超临界R134a在ORC系统中的换热特性分析

Numerical Investigation on Heat Transfer Characteristics of R134a in the Supercritical Organic Rankine Cycles

采用有限元分析软件FLUENT对超临界有机朗肯循环系统中的换热器进行数值分析,进而对其进行设计和优化。超临界R134a在长为2100mm,直径为4mm的光管换热器中分别进行向上流动和向下流动。换热边界条件是定热流密度,流体的进口压力P为4.5MPa,进口温度Tin为349K。分别探究热流密度q、质量流量G、热流质量比q/G和浮升力对传热特性的影响。采用无量纲数Bo来预判浮升力对传热的影响。虽然Morky的工作流体不是超临界R134a,但他们的经验公式也能用来更好地预测超临界R134a在光管中向上流动的传热特性。

This paper uses the FLUENT software to numerically analyze the heat transfer of the heat exchanger which is one of the significance part in the supercritical organic Rankine cycle system,and then design and optimize it.The supercritical R134a flows upward and downward,respectively,in a straight tube that have a length of 2 100 mm and diameter of 4 mm.The thermal boundary condition is the constant heat flux.The operation pressure P is 4.5 MPa,and the inlet temperature is 349 K.The heat flux q,mass flow rate G,heat flux mass ratio q/G,and buoy.ancy were investigated to analyse heat transfer characteristics.The dimensionless number Bo is used to predict the effect of buoyancy.Although Morky’s empirical formula obtained base on the working fluid of supercritical CO2,However,the heat transfer characteristics of supercritical R134a flowing upward also can be predicted better by their fomula.