Exergy optimization of flow rates in flat-plate solar collectors

Abstract

The optimal flat‐plate collector mass flow rate is determined by maximizing the exergy (available energy) delivery of the collector as the objective function. Collector and storage dynamics are neglected. Although the case where the pumping power loss is ignored results in bang‐bang control, the case where this loss is included in the exergy equation results, after some assumptions, in an optimal mass flow rate that is a function of collector parameters, inlet and ambient temperatures and solar heat gain. Daily performance of a typical flat‐plate solar collector with optimum mass flow rate is compared with the performance of the same collector using the mass flow rate obtained by maximizing the difference between the collected thermal energy and the required pumping power.

Exergy analysis and parametric study of concentrating type solar collectors

“…The hourly solar radiation (I S ) in W m −2 and corresponding ambient temperature (T a ) used in this study are taken from the literature [8,12,18]. We have studied the effect of the mass flow rates and the concentration ratio on the stagnation temperature, exergy output, optimum fluid inlet temperature, exergy efficiency and thermal efficiency of the collector and the discussion of results are given as below:…”

“…C = A R /A A = 1.0) in Eqs. (13), (14) after neglecting the radiation losses, the expressions obtained above (for concentrating collector) reduce to the flat plate collector expressions as obtained by earlier workers [8,11,12].…”

“…Bejan [5,6] studied the second law analysis and exergy extraction from solar collector under time varying conditions. Later on, the exergy analysis [7] of flat plate solar collectors for different mode of operations was further advanced by Fuziwara [8], Kar [9], Seltiel and Sokolov [10], Suzuki et al [11], Kar [12], Kar and Shaahid, [13] which are suitable to get the outlet fluid temperature of around 80-100 • C.…”

“…At the other limit low flow rates result in high fluid outlet temperatures with high specific work potential but the energy losses increase due to the temperature differences, therefore, the optimum mass flow rate is required. [1][2][3][4][5][6][7][8][9][10][11][12]. Kovarik and Lesse [1] studied the optimal flow for low temperature solar heat collector while Farries et al [2] studied the energy conservation by adaptive control for a solar heated building.…”

Examination the effectiveness of flow control in a solar system

“…Kar [3] determined the optimal flat-plate collector mass flow rate by maximizing the exergy delivery of the collector as the objective function. Badescu [4] gave an optimal control of flow in solar collector system in case of fully mixed water storage tanks.…”