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Brazilian Journal of Chemical Engineering, Volume: 22, Número: 2, Publicado: 2005
  • Modelling and simulation of drying phenomena with rheological behaviour Drying Science And Technology

    Chemkhi, S.; Zagrouba, F.; Bellagi, A.

    Resumo em Inglês:

    Foods have high moisture contents which are lost during the drying process. This water loss can produce important changes in size that hinder the analysis of heat and mass transport. A model of simultaneous heat and moisture transfer in parallelepiped-shaped potato samples was coupled with a model of its elastic behaviour. Governing equations and boundary conditions were solved numerically using the finite difference method. To check the validity of the mathematical model, drying experiments were carried out. Experimental conditions were as follows: drying temperatures of 38, 42 and 47°C; relative humidities of 14, 20 and 23% and air velocities of 1.5, 3 and 4.5 m/s. The different air velocities and temperatures were used in the drying process to determine their effects on drying time. It was obtained the range of moisture content in the sample and the range of temperature and stress during drying time. Comparison between predicted and experimental results provides satisfactory agreement.
  • Investigation of coalescence kinetics of microcristalline cellulose in fluidised bed spray agglomeration: experimental studies and modelling approach Drying Science And Technology

    Peglow, M.; Kumar, J.; Mörl, L.

    Resumo em Inglês:

    In this paper a model for fluidized bed spray agglomeration is presented. To describe the processes of heat and mass transfer, a physical based model is derived. The model takes evaporation process from the wetted particles as well as the effects of transfer phenomena between suspension gas and bypass gas into account. The change of particle size distribution during agglomeration, modeled by population balances, is linked to the heat and mass transfer model. A new technique is derived to extract agglomeration and nucleation rates from experimental data. Comparisons of experiments and simulations are presented.
  • Experimental determination of the effect of temperature and humidity on the development of colour in Pinus radiata Drying Science And Technology

    McCurdy, M.; Pang, S.; Keey, R.

    Resumo em Inglês:

    Experiments were undertaken to determine the effects of drying conditions (temperature and humidity) on the development of kiln brown stain in radiata pine during drying. Eight schedules were tested with temperatures ranging from 50°C to 120°C and relative humidity from 14% to 67%. The variables measured were moisture content, color expressed using the CIELab color space, and nitrogen content. The experiments have shown that the kiln brown stain is influenced by drying temperature and drying time. The recommendation is therefore that low-temperature and low-humidity schedules be developed for controlling color development.
  • Fluidized bed spray granulation: analysis of heat and mass transfers and dynamic particle populations Drying Science And Technology

    Heinrich, S.; Henneberg, M.; Peglow, M.; Drechsler, J.; Mörl, L.

    Resumo em Inglês:

    A model was developed taking into consideration the heat and mass transfer processes in liquid-sprayed fluidized beds. Such fluidized beds (FB) are used for granulation, coating and agglomeration. Conclusions are drawn on the relevance of particle dispersion, spraying and drying to temperature and concentrations distributions. In extension, the model was coupled with a population balance model to describe the particle size distribution and the seeds formation for continuous external FBSG (fluidized bed spray granulation) with non-classifying product discharge and a screening and milling unit in the seeds recycle. The effects of seeds formation on the stability of the process is discussed.
  • Overview of new techniques for drying biological materials with emphasis on energy aspects Drying Science And Technology

    Raghavan, G.S.V.; Rennie, T.J.; Sunjka, P.S.; Orsat, V.; Phaphuangwittayakul, W.; Terdtoon, P.

    Resumo em Inglês:

    With increasing concern about environmental degradation, it is desirable to decrease energy consumption in all sectors. Drying has been reported to account for anywhere from 12 to 20% of the energy consumption in the industrial sector. Drying processes are one of the most energy intensive unit operations. There are a number of approaches to reduce energy consumption in dryers. This paper reviews some novel strategies used to decrease energy consumption in drying operations. Drying conditions can be modified or the drying equipments can be modified to increase overall efficiencies. Hybrid drying techniques can also be used, such as combining vacuum or convective drying with electro-technologies (microwave, radio frequency, infrared heating). There is much debate on how to define drying and energy efficiencies. Some techniques to determine these efficiencies can be misleading when the goal is to take a holistic approach to determining energy consumption.
  • Drying kinetics of some building materials Drying Science And Technology

    Moropoulou, A.; Karoglou, M.; Giakoumaki, A.; Krokida, M.K.; Maroulis, Z.B.; Saravacos, G.D.

