Changes in particle morphology during drying of drops of carbohydrate solutions and food liquids. 1. Effect of composition and drying conditions (original) (raw)
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Industrial & Engineering Chemistry Research, 1990
Drying rates and the development of particle morphology were monitored simultaneously for initially uniform size drops falling through a column having a known temperature profile. A sampler with continuously flowing dimethyl sulfoxide solvent was used to determine the extents of drying of the captured particles. Measured water contents were compared with predictions of a model based upon diffusion within a noncirculating, voidless sphere. Drying rates for drops of aqueous solutions of sucrose and maltodextrin agreed well with this model, as did rates for drops of coffee extract drying a t low (189 " C ) air temperature. At higher air temperatures (219 and 254 "C), coffee drops dried at rates greater than predicted by the model. These results correspond t o observed tendencies for particles of partially dried coffee extract to exhibit residual blowholes and for suspended drops to push wet material from the interior of the drops outward through surface ruptures during drying.
International Journal of Food Properties, 2000
Levitation and free-flight techniques applied to investigate the drying kinetics and morphology of single drops containing dissolved solids and suspensions are reviewed. A review of works related to receding interface model proposed to quantify the drying kinetics of single drops along with techniques to measure the kinetic parameters such as moisture diffusivity, thermal conductivity and specific heat capacity is presented. Problems associated with spray drying of sugar-rich compounds are briefly discussed and possible links of stickiness and flavor retention with glass transition temperature (T g), temperature history, drying rate and morphological changes including skin formation, as monitored through single drop experiments, are explored.
Experimental Determination of Drying Kinetics of Skim-Milk Suspended Droplet
The article presents a detailed report of the measurements and analysis of the drying kinetics obtained using suspended droplet technic. Measurements of drying process of milk, whey and lactose solutions were performed in range of temperatures 60-140°C. The drying rate, locking point and critical moisture content of particle have been obtained on a base of recorded images and measurements of exhausted air humidity. Influence of drying air temperature on particle morphology has been observed. Highly porous, hollow particles were created in air temperatures higher than 100°C due to intensive inflation-deflation period. Smaller and compact particles were produced in low air temperatures (T g < 100°C). Dry particle structure was analyzed by X-ray computed tomography. Experimentally obtained drying curves can be used in determination of drying parameters and validation of single droplet drying models.
2009
Changes in fluidization behaviour behaviour was characterised for parallelepiped particles with three aspect ratios, 1:1, 2:1 and 3:1 and spherical particles. All drying experiments were conducted at 50 0 C and 15 % RH using a heat pump dehumidifier system. Fluidization experiments were undertaken for the bed heights of 100, 80, 60 and 40 mm and at 10 moisture content levels. Due to irregularities in shape minimum fluidisation velocity of parallelepiped particulates (potato) could not fitted to any empirical model. Also a generalized equation was used to predict minimum fluidization velocity. The modified quasi-stationary method (MQSM) has been proposed to describe drying kinetics of parallelepiped particulates at 30 o C, 40 o C and 50 o C that dry mostly in the falling rate period in a batch type fluid bed dryer.
Chemical Engineering and Processing: Process Intensification, 2007
The distribution of moisture within fructose and lactose droplets, subjected to convective drying conditions, was predicted using a convectivediffusion equation based on a solute fixed coordinate system. The partial differential equation was solved using the method of lines. Neumann and Robbins type boundary conditions were imposed at the centre and at the droplet-air interface, respectively. The temperature history was predicted by coupling the heat balance equation with the rate of change in average moisture. The distribution of glass transition temperature (T g) within the droplet and at the surface layer was predicted. The concept of sticky point temperature (T sticky) was introduced and used as an indicator of the development of stickiness at the droplet surface. Single droplets were dried in a controlled air stream and their moisture and temperature history were measured experimentally. These data were used to compare with the model predictions. A custom built in situ surface stickiness testing instrument was used to experimentally determine the development of surface stickiness at the droplet surface. These data were used to validate the model on surface stickiness. The model predicted the experimental moisture and temperature histories of fructose and lactose droplets within ±5-7% absolute error and ±1-2 • C accuracy. It also predicted the development of surface stickiness of fructose and lactose droplets reasonably well. In test conditions, lactose surface attained non-sticky state through crystallization or transformation into glassy state. Fructose droplets remained sticky even in a bone dry state due to their low T g .
