Min Of Drying Research Articles

Simulation of fluid flow and heat-moisture transfer mechanism in packed bed based on double-diffusion model

Based on the discrete element method (DEM), four packed beds composed of soybean kernels with diameters of 6.4, 6.8, 7.4 mm, and the mixture of three kinds of particles were established. Then, a double-diffusion heat and mass transfer model between the grain pile and the interstitial air was established based on the local mass and thermal non-equilibrium (LMTNE) mechanism. Finally, employing particle-resolved computational fluid dynamics (PRCFD), the heat and mass transfer between the grain kernels and air during the drying process in the four packed beds were numerically resolved. It was found that the packed bed formed by stacking particles of different diameters had a minimum porosity of 0.4547. The radial porosity of the packed bed oscillates and decreases toward the central axis, while the tortuosity of the airflow path oscillates and decays toward the periphery. The mass transfer Biot number for soybean kernels with diameters of 6.4, 6.8, and 7.4 mm were 2.38 × 106, 2.44 × 106, and 2.53 × 106, respectively. This indicates that the mass transfer rate in the grain pile primarily depends on the magnitude of the moisture diffusion coefficient within the grain kernels. Compared with mass diffusion, thermal diffusion occurs much faster, which results in temperature gradients in packed beds only existing in the first 5 min of drying, and the drying rate in the early stage is higher than that in the later stage. Most importantly, the airflow characteristics, heat and moisture content are not in local equilibrium in the packed bed, and should be considered when designing drying systems.

Obtenção de produto farináceo a partir de resíduos agroindustriais por diferentes métodos de Secagem

O objetivo do trabalho foi a obtenção e caracterização física e química do produto farináceo originado de resíduos agroindustriais, elaborados a partir da secagem em estufa e forno micro-ondas (FMO). A aquisição dos resíduos foi realizada diretamente junto a uma empresa de fabricação de sucos concentrados, localizada da cidade de Nova Floresta, Paraíba. E assim realizados diversos experimentos. A elaboração do produto farináceo em estufa ocorreu na temperatura de 60 °C por 8 h e apresentou 8,82 % de Teor de Água (TA), aw 0,53, pH de 4,13, Sólidos Solúveis Totais (SST) de 12 °Brix, Resíduo Mineral Fixo (RMF) de 4,51 % e Proteína Bruta (PB) de 6,0 %. A rampa de aquecimento utilizada para obtenção da farinha em FMO foi constituída de 3 ciclos de 6 min, totalizando 18 min de secagem, utilizando 50 % de potência do forno e 50 g de amostra. Ao final desse processo o produto apresentou 14,01 % de TA, aw 0,53, pH 4,12, SST de 11 °Brix, RMF de 3,31 % e PB de 5,24 %. Os produtos apresentaram características físicas e químicas dentro dos padrões estabelecidos, demonstrando ser um produto que poderá, posteriormente, ser utilizado na formulação de novos produtos alimentícios.

Structure evolution of pullulan–alginate edible films during drying studied by low‐field NMR

AbstractThe evolutions of spatial structure for pullulan, alginate, and pullulan–alginate blend aqueous solutions during drying were investigated by low‐field nuclear magnetic resonance. For pullulan solutions, during the first 1,320 min of drying, NMR signal intensity in profiles did not vary with position. Thereafter, the apparent shift of the air–pullulan interface began at 1,440 min, indicating the onset of progressive shrinkage of pullulan samples. Similar shrinkage phenomena were observed for alginate and pullulan–alginate blend solutions. In contrast, spatial structural heterogeneity was observed for alginate solution during drying time from 1,200 to 1,560 min, due to the formation of a skin layer near the air–alginate interface. Based on the change of polymer solutions during drying, two‐stage evaporation process was detected in the aqueous pullulan, alginate, and their blend solutions. Moreover, the evaporation rate of water during the second stage of drying was significantly lower than that of the first stage.Practical applicationsEdible films have emerged as an alternative to synthetic petroleum‐based polymers for food packaging. The evolutions of spatial structure of pullulan–alginate solutions during drying were studied by monitoring of their NMR profiles. Information shown in this study would provide some scientific basis for studying film‐forming mechanism of edible films and their applications in the food field.