    Resumo em Inglês:

    Moisture is one of the most deteriorating factors of buildings. The deteriorating effect of moisture occurs mainly during the drying phase, and not in the wetting phase. Appropriate parameters of the drying kinetics are required for the building materials. Environmental factors, such as air temperature, air humidity, and air velocity affect drying. An experimental air dryer of controlled drying air conditions was used to investigate the drying performance of 4 stone materials, 2 bricks and 7 plasters. Drying kinetics was examined at 4 air temperatures, 6 air humidities, and 3 air velocities. A first-order kinetics model was obtained, in which the drying time constant was a function of the drying conditions, and the equilibrium material moisture content was described by the Oswin equation. The parameters of the proposed model were found to be affected strongly by the material and the drying air conditions. The results obtained are very useful in selecting the appropriate plaster to protect existing historic buildings.
  • Drying and shrinkage of polymer gels Drying Science And Technology

    Waje, S. S.; Meshram, M. W.; Chaudhary, V.; Pandey, R.; Mahanawar, P. A.; Thorat, B. N.

    Resumo em Inglês:

    The polymer hydrogel was synthesized by photo-polymerization process (UV light, 60 ºC) in presence of Photo-initiator (IrgacureR) and Cross-linker (NN'-methylene bisacrylamide; MBAM). In the present work, the drying of polymer hydrogel was carried out to study the effect of temperature, gel-sheet thickness, monomer ratio of acryl acid to acrylamide (AA/AM), concentration of MBAM and quantity of monomers. A correlation has been developed for modified sheet thickness as a function of contraction coefficient and degree of drying. Effective diffusivity was estimated from Fickian-diffusive model considering modified sheet thickness and was found to be in the range of 1.1 <FONT FACE=Symbol>´</FONT> 10-10-5.93 <FONT FACE=Symbol>´</FONT> 10-10 m²/s. The activation energy obtained using Arrhenius type equation was found to be in the range of 2979-10737 kJ/kmol H2O. The drying behavior shows an initial shoot-up in drying rate followed by constant rate and two falling rate periods.
  • Investigation of paper dryer picking, web transfer and quality issues using a new web adhesion and drying simulator Drying Science And Technology

    Ahrens, F.; Patterson, T.; Mueller, S.; Hojjatie, B.

    Resumo em Inglês:

    Paper dryer surface contamination can influence the severity of fiber picking, result in increased adhesion of the paper web to the surface, and impact the severity of cockle (out-of-plane deformation), a paper quality issue. The Web Adhesion and Drying Simulator (WADS) is a unique apparatus designed for investigation of paper sticking and fiber picking. Using the WADS, it has been found that the work of separation and amount of picking depend on roll surface material, contamination and temperature, and on the composition, moisture content and temperature of the web, and contact time. The WADS was also found to be convenient for studying the effect of drying conditions on severity of cockle. Cockle was found to depend on ingoing sheet solids content, surface temperature and degree of heat transfer non-uniformity.
  • Drying of municipal sewage sludge: from a laboratory scale batch indirect dryer to the paddle dryer Drying Science And Technology

    Arlabosse, P.; Chavez, S.; Prevot, C.

    Resumo em Inglês:

    Among available technologies, disk and paddle dryers are often encountered in France to process municipal sewage sludge but their thermal design is still a question of know how rather than scientific knowledge. From experiments performed on an industrial Naratherm® paddle dryer and the literature, a simple model has been developed. The dryer is divided into two parts depending on the sludge consistency. A constant evaporating flow rate is assumed in the pasty zone whereas its linear decrease with the moisture content is taken into account in the granular zone. To compute this model, some of the sludge properties have to be characterized with a set of laboratory scale experimental techniques. The agreement with the experimental data is good.
  • Modelling the drying of a parallelepipedic oil shale particle Drying Science And Technology

    Porto, P. S. S.; Lisbôa, A. C. L.

    Resumo em Inglês:

    A numerical model is proposed to describe the process of drying a parallelepipedic oil shale particle. Assuming Fick's law, the diffusion equation for the shape of the particle was used. The objective of the study was to develop a computer program in Fortran to estimate the moisture content of an oil shale particle undergoing drying as a function of time and position. The average moisture content was also obtained. The model takes into account the migration of water by diffusion within the solid and its loss at the interface. The model results were compared to experimental data from an apparatus which measured the mass loss of a particle. The apparatus comprised an electronic balance attached by a thin wire to the particle placed inside an incubator.
  • Spouted bed drying of Bauhinia forficata link extract: the effects of feed atomizer position and operating conditions on equipment performance and product properties Drying Science And Technology

    Souza, C. R. F.; Oliveira, W. P.

