CFD-Based Simulation and Analysis of Hydrothermal Aspects in Solar Channel Heat Exchangers with Various Designed Vortex Generators

Abstract

The hydrothermal behavior of air inside a solar channel heat exchanger equipped with various shaped ribs is analyzed numerically. The bottom wall of the exchanger is kept adiabatic, while a constant value of the temperature is set at the upper wall. The duct is equipped with a flat rectangular fin on the upper wall and an upstream V-shaped baffle on the lower wall. Furthermore, five hot wall-attached rib shapes are considered: trapezoidal, square, triangular pointing upstream (type I), triangular pointing downstream (type II), and equilateral-triangular (type III) cross sections. Effects of the flow rates are also inspected for various Reynolds numbers in the turbulent regime (1.2 × 104–3.2 × 104). The highest performance (η) value is given for the II-triangular rib case in all Re values, while the square-shaped ribs show a significant decrease in the η along the achieved Re range. The η value at Remax is 2.567 for the II-triangular roughness case. Compared with the other simulated cases, this performance is decreased by about 3.768% in the case of I-triangular ribs, 15.249% in the case of III-triangular ribs, 20.802% in the case of trapezoidal ribs, while 27.541% in the case of square ribs, at the same Remax. Also, a comparison is made with air-heat exchangers that have non-rough walls and contain cross-shaped VGs presented previously, in order to highlight the effectiveness of the rough surface presence in the baffled and finned channels. The obtained results indicated that the triangular-shaped rib (type II) has the most significant hydrothermal behavior than the other cases. This indicates the necessity of roughness heat transfer surfaces for finned and baffled channels to improve significantly the performance of the air-heat exchangers they contain.