Solar Thermal Characterisation of Micro-Patterned High Temperature Selective Surfaces applied to a Thermionic Device

Abstract

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
Original language	English
Awarding Institution	The University of Bristol
Supervisor	Martin J Cryan (Supervisor)