qualities of dried squid products. We also compared it with the conventional hot-air drying (HAD) and advanced microwave vacuum drying (MVD). The infrared heating rate increase was faster than that of HAD. The heating and drying at the wavelength of 2.5–3.0 µm were more effective than those at the infrared wavelength of 5.0–6.0 µm. Specific energy consumption linearly increased with the air velocity. Microstructure observation showed that the infrared-dried rehydrated sample displayed a muscle fiber structure similar to the fresh sample. The infrared-dried squids had less drying shrinkage, brighter color, and better rehydration capacity than HAD products. Their sensory qualities were better than HAD and MVD products. Above all, infrared drying with wavelength of 2.5–3.0 µm and air velocity of 0.5 m/s was suggested as the best drying condition for squids in this study. [ABSTRACT FROM AUTHOR]

This articles provides results of an experimental investigation of three hybrid drying technologies on the drying characteristics and key quality parameters of shiitake mushroom (Lentinus edodes). The drying techniques tested at the laboratory scale are mid-infrared-assisted convection drying (MIRCD), hot air coupled with radio frequency drying (HCRFD), and hot air coupled with microwave drying (HCMD). For comparison, the standard drying technique using hot air was also tested. The quality parameters include texture, color, rehydration rate, shrinkage, nutrient retention, microstructure, etc. These four drying tests were conducted at fixed air temperature (60°C), and the power level for HCRFD, MIRCD, and HCMD was fixed at 4 W/g. The results showed that hot air coupled with microwave drying gave the shortest drying time, and mid-infrared-assisted convection and hot air coupled with radio frequency drying showed better color attributes and nutrient retention. Under the conditions tested, mid-infrared-assisted convection drying yielded minimal shrinkage (maximal rehydration) and lower hardness upon rehydration. The uniform honeycomb network and less collapsed structure of MIRCD samples can be used to explain these better quality characteristics. [ABSTRACT FROM AUTHOR]

In this study, Fuji apple slices were dehydrated using freeze drying (FD) combined with microwave assisted with vacuum drying (VMD). The optimal parameter for the diversion point of moisture content from FD to VMD process was at the moisture level of 21%, and for VMD the optimal parameter for vacuum pressure was at 9.15 kPa and microwave power density was at a level of 3.18 w/g. The results show that the two-step technique can significantly reduce total FD time required by up to 40%, while the nutritional value of the dried apple chips remained unchanged compared to FD used alone. [ABSTRACT FROM AUTHOR]

Microwave-assisted pulse-spouted vacuum drying (MPSVD) of apple cubes was examined in a laboratory-scale apparatus. Aside from the drying time, structural and textural properties of the dried cube were measured. Results are compared with alternative drying techniques developed earlier in our laboratory. These include microwave-spouted bed drying (MSBD), microwave vacuum drying (MVD), and conventional vacuum drying (VD). Comparison is made in terms of the key quality parameters, viz. color, texture, apparent density, rehydration property, and sensory evaluation. Over the range of operating conditions tested, MPSVD apple cubes had the best color and significantly highest sensory evaluation score. [ABSTRACT FROM AUTHOR]

The objective of this study was to compare the drying characteristics and the quality of dried Shiitake mushroom (Lentinus edodes) cubes obtained by hot-air drying (HAD), intermediate-infrared drying (IIRD), and vacuum microwave spouted-bed drying (VMSD). Several quality parameters of products, including color, texture, and rehydration capacity, were investigated. Compared to IIRD and VMSD, HAD turn out to be the most undesirable method due to its longer drying time and poor product quality. With similar rehydration capacity, the color of the VMSD product was closest to the original material. In terms of texture, total sugar content, and sensory evaluation, the VMSD product has the best quality. [ABSTRACT FROM AUTHOR]

A number of contributions have been made in the field of chemical process monitoring and control with applications ranging from simple flow and temperature control to highly complex inferential adaptive control systems in biochemical and polymer production. These technologies face difficulties when applied to drying equipment, due to the inherent complexity of the operation. This article shows some recent trends in monitoring and control of drying processes. This review is organized in sections according to the transport phenomena involved in the operation of a dryer. In each section, examples of recent trends in monitoring and control strategies of key variables directly related to these transport phenomena are discussed. [ABSTRACT FROM PUBLISHER]

