Analysis of Flow and Heat Transfer in a Flat Solar Collector with Rectangular and Cylindrical Geometry Using CFD

The present investigation describes the construction and experimentation of two solar energy absorbersusing water as working fluid and its simulation in Computational Fluid Dynamics (CFD). For Absorber A with rectangular cross section and Absorber B with circular cross section, water temperature was calculated using solar radiation and ambient temperature measure- ments showing increases of up to 62.5°C for both absorbers. The maximum thermosiphonic flow measurement in Absorber A was 70l/h and 79l/h in Absorber B. On this basis, finite element method and CFD were used to ana- lyze the difference between both flows, with 45, 50, 55, 60, 65 and 70 l/h as simulation values. With the simulation results the Reynolds numbers were determined, finding that the maximum flow (70 l/h) gives the largest Reyn- olds number variation: 25 ≤ Re ≤ 115 for Absorber A and 199 ≤ Re ≤ 235 for Absorber B. With a smaller variation in Absorber B, the flow at all ducts turns out to be more uniform, which results in more ducts transferring heat to the working fluid.