Showing papers by "Arun S. Mujumdar published in 2008"
TL;DR: In this article, a review summarizes recent research on theoretical and numerical investigations of various thermal properties and applications of nanofluids, as such suspensions are often called, indicate that the suspended nanoparticles markedly change the transport properties and heat transfer characteristics of the suspension.
Abstract: Research in convective heat transfer using suspensions of nanometer-sized solid particles in base liquids started only over the past decade. Recent investigations on nanofluids, as such suspensions are often called, indicate that the suspended nanoparticles markedly change the transport properties and heat transfer characteristics of the suspension. This first part of the review summarizes recent research on theoretical and numerical investigations of various thermal properties and applications of nanofluids.
527 citations
TL;DR: In this article, a review of the fluid flow and heat transfer characteristics of nanofluids in forced and free convection flows and potential applications of nanopharticles is presented.
Abstract: Research in convective heat transfer using suspensions of nanometer-sized solid particles in base liquids started only over the past decade. Recent investigations on nanofluids, as such suspensions are often called, indicate that the suspended nanoparticles markedly change the transport properties and heat transfer characteristics of the suspension. This second part of the review covers fluid flow and heat transfer characteristics of nanofluids in forced and free convection flows and potential applications of nanofluids. Opportunities for future research are identified as well. Keywords: Nanofluids; Nanoparticles; Heat transfer; Thermal conductivity.
430 citations
TL;DR: In this article, the use of phase change material (PCM)-based heat sink in transient thermal management of plastic quad flat package (QFP) electronic devices was investigated experimentally and numerically.
407 citations
TL;DR: In this article, a numerical study is conducted to evaluate the thermal characteristics of a PCM-based heat sink which can be potentially used for cooling of mobile electronic devices such as personal digital assistants (PDAs) and notebooks.
108 citations
TL;DR: In this paper, a new pretreatment method involving use of ultrasound prior to microwave freeze drying of sea cucumber was examined experimentally and it was observed that ultrasound-assisted osmotic pretreatment can reduce by about 2h the time needed for microwave freeze-drying.
Abstract: A new pretreatment method involving use of ultrasound prior to microwave freeze drying of sea cucumber was examined experimentally It was observed that ultrasound-assisted osmotic pretreatment can reduce by about 2 h the time needed for microwave freeze drying An optimization study using response surface analysis was carried out to determine the optimal operating parameters to minimize drying time while maximizing quality
95 citations
TL;DR: In this article, a cylindrical spouted bed and a three dimensional spout-fluid bed of spherical particles were simulated using the Eulerian-Eulerian two-fluide modeling approach, incorporating a kinetic-frictional constitutive model for dense assemblies of the particulate solid.
91 citations
TL;DR: In this paper, a nanoscale silver coating technique was combined with microwave freeze-drying for sea cucumber dewatering, which reduced the microorganism number with no significant effect on drying efficiency and sensory quality.
Abstract: To develop an improved dehydration method for sea cucumber, microwave freeze drying was tested as a potential method. According to our experimental results, microwave freeze drying can reduce drying time to about half of the traditional vacuum freeze-drying process. To ensure a high degree of sterilization, a novel nanoscale silver coating technique was combined with microwave freeze drying. Microwave freeze drying combined with nanoscale silver coating treatment leads to a much lower microorganism number with no significant effect on drying efficiency and sensory quality.
90 citations
TL;DR: In this article, a convective air drying of sapota pulp was carried out and compared with low-temperature drying techniques such as heat pump-assisted drying and freeze drying.
Abstract: Sapota (Achras zapota) is a tropical fruit found in several parts of India. It is one of the most popular fruits besides mango, custard apple, and several others. Once ripe, it needs to be consumed within a couple of days due to the highly perishable nature of this exquisite fruit variety. The best way to increase the shelf-life is through the process of dehydration of peeled sapota. In the present study, the convective air drying of sapota pulp was carried out and compared with low-temperature drying techniques such as heat pump–assisted drying and freeze drying. The sapota paste was dried in a convective dryer to study the effect of operating parameters such as air temperature and air velocity. In addition, the effect of additives such as oat and wheat fibers and the paste thickness on drying was also studied. The critical analysis of dehydrated sapota was carried out in terms of water activity, sugar content, color, and rehydration ratio. The drying data were analyzed using Page's model and Newton's mo...
