Optimization of a solar collector with evacuated tubes using the simulated annealing and computational fluid dynamics

In this work, the optimization of a low temperature, water-in-glass, evacuated tubes solar collector is presented. The process of optimization combined the simulated annealing method and a computational fluid dynamics model. The numerical study was carried out in three dimensions, steady-state and laminar regime. A design of experiments study via computational fluid dynamics was carried out with two levels and five parameters, 25, the parameters with significance in the performance of the collector were found from a commercial collector. This collector was used as base case in the process of optimization. In the optimization process, the absorber area was analyzed under three different cases because of the combination of geometrical parameters: length, diameter and number of tubes. Thus, 259 different collector geometries were constructed and modeled. Results from the design of experiments showed that the significant parameters on the thermal performance of the solar collector are: the diameter of the tubes, the absorber area, and the mass flow rate. Results of the optimization process showed that the minimum absorber area for an optimal geometry is 2.49 m2, which is 19.4% lower than the commercial geometry considering the same outlet temperature. The diameter of the tubes increased around 30%, the length of the tubes decreased 40%, the cost of the optimal geometry and the number of evacuated tubes decreased 38.9% and the thermal efficiency increased 26.3%, compared to the commercial geometry. The results of this work can be helpful in further specific applications where the maximum performance and the minimum costs are important, such as: the design of low temperature, water-in-glass, evacuated tubes solar collector networks for heating water in swimming pools, buildings, hospitals and industries.