Modeling and performance comparisons of the grading and single solar collector/ regenerator systems with heat recovery

A novel solar grading collector/regenerator system with heat recovery is proposed in this paper and a mathematical model of system is established. Numerical simulation shows that heat recovery does increase the performance of system reaching increments of 104% and 320% respectively for grading solar collector/regenerator with all heat recovery (Mode E) and single solar collector/regenerator with heat recovery (Mode C). There occur critical points of performances between the single and grading collector/regenerators. The regeneration efficiencies of Mode E were increased by 12.2%, 10.7% and 75% at ambient temperature of 40 °C, relative humidity of 90% and solar radiation intensity of 600 W/m2 respectively compared with Mode C. The critical flow-rates of air and solution are in the ranges of 220 kg/h to 260 kg/h and 17 kg/h to 42 kg/h respectively corresponding with the plate of 1 ∼ 3 m length. The regeneration efficiency of Mode E with a 3-m plate was increased by 24% compared with 1-m plate. The application scopes of environmental parameters and solution concentration are given in this paper and it is concluded that the grading regeneration is beneficial to regenerating the solution of high concentration in the conditions of low solar radiation intensity and high temperature as well as high humidity.