Function-cost optimization of ORC evaporators using integrated FAST analysis and value engineering principles

• First integration of FAST diagrams with Value Engineering for thermal system optimization. • Demonstration of simultaneous cost reduction (22.8 %) and efficiency improvement (15.3 %). • Development of scalable methodology for 40–100 kW ORC systems. • Comprehensive CFD validation with 27 design points and grid independence study. • Realistic value-to-cost ratio of 1.28:1 annually with 9.4-month payback period. The global waste crisis, generating 2.01 billion tons annually and projected to reach 3.40 billion tons by 2050, demands innovative waste-to-energy solutions. Organic Rankine Cycle (ORC) evaporators, comprising 35–40 % of system costs while determining thermal efficiency, have traditionally faced conflicting optimization objectives between cost and performance. This study introduces an integrated Function Analysis System Technique (FAST) diagram and Value Engineering (FAST-VE) framework for evaporator optimization in waste-to-energy ORC systems. The methodology encompasses four phases: (1) baseline cost-performance assessment via bottom-up analysis and thermal modeling; (2) functional mapping using FAST diagrams; (3) Value Engineering workshops with weighted criteria; and (4) CFD validation across 27 design points with grid independence studies. Applied to a 40 kW baseline shell-and-tube evaporator targeting 100 kW, the framework achieved 22.8 % cost reduction ($4158 savings from $22,529) and 15.3 % efficiency improvement. Pareto analysis identified tubes, baffles, and shell as 79 % of costs, guiding targeted optimizations. Heat transfer coefficient rose from 850 to 980 W/m²·K, thermal effectiveness from 0.72 to 0.83, and system efficiency from 32 % to 36.5 %. CFD with 2.5 million elements confirmed superior thermal performance in turbulent configurations. Economic analysis yielded a realistic 1.28:1 annual value-to-cost ratio with 9.4-month payback period and 127 % internal rate of return. CFD validation with 2.5 million elements confirmed superior thermal performance across 27 design points. This FAST-VE integration overcomes traditional trade-offs, offering a scalable methodology for 40–100 kW systems and broader thermal applications, advancing circular economy and sustainable waste management.