Solar absorber tube analysis: thermal simulation using CFD

Solar–thermal power plants are being deployed world-wide. These plants have traditionally used steel absorber pipes. Two types of fluids have been used in such ventures, synthetic aromatic fluid or water. Fluid flow in parabolic trough systems leads to instability in the tube due to the concentrated solar flux on only one-half of the absorber tube, resulting in temperature asymmetricity. The resulting stresses cause deflection and bending of the tube. This paper deals with direct steam systems and proposes incorporation of internal helical fins within the tube to reduce temperature variation. The fins provide an orderly distribution of flow from the ‘hot’ to the ‘cold’ side of the tube. A CFD simulation was carried out for three fin pitches, and an aluminium pipe without fins. The effect on heat transfer improvement and temperature asymmetry is presently reported. It is shown that the thermal gradient between the upper and lower temperature for the pipe without a helical fin (20 K) is considerably higher compared with the pipes with 100, 200 and 400 mm pitch helical fins, i.e. 10.8, 13, 14.9 K, respectively. Also, the thermal gradient for the aluminium pipe was also much lower when compared with the steel pipe. Copyright , Oxford University Press.