Solar thermal energy converters have been widely studied for many years and are suitable for both small and large-scale deployment. Solar thermionic energy converters are a much more direct and potentially more efficient way of generating electricity from solar energy. An ideal absorber aims to maximise solar absorption while minimising infra-red emissivity in order to achieve the highest possible temperature. Preventing conduction and convection heat loss of the solar absorber is also a key to obtain a higher temperature.
In this thesis, molybdenum samples were fabricated using laser micromachining. Finite Difference Time Domain modelling of the microstructure has shown the absorptivity increased over the visible and near-infrared region. The microstructures were characterised using an integrating sphere and an infrared microscope.
In-air solar simulator-heated temperature results for the molybdenum samples with different microstructures showed good agreement with the absorptivity measurements. Two vacuum devices were developed to reduce the convection heat loss with a mount designed to minimise conduction loss. The molybdenum samples were heated in the vacuum devices with a solar simulator and focused sunlight and >400℃ has been achieved.
COMSOL Multiphysics has been used to model the heat transfer between the molybdenum sample and the holder. Based on the simulation results, a prototype of fully sealed thermionic emission convertor was proposed which has a new design of the sample and the holder. Overall, this work shows that low-cost laser micro-patterned molybdenum samples have good potential to obtain high temperature for thermionic emission applications.
|Date of Award||29 Sep 2020|
- The University of Bristol
|Supervisor||Martin J Cryan (Supervisor)|