Showing papers by "Arun S. Mujumdar published in 2012"
TL;DR: In this paper, the melting of paraffin wax dispersed with Al2O3 that is heated from one side of a square enclosure with dimensions of 25mm × 25mm is investigated numerically.
227 citations
TL;DR: In this article, a two-dimensional, transient mathematical model comprising conservation of charges, species, and energy together with electroneutrality, constitutive relations and relevant initial and boundary conditions for a spiral-wound cylindrical Li-ion battery is derived and solved numerically for passive thermal management with and without a phase change material (PCM) at various galvanostatic discharge rates.
158 citations
TL;DR: Green banana flour (GBF) was used to partially substitute cassava starch in two types of snacks, viz. fish cracker (FC) and cassava cracker(CC).
Abstract: Green banana flour (GBF), as a functional ingredient, was used to partially substitute cassava starch in two types of snacks, viz. fish cracker (FC) and cassava cracker (CC). It is observed that use of GBF increased the nutritional value including enhancement of dietary fiber, essential minerals, polyphenol content, antioxidant capacity and decreased oil content to varying degrees depending on the substitution level in these two crackers. However, its use compromised the textural properties in terms of the linear expansion ratio, crispness, bulk density, porosity and color. Sensory evaluation showed that the products with not more than 40 g substitution level by GBF from 100 g cassava starch in CC and not more than 15 g in FC were acceptable by the panelists.
122 citations
TL;DR: In this paper, microwave vacuum drying (FD) and freeze-drying (FD+MWVD) were compared for texture, aroma, and microstructure analysis of apple slices, and the results showed that microwave application had a significant effect on total phenols, pectin and aroma.
Abstract: Apple slices dried by two combination drying methods and by freeze-drying (FD) were evaluated for their composition and analyzed for texture, aroma and microstructure. FD and followed by microwave vacuum drying (FD + MWVD) yielded dried samples of higher reducing sugars, total pectin and lower total phenols comparing to FD samples. On the other hand, MWVD + FD samples had lower sugars, total phenols and total pectin than FD + MWVD samples. On the whole, aroma retention in FD + MWVD samples is better than MWVD + FD products and worse than FD samples. Moreover, the crispness of FD + MWVD samples was higher than MWVD + FD samples and the hardness of FD + MWVD samples was lower than MWVD + FD samples. Microwave application had a significant effect on total phenols, pectin and aroma. In addition, longer time high temperature at desorption drying stage and short time higher temperature at MWVD stage during FD + MWVD process resulted in lower reducing sugars and worse aroma retention, respectively. Faster drying rate in MWVD process induced worse cell structure.
107 citations
TL;DR: Increasing globalization is driving agricultural production in developing countries toward better recovery levels and high additional value as discussed by the authors, and a great opportunity is thus offered to emerging economies in the developing world by globalization.
Abstract: 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 economie...
87 citations
TL;DR: In this paper, the authors evaluate numerically the performance of various gas and coolant channel designs simultaneously, e.g. parallel, serpentine, oblique-fins, coiled, parallel serpentine and a novel hybrid parallel-serpentine-oblique fins designs.
67 citations
TL;DR: In this paper, the effects of nanoparticle volume fraction on both the melting and solidification rates of paraffin wax are analyzed and compared for Al2O3 and CuO nanoparticles.
Abstract: The heat transfer enhancement of paraffin wax, a cheap and widely used latent heat thermal energy storage material, using nanoparticles is investigated. The effects of nanoparticle volume fraction on both the melting and solidification rates of paraffin wax are analysed and compared for Al2O3 and CuO nanoparticles. Present results show that dispersing nanoparticles in smaller volumetric fractions increase the heat transfer rate. The enhancement in thermal performance of paraffin wax is greater for Al2O3 compared with that for CuO nanoparticles. .
51 citations
TL;DR: In this paper, the authors carried out a parametric study of flow and heat transfer characteristics of coils made of tubes of different cross-sections e.g. square, rectangular, half-circle, rectangular and trapezoidal.
