Study of parameters influence on the measurement of vacuum level in parabolic trough collectors’ receivers using infrared thermography

The receiver tube of the parabolic trough collectors may suffer a degradation of the vacuum atmosphere between the glass envelope and the absorber tube due to the permeation of gases, mainly hydrogen or air. This is one of the most common issues of heat loss increase in solar fields with this type of solar collectors. The Surface Temperature Method has been used to determine the complete and partial vacuum loss in the annulus of receiver tubes, by measuring the temperature of the glass envelope. In this work, the influences of the meteorological variables and the source distance on the measurement of the temperature by infrared thermography are analysed, as well as the feasibility of using the reflector of the collector itself to measure the sky temperature, parameter necessary to correctly measure the temperature by means of an infrared sensor.