Abstract

Richard Mott

Natural ventilation of an enclosed space driven by periodic gusting of wind

We investigate the mixing of a warm enclosed space by a series of discrete gusts of cold air from a high level opening. Initially we examine the case of a series of gusts of identical size each modelled as a turbulent buoyant thermal and develop a model of the filling box like flow which develops in the space. We successfully test the predictions of the model with a series of new laboratory experiments. The experiments combined with the model also provide a new independent estimate for the entrainment coefficient of a thermal, based on the propagation speed of a filling box front. We then examine the mixing produced by a series of thermals of non identical size which we characterise in terms of a mean size and coefficient of variation. We find that as the coefficient of variation increases, the density profile becomes progressively more stratified owing to the asymmetry of dilution through entrainment of large and small thermals.

Seung Yeon Lee

Interfacial Studies on a Charged Surface in Oil by Contact Angle Measurements

Contact angles are dependent upon three interfacial energies: γsolid/liquid, γsolid/vapour, and γliquid/vapour according to Young’s relation. Solid, liquid and vapour phases in this work are respectively amorphous silicates, water droplets and oil media. Due to the three variables, contact angles could be insufficient but necessary to study the surface modification and water adsorption on the surfaces in situ. Surfactants, Ca(AOT)2 added in the oil phase can modify the surface via a cation bridging and hence the surface tension, γsolid/liquid. Added electrolytes in water droplets can vary the water adsorption on the modified surfaces.