Three alternate dying methods—vacuum drying (VD), vacuum microwave drying (VMD), and pulse-spouted vacuum–microwave drying (PSVMD)—were examined experimentally for their potential as an industrial scale technology to produce granules of fish. Drying kinetics as well as key quality parameters such as expansion ratio, texture, color, sensory characteristics, and microstructure of crispy granules produced by these drying techniques were examined. Results showed that the drying time is reduced with an increase in microwave power level and with reduced pressure as expected. The quality of the granules is affected by the drying method and the operating parameters employed. Granules obtained using PSVMD at a microwave power density of 6.0 W/g displayed optimal quality required for the commercial product accepted by consumers. [ABSTRACT FROM AUTHOR]

Fluidized bed dryers (FBD) are commonly employed in many industries to dry particulate solids. FBDs provide good solids mixing, high rates of heat and mass transfer, and relative ease of material handling. For efficient operation, it is important to be able to monitor and control the fluidization regime, particle size distribution (PSD), moisture content, and bulk density as well as product chemical properties. This review provides an overview of the trends in the application of different experimental techniques to monitor and control the hydrodynamic conditions of FBDs which influence the particle physiochemical properties. This review covers a wide range of measurement techniques, including infrared moisture sensor (IR), near infrared (NIR) spectroscopy, analysis of pressure fluctuations, optical imaging techniques, acoustic emission (AE), electrical capacitance tomography (ECT), spatial filter velocimetry (SFV), Raman spectroscopy, focused beam reflectance measurement (FBRM), microwave resonance technology (MRT), triboelectric probes, positron emission particle tracking (PEPT), and some novel techniques for monitoring and control of FBDs. The present review summarizes the use of the diverse techniques and outlines their merits and limitations. Prospects for future research in this area are also identified. The measurement techniques can be used for research, development, and operation of fluidized bed equipment used in non-drying applications as well. [ABSTRACT FROM AUTHOR]

The drying homogeneity of the microwave–pulsed spouted bed drying (MPSBD) method was studied via preparing tubers granules by MPSBD under different predefined conditions. The effects of three parameters (microwave power, moisture content transition point, and loading) on the homogeneity of prepared tubers granules were studied. Based on response surface analysis results, it was concluded that the optimum conditions for tuber granules prepared by MPSBD method is 1.10 W/g microwave power, 80% moisture content transition point, and 90 g material loading. It was proven that the experimental result from the predicted optimal condition agreed with the model-predicted results, which evidenced the accuracy of the response surface analysis. Furthermore, the brighter color and higher rehydration capacity of samples prepared by MPSBD indicates that MPSBD is a promising method that can be applied in the food dehydration industry. [ABSTRACT FROM AUTHOR]

This article presents experimental results and analysis of four drying methods, viz. hot air drying (AD), hot air-assisted radio frequency drying (ARFD), infrared drying (IRD), and microwave-assisted hot air drying (MAD), on color, microstructure, density, rehydration capacity, and texture after rehydration of stem lettuce slices (Lactuca sativaL.). The drying time required for these drying protocols was also compared. These four drying tests were conducted at fixed air temperature (60°C) and velocity (1 m/s), as well as identical sample load (300 g), bed depth (20 mm), and the power level for ARFD, IRD, and MAD, which was fixed at 4 W/g. The results showed that the drying time required for stem lettuce slices using ARFD was the shortest (120 min), followed by MAD (140 min) and IRD (180 min); AD required the longest time (360 min). Notably, ARFD yielded uniform drying and the quality of the dried samples using ARFD was also the best among these four drying methods. [ABSTRACT FROM AUTHOR]

This article presents a software tool, Simprosys, and its newly added burner unit operation model for process modeling and simulation of drying. Combustion generation using the burner unit operation is described briefly. Humid gas properties of combustion are compared and found to be different from those of air. The effects of pressure on both air and combustion humid gas properties are investigated. It is found that both combustion and air could be significantly different in their moisture carrying capability when the operating pressure is different from standard atmospheric pressure, especially for some vacuum drying cases where the operating pressure is well below atmospheric pressure. A model combustion drying flowsheet is simulated with Simprosys 3.0 and simulation results are presented and discussed. [ABSTRACT FROM AUTHOR]