83 citations
TL;DR: In this article, the authors developed a model to describe the heat and mass transfer during the drying of carrot cubes in a spout-fluidized-bed drier, taking into account the nonhomogeneous shrinkage of the material.
79 citations
TL;DR: In this paper, a comparison of two drying kinetics models: Characteristic Drying Curve (CDC) and Reaction Engineering Approach (REA) is made with experimental data with application to carbohydrate droplet drying obtained from past workers.
Abstract: CFD simulation is used to study wall deposition and agglomeration phenomena commonly encountered in industrial spray dryers. This paper initially provides a comparison of two drying kinetics models: Characteristic Drying Curve (CDC) and Reaction Engineering Approach (REA). Comparisons are made with experimental data with application to carbohydrate droplet drying obtained from past workers. These models were then extrapolated to actual drying conditions to assess their performance. The REA model predicts the progressive reduction in drying rate better than the CDC model for the carbohydrate droplets. A modified CDC model incorporating a convex falling rate produced better agreement than the conventional linear falling rate model. Further analysis showed that the REA model can be extended to simulate the particle surface moisture which may affect the agglomeration process. The proposed concept was compared with reported simulation results from a diffusion model which showed reasonable fit with data.
65 citations
TL;DR: In this paper, an experimental setup was designed and built to permit simultaneous application of convection, conduction, and radiation heat input to the drying material above its freezing point to ensure sublimation.
Abstract: Atmospheric freeze drying (AFD) in a vibro-fluidized bed dryer coupled with an adsorbent and multimode heat input is proposed for dehydration of food products at lower cost than the traditional freeze-drying process under vacuum. The aim of this project is to study the proposed AFD system using a vortex tube to produce low-temperature dry air, an alternative for producing dried food products of high quality. An experimental setup was designed and built to permit simultaneous application of convection, conduction, and radiation heat input to the drying material above its freezing point to ensure sublimation. A parametric evaluation over a broad range of possible parameter values was carried out using cubic-shaped potato and carrot as model heat-sensitive products. The influence of various system parameters on drying kinetics, quality, and functional properties of the dried products (color, rehydration properties, and morphology) were investigated. Comparison between physical quality and drying characterist...
TL;DR: Fractal geometry has been widely used in various dried materials and drying processes and identifies the opportunities for future investigation as mentioned in this paper. But the application of fractal concept on drying can be categorized into describing microscopic and macroscopic structure of material in drying with fractal geometry and theoretical models with Fractal theory for drying mechanism.
Abstract: Fractal geometry has been widely used in various dried materials and drying processes. This review summarizes the related studies and identifies the opportunities for future investigation. The application of fractal concept on drying can be categorized into describing microscopic and macroscopic structure of material in drying with fractal geometry and theoretical models with fractal theory for drying mechanism. And also, the capillary and network models for drying of capillary porous media are discussed and a fractal tortuous capillary model for drying of capillary porous media is proposed. From the selected examples, it is clear that the fractal theory has many advantages for identifying the complex structure of products and investigating drying mechanism. At last, some comments are made for the current investigations and also some prospects for the future development of this field are pointed out.
TL;DR: In this article, a gamma ray tomography (GRT) study was carried out in the form of chordal solid hold-up, which was found to be greatly influenced by the gas distributor design.
TL;DR: The application of electrical fields to dewatering and drying is reviewed in this article, where the potential applications of this emerging technique are evaluated along with a discussion of R&D needs in these areas.
Abstract: The application of electrical fields to dewatering and drying is reviewed. In particular, the developments in electroosmotic dewatering (EOD) of colloidal slurries are discussed in terms of fundamental associated phenomena, as well as the methods of enhancement of EOD. The electrohydrodynamic (EHD) drying of biological materials are discussed in terms of its fundamentals, current status, and advantages and disadvantages. The potential applications of this emerging technique are evaluated along with a discussion of R&D needs in these areas.