    Resumo em Inglês:

    In this paper the effects of feed atomizer position and operating conditions on equipment performance (accumulation rate, product recovery, elutriation and thermal efficiency) and product properties (moisture content, size distribution, flavonoid degradation and flow properties) during spouted bed drying of Bauhinia forficata Link extract are evaluated. The parameters studied were the position of the atomizer system (top spray or bottom spray), the inlet temperature of the spouting gas (80 and 150oC) and the feed mass flow rate of concentrated extract relative to the evaporation capacity of the dryer, Ws/Wmax (15 to 100%). Higher accumulation rate values were obtained with the atomizer placed at the bottom of the bed. In this configuration, the accumulation rate increases with the increase in the Ws/Wmax ratio. The best drying performance was obtained for the top spray configuration.
  • Effects of drying temperature and relative humidity on the mechanical properties of amaranth flour films plasticized with glycerol Drying Science And Technology

    Tapia-Blácido, D.; Sobral, P. J.; Menegalli, F. C.

    Resumo em Inglês:

    Biofilms are made of biopolymers. In the casting technique, biofilms are obtained by the drying of a polymer suspension in the final stage of processing. The aim of the present paper was to analyze the effect of this drying process on the mechanical properties of films produced with amaranth flour. Variables considered include glycerol content (30, 35 and 40%, g/g dry flour) and air-drying conditions (air temperatures of 30, 40 and 50ºC and relative humidities of 40, 55 and 70%). As amaranth flour films constitute a complex mixture of amylopectin and amylose as well as native protein and lipid, certain unexpected results were obtained. The toughest films were obtained at the lowest temperature and the lowest relative humidity (30ºC, 40%).
  • The effects of fixed-bed drying on the yield and composition of essential oil from long pepper (Piper hispidinervium C. DC) leaves Drying Science And Technology

    Braga, N. P.; Cremasco, M. A.; Valle, R. C. C. R.

    Resumo em Inglês:

    Piper hispidinervium C.DC (Piperaceae) is popularly known as long pepper. It grows in degraded areas of natural fields in the state of Acre, Brazil. Its leaves are 3 to 4 % essential oil rich in safrole, within the range of 90 to 94 %. In the chemical industry, safrole is an important raw material, mainly due to two of its derivatives: heliotropin, which is widely used as a fragrance and flavoring agent, and piperonyl butoxide (PBO), a vital ingredient of pyrethroid insecticides. Natural pyrethrum in particular would not be an economical insecticide without the synergistic effect of PBO; therefore, its industrial future is linked to the continued availability of PBO. As a fragrance, safrole has many applications in household products such as floor waxes, polishes, soaps, detergents and cleaning agents. In this work, leaves were dried in a fixed-bed dryer using different drying-air temperatures (35, 40, 45, 50, 55 and 60 ºC) and drying times (900, 2700 and 3600 seconds). Essential oil was extracted by cohobation (meaning that the condensed water that comes out of the flask is recycled) from both raw and dried leaves. The essential oil yield and safrole content are susceptible to rapid loss of moisture by Piper hispidinervium C. DC leaves. It was observed that the essential oil yield increased twice after the drying process. However, safrole content decreased about 20 percent when temperature was above 50 ºC and drying times were more than 2700 minutes.
  • A study of the fluid dynamics of the spouted bed using CFD Drying Science And Technology

    Duarte, C. R.; Murata, V. V.; Barrozo, M. A. S.

    Resumo em Inglês:

    The spouted bed has been used in drying, granulation, catalytic polymerization, residue treatment and coating of several materials. Its success is attributed to its solids circulation characteristics and excellent gas-particle contact. In this work the pattern of solids and gas flows in a spouted bed was numerically simulated using a Eulerian multiphase model. The computational work was significantly reduced for axisymmetric gas-solids flows. The simulated velocity and voidage profiles were compared with results obtained in our laboratory (with a two-dimensional spouted bed using soybean seed) and by He et al. (1994) (with a cylindrical spouted bed and glass sphere). The simulated results showed good agreement with the experimental data for both geometries studied.
  • The drying of sewage sludge by immersion frying Drying Science And Technology

    Silva, D. P.; Rudolph, V.; Taranto, O. P.

    Resumo em Inglês:

    The objective of this work was to dry sewage sludge using a fry-drying process. The frying experiments were carried out in commercial fryers modified by adding thermocouples to the setup. During frying, typical drying curves were obtained and it was verified that, in relation to the parameters: oil temperature, oil type and shape of the sample, the shape factor the most effect on the drying rate, at least within the range chosen for the variables studied. Oil uptake and calorific value were also analyzed. The calorific value of the samples increased with frying time, reaching values around 24MJ/kg after 600s of frying (comparable to biocombustibles such as wood and sugarcane bagasse). The process of immersion frying showed great potential for drying materials, especially sewage sludge, obtaining a product with a high energy content, thereby increasing its value as a combustible.
  • A solar collector design procedure for crop drying Drying Science And Technology

    Santos, B. M.; Queiroz, M. R.; Borges, T. P. F.

