Numerical investigation of a novel sinusoidal tube receiver for parabolic trough technology

Within the continuous improvement effort of parabolic trough collector (PTC) performances, a three-dimensional numerical model is carried out to investigate the turbulent flow and potential heat transfer enhancement in a novel parabolic trough receiver (PTR) where the conventional straight and smooth tube (CSST) receiver is replaced by a newly designed S-curved/sinusoidal one. Heat transfer performance and pressure drop penalty comparisons between CSST receiver and S-curved/sinusoidal tube receiver are conducted using synthetic oil as a heat transfer fluid (HTF). The validity of the model has been tested by comparing the numerical results with the available experimental data of the sinusoidal pipe heat exchangers. As a consequence of the shape of the novel tube receiver, the heat density distribution on the outer surface varies in both longitudinal and circumferential directions while it varies only in the circumferential direction on the corresponding CSST receiver. The analysis of the HTF flow through the novel PTR S-curved/sinusoidal tube showed the emergence of vortices at bends. It is established that, without any additional devices, the mean Nusselt number is expected to increase by 45%-63%, while the friction coefficient increases by less than 40.8%, which leads to a maximum performance evaluation criteria about 135%. The maximum circumferential temperature difference of the novel PTR S-curved tube decreases below 35 K for almost all the range of the mass flow rates and should result in the reduction of thermal stresses and heat losses.