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 samples’ properties is necessary, and it can be evaluated using statistical analysis. In this work, the variation in banana properties—colour, texture, moisture and sugar contents— 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

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

The mathematical modelling of cascading rotary dryers

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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 - ε turbulence model to predict the droplet and fluid turbulent correlations, respectively. We have shown that the k - ε 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 - ε 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