ORC工况R134a在强化管内流动换热研究

Investigation of R134a Flow Boiling in Enhanced Tubes Under ORC Conditions

ORC是余热回收的重要方式,蒸发器设计是其中非常重要的环节。针对目前ORC工况下有机工质在强化管内流动换热的实验数据非常缺乏的现状,本文进行了实验研究,得到ORC工况下R134a在强化管内流动换热数据,为ORC换热器的设计提供参考。本文得到了换热系数和壁温随干度的变化规律,分析了质量流量和饱和压力等因素对换热效果的影响。结果表明,换热系数随干度增加而降低,增加质量流量可提高换热系数,而增加系统压力不利于强化换热。通过对比光管和强化管的实验数据,可以看出强化管可以显著地抑制壁温分离,从而强化换热。

ORC is an effective method to recover waste heat,in which the evaporator is a vital part.However,flow boiling characteristics of organic fluids in enhanced tubes for ORC conditions has not been studied well.Therefore,experiments of R134a flow boiling in enhanced tubes for the ORC working conditions were conducted to obtain the flow boiling characteristics and provide references for the design of evaporators.In this study,variation of heat transfer coefficient and wall temperature with vapor quality is obtained,and the effects of mass flow rate and saturation pressure on the heat transfer are analyzed.The results showed that the heat transfer coefficient decreases with the increase of vapor quality.Increasing mass flow rate can increase heat transfer coefficient,while increasing system pressure is not conducive to heat transfer enhancement.Comparison between the experimental data of smooth tube and enhanced tube shows that the enhanced tube can significantly inhibit wall temperature separation,thereby enhancing heat transfer.