Bubble formation in selected industrial problems

Foam and bubbles are ubiquitous in industry and nature. They have a wide range of applications but are also an undesirable product of certain processes. This thesis considers two individual industrial problems with the common phenomenon of bubble and foam formation. Bubble nucleation is a phenomenon observed in many different physical situations from decompression sickness to champagne effervescence. It is of vital importance to the formation of a creamy head that is distinctive to stout beers. I present experimental work that demonstrates that cellulose fibres can be used to initiate stout beers and could serve as an alternative to widget technology. I derive mathematical models for the various gas pocket geometries I observed in cellulose fibres that produce bubbles when submerged in stout beer. These models are solved and compared to experimental results where possible to give the first quantitative evaluation of the current models of bubble nucleation. I present the work done to model a novel design for accurate volume measurement of milk. The new design proposes a modification of the air elimination vessel used in current milk pumping systems to increase accuracy by preventing air bubbles being pumped with milk. We consider the operation of the entire system to pump milk, the flow of milk inside the air elimination vessel, the entrainment of air bubbles into a pool of milk and the drainage of foam

Temperature Dependence of the Heat Diffusivity of Proteins

In a combined experimental–theoretical study, we investigated the transport of vibrational energy from the surrounding solvent into the interior of a heme protein, the sperm whale myoglobin double mutant L29W-S108L, and its dependence on temperature from 20 to 70 K. The hindered libration of a CO molecule that is not covalently bound to any part of the protein but is trapped in one of its binding pockets (the Xe4 pocket) was used as the local thermometer. Energy was deposited into the solvent by IR excitation. Experimentally, the energy transfer rate increased from (30 ps)⁻¹ at 20 K to (8 ps)⁻¹ at 70 K. This temperature trend is opposite to what is expected, assuming that the mechanism of heat transport is similar to that in glasses. In order to elucidate the mechanism and its temperature dependence, nonequilibrium molecular dynamics (MD) simulations were performed, which, however, predicted an essentially temperature-independent rate of vibrational energy flow. We tentatively conclude that the MD potentials overestimate the coupling between the protein and the CO molecule, which appears to be the rate-limiting step in the real system at low temperatures. Assuming that this coupling is anharmonic in nature, the observed temperature trend can readily be explained

Silver(I) complexes of 9-anthracenecarboxylic acid and imidazoles: synthesis, structure and antimicrobial activity

[Ag2(9-aca)2] (1) (9-acaH = 9-anthracenecarboxylic acid) reacts with a series of imidazoles to give [Ag(imidH)2.3(CH3CN)0.7](9-aca) (3), [Ag6(imidH)4(9-aca)6(MeOH)2] (4), {[Ag(1-Me-imid)2]2[Ag4(9- aca)6]} (5), {[Ag(1-Bu-imid)2]2[Ag4(9-aca)6]} (6) and [Ag(apim)](9-aca)·H2O (7) (imidH = imidazole; 1-Me-imid = 1-methylimidazole; 1-Bu-imid = 1-butylimidazole; apim = 1-(3-aminopropyl)imidazole). The mononuclear complex 3, hexanuclear 4–6, and polymeric 7, were all characterised using X-ray crystallography. While many of the complexes possess excellent in vitro antifungal and antibacterial activities they are, unanimously, more effective against fungal cells. The insect, Galleria mellonella, can survive high doses of the Ag(I) complexes administered in vivo, and a number of the complexes offer significant protection to larvae infected with a lethal dose of pathogenic Candida albicans cells