The motion and drying characteristics of a single particle in a novel two-dimensional pulsed opposing jet contactor (POJC) are modeled and discussed. Hot air is used as the drying medium. To simulate particle drying, the gas phase and dispersed phase conservation equations are considered in the Eulerian reference frame and the Lagrangian reference frame, respectively. The RNG turbulence model is used to determine the turbulent characteristics of the gas phase. The particle motion is described by the BBO (Basset-Boussinesq-Oseen) equation. The effects of the key parameters, such as the jet Reynolds number, amplitude of pulsation, frequency of pulsation, particle diameter, location of release of particle from one jet as well as velocity profile on residence time (RT) and particle penetration depth (PN) into the opposite jet, are examined. Results show that POJC has strong potential for particulate heat transfer as well as drying; it can improve evaporation rate relative to the corresponding steady OJC by up to 30% as a result of increased residence time in the impingement zone within the parameter ranges simulated. [ABSTRACT FROM PUBLISHER]

Fresh duck egg white (FDEW) powders and desalted duck egg white (DDEW) powders were produced by using a novel pulse-spouted bed microwave freeze dryer and a conventional freeze dryer. The desalting process of the salted egg white was carried out in the presence or absence of ultrasound pretreatment. The drying time, microstructure, apparent density, color, and functional properties (gelling, foaming, and emulsifying) of FDEW and DDEW powders obtained from both the pulse-spouted bed microwave freeze-drying (PSMFD) and a conventional freeze-drying (CFD) were studied in order to evaluate the physicochemical and functional properties of these powders. The results show that PSMFD produced FDEW powders with better color appeal (higher L*and lower b*), lower apparent density, as well as shorter drying time compared to the FDEW powders produced by the CFD. FDEW powders produced from PSMFD produced more transparent gels, emulsions with higher foam stability, and higher emulsifying activity index compared to the FDEW powders obtained from CFD. Regarding the powders obtained from DDEW by using PSMFD, the ultrasound pretreatment during the desalting process produced DDEW powders with higher gel strength, higher foaming capacity, higher foam stability, higher emulsion stability index, as well as shorter drying time compared to the DDEW powders in which ultrasound treatment was not carried out during the desalting process in the upstream. [ABSTRACT FROM AUTHOR]

Porcine placenta was hydrolyzed using papain and trypsin in a combined formulation. An orthogonal experimental design (L9(3)4) was applied in order to obtain porcine placenta hydrolysates (PPH) having the best antioxidant activities. The PPH was dried using vacuum drying (VD), spray drying (SD), and freeze drying (FD) and the effects of these drying methods on the antioxidative activity and solubility were investigated. The DPPH scavenging activity of these PPH reached 44.45 ± 0.46% and the molecular weight of 83.39% of these PPH peptides was below 3000Da. The proportion of highly antioxidative amino acid residues in these PPH reached 60.14%. The VD-PPH showed the lowest antioxidantive activities (DPPH, superoxide and hydroxyl radical scavenging activities, and lecithin liposome antioxidant activity) and the lowest solubility. The FD-PPH exhibited the highest antioxidative properties and the highest solubility. Both the antioxidative properties and the solubility of SD-PPH remained in between those of FD-PPH and VD-PPH. Spray drying can be a method of choice to produce PPH powders due to its higher throughput. [ABSTRACT FROM AUTHOR]

Passive heat transfer enhancement using a slurry of microencapsulated phase-change material (MEPCM) flowing in a laminar regime through a coiled duct of square cross section was evaluated. The phase-change material is n-octadecane. The flow behavior and heat transfer performance of water and MEPCM suspensions in various configurations (conical spiral, in-plane spiral, and helical spiral) of coiled tubes of square cross section was investigated. The results are compared with those for water as the base fluid flowing through a straight tube. A computational fluid dynamics (CFD) approach is used to simulate the laminar flow of water with MEPCM suspension in these geometries. The liquid suspension properties are expressed as functions of the volumetric concentration of MEPCM particles and the temperature. Improved heat transfer performance was obtained as the concentration of MEPCM suspension increased from 1 to 10%. However, the overall performance in terms of the pumping power consumed for unit heat transferred worsened. [ABSTRACT FROM AUTHOR]