Abstract: The objective of this study was to carry out a parametric study of laminar
flow and heat transfer characteristics of coils made of tubes of several
different cross-sections e.g. square, rectangular, half-circle, rectangular
and trapezoidal. For the purpose of ease of comparison, numerical experiments
were carried out base on a square-tube Reynolds number of 1000 and a fixed
fluid flow rate while length of the tube used to make coils of different
diameter and pitch was held constant. A figure of merit was defined to
compare the heat transfer performance of different geometry coils;
essentially it is defined as total heat transferred from the wall to the
surroundings per unit pumping power required. Simulations were carried out
for the case of constant wall temperature as well as constant heat flux. In
order to allow reasonable comparison between the two different boundary
conditions - constant wall temperature and constant wall heat flux - are
tested; the uniform heat flux boundary condition was computed by averaging
the heat transferred per unit area of the tube for the corresponding constant
wall temperature case. Results are presented and discussed in the light of
the geometric effects which have a significant effect on heat transfer
performance of coils.
51 citations
TL;DR: In this article, the effects of boiling water and microwave blanching methods on the dielectric properties, electrical conductivity as well as microstructure of stem lettuce cubes (as a model for plant tissue) were studied.
51 citations
TL;DR: In this article, a mathematical model comprising conservation of mass, momentum, and ions for a hydrogel subject to alterations of the solution pH is derived, analyzed, validated and presented.
50 citations
TL;DR: In this paper, the effect of various fan and stack configurations, operating conditions and their impact on the fan and system characteristic curves as well as stack performance are investigated with a model considering two-phase flow and conservation of mass, momentum, species, charge, and energy in the PEFC stack and ambient; the fans are treated as interface conditions.
TL;DR: In this paper, a computational fluid dynamic analysis was carried out for a micro-reactor in the form of a square cross-section channel of eight different configurations, including parallel, pin-hole, wavy, oblique fin, serpentine, coiled, coiling with serpentine and coiled with double serpentine channel geometries.
TL;DR: In this paper, three drying methods, namely microwave assisted freeze-drying (MWFD), microwave assisted vacuum drying (MWVD), and microwave assisted spouted bed drying, were compared in the drying of purple-fleshed sweet potato (PFSP) granules.
Abstract: Summary
Purple-fleshed sweet potato (PFSP) with high anthocyanin level was attractive to health concern Three drying methods, namely microwave-assisted freeze-drying (MWFD), microwave-assisted vacuum drying (MWVD) and microwave-assisted spouted bed drying (MWSBD), were compared in the drying of PFSP granules Product’s texture, colour, anthocyanin level and energy consumption were investigated Drying periods varied among drying methods MWSBD needed the least time to finish the drying process Different drying methods had a significant effect (P < 005) on texture and anthocyanin level Maximum penetration force of MWSBD treated sample was lowest (1499 N) Anthocyanin level of MWSBD products was not as high as that of MWFD products, but colour and appearance were fine MWFD products owned good crispness through sensory evaluation Energy consumption of MWFD was about two times higher than that of MWVD Final results indicated that MWSBD may be an alternative way to MWFD with measurements to maintain the anthocyanin level
TL;DR: In this paper, the authors proposed a new conceptual design for effective cooling of a PEFC stack by periodically reversing the flow direction of the air used for convective cooling, and the impact of the flow reversal scheme is studied via mathematical model of the three-dimensional two-phase flow and associated conservation equations of mass, species, momentum, charge, and energy.
TL;DR: In this paper, a numerical approach is carried out to investigate the heat transfer performance of in-plane spiral ducts with various cross-sections, including rectangular, square, triangular, trapezoidal, circular and half circular.
TL;DR: In this article, the authors studied the distribution and migration of unfrozen water in stem lettuce cubes during the microwave freeze drying (MFD) step using differential scanning calorimetry (DSC) and low-field pulsed nuclear magnetic resonance (LF-NMR).
