ABSTRACT
This chapter presents a detailed thermal model of trough collectors and develops an efficiency equation in terms of the absorber wall temperature, rather than the conventional fluid temperature correlation by modelling radiation loss, convection loss from the absorber and conduction loss through the vacuum tube bellows. Parabolic trough solar concentrators with evacuated tubular absorbers are the main technology currently used in solar thermal electric power generation plants. In the direct steam generating trough collector, the absorber tube will be horizontal or at a shallow slope and the incident energy input can be considered uniform along the length of the absorber. A trough collector absorber element consists of a steel tube surrounded by an evacuated glass envelope, joined together at each end by metallic bellows. The two-phase flow heat transfer coefficients apply for uniform heat flux conditions which may not occur during the operating of a direct steam generation collector due to transient radiation.
