Effect of angle of incidence of sun rays on the bending of absorber tube of solar parabolic trough concentrator

In a parabolic trough system, the solar flux distribution on the surface of absorber tube is non-uniform which results in circumferential temperature gradient. Thus, bending moment is induced and leads to the deflection in absorber tube from the focal line of trough. It is concluded that during zero angle of incidence of sun rays (angle made by sun rays with trough's aperture normal), absorber tube will not deflect from the focal line. However, during non-zero angle of incidence, the absorber tube will deflect. It is because of the fact that during non-zero angle of incidence, the absorber tube does not receive any concentrated flux near the end facing the sun. In the current work, an analytical expression is derived for finding the deflection in the central axis of absorber tube from the focal line of trough. Results for deflection are plotted for different values of angle of incidence taking the dimensions of LS3 parabolic trough with Schott 2008 PTR70 receiver.