Exergetic analysis and multiparametric optimization of a novel three-fluid-based organic Rankine cycle evaporative system via Taguchi method

Evaluations were conducted on the thermal performance of an organic Rankine cycle (ORC) system using three fluids as the evaporative system at a low-grade heat source. The modified ORC evaporators were replaced with a three-fluid system, which included hot fluids at the top and bottom and an isopentane working fluid in the middle section. Furthermore, the thermal performance assessment with a hot fluid heat transfer ratio in the outer and inner tubes (Q₂/Q₁) varying from 25:75 to 75:25 has been investigated. The impact of the hot fluid's (Q₂/Q₁) heat transfer ratios to saturated steam on the modified ORC's thermal performance assessment was examined, with an evaporative temperature range of 45–65°C and a pinch point temperature difference (PPTD) of 3–10°C. The Taguchi technique solves multiparameter optimization using the L9 orthogonal array. The findings showed that in three-fluid-based modified ORC systems, the network output, exergetic efficiency, and irreversibility went down with PPTD for all three Q₂/Q₁ cases. For Q₂/Q₁ of 75:25, the ORC's energetic efficiency and overall irreversibility reached their optimum, while a PPTD of 3–10°C reduced the exergetic efficiency by 19.71%. Also, Q₂/Q₁ of 75:25 showed the highest and 200% higher ORC system work done at PPTD of 3°C than Q₂/Q₁ of 25:75—the lowest. Modified ORC network generation, energy output, and heat transfer rate showed excellent results at an evaporative temperature of 58.33°C. For optimal network productivity, Q₂/Q₁ of 75:25 was 160% and 40% greater than 50:50 and 25:75 at 58.33°C, respectively. The three-fluid-based modified ORC system performs better with a 75:25 Q₂/Q₁ ratio. According to Taguchi's analysis, evaporation temperature affects the improved ORC system's thermal, exergy, and network generation. Also, heat transfer ratios (F = Q₂/Q₁) largely affect system irreversibility.