（１）Large Eddy Simulations of dust devils in the terrestrial Convective Boundary Layer
Large Eddy Simulations (LES) of vertical convective vortices and dust devils in the terrestrial Convective Boundary Layer (CBL) are presented. A CBL-scale simulation and a dust-devil-scale simulation are preformed at different resolutions. The CBL-scale simulation is performed to study the generation of vertical vortices and the dust-devil-scale simulation is performed to study the detailed structures and stages of dust devil development. The simulation results show that dust devils undergo three stages of development as the swirl ratio increases: a weak vortex stage, a single-celled vortex stage and a two-celled vortex stage. The structure of a dust devil can be divided into four regions: outflow, core, corner and inflow layer. The different structures and characteristics of the modelled dust devil during various stages of development and the influence of the surface on the dust devil profile are described using some of the simulation results as illustrations. The causes of the different structures and characteristics are analysed through the interplay between the rotation, the radial pressure gradient, the buoyancy and the axial pressure gradient. Dust devils are a type of concentrated vortex similar to tornadoes. The differences in the structure and characteristics of tornadoes and the modelled dust devils are discussed. The carrying aloft of sand particles within the modelled dust devil is explored using a Lagrangian coordinate system. Sand particles can be transported by the updraft with particles of varying diameters follow different tracks.
（２）A recovery system using phase change materials to store the rejected heat
Latent heat thermal energy storage systems can be used to recover the rejected heat from air conditioning systems, which can be used to generate low-temperature hot water. It decreases not only the consumption of primary energy for heating domestic hot water but also the calefaction to the surroundings due to the rejection of heat from air conditioning systems. A recovery system using phase change materials (PCMs) to store the rejected (sensible and condensation) heat from air conditioning system has been developed and studied, making up the shortage of other sensible heat storage system. Also, PCMs compliant for heat recovery of air conditioning system should be developed. Technical grade paraffin wax has been discussed in order to develop a paraffin wax based PCM for the recovery of rejected heat from air conditioning systems. The thermal properties of technical grade paraffin wax and the mixtures of paraffin wax with lauric acid and with liquid paraffin (paraffin oil) are investigated and discussed, including volume expansion during the phase change process, the freezing point and the heat of fusion.