Abstract: 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, mois...
TL;DR: The immersion frying method using spent cooking oil as the heating medium was applied to dry and convert wet sewage sludge into a solid fuel and the experimental results showed the solid fuel had a porous internal structure and a low ignition temperature of 250°C due to presence of oil.
TL;DR: In this paper, the authors proposed mass-transport enhancement in a microchannel T-junction by utilizing various configurations of coiled base channel design (e.g., conical spiral, in-plane (flat) spiral, and helical spiral coils).
Abstract: Microchannel T-junction configuration is used in chemical processing for passive mixing and reactions, because of its relatively easy control of the reaction environment. However, poor mixing and low reaction rate are some of the main drawbacks of this design. This study proposes mass-transport enhancement in a microchannel T-junction by utilizing various configurations of coiled base channel design (e.g., conical spiral, in-plane (flat) spiral, and helical spiral coils). Their mass-transport performance is investigated numerically and compared with that of the conventional straight microchannel T-junction. Laminar flow of gas flow with reactions is investigated using a three-dimensional computational fluid dynamics (CFD) model. Four different microchannel designs, three different channel Reynolds numbers, and three different helical coil diameters are investigated. The coils are made of a square cross-section tube. The results indicate that the coiled base channel displays improved mixing and conversion ...
TL;DR: In this paper, the authors proposed several innovative channel designs to improve mixing and reaction kinetics, e.g., innovative circular and rectangular configuration, flow splitting, redirection, recirculation and impingement, and showed that the rectangular design yields better conversion rate than the rate obtained with its circular counterpart.
Abstract: Laminar mass transport enhancement of gaseous mixing and catalytic reaction in a semi T-shaped microreactor was examined via numerical simulations. The mathematical model considers a multi-component species mixture with multi-step heterogeneous reactions and comprises of conservation equations of mass, momentum, species and energy. The mass transport performance is evaluated by modeling the catalytic reaction of a mixture of methane and air. Several innovative channel designs are proposed to improve mixing and reaction kinetics, e.g. innovative circular and rectangular configuration, flow splitting, redirection, recirculation and impingement. The results suggest that the rectangular design yields better conversion rate than the rate obtained with its circular counterpart. Flow splitting and impingement are found to be beneficial to improve mixing and reaction rate; albeit this imposes a greater pressure drop penalty. Effect of pre-mixing is also investigated with regard to the mass transport performance. Finally, advantages and limitations of each design are discussed in the light of the numerical results.
TL;DR: In this paper, the effect of sinusoidal pulsation on the local Nusselt number distribution of the wet target surface being dried was investigated. But the authors did not consider the thermophysical properties of jet flows.
Abstract: 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. E...
TL;DR: In this paper, the potential advantages of pulsed laminar opposed impinging jets are evaluated using the computational fluid dynamic approach, where sinusoidal flow pulsations are induced at both jets to improve the mixing performance.
Abstract: Fluid mixing performance and flow dynamics are key issues in opposed impinging jets and their industrial applications. Prior work has considered steady jets impinging normally against each other. Here the potential advantages of pulsed laminar opposed impinging jets are evaluated using the computational fluid dynamic approach. Two-dimensional confined opposing jets in the laminar flow regime are numerically studied, where sinusoidal flow pulsations are induced at both jets to improve the mixing performance of opposed impinging jets. The present mathematical model is validated by comparing the flow field with that of experimental results. The fluid temperature can be used as a passive tracer to evaluate the mixing rate, and the effect of Reynolds number and flow pulsation on the mixing performance is discussed for optimization of opposed jets. The periodic oscillations induced by pulsation have been shown as an effective way to improve mixing performance of laminar opposed impinging jets. The hydro...
TL;DR: In this article, a sludge of pasty consistency was atomized and dried using a high-temperature, highly turbulent gas flow in the tailpipe generated by a Helmholtz gas-fired pulse combustor.
Abstract: 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). Param...