TL;DR: Motivation, principles, and applications of the new drying software package, Simprosys, which represents a major step toward development of a comprehensive drying software suite, are presented.
Abstract: Available commercial software to simulate flowsheets incorporating drying is reviewed briefly. Such software can be very cost effective in the design, analysis, trouble-shooting, as well as control and optimization of drying systems. A new comprehensive drying software suite is proposed and analyzed. Key factors to the success of drying software products are discussed. Motivation, principles, and applications of the new drying software package, Simprosys, which represents a major step toward development of a comprehensive drying software suite, are presented.
TL;DR: In this article, a new impingement oven was designed and tested for its thermal and quality performance for baking of thin flat bread, and the test facility was instrumented to monitor and record during the baking process.
Abstract: A new impingement oven was designed and tested for its thermal and quality performance for baking of thin flat bread. The test facility was instrumented to monitor and record during the baking process. Bread temperature and weight loss were recorded on-line during baking at oven temperatures of 150, 175, 200, 225, and 250°C and 1, 2.5, 5, 7.5, and 10 m/s jet velocities, respectively. Image processing was used for monitoring the bread volume and surface color changes during baking. Better baking conditions were obtained with the impingement oven in comparison with the conventional direct fired ovens. Experiments showed that a higher jet velocity can be used for flat bread baking at lower oven temperatures and yield shorter baking times for the same quality product. For very thin breads (such as the Iranian breads), results show that conduction heat transfer from the bottom surface of the tray must also be considered along with the convective heat transfer from the jets in selection of optimal operating par...
TL;DR: In this paper, the evaporation of sessile drop comprising ethanol and water mixture on horizontal poly methyl methacrylate surface was investigated with time, considering the impacts of presence of ethanol.
Abstract: This study investigates the evaporation of sessile drop comprising ethanol and water mixture on horizontal poly methyl methacrylate surface The contact angle (θ) and contact radius (R) of ethanol-water mixture drop are recorded with time, considering the impacts of presence of ethanol With excess ethanol, the drop evaporation is principally controlled by a phase in which both the contact angle and contact radius are falling A diffusional model assuming linear relation between contact radius and time is proposed as θ = eR −3 + cR −1, where e and c denote fitting coefficients This model correlates with the experimental data
TL;DR: In this paper, a solar energy assisted photocatalytic closed-type dryer (SEPCD) was developed to produce dried agrofoods without using chemical additives for antisepsis and/or color retention and to retain higher nutritive value of the fresh produce.
Abstract: A novel patented solar energy-assisted photocatalytic closed-type dryer (SEPCD) was developed to produce dried agro-foods without using chemical additives for antisepsis and/or color retention and to retain higher nutritive value of the fresh produce. The SEPCD was designed to simulate open sun drying with moving dry air and mild temperature. The air temperature in the drying cabinet is maintained at 40–45°C; it is supplied partially by a dehumidification system and partially by a solar energy system. Additionally, the inside of the cabinet was coated with titanium dioxide (TiO2) to cause a bactericidal effect during the drying process. Results showed that the total mold and bacterial counts for the drying cabinet and dried pineapple slices are significantly reduced in the SEPCD while the dried food quality is also better than that dried by conventional hot air drying.
TL;DR: In this paper, the authors focus on the current developments in thermal drying as well as recent trends and identify some areas where more R&D is needed and which provide opportunities to make definitive contributions.
Abstract: Research and development activity in the inter- and cross-disciplinary area of thermal drying has been escalating rapidly over the past two decades. It is clearly motivated by economic incentive to improve the operation to produce a better quality product at a lower cost in terms of resources, energy consumption as well as environmental impact. The focus to date has been on improving the engineering aspects of design and operation to produce “engineered” products of desired characteristics. Much remains to be achieved in relation to the material science aspects of drying, e.g. the prediction of quality parameters which are product-dependent. What is needed is a generalised drying theory that incorporates the transient transport phenomena involved in drying along with appropriate models to account for the morphological changes, as well as chemical processes that may occur during drying.
