Department of Chemical Engineering, Northeastern University, Boston, Massachusetts 02115, United States.
Cain Department of Chemical Engineering, Louisiana State University, Baton Rouge, Louisiana 70803, United States.
J Phys Chem B. 2020 Jun 4;124(22):4536-4550. doi: 10.1021/acs.jpcb.0c01860. Epub 2020 May 21.
Molecular simulations were performed to evaluate mixtures of fluorinated refrigerants with deep eutectic solvents (DESs), for potential use in single-effect absorption refrigeration cycles that use low quality waste heat sources at temperatures of ∼80 °C. The refrigerants considered were the hydrofluorocarbon R245fa and the hydrofluoroolefins R1234zeE and HFO1336mzzE, whereas the DESs evaluated were 1:2 molar mixtures of choline chloride with either ethylene glycol (ethaline) or levulinic acid (levuline) as hydrogen bond donors (HBDs). Assuming the same cycle operating conditions, the waste heat cycle efficiency η was computed for all working fluid mixtures from molecular simulation results of the mixture densities and Henry's law constants of the refrigerants in the DESs, coupled with phase equilibrium calculations and the enthalpies of the pure refrigerants. The largest efficiency was obtained for the mixture R245fa-ethaline (η = 6.82), followed by R245fa-levuline (η = 4.64) and HFO1336mzzE-levuline (η = 2.10). These modest efficiency values could be further increased by tailoring the cycle operating conditions to each particular refrigerant-DES system, as well as optimizing our choice of working fluid mixtures, neither of which we attempted in this study. Strong interactions were observed between the chlorine anions and some of the hydrogen atoms of the refrigerants, but in general the cation-refrigerant and HBD-refrigerant interactions are weaker compared to the refrigerant-refrigerant interactions. Refrigerant molecules have the largest diffusivities and make the cations, anions and HBD to move faster compared to systems of DESs without refrigerant; in general, species in refrigerant-ethaline mixtures have larger diffusivities compared to those for refrigerant-levuline mixtures. We also computed waste heat cycle efficiencies for the same R134a-DES mixtures studied in our previous work, finding significant differences between the efficiencies determined from molecular simulation data and those determined before using the COSMO-RS approach using two standard parametrizations. This observation suggests that further work is needed to improve the accuracy of the COSMO-RS predictions for these systems.
采用分子模拟方法评估了氟化制冷剂与深共晶溶剂（DESs）的混合物，以潜在应用于单效吸收式制冷循环，该循环使用 80°C 左右的低品位余热热源。所考虑的制冷剂为氢氟碳化合物 R245fa 以及氢氟烯烃 R1234zeE 和 HFO1336mzzE，而评估的 DES 则是 1:2 摩尔比的氯化胆碱与乙二醇（乙撑）或乙酰丙酸（乙酰）作为氢键供体（HBD）的混合物。在假设相同的循环操作条件下，根据制冷剂在 DES 中的混合物密度和亨利定律常数的分子模拟结果，以及相平衡计算和纯制冷剂的焓，计算了所有工作流体混合物的余热循环效率 η。从模拟结果中得到的效率值最大的混合物是 R245fa-乙撑（η = 6.82），其次是 R245fa-乙酰丙酸（η = 4.64）和 HFO1336mzzE-乙酰丙酸（η = 2.10）。通过针对每个特定的制冷剂-DES 系统调整循环操作条件以及优化我们对工作流体混合物的选择，可以进一步提高这些适度的效率值，而在这项研究中，我们都没有尝试这些方法。观察到制冷剂中的氯阴离子与某些氢原子之间存在强烈相互作用，但通常阳离子-制冷剂和 HBD-制冷剂之间的相互作用比制冷剂-制冷剂之间的相互作用弱。制冷剂分子具有最大的扩散系数，使阳离子、阴离子和 HBD 比没有制冷剂的 DES 系统更快地移动；一般来说，在制冷剂-乙撑混合物中的物质比在制冷剂-乙酰丙酸混合物中的物质具有更大的扩散系数。我们还计算了与我们之前工作中研究的相同 R134a-DES 混合物的余热循环效率，发现从分子模拟数据确定的效率与使用两种标准参数化方案的 COSMO-RS 方法之前确定的效率之间存在显著差异。这一观察结果表明，需要进一步的工作来提高 COSMO-RS 对这些系统预测的准确性。