Fundamental Investigation of the Drying of Solid Suspensions
Industrial & Engineering Chemistry Research
In this work, a comprehensive series of experiments is conducted to investigate the drying behavior of micro-and nanosized particle dispersions. To this end, an acoustic levitator was used to study the drying kinetics of single droplets. The temporal evolution of the actual droplets was recorded using a complementary metal oxide semiconductor (CMOS) camera, and the solid grains produced at the end of drying were investigated by scanning electron microscopy (SEM) imaging. At the end of drying, the grains show different morphologies as a function of the particle size, concentration, and initial droplet volume. We combine these experimental data to show the drying behavior is dependent on all the parameters and that the data all collapse when plotted against the Pećlet number. This resulted in a novel characteristic diagram which allows one to predict the shape of the dried colloidal droplet based on Pe. Our results extend the fundamental understanding of the mechanisms controlling the drying of droplet suspensions.
This work deals with the study of drying kinetics of high water content materials such as agro-food particles. These materials exhibit significant structural and geometry changes during drying showing complex non-Fickian drying kinetics. Indeed, drying rate curves in these cases show multiple stages differing significantly from typical constant and falling rates periods. These observations justify the need to characterize the drying curves differently to account for this behavior. For instance, following experimental measurements, it has been found that Fickian type kinetics ( do not hold for characterizing the drying curves; instead, the suitability of a modified Page's type model (1-term :
Journal of Food Engineering, 2004
The effect of addition of maltodextrin on drying kinetics of drops containing fructose, glucose, sucrose and citric acid individually and in mixtures was studied experimentally using single drop drying experiments and numerically by solving appropriate mass and heat transfer equations. The numerical predictions agreed with the experimental moisture and temperature histories within 5-6% average relative (absolute) errors and average differences of ±1°C, respectively. The stickiness of these drops was determined using the glass transition temperature ðT g Þ of the dropsÕ surface layer as an indicator. The experimental stickiness histories followed the model predictions with reasonable accuracy. A safe drying (non-sticky) regime in a spray drying environment has been proposed, and used to estimate the optimum amount of addition of maltodextrin for successful spray drying of 120 micron diameter droplets of fruit juices.
Beyond Coffee Rings: Drying Drops of Colloidal Dispersions on Inclined Substrates
ACS Omega
The patterns resulting from drying particle-laden sessile drops (for example, coffee rings, where the particles are concentrated more at the edge, and their complete suppression, where the particles are uniformly distributed throughout the pattern) have been well studied for more than two decades. For the ubiquitous instance of occurrence of drying of drops containing nonvolatile species (either dissolved or dispersed) on substrates oriented at different angles with respect to gravity, the investigation of resulting evaporative patterns has not received much attention. This mini-review addresses the need to investigate the drying of drops residing on inclined surfaces and highlights recent advances in this field.
Density Variation of Different Shaped Food Particulates in Fluid Bed Drying: Empirical Models
Journal of Agricultural and Marine Sciences [JAMS], 2009
Three particular geometrical shapes, parallelepiped, cylindrical and spherical, were selected from potatoes (aspect ratio = 1:1, 2:1, 3:1), cut beans (length:diameter = 1:1, 2:1, 3:1) and peas respectively. The density variation of food particulates was studied in a batch fluidised bed dryer connected to a heat pump dehumidifier system. Apparent density and bulk density were evaluated with non-dimensional moisture at three different drying temperatures of 30, 40 and 50 oC. Relative humidity of hot air was kept at 15% in all drying temperatures. Several empirical relationships were developed for the determination of changes in densities with the moisture content. Simple mathematical models were obtained to relate apparent density and bulk density with moisture content.