Dewatering of a wet material is composed of two steps: free the moisture from the associated material surface and move the freed water out of the material matrix. In this review paper, the concept of bound water and the development of characterization of the binding strength between moisture and material surface were described. Then an example revealing the correlation between binding strength and the residual moisture after coagulation-filtration ofChlorellasp. was discussed. [ABSTRACT FROM AUTHOR]

Membrane filtration can efficiently harvest microalgae from culture broth. The performances of cyclic filtration and cleaning tests onChlorella vulgariswere evaluated with polyaluminum chloride (PACl) coagulation and with a surface-modified hydrophilic polytetrafluoroethylene (PTFE) membrane under 1 bar pressure drop. Filtration of the original algal suspension without PACl coagulation could lead to severe irreversible fouling on the PTFE membrane. Coagulation using 10 mgl−1PACl can mitigate pore blocking but cannot enhance filtration flux. With 500 mgl−1PACl, most fines were incorporated into large flocs to build up cakes of low resistance and protect membrane pores from severe blocking. Flux recovery all exceeded 95% with ≥10 mgl−1PACl dosage. The PACl-coagulation and surface modified PFTE membrane are feasible to dehydrateChlorella vulgarisESP-6 isolate using cyclic filtration-cleaning process. Supplemental materials are available for this article. Go to the publisher's online edition ofDrying Technologyto view the free supplemental file. [ABSTRACT FROM AUTHOR]

Drying uniformity, shrinkage, rehydration, and textural properties were measured to evaluate the quality of pulsed spouted microwave–vacuum-dried stem lettuce slices. Drying was carried out in a 5-cm (od) vacuum drying chamber at 7–10 kPa and microwave power level of 2.4 Wg−1. Pulsed spouted microwave–vacuum-dried products were found to be more uniform compared to those obtained in a conventional rotating turntable microwave–vacuum dryer. The pulsed spouted mode also resulted in dried stem lettuce slices with low discoloration and high rehydration capacity as well as high hardness after rehydration. The total drying time required for pulsed spouted bed microwave–vacuum-dried products was approximately 60 min, reduced by 50% compared to conventional rotating turntable microwave–dried ones. [ABSTRACT FROM AUTHOR]

Increasing globalization is driving agricultural production in developing countries toward better recovery levels and high additional value. A great opportunity is thus offered to emerging economies. By adopting appropriate and improved methods that allow better preservation, transport, and storage and that conform to the rigorous requirements and standards of organoleptic and nutritional quality as well as stringent hygienic criteria, emerging economies can derive significant benefits. Drying of biological materials usually results in shrinkage. The impact of shrinkage is often highly prejudicial for both the function and use of these materials. On the one hand, shrinkage results in a sharp decrease in water diffusivity through the porous structure (for dehydration and rehydration processes). On the other hand, the compact structure of dried biological material is usually unsuitable in terms of organoleptic quality and is inadequate for grinding. Thus, it is becoming very important to include retexturing and structure-expanding processes in standard drying processes. To this end, the instant controlled pressure drop (DIC) technology has been proposed and successfully tested as a texturing process for partially dried materials, which should normally intensify the whole operation. The quality of the final product as well as the performance of the drying process can also be dramatically improved. Finally, for a large category of dried fruits and vegetables, and even freeze-dried materials, microbiological contamination and the presence of insects and larvae are serious problems. DIC technology can be used as an ultra-high-temperature treatment for a controlled decontamination. Such dried, expanded, and completely decontaminated products can be used as highly nutritional snacks. They can easily be ground to produce expanded granulated powders with excellent sensory, nutritional, functional, and textural properties. [ABSTRACT FROM PUBLISHER]

Stem lettuces are an important vegetable due to its nutritional characteristics. Stem lettuce was used as the model in this investigation. The ice-melting and freezing point temperature as well as distribution and migration of unfrozen water in stem lettuce cubes during the microwave freeze drying (MFD) step were studied using differential scanning calorimetry (DSC) and low-field pulsed nuclear magnetic resonance (LF-NMR). MFD of stem lettuce cubes was carried out in three circular conduits with different diameters (40, 55, and 70 mm) at a microwave frequency of 2,450 MHz. The total drying time for MFD was almost the same for all circular conduits; that is, approximately 4.5 h. This was less than the 7.0 h required for conventional radiation freeze drying (FD) in a 40-mm-diameter circular conduit and far less than the 20 h required for FD in a flat slab model. The microwave energy supplied and specimen temperature profiles during MFD were strongly influenced by the tissues, unfreezable water content, moisture distribution, and ionic characteristics of the samples. It was also found that the MFD process involving the conduits can be divided into three steps based on the amount and distribution of unfrozen water in the frozen samples and how heat is supplied in order to prevent corona discharge. [ABSTRACT FROM AUTHOR]

