Heat Conduction of Inert Gas-Hydrogen Mixtures in Parabolic Trough Receivers

Abstract

The annulus of a parabolic trough receiver is normally evacuated to prevent heat conduction between the internal absorber pipe and the external glass envelope. In the past, this vacuum has sometimes been compromised by hydrogen permeation from the heat transfer fluid through the absorber pipe. Heat conduction, and consequently receiver thermal loss, can be significantly increased by the presence of hydrogen in the annulus. Supplying receivers with inert gases in the annulus, or injecting receivers with inert gases after the vacuum has been compromised, could mitigate these heat losses. This study measures parabolic trough receiver heat conduction in the transition, temperature jump, and continuum regimes for argon-hydrogen and xenon-hydrogen mixtures at an absorber temperature of 350°C. Test results show that small heat loss increases over evacuated values are associated with the 95% inert gas/5% hydrogen mixtures and that from a performance perspective gas-filled HCEs would likely induce a 1–3% plant revenue decrease relative to evacuated receivers, but would protect against hydrogen-induced heat loss as long as there was sufficient quantity of inert gas in the annulus. Sherman’s interpolation formula predicted the inert gas and 95% inert gas/5% hydrogen mixture test results within experimental and model uncertainty, but did not accurately capture the larger hydrogen molar fraction test results. The source of this discrepancy will be further investigated.