Heat collection characteristics of nanofluids in direct absorption solar collector with built-in rotors

As for the uneven heating of the working medium in direct absorption solar collector (DASC),this paper proposed the method of optimizing the flow pattern in DASC by inserting combined rotors into the collector tube to improve the heat collection performance. The working medium used in this paper is Chinese ink nanofluid. The heat collection performance of the collector was studied, and the enhanced mechanism was explained through simulations. Results demonstrated that inserting rotors improved the temperature rise rate in the circuit, and the temperature of the medium after inserting rotors increased by about 56 % compared with that before inserting rotors when the mass fraction of nanoparticles was 0.2 %. In some cases, a small number of rotors can achieve an enhancement effect similar to that of enormous rotors, and improve the economic performance of the system. The numerical simulation results showed that the high-temperature medium in the plain tube is concentrated near the light side, while the medium in the centre and backlight side of the tube cannot easily absorb solar radiation. After rotors were inserted into the tube, the back-side and light-side media were displaced and mixed by the turbulence of rotors, which can improve heat collection.