Impinging jets issuing from the tailpipe of pulse combustors have been evaluated in recent studies for possible applications in rapid drying of continuous sheets such as grades of paper, textiles, etc. In order to further understand the effect of pulsed flows on the heat and mass transfer rates of impinging jets, a numerical study was performed on a two-dimensional pulsating impinging jet array. A computational fluid dynamics approach was used to examine the effect of periodic sinusoidal pulsation on the local Nusselt number distribution of the wet target surface being dried. Because a high temperature and large temperature difference between the jet flow and impingement surface are used to obtain high heat transfer rates in impingement drying, the thermophysical properties of jet flows were taken into account in the present mathematical model. A parametric study including phase angle and frequency as well as amplitude of pulsating flows was conducted for optimization and design of pulsating jet arrays. Examination of the velocity and thermal fields showed that the instantaneous heat transfer rate on the target surface was highly dependent on the mass transfer characteristic and development of the hydrodynamic boundary layer with time. [ABSTRACT FROM AUTHOR]

Sewage sludge of pasty consistency was atomized and dried directly using a high-temperature, highly turbulent gas flow in the tailpipe generated by a Helmholtz gas-fired pulse combustor (PC). Parametric studies were carried out to investigate the effect of drying pipe length and sludge feed tube size on the PC sludge drying process. Experimental results showed that the pulsating gas stream can disperse the sludge into small particles with a narrow size distribution between 0.01 and 4 mm and the granular sludge was dried rapidly due to the increased particle surface area and the high temperature of the drying medium. PC drying of sewage sludge was compared to convective- and microwave-drying processes. The application potential of the PC sludge-drying process is discussed based on the experimental results. [ABSTRACT FROM AUTHOR]

Despite being geographically dispersed, abundant, and accounting for almost half of the world's coal reserves, low-rank coals (LRCs) find limited use due to their high moisture content and high propensity for spontaneous combustion. Reducing the moisture content of low-rank coal enhances its heating value and reduces transportation costs, thus increasing its economic value. In addition, dried low-rank coals have been proven to improve plant efficiency, enhance safety, and reduce greenhouse gas emissions. Although numerous technologies for coal drying already exist, it is often challenging, if not impossible, to find one that is cost-effective in all aspects. When selecting a dryer for coal upgrading applications, factors such as particle size/size distribution, throughput, energy consumption, material handling capabilities, safety, carbon footprint, capital and operating costs, return on investment, etc., are important considerations. This article provides an overview of the patent literature along with the archival literature that deals with drying of coal as well as biomass, which is relevant to coal drying. [ABSTRACT FROM AUTHOR]

During osmotic dehydration of fruits and vegetables, as water and/or other substances are removed from the material, shrinkage follows depending on the extent of net mass loss. Mass transfer is usually predicted through modeling. However, common models developed for osmotic dehydration of fruits and vegetables make assumptions that often deviate far from reality, including large heterogeneity, variability and complexity in properties of fruits and vegetables. This generates some skepticism about such models and minimizes their potential industrial reliability. This paper reviews osmotic dehydration of fruits and vegetables through a basic approach, provides a critical view on modeling and points out the factors that affect shrinkage and mass transfer based on an extensive evaluation of pertinent literature. [ABSTRACT FROM AUTHOR]

Fresh aquatic products are rich in nutritional compounds and are an important source of good protein for humans. Dehydration processing technologies of aquatic products used in practice are a mix of old and new technologies. With the rapid development of drying technologies and steadily increasing living standards, drying processing techniques as well as types of products produced have changed fundamentally. Two broad types of dried aquatic products are commercially available on a large scale: traditional products and snack foods. In this article, the development of dried aquatic product processing technologies will be expounded along with an overview of the necessary quality attributes and control strategies to produce high-quality dried products of aquatic origin. [ABSTRACT FROM AUTHOR]

