Swelling and hydration studies on egg yolk samples via scanning fluid dynamic gauge and gravimetric tests

AbstractHydration and swelling in initially dry protein-based samples represent the first stage in their cleaning from hard surfaces. These phenomena have been studied in technical egg yolk stains via scanning Fluid Dynamic Gauge (sFDG) and gravimetric tests. Temperature (30 °C to 55 °C) and pH (9.5 to 11.5) were investigated as factors influencing the process. The kinetics did not appear to be significantly different as 95% of the equilibrium swelling was reached at approximately 90 min in all tests. No removal of the egg yolk layer was observed in most cases, except at high alkaline conditions (pH 11.5), where a lift-up followed by a partial removal of the protein network was seen when an external shear stress was applied. The process mimicked creep behaviour of plastic materials. Gravimetric data on the hydration of the sample suggested a Fickian diffusion transport (Case I), where solvent diffusion is the rate limiting stage. The initial hydration was proved to be linear. Two diffusion theories of increasing complexity were applied to estimate effective diffusion coefficients: Fick's second law (with moving boundaries) and a non-linear poroelasticity theory. The temperature dependence of different diffusion coefficients assuming an Arrhenius equation gave an activation energy in the range of 16.4 (±6.7) KJ/mol to 18.4 (±9.0) KJ/mol

Development of a swelling-removal model for the scanning fluid dynamic gauge

AbstractA mathematical mechanistic swelling-removal approach has been developed for modelling the cleaning process in dried protein samples using the scanning fluid dynamic gauge (sFDG). The algorithm combines swelling phenomena with removal mechanisms (shear stress removal and soil dissolution). Swelling phenomena were described by applying analytical expressions based on poroelasticity theory. The nonlinear partial differential equation (PDE) describing the thickness swelling ratio was solved numerically, allowing the soil to be divided into theoretical layers. The novelty is presented as the cleaning process is integrated by the elimination of those layers. The model predicts the variation of the soil thickness over time. To describe kinetics of removal, experimental results were considered. Constant removal rates were found after an initial transition period. Removal rates were dependent on the different chemical and physical factors acting: temperature, chemistry concentration (pH, enzyme level), shear stress and frequency of application of shear stress. Soil remaining, total mass or percentage of cleaning over time can also be calculated as outputs. Overall the model has the potential to apply varying cleaning conditions over time and grow to a more theoretical approach in the future by applying enzyme kinetics

Positron Emission Particle Tracking (PEPT) for the analysis of water motion in a domestic dishwasher

AbstractMotion of water inside a household dishwasher has been characterised via Positron Emission Particle Tracking (PEPT). The technique enables the visualisation of the motion of a radioactive tracer in three-dimensional and opaque systems. Results showed a periodic sequence of the water over time, encompassing the following steps: movement inside internal equipment and spray arm, ejection via jets, impact over walls and crockery, downfall (either over walls, crockery or free falling) and recirculation of the bulk water from the bottom of the dishwasher. This sequence was shown to occur within a few seconds and the highest velocities, and therefore, the highest kinetic energies, were found upon ejection. Jet paths were observed to follow a straight line. Increased pump speeds increased velocity ejection profiles, but the effect over the downfall step was negligible. In fully loaded dishwasher (with crockery), the tracer moved slower in these high packing zones, showing low velocity profile areas with higher residence times. Other stagnant areas were found at the edges of the bulk of water remaining at the bottom of the dishwasher. Use of detergent did not seem to affect water motion. Finally, data generated via CFD was compared with equivalent PEPT data, showing good agreement for the spray arm and ejection steps but disagreement in the free falling step. The divergences in the results can be explained by a combination of PEPT data processing and CFD model constraints. Information gathered is helping the development of more sustainable and efficient dishwashing systems

Molecular excitation in the Interstellar Medium: recent advances in collisional, radiative and chemical processes

We review the different excitation processes in the interstellar mediumComment: Accepted in Chem. Re