This paper will focus on the current developments in drying as well as recent trends. Some areas where more R&D is needed and which provide opportunities to make definitive contributions will be identified. For example, sophisticated analytical measurements at the micro-scale are needed in order to examine the movement of moisture during drying, and also detect any changes in the physical structure as well as solute transport that can occur in drying of foodstuffs or solids containing a dissolved solid in the liquid phase. Even today, there is need to devise more efficient and compact dryers. Whether we will ever need “micro-scale” dryers is a speculative question but certainly there will be the need to design dryers with high “volumetric” efficiency, unlike most dryers built today. Finally, there will be further developments and extended applications for superheated steam dryers, heat pump-assisted hybrid dryers and multi-stage dryers using different dryer types in each stage. Mathematical models for drying as well as for dryers will continue to be in demand to allow reliable design and scale-up, as well as the control of industrial dryers.
TL;DR: In this article, the effect of the atomizer rotational speed on the product size distribution was studied. And the particle size distributions under atomizer rotating speeds in the 9,000-10,000rpm range were measured and discussed.
Abstract: Spray drying is the most commonly used method in industry to produce powders on a large scale. One of the major problems in spray drying is control of the product particle size distribution since it is very important for most industries; e.g., catalyst, chemicals, foods, pharmaceuticals, ceramics, etc. The objective of this work is to study the effect of the atomizer rotational speed on the product size distribution. In order to obtain the typical particle size distribution of the required product, a specially designed atomizer disk is used in the study. The particle size distributions under atomizer rotating speeds in the 9,000–10,000 rpm range were measured and discussed.
TL;DR: No significant improvement was observed between lidded and unlidded packages when fitted with a heat sink subjected to forced convection, but the package thermal budget estimate with and without heat sinks was discussed.
TL;DR: In this paper, the authors analyzed convective drying of wastewater sludge cakes with three-dimensional cake structures probed using an X-ray micro-computerized tomography scanner (micro-CT), considering the development of cracks and cake morphology.
Abstract: This study analyzed convective drying of wastewater sludge cakes with three-dimensional cake structures probed using an X-ray micro-computerized tomography scanner (micro-CT), considering the development of cracks and cake morphology. The presence of artificial cracks on cake surface assist drying, but those occurred naturally cannot. The cake surface is noted far from saturation over drying. Moreover, the cracks transport easily moisture to cake surface, hence yielding high surface humidity (and rates) for drying. Comprehensive drying model has to incorporate real boundary conditions for success modeling.
TL;DR: In this paper, the authors investigated the drying characteristic and drying kinetics of the Ganoderma slices under constant air velocity and slice thickness, and the effect of drying temperatures on the size and surface structure of basidiospores were studied.
Abstract: In this study, drying of Ganoderma tsugae Murrill slices was carried out at different temperatures in a hot air circulating oven. The objectives were to investigate the drying characteristic and drying kinetics of the Ganoderma slices under constant air velocity and slice thickness. In addition, the effect of drying temperatures on the size and surface structure of Ganoderma tsugae basidiospores were studied. Using statistical analysis, a two-term model was found to fit best with the experimental data. Convective drying of Ganoderma tsugae slices at 60°C shows the minimum heat deformation to the size and surface structure of basidiospores.
TL;DR: In this paper, an impingement oven designed for flat breads baking was instrumented to monitor the processing conditions and record variables responsible for changes in dough characteristics, including temperature and jet velocity.
Abstract: An impingement oven designed for flat breads baking was instrumented to monitor the processing conditions and record variables responsible for changes in dough characteristics. Image processing was used to monitor the volume and surface color changes during baking. Fluctuations of oven temperature and jet velocity were minimized using electronic controllers, leading to better repeatability and accuracy. Impingement heat transfer distribution effects on flat bread baking was investigated by numerical simulation and related to the bread color. Considerable effect of local variations in impingement heat transfer and nonuniform nozzle exit velocity distribution on the color of baked bread was observed. At H/D > 4, jet temperatures < 200°C, and jet velocity of 10 m/s, local heat transfer distribution and surface darkening was negligible and a uniform surface color was obtained. Notably, velocity variations of ±20% inherent in the finger nozzles used in the oven design did not result in significant color change...