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TL;DR: In this article, the Prince of Wales' charity Practical Action is described as "a registered charity and company limited by guarantee" and is based at the Royal Court of the Barbican in London.
Abstract: T +44 (0)1926 634400 | F +44 (0)1926 634401 | E infoserv@practicalaction.org.uk | W www.practicalaction.org ___________________________________________________________________________________________________________ Practical Action is a registered charity and company limited by guarantee. Company Reg. No. 871954, England | Reg. Charity No.247257 | VAT No. 880 9924 76 | Patron HRH The Prince of Wales, KG, KT, GCB DRYING OF FOODS
TL;DR: In this paper, the deformation kinetics of a hydrogel are significantly influenced by its geometry; however, the equilibrium swelling ratio of the hydrogels is found to be independent of their geometries.
TL;DR: In this paper, the flow pattern in an Agitated thin film evaporator (ATFE) was analyzed using ANSYS-CFX 10.0 software and the flow phenomenon was simulated using free surface multiphase model considering two continuous phases, water and water vapour.
Abstract: Agitated thin film evaporator (ATFE) is widely used in chemical, pharmaceuticals and food industries to concentrate the feed solutions. The flow pattern in ATFE has been analyzed using ANSYS-CFX 10.0 software. The flow phenomenon is simulated using free surface multiphase model considering two continuous phases, water and water vapour. The geometry is created in ANSYS-ICEM-10 with 110,300 tetrahedral nodes. The k–ɛ and Reynolds stress homogeneous turbulence models are used with appropriate boundary conditions. The occurrence of bow wave and its variation with respect to flow rate is studied. A thin film of thickness equal to the clearance between blade tip and inner wall is found to adhere to the inner wall. The bow wave is found to travel helically along the inner wall of the evaporator. The shear rate and kinetic energy dissipation is found to be significant at the clearance between blade and inner wall. These values are 10–50 times more than that observed in rest of the volume.
TL;DR: In this paper, a spray dryer fitted with a rotary disc atomizer was used to experimentally assess the highly swirling flow characteristics in spray dryers fitted with an atomizer, and the numerical simulation captured key features of the flow field.
Abstract: Cotton turf and hotwire measurements were used to experimentally assess the highly swirling flow characteristics in a spray dryer fitted with a rotary disc atomizer. The numerical simulation captured key features of the flow field. Analysis revealed that rapid rotation of an atomizing disc tends to centrifugally split the central inlet jet. The flow field exhibited significant long time-scale transient behaviour. However, this centrifugally split jet resulted in a balanced upward recirculation region in the chamber as expected by the jet-feedback mechanism. Detailed analysis using a ‘transient air-steady particle’ approach revealed that this approach is applicable for such highly swirling transient flows as well. However, caution should be exercised when interpreting the deposition results, particularly in regions of low particle velocities. This is anticipated be an important consideration in future attempts to simulate the predominantly transient flows in spray dryers.
16 Jan 2012
26 Jan 2012
TL;DR: The reformulated mathematical model in combination with automated model generation thus opens up avenues for wide-ranging parameter studies, automated multi-objective optimization of design, layout, management strategies and operating conditions of a battery module.
TL;DR: Overall, good agreement is achieved between model predictions and their experimental counterparts; the rigid skin formation and rigid core presence are also captured reasonably well.
Abstract: A phenomenological model for stimuli sensitive hydrogels immersed in water subject to changes in temperature is presented and analyzed. In short, the model takes into account conservation of mass and momentum for polymer network and interstitial fluid with an expression for permeability to capture the rigid skin formation during shrinking. The nature of this expression is secured from the observation of and validation with experimental deformation kinetics. Overall, good agreement is achieved between model predictions and their experimental counterparts; the rigid skin formation and rigid core presence are also captured reasonably well. The model can be extended to account for arbitrary-shaped hydrogels as well as for other types of stimuli-sensitive hydrogels that exhibit rigid-skin formation during shrinking.