Process and Chemical Engineering
http://hdl.handle.net/10468/347
2017-04-27T16:54:54ZCaking behaviour of food powder binary mixes containing sticky and non-sticky powders
http://hdl.handle.net/10468/3748
Caking behaviour of food powder binary mixes containing sticky and non-sticky powders
Fitzpatrick, John J.; O'Connor, J.; Cudmore, M.; Dos Santos, D.
Caking of food powders is highly undesirable. Many food powders are powder ingredient mixes and there is little work reported on the caking of food powder mixes. This study focusses on the caking of food powder binary mixes consisting of a “sticky” powder (whey permeate WP or maltodextrin MD) and a “non-sticky” powder (salt, flour or paprika). The powders were exposed to 76% relative humidity to make the WP and MD sticky. Force-displacement testing coupled with visual assessment of 2 particles in contact using a microscope were used to investigate the caking behaviour of the binary mixes. A “sticky” powder mass fraction of at least 20% was required to initiate caking and formation of weak cakes. Increasing percentage “sticky” powder fraction above the initial caking percentage resulted in progressively stronger cakes, however the rate of this progression was much less for the stickiest MD powder. The “non-sticky” powders and how they interacted with the “sticky” powders influenced the caking behaviour of the mix. For example, salt formed the strongest cakes in the WP mixes but formed the weakest in the MD mixes. Ability of a “sticky” powder to deform and flow influenced caking behaviour.
2017-02-23T00:00:00ZAnalysis of the failure of cracked biscuits
http://hdl.handle.net/10468/3318
Analysis of the failure of cracked biscuits
Garcia-Armenta, Evangelina; Gutierrez, Gustavo; Anand, Saurabh; Cronin, Kevin
Cracks or checks in biscuits weaken the material and cause the product to break at low load levels that are perceived as injurious to product quality. In this work, the structural response of circular digestive biscuits, with diameter 72 mm and thickness 7.2 mm, simply supported around the circumference and loaded by a central concentrated force was investigated by experiment and theory. Tests were conducted to quantify the distribution in breakage strength for structurally sound biscuits, biscuits with natural checks and biscuits with a single known part-through crack. For sound biscuits the breakage force is Normally distributed with a mean of 12.5 N and standard deviation of 1.2 N. For biscuits with checks, the corresponding statistics are 9.6 N ± 2.62 N respectively. The presence of a crack weakens the biscuit and strength, as measured by breakage force falls almost linearly with crack length and crack depth. The orientation of the crack, whether radial or tangential, and its location (i.e. position of the crack mid-point on the biscuit surface) are also important. Deep, radial, cracks located close to the biscuit centre can reduce the strength by up to 50%. Two separate failure criteria were examined for sound and cracked biscuits respectively. The results from these tests were in good accord with theory. For a biscuit without defects, breakage occurred when maximum biscuit stress reached or exceeded the failure stress of 420 kPa. For a biscuit with cracks, breakage occurred as above or alternatively when its critical stress intensity factor of 18 kPam0.5 was reached.
2016-10-12T00:00:00ZSustainability as contingent balance between opposing though interdependent tendencies; a process approach to progress and evolution
http://hdl.handle.net/10468/3294
Sustainability as contingent balance between opposing though interdependent tendencies; a process approach to progress and evolution
Byrne, Edmond P.
2016-07-04T00:00:00ZEvaporation maps for ternary non-ideal liquid mixtures
http://hdl.handle.net/10468/2239
Evaporation maps for ternary non-ideal liquid mixtures
Dillon, Paul
This thesis deals with the evaporation of non-ideal liquid mixtures using a multicomponent mass transfer approach. It develops the concept of evaporation maps as a convenient way of representing the dynamic composition changes of ternary mixtures during an evaporation process. Evaporation maps represent the residual composition of evaporating ternary non-ideal mixtures over the full range of composition, and are analogous to the commonly-used residue curve maps of simple distillation processes. The evaporation process initially considered in this work involves gas-phase limited evaporation from a liquid or wetted-solid surface, over which a gas flows at known conditions. Evaporation may occur into a pure inert gas, or into one pre-loaded with a known fraction of one of the ternary components. To explore multicomponent masstransfer effects, a model is developed that uses an exact solution to the Maxwell-Stefan equations for mass transfer in the gas film, with a lumped approach applied to the liquid phase. Solutions to the evaporation model take the form of trajectories in temperaturecomposition space, which are then projected onto a ternary diagram to form the map. Novel algorithms are developed for computation of pseudo-azeotropes in the evaporating mixture, and for calculation of the multicomponent wet-bulb temperature at a given liquid composition. A numerical continuation method is used to track the bifurcations which occur in the evaporation maps, where the composition of one component of the pre-loaded gas is the bifurcation parameter. The bifurcation diagrams can in principle be used to determine the required gas composition to produce a specific terminal composition in the liquid. A simple homotopy method is developed to track the locations of the various possible pseudo-azeotropes in the mixture. The stability of pseudo-azeotropes in the gas-phase limited case is examined using a linearized analysis of the governing equations. Algorithms for the calculation of separation boundaries in the evaporation maps are developed using an optimization-based method, as well as a method employing eigenvectors derived from the linearized analysis. The flexure of the wet-bulb temperature surface is explored, and it is shown how evaporation trajectories cross ridges and valleys, so that ridges and valleys of the surface do not coincide with separation boundaries. Finally, the assumption of gas-phase limited mass transfer is relaxed, by employing a model that includes diffusion in the liquid phase. A finite-volume method is used to solve the system of partial differential equations that results. The evaporation trajectories for the distributed model reduce to those of the lumped (gas-phase limited) model as the diffusivity in the liquid increases; under the same gas-phase conditions the permissible terminal compositions of the distributed and lumped models are the same.
2016-01-01T00:00:00Z