This article presents a case study of Simprosys applied to the energy efficiency evaluation of an exisisting fiberboard drying production line. An energy examination of the dryer and the drying system under current operating conditions was performed using Simprosys 2.1 (Simprotek, Cupertino, CA). Detailed parametric studies of the drying system were carried out. Possible improvements for the enegry efficiency of the dryer itself and the drying system are proposed and discussed. [ABSTRACT FROM AUTHOR]

The operation of proton exchange membrane fuel cell (PEMFC) stacks requires careful thermal and water management for optimal performance. Appropriate placement of cooling plates and appropriate cooling conditions are therefore essential. To study the impact of these design parameters, a two-phase model accounting for the conservation of mass, momentum, species, energy, and charge, a phenomenological model for the membrane, and an agglomerate model for the catalyst layer, is developed and solved. The model is validated for a single cell, in terms of both the local and the global current density, and good agreement is found. Four repetitive computational units are then identified for the number of single cells placed between the coolant plates: (i) one cell; (ii) two cells; (iii) three cells; and (iv) four cells. The flow fields in the single cells and the cooling plates are of a net type. The results show that there is a strong correlation between stack performance and the operating conditions/placement of the coolant plates. For the limiting case of one coolant plate between each unit cell, similar operating conditions can be achieved in every individual cell throughout the stack. As more cells are placed in between coolant plates, the stack performance drops due to an increase in temperature and decrease in water content in the membranes, unless the cooling temperature is lowered. The coolant temperature and inlet velocity need to be monitored carefully and adjusted to the operating conditions of the stack. This model can be employed for design and optimization of liquid water cooling of a PEMFC stack. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 proteins and Mg2+ from the TB-EPS to LB-EPS fractions. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

To remove water from a suspension one needs to break down the binding energy between the adjacent water and the solid surface and to convey this water out of the suspension system. Using the binding energy between water and solids and the disrupting energy provided by mechanical and thermal means, this work presents a unified analysis on the dewatering of wet materials using binding energy as a clarification index. The binding energy versus residual water content plot for a wastewater sludge estimated the extent of dewatering each stage and the corresponding energy requirement. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 technologies and fundamental studies are reviewed and evaluated to examine their suitability and optimization for different forms of the biomass. The dryer types considered include a packed moving bed dryer (conveyor dryer), a rotary dryer, and a pneumatic dryer. Issues involved in biomass drying and possible solutions are addressed. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 powder was mainly affected by the feed concentration. Increasing feed concentration increased mean particle size. Color difference of GB seed powder was significantly affected by the inlet and outlet air temperatures and feed concentration. Furthermore, the optimal conditions of GB seed spray drying, i.e., inlet air temperature 190°C, air flow rate 120 m3/h, outlet air temperature 110°C, feed concentration 10%, were obtained from an L1644 orthogonal experiment. At last, correlation equations for GB seed powder properties with operating parameters were obtained using multivariable regression analysis. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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, the effect of height-to-diameter ratio (H/D) of the chamber on flow distribution was studied. Chambers of different H/D ratios and different air inlet nozzle diameters at various positions were examined to evaluate their effect on flow uniformity across the distributor. Three-dimensional computational fluid dynamic studies were carried out to evaluate the effects of pertinent parameters on flow uniformity, which has a direct bearing on the quality of fluidization and hence heat and mass transfer rates obtained. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 excess of greenhouse gases (GHG). The energy savings, use of renewable energies, optimization of each part of the drying process, and use of control devices for detecting and minimizing the atmospheric injection of GHG are some of a large number of possible actions to be taken in this respect. A nice example of how a planetary problem can be solved with the global participation of scientists, professionals, authorities and general public is the stopping of the destruction of the ozone layer and its possible recuperation in the near future, as discussed in the WMO related report (“Scientific Assessment of Ozone Depletion: 2006”, that can be obtained at http://www.wmo.int/pages/prog/arep/gaw/ozone2006/ozoneasstreport.html).[10] [ABSTRACT FROM AUTHOR]

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 hydroscopicity of nanosheets A is the strongest and that of microparticles is the weakest. [ABSTRACT FROM AUTHOR]