One-pass drying of rough rice with an industrial 915 MHz microwave dryer: Quality and energy use consideration

Microwave (MW) at 915 MHz has potential to achieve one pass rough rice drying. However, optimising processing parameters to maintain the rice quality is crucial. Effects of MW treatment on rice moisture removal, milled rice characteristics, and energy requirements for continuous one pass drying operation were quantified. Freshly harvested rough rice with initial moisture content of 25% wet basis was dried in a pilot-scale 915 MHz microwave dryer. The dryer was set to transmit MW power ranging between 3 and 24 kW during 8 min of drying. During treatments, rough rice was conveyed at bed thicknesses, 0.01, 0.03, and 0.05 m; supplied specific energy was maintained at 450, 600 and 750 kJ kg −1 of rough rice. Moisture removed varied between 6% and 15% points, depending on rice bed thickness (0.01–0.05 m) and applied specific energy (450–750 kJ kg −1 ). Increasing rice bed thickness and specific energy reduced milling and head rice yields, increased final viscosity of milled rice, but marginally affected rice peak viscosity and surface lipid and protein contents (p −1 and 750 kJ kg −1 of rough rice, 4574 kJ and 5986 kJ were required per kg of water removed, respectively; this translated to 13 and 16 USD per metric ton of dried rice, respectively. The study demonstrated feasibility of one pass MW drying of rough rice; 450–600 kJ kg −1 of rough rice was recommended to preserve rice quality and achieved better energy use efficiency.

Fluid Dynamics and Drying of Cohesive Particles of a Biodegradable Polymer (Poly-Hydroxybutyrate) in a Rotating Pulsed Fluidized Bed

This article presents the results of fluid dynamics and drying of poly-hydroxybutyrate (PHB) granules in a rotating pulsed fluidized bed (RPFB) dryer. Cohesiveness of PHB results in problems when using conventional drying techniques, such as a fluidized bed dryer. The excess surface water on the particles may form agglomerates that damage the flowability of the material inside the dryer. The drying study in RPFB consisted of adjusting mathematical models for predicting the moisture evaporation during the constant drying rate period (linear fit) and the decreasing drying rate period (analytical solution of Fick's second law). The influence of temperature, rotation frequency, and velocity of the drying air on the constant drying rate (Nc), effective diffusivity (Deff), and mass of particles elutriated (me) during drying was evaluated. Particle porosity was analyzed before and after drying and scanning electronic microscopy (SEM) was employed to verify structural changes on the PHB granules after drying. The RPFB dryer proved to be appropriate to dry the PHB granules, resulting in an excellent fluid dynamics behavior of the particles inside the bed and providing uniform drying of the solids. Temperature and velocity of the air had a significant influence on the drying process, but rotation frequency did not affect the process in the ranges analyzed. Fine particle elutriation occurred during the first 10 min of drying. After drying, the porosity changed and breakage of the particles was observed due to attrition inside the bed.

Volume regulatory activity of the Ehrlich ascites tumor cell and its relationship to ion transport.

The volume regulatory response of the Ehrlich ascites tumor was studied in KCl-depleted, Na+-enriched cells. Subsequent incubation in K+-containing NaCl medium results in the reaccumulation of K+, Cl-, water and the extrusion of Na+. The establishment of the physiological steady state is due primarily to the activity of 2 transport systems. One is the Na/K pump (KM for K+o = 3.5 mM; Jmax = 30.1 mEq/kg dry min), which in these experiments was coupled 1K+/1 Na+. The second is the Cl--dependent (Na+ + K+) cotransport system (KM for K+o = 6.8 mM; Jmax = 20.8 mEq/kg dry min) which mediates, in addition to net ion uptake in the ratio of 1K+:1Na+:2Cl-, the exchange of K+i for K+o. The net passive driving force on the cotransport system is initially inwardly directed but does not decrease to zero at the steady state. This raises the possibility of the involvement of an additional source of energy. Although cell volume increases concomitant with net ion uptake, this change does not appear to be a major factor regulating the activity of the cotransport system.

Heat and mass transfer analysis of intra-kernel wheat drying and rewetting

Wheat drying and rewetting are analysed by applying a model based on non-equilibrium thermodynamics. Physical properties needed for the model were obtained either from the literature or from experiments. Liquid and vapour conductivities were determined from the drying data. Validation of the proposed models for both conductivities was made by comparing predicted and experimental data for wheat kernel centre temperatures and rewetting curves. The same liquid and vapour conductivities determined from the drying (desorption) curves accurately predicted the rewetting (adsorption) curves. The proposed model predicted single kernel drying rates and centre temperatures in the dry-bulb range between 26·7 and 87·8°C and moisture contents between 0·1 and 0·35 dry basis. Moisture movement under these drying conditions is shown to occur mainly in the liquid phase for regions inside the kernel and in the vapour phase for drier regions (closer to the evaporation front) and isothermal conditions can be assumed after 2 to 3 min of drying. The drying model accurately predicted wheat rewetting. The model does not apply to early harvested wheat due to the fact that wheat is physiologically immature above 0·4 d.b., (28·5% wet basis).