Experimental Study On Flow Boiling Heat Of Mixed Refrigerant R123/R245fa

Organic Rankine cycle power generation technology is one of the effective means to solve the power supply problem of deep-sea equipment.One of the factors affecting the power generation efficiency of the organic Rankine cycle is the selection of the type of organic working fluid.The non-azeotropic mixed working fluid is used as the circulating working fluid.The unique temperature slip characteristic of the non-azeotropic mixed working fluid in the phase transformation process can reduce the irreversible loss caused by the heat transfer temperature difference and improve the power generation efficiency of the system.In this paper,the flow boiling heat transfer and pressure drop characteristics of non-azeotropic mixed working fluid and its pure components are studied.In order to clarify the basic variation law of flow boiling heat transfer of non-azeotropic mixed working fluid,an experimental system of flow boiling heat transfer of organic working fluid was built independently.R123,R245fa and their mixture were used as working fluid to conduct experimental research on flow boiling characteristics.The experimental operating parameters were mass flow rate 21-37kg/m~2·s and heat flow density 13-19.6k W/m~2.Two heating surfaces,smooth surface and metal foam,were selected to compare and analyze the influence of heating surface structure on heat transfer performance.The flow boiling experiment results of R123 and R245fa pure working fluid show that:Under the smooth heating surface structure,the heat transfer coefficients of R123 and R245fa have similar trends with operation parameters.The heat transfer coefficients decrease with the increase of mass flow rate and increase with the increase of heat flow density,but the heat transfer coefficients of R245fa are much higher than those of R123.Under the metal foam structure of heating surface,both of the heat transfer coefficient is much higher than smooth and heating surface structure of the heat transfer coefficient,most of the operation parameters under the condition of metal foam under the structure of heating surface heat transfer coefficient of R245fa with heat flux density increases,but in G=21kg/m~2·s under the condition of heat transfer coefficient with the increase of heat flux decline after rising first;The pressure drop is always maximum at lower mass flow rate under both heating surfaces.The flow boiling experiment results of R123/R245fa non-azeotropic mixed working fluid with a component ratio of 80/20%show that the heat transfer coefficient of the mixed working fluid is between that of the pure working fluid and that of the pure working fluid,and the increase of the heat transfer coefficient is larger than that of the pure working fluid at higher heat flux density.Under the metal foam heating surface structure,the heat transfer coefficient of the mixed working fluid also increases first and then decreases with the increase of heat flux at G=21kg/m~2·s,and the heat flux at the decreasing point is larger and smaller than that at the decreasing point of R245fa.When the mass flow rate is larger,the pressure drop increases with the increase of heat flux,while when the mass flow rate is smaller,the pressure drop increases first and then decreases.It is found that the heat transfer coefficient of the mixed fluid with a higher proportion of R245fa increases with the increase of heat flow density.The heat transfer coefficient of 35/65%and 22/78%mixed fluid at q=19.6k W/m~2exceeds that of R245fa under the same working condition.The pressure drop of 35/65%and22/78%mixed fluid is smaller than that of 78/22%.