超临界工质布雷顿循环热力学分析

Thermodynamic Analysis of Supercritical Working Fluid Brayton Cycle

[目的]N_2O、C_2H_6、SF_6用于制冷剂或朗肯循环的工质,这些工质的临界点和物性特征使其具有作为超临界布雷顿循环工质的潜力。[方法]采用自行开发的MATLAB程序并调用美国国家标准与技术研究所(NIST)发布的REFPROP物性数据库,对超临界N_2O(S-N_2O)、超临界C_2H_6(S-C_2H_6)、超临界SF_6(S-SF_6)布雷顿循环进行热力学分析,并与超临界CO_2(S-CO_2)布雷顿循环进行对比。选择再压缩循环方式,分别计算得到了透平入口温度为300～550℃、压力为15～25 MPa,预冷器出口温度为32℃和47℃的各种工况。[结果]热效率计算表明:S-N_2O、S-C_2H_6、S-SF_6再压缩循环均表现较高的热效率,且比相对应的S-CO_2再压缩循环的热效率高,再压缩循环热效率总是随着透平入口温度的提高而提高,但提高压力不一定总是提高循环热效率,提高预冷器出口温度导致循环热效率显著下降。流量计算表明,S-N_2O、S-C_2H_6、S-SF_6、S-CO_2循环的总质量流量和透平入口体积流量均远高于同等参数条件的蒸汽朗肯循环,但这四种超临界工质循环的透平出口体积流量相近。[结论]S-N_2O、S-C_2H_6、S-SF_6、S-CO_2循环均有潜在应用价值。

[Introduction]N2O、C2H6、SF6 are used as refrigerants or working fluids in Rankine cycle. The critical and physical properties of these refrigerants make them as potential supercritical Brayton cycle fluids. [Method]By using a self-developed M ATLAB program and REPROP physical property database published by the National Institute of Standards and Technology（ NIST）,thermodynamic analysis of supercritical N2O（ S-N2O）,supercritical C2H6（ S-C2H6） and supercritical SF6（ S-SF6） Brayton cycle was conducted with comparison to supercritical CO2（ S-CO2） Brayton cycle. Recompression cycle was selected for study,and a variety of conditions were calcuted with turbine inlet temperature in range of 300 ～ 550 ℃,pressure in range of 15 ～ 25 MPa,and pre-cooler outlet temperature of 32 ℃ and 47 ℃. [Result]Thermal efficiency calculation results show that S-N2O,S-C2H6,S-SF6 Brayton cycles all exibit high efficiency,and the efficicy is higher than the coresponding thermal efficiency of S-CO2 Brayton cycle,and the thermal efficiency is alw ays improved with the increase of the inlet temperature of the turbine,but the increase of the pressure does not alw ays increase the cycle thermal efficiency. The increase of the outlet temperature of the precooler leads to a significant decrease in the cyclic thermal efficiency.. Flow calculation shows that the total mass flow rate and turbine inlet volume flow rate of S-N2O,S-C2H6,S-SF6,S-CO2 cycle are much higher than steam Rankine cycle with similar parameters,but the turbine outlet volume flow rates of these four supercritical fluids are close to each other. [Conclusion]S-N2O,S-C2H6,S-SF6 and S-CO2 cycle all have potential application value.