Thermo-Fluid Optimization of a Solar Porous Absorber With a Variable Pore Structure

Optimization based on reconstruction of the velocity, temperature, and radiation fields in a porous absorber with continuous linear porosity or pore diameter distribution is carried out in this work. This study analyzes three typical linear pore structure distributions: increasing (“I”), decreasing (“D”), and constant (“C”) types, respectively. In general, the D type porosity (ϕ) layout combined with the I type pore diameter (d_p) distribution would be an excellent pore structure layout for a porous absorber. The poor performance range, which should be avoided in the absorber design, is found to be within a wide range of porosity layouts (ϕ_i = ∼0.7 and ϕ_o > 0.6) and pore diameter layouts (d_i = 1.5–2.5 mm), respectively. With a large inlet porosity (ϕ_i > 0.8), the D type layout with larger porosity gradient (G_p) has a better thermal performance; however, the I type d_p layout with a smaller inlet pore diameter (d_i < 1.5 mm) and a larger pore diameter gradient (G_dp) is recommended when considering the lower pressure drop. Different pore structure layouts (D type or I type) have a significant effect on the pressure drop, even with the same average ϕ_a and d_a, the maximum deviation can be up to 70.1%. The comprehensive performance evaluation criteria (PEC) value shows that the D type ϕ layout with a larger ϕ_a has an excellent thermopressure drop performance, and a part of PEC values for the I type d_p layout are greater than unity.