Multi-objective optimization design of working fluids for Carnot battery system based on CAMD

In today's digital age, data centers play a crucial role as an indispensable infrastructure, but their operation consumes significant energy and leads to severe environmental issues due to substantial carbon emissions. Therefore, this paper focuses on recovery of waste heat resources from data centers by introducing a cold layout thermal integrated Carnot battery technology. The Carnot battery system not only enables the recovery of waste heat but also provide cooling to the data center simultaneously. Working fluid plays a crucial role in Carnot battery system, thus a computer-aided molecular technology-based model for designing the working fluid is established in this study to obtain better thermodynamic performance. This model employs four physical property parameters to characterize the working fluid, and a multi-objective synchronous optimization approach is employed to integrate the working fluid design with the thermodynamic process of the system. Through sensitivity analysis, it is observed that the power-to-power efficiency (η_p2p) exhibits a positive correlation with the increase in critical temperature (T_crit) and a negative correlation with boiling point temperature (T_boil) and critical pressure (P_crit). η_ex and ρ_sto both increase with the increase of T_boil and P_crit, and decrease with the increase of T_crit and ω. It becomes evident that the maximization of η_p2p, η_ex and ρ_sto concurrently is unattainable. Therefore, a multi-objective optimization is adopted to achieve a balance between the three performance indicators, and using T_boil, T_crit, P_crit, and ω as decision variables. The results reveal that the optimal compromise solution is CH3CH2N=C=CH2. It is worth noting that molecules with the value of T_boil in the range of 350–580 K, the value of T_crit in the range of 500–800 K, the value of P_crit in the range of 20–30 bar, and the value of ω in the range of 0.2–0.5 meet the objectives of high power-to-power efficiency, high exergy efficiency, and high energy storage density.