    Resumo em Inglês:

    A design procedure was proposed for sizing solar-assisted crop-drying systems and assessing the combination of solar collector area and auxiliary energy needs that meets the requirements of the load. Two empirical correlations were compared for use with high thermal inertia solar collectors that are cheap and appropriate for rural areas. A case study as performed in the city of Campinas in southeastern Brazil. Grain drying with partial air heating by solar energy can provide an annual savings of 30% in fuel consumption for 1.80m² collector area during the drying of 1.2t of corn at 50ºC at a daily air rate of 1526.8 m³/day.
  • Crispy banana obtained by the combination of a high temperature and short time drying stage and a drying process Drying Science And Technology

    Hofsetz, K.; Lopes, C. C.

    Resumo em Inglês:

    The effect of the high temperature and short time (HTST) drying stage was combined with an air drying process to produce crispness in bananas. The fruit was dehydrated in an air drier for five minutes at 70°C and then immediately set at a HTST stage (130, 140, 150°C and 9, 12, 15 minutes) and then at 70°C until water activity (a w) was around 0.300. Crispness was evaluated as a function of water activity, using sensory and texture analyses. Drying kinetics was evaluated using the empirical Lewis model. Crispy banana was obtained at 140°C-12min and 150°C-15min in the HTST stage, with a w = 0.345 and a w = 0.363, respectively. Analysis of the k parameter (Lewis model) suggests that the initial moisture content of the samples effects this parameter, overcoming the HTST effect. Results showed a relationship between sensory crispness, instrumental texture and the HTST stage.
  • Modeling and simulation of milk emulsion drying in spray dryers Drying Science And Technology

    Birchal, V. S.; Passos, M. L.

    Resumo em Inglês:

    This work aims at modeling and simulating the drying of whole milk emulsion in spray dryers. Drops and particles make up the discrete phase and are distributed into temporal compartments following their residence time in the dryer. Air is the continuous and well-mixed phase. Mass and energy balances are developed for each phase, taking into account their interactions. Constitutive equations for describing the drop swelling and drying mechanisms as well as the heat and mass transfer between particles and hot air are proposed and analyzed. A set of algebraic-differential equations is obtained and solved by specific numerical codes. Results from experiments carried out in a pilot spray dryer are used to validate the model developed and the numerical algorithm. Comparing the simulated and experimental data, it is shown that the model predicts well the individual drop-particle history inside the dryer as well as the overall outlet air-particle temperature and humidity.
  • The drying of amaranth grain: mathematical modeling and simulation Drying Science And Technology

    Calzetta Resio, A.; Aguerre, R. J.; Suarez, C.

    Resumo em Inglês:

    A model for isothermal diffusion of bound water was used to simulate the thin-layer drying kinetics of amaranth grain. The model assumes that the driving force for the transport of bound water is the gradient of spreading pressure. The gradient of spreading pressure was related to the moisture gradient using the GAB isotherm. This variation shows a relative maximum moisture content about 8% (d.b), after which the diffusion coefficient falls sharply as the moisture content is further reduced. To verify the model, drying tests of amaranth grain were conducted at 40 to 70ºC in a laboratory drier from 32.5 to 6% moisture (d.b.). Equilibrium moisture contents were also determined using an electronic hygrometer at temperatures and relative humidities corresponding to drying conditions. The applicability of the model to simulation of drying curves was satisfactory in the full range of moisture.
  • Concurrent drying of soybean seeds: the effect of the radial air profile Drying Science And Technology

    Assis, A. J.; Lira, T. S.; Murata, V. V.; Barrozo, M. A. S.

    Resumo em Inglês:

    The aim of this work was to analyze the heat and mass transfer between the air and soybean seeds in a concurrent moving bed dryer with an air profile that is not flat. The modelling of heat and mass transfer in moving bed dryers is generally based on the application of mass and energy balance equations for both solid and fluid phases (two-phase model). In the establishment of these equations some classical hypotheses such as that the fluid velocity profile is flat, are assumed. The main goal of this work was to verify the validity of this assumption by means of an experimental and simulation study in a concurrent moving bed, using soybean seeds as particles. In this work, the radial air profile was taken into account by means of a suitable empirical correlation and a mechanistic model validated by experimental results. The numerical solution of the one-dimension boundary value problem was obtained by means of a computational code based on axial integration through the DASSL code. By comparison of the experimental data and the simulated responses for air temperature and seed moisture content, it was possible to verify the significant effect of air velocity distribution.
  • Comment on 'Biosorption of Cadmium Using the Fungus Aspergillus niger.' by Barros, L.M., Macedo, G.R., Duarte, M.M.L., Silva, E.P. and Lobato, A.K.C.L.

    Ho, Yuh-Shan
Brazilian Society of Chemical Engineering Rua Líbero Badaró, 152 , 11. and., 01008-903 São Paulo SP Brazil, Tel.: +55 11 3107-8747, Fax.: +55 11 3104-4649, Fax: +55 11 3104-4649 - São Paulo - SP - Brazil
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