Abstract: Aiming at the impact of the coking product on the inner wall of the parabolic trough receiver on the heat transfer of the heat conduction oil and the safety of the receiver, the apparent morphology and characteristics of the coking product in the receiver of a trough solar thermal system after three years of operation were studied. The results show that the coking product presents a thick, pit-like rough surface in the circumferential direction of the metal tube, and a thin non-uniform distribution on the non-focusing side. Additionally, the particles of coking products display distinct three-dimensional characteristics, appearing as two forms of coking agglomeration focusing and dispersed coking. The true density of coking products after stacking is 1.259 7 g/cm³, and their specific heat capacity ranged from 0.83 to 2.11 J/(g·K) as measured by the Differential Scanning Calorimetry (DSC) Sapphire method. Furthermore, the thermal conductivity of bulk metal tube samples with coking products is 24.05 W/(m·K), measured using the flash method at 400 ℃, indicating a 21.7% decrease compared to non-coking metal tubes. The coking product significantly affected the heat transfer performance of the metal tube for the parabolic trough receiver.

Key words: parabolic trough receiver, coking product, heat-transfer performance