28 research outputs found
Variations in banana properties
Samples prepared from different bananas and
from different parts of a banana may vary in their properties,
which may cause variations in the final results in
experiments. Therefore, assessment of variation in the samplesâ
properties is necessary, and it can be evaluated using
statistical analysis. In this work, the variation in banana
propertiesâcolour, texture, moisture and sugar contentsâ
within and between bananas were assessed statistically
using a two-stage nested design test and the two-sample
t-test. Results show that the variation of properties is significant
for bananas with different degrees of ripeness. This
finding suggests that samples can be prepared from different
parts of the bananas provided that the bananas are
at the same degrees of ripeness. It was also found that the
location of sample in the drying chamber did not affect the
measured properties of the drying bananas, significantly.
The tests performed for banana texture using a laboratory
apparatus produced results that were similar to those performed
using a dynamic mechanical analyzer. This suggests
that the use of highly-sophisticated instruments in
the texture analysis of dried fruit in terms of the apparent
modulus is not crucial
A Study of Particle Histories during Spray Drying Using Computational Fluid Dynamic Simulations
Particle size control of detergents in mixed flow spray dryers
Particle size is a key quality parameter of a powder detergent as it determines its performance, the bulk density and the look and feel of the product. Consequently, it is essential that particle size is controlled to ensure the consistency of performance when comparing new formulations. The majority of study reported in the literature relating to particle size control, focuses on the spray produced by the atomisation technique. One approach advocated to achieve particle size control is the manipulation of the ratio of the mass slurry rate and mass flow rate of gas used for atomisation. Within this study, ratio control was compared with an automatic cascade loop approach using online measurements of the powder particle size on a small-scale pilot plant. It was concluded that cascade control of the mean particle size, based on manipulating the mass flow rate of gas, resulted in tighter, more responsive control. The effect of a ratio change varied with different formulations and different slurry rates. Furthermore, changes in slurry rate caused complications, as the impact on particle size growth in the dryer is non-linear and difficult to predict. The cascade loop enables further study into the effect of particle size on detergent performance
Water adsorption isotherms and isosteric sorption heat of spray-dried and freeze-dried dehydrated passion fruit pulp with additives and skimmed milk
The mathematical modelling of cascading rotary dryers
SIGLEAvailable from British Library Document Supply Centre- DSC:D89480 / BLDSC - British Library Document Supply CentreGBUnited Kingdo
Experimental and modelling investigations of droplet dispersion in a turbulent jet
The turbulent dispersion of non-evaporating droplets in an axisymmetric round jet issuing from a nozzle is investigated both experimentally and theoretically. The experimental data set has a well-defined inlet boundary with low turbulence intensity at the nozzle exit, so that droplet dispersion is not affected by the transport of nozzle-generated fluctuating motion into the jet, and is influenced solely by gaseous turbulence produced in the shear layer of the jet. This data set is thus ideal for testing algebraic models of droplet fluctuating motion that assume local equilibrium with the gaseous turbulence. A two-fluid turbulence modelling approach is adopted, which uses such an algebraic model and the k - Δ turbulence model to predict the droplet and fluid turbulent correlations, respectively. We have shown that the k - Δ turbulence model lacks generality for predicting the spread of momentum in jets with and without a potential core. However, in general, the model predicts the radial dispersion of droplets in the considered turbulent jet with reasonable accuracy over a broad range of droplet sizes, once deficiencies in the k - Δ turbulence model are taken into account
The effect of surface composition on the functional properties of milk powders
The migration of lactose, protein and fat within milk droplets and particles in a spray dryer is investigated with a view to eventually modelling this process using computational fluid dynamics. Both protein and fat accumulate preferentially at the surface of the milk particles as they dry, at the expense of lactose. This has repercussions for the rate of particle agglomeration and wall deposition within the spray dryer, and the functional properties of the dried powder, because the fat and lactose surface concentrations affect the stickiness of the milk particles. The surface fat coverage, and hence the particle stickiness, is particularly sensitive to small changes in fat content between 0% and 5%, which is likely to be important for the control of powder properties and the operation of spray drying equipment in skim milk production. In addition, a higher drying temperature favours the appearance of lactose over protein at the surface of the milk particle. We postulate that higher temperatures hasten the formation of a surface skin, which hinders the migration of surface-active protein towards the surface. Finally, we have confirmed observations made by various other researchers on the morphological evolution of a milk droplet as it dries, which involves the formation of a skin and a vacuole, and the inflation and subsequent shrinkage of the particle
Lagrangian and Eulerian models for simulating turbulent dispersion and coalescence of droplets within a spray
Lagrangian and Eulerian modelling approaches are compared for simulating turbulent dispersion and coalescence of droplets within a spray. Both models predict similar droplet dispersion rates and shifts in droplet size distribution due to coalescence within the spray, over a wide range of droplet and gas flows, and for sprays with different droplet-size distributions at the nozzle exit. The computer time required for simulating coalescence within a steady axisymmetric spray is of a similar order of magnitude regardless of which formulation, Eulerian or Lagrangian, is adopted. However, the Lagrangian formulation is more practical in terms of the range of applicability and ease of implementation
Validation of the Lagrangian Approach for Predicting Turbulent Dispersion and Evaporation of Droplets within a Spray
The accuracy of the Lagrangian approach for predicting droplet trajectories and evaporation rates within a simple spray has been addressed. The turbulent dispersion and overall evaporation rates of droplets are modeled reasonably well, although the downstream velocity decay of the larger droplets is underpredicted, which is attributed to a poor estimate of the radial fluctuating velocity of these droplets at the inlet boundary. Qualitative agreement is found between the predicted and experimental evolution of the droplet size distribution downstream of the nozzle. These results show that smaller droplets evaporate preferentially to larger droplets, because they disperse more quickly toward the edge of the jet, where the entrainment of fresh air from the surroundings produces a significant evaporative driving force. Droplet dispersion and evaporation rates are highly influenced by the rate of turbulence generation within the shear layer. This work demonstrates the potential of the Lagrangian approach for analyzing particle trajectories and drying within the more complex spray dryer system