Generalized mixed-mode, heat-transfer studies to enhance power and work atoptimum power in reciprocating regenerative Stirling-like and Carnot heat engines with interactive finite thermal reservoirs

This study explores how to enhance both the power and the efficiency (at op timum power) for the family of reciprocating Stirling-like heat engines (in cluding Carnot) with ideal regeneration and either finite or infinite heat reservoirs. To accomplish this, a generalized mixed-mode, heat-transfer app roach is developed and employed at cycle thermal ends. Additionally, the di fference in the effect on power optimization of operating with either inter active or non-interactive finite reservoirs is examined. The approach developed makes use of a unique time symmetry procedure to min imize cycle time. This procedure ensures the proper allocation of the hot- and cold-end, heat-exchanger capacitance. Furthermore, time symmetry ensure s the concurrent employment of the first and second laws of thermodynamics. This in turn guarantees the minimization of internal entropy generation an d the maximization of specific cycle work (for a given set of operating tem peratures). The general case formulation produces a semi-decoupling of the solution exp ressions for the upper and lower power-optimized operating temperatures. Th is semi-decoupling allows the use of various combinations of single and mix ed-mode, heat-transfer arrangements at the hot and cold thermal ends of the se cycles. Hence, semi-decoupling permits examination of the power and work potentials of different combinations of heat modes under power-optimized c onditions. The results point conclusively to the strong preference of using the radiation mode (with or without transfer by the linear mode, but bette r with as little as possible) in the high-temperature-end, heat-exchange pr ocess and of using essentially only linear modes at the low-temperature end of the cycle (i.e. only as small a percentage as possible by radiation). S uch cycles are found capable of exceeding the one-half ideal work limit of power-optimized cycles that exclusively employ linear modes at both thermal ends (i.e. W-opt greater than 1/2 W-rev). Also, the efficiency at optimum power of these cycles exceeds the Curzon and Ahlborn efficiency (i.e. eta(o pt) greater than 1 - (T-L/T-H)(0.5)). No other combination of heat-transfer modes is found capable of exceeding either the Curzon and Ahlborn efficien cy or the 1/2 W-rev limit for power-optimized cycle work for such cycles. Finally, comparing the effects of interactive and non-interactive heat rese rvoirs on power optimization shows that the heat-exchanger operation (outle t temperatures) should also be included in the overall optimization procedu re.