TL;DR: In this article, the combustion of a gas-fired pulse combustor was simulated using a computation fluid dynamic model to understand the flame structure, gas flow, and combustion characteristics in the burner and the resulting pulsation phenomenon.
Abstract: The combustion of a gas-fired pulse combustor was simulated using a computation fluid dynamic model to understand the flame structure, gas flow, and combustion characteristics in the burner and the resulting pulsation phenomenon. The specific impulse and thrust output to power input are computed and compared. Some typical gaseous fuels such as low molecular weight hydrocarbons, high molecular weight hydrocarbons, biofuels, and mixed fuels are tested via simulation of the pulse combustor, and their operation characteristics are summarized. It was found that the combustor can adjust itself automatically over a certain range of parameters and make it suitable for different gaseous fuels. Pulse combustion performance of fuels with low and high heating values is also compared.
TL;DR: In this article, the effect of combinatorial IR-convective drying on the quality aspect of organic pigments was analyzed in terms of Biot number to ascertain the role of infrared in bringing down the drying time without compromising pigment qualities.
Abstract: The drying of organic pigments is a challenging assignment due to the complex relationship between heat and mass transfer and the quality attributes such as color, shade, and strength. There is an urgent need to address the drying technology-related issues of this industrially important class of specialty chemicals. The widely used tray dryers and band dryers need further attention due to abysmally low energy efficiency. One of the ways to overcome the longer drying time is to make use of infrared source in addition to convective air drying. The present article discusses the effect of combinatorial IR-convective drying on the quality aspect of organic pigments. The heat and mass transfer rates were analyzed in terms of Biot number to ascertain the role of infrared in bringing down the drying time without compromising the pigment qualities. The mathematical analysis of drying of preformed pellet of pigments was carried out in terms of effective diffusivity, which was obtained in the range of 10−9 to 10−10 ...
TL;DR: In this paper, the effects of natural organic matter (NOM) on Al-floc stability were investigated by on-line probing of changes in floc diameters and interior fractal dimensions at alternative shearing using the small angle light-scattering technique.
Abstract: The effects of natural organic matters (NOM) on Al-floc stability were investigated by on-line probing of changes in floc diameters and interior fractal dimensions at alternative shearing using the small angle light-scattering technique. Fine kaolin particles coagulated with polyaluminum chloride (PACl) formed flocs of size adjusted during subsequent alternative shearing. The presence of humic acid or chitosan reduced or boosted floc formation. Floc breakage is completely irreversible at high humic acid concentrations. Certain master curves for floc size versus time curves were assessed, depending on shearing rate and added organic substances but not on the alternative shearing rates. A two-level floc breakage and reformation scheme was proposed in this study to interpret the observation results.
TL;DR: In this paper, a detailed structural analysis on real floc architecture is determined for building up a comprehensive floc model, interpreting structural characteristics of flocs using multifractal analysis.
Abstract: Naturally occurring aggregates are considered of fractal or fractal-of-fractals interior structure. Recent studies utilizing dye staining and confocal laser scanning microscopy (CLSM) techniques have revealed the extremely complex, interconnected pore networks for floc interior. Detailed structural analysis on the real floc architecture is determined for building up a comprehensive floc model. This work interprets structural characteristics of flocs using multifractal analysis. A direct method by Chhabra and Jensen properly evaluated the singularity strength and singularity spectrum on architectures of two artificial fractal systems. However, direct evaluation of multifractal characteristics of wastewater flocs has limitations, alternatively acquiring analytical results to be misleading. Particularly, the singularity spectrum presents excessively large values in the limit as q → +∞ and exhibits very large error bars in the limit as q → −∞. This is attributable to the uneven distribution of mass in flocs a...
TL;DR: In this paper, a review on literature works that investigated the mechanisms controlling particle-bubble interactions in the froth flotation process is provided, and the three-zone model comprising collision step, attachment step, and detachment step is discussed in detail.
Abstract: This work provides a review on literature works that investigated the mechanisms controlling particle-bubble interactions in the froth flotation process. The three-zone model comprising collision step, attachment step, and detachment step was discussed in detail. Theoretical and experimental studies were summarized.