Analysis on the suitable working temperature range of nanofluid-based direct absorption solar collection.

Solar energy is often used as heat source in the refrigeration and heating system and the solar collector is the core device of solar energy heat utilization system. To solve the technical bottleneck of the coated metal-glass evacuated tube in solar medium-temperature collection, a novel solar medium-temperature heat collection method named Direct Absorption Collection (DAC) was proposed. Nano-fluid with strong solar light absorption properties as working fluid, and transparent vacuum tubes without coating was employed as solar absorber tubes. Compared with conventional solar absorber with selective coating, the solar DAC was theoretically modeled and simulated for its collection performance. The models were verified to be credible by experimental results. Both the simulative and experimental results indicated that the collection efficiency of DAC was higher than conventional coated solar absorber under a certain working temperature range. Furthermore, the performances of DAC and conventional solar collector under different operating conditions were simulated and comparatively analyzed. The suitable working temperature range of the proposed DAC under different were also obtained, providing a theoretical basis for the application of DAC.