结霜工况下空温式翅片管气化器传热试验研究

为深入掌握低温液体在空温式翅片管汽化器内的气化情况以及其与翅片管表面霜层生长的相互影响规律,以液氮为介质进行了低温液体在空温式翅片管气化器内的气化试验。通过热电偶和刻度带分别对翅片管上不同位置的温度和霜层厚度进行了测量,并分析了翅片管表面霜层的生长规律及翅片管内低温液体的流动特性。结果表明:气化器表面结霜过程受冷表面温度影响较大,冷表面温度越低,结霜速率越大,霜层越厚。结霜工况下的气化器工作状态分预冷和稳态两种工作状态。预冷工作状态低温液体进入气化器后迅速气化,其过程包含气液两相和单气相两个换热段。稳态工作状态低温液体在气化器内气化经历单液相、气液两相、单气相三个换热段,单液相段翅片管表面结霜最为严重,单气相段翅片管表面无霜晶形成。因此认为,可通过分状态分段设计空温式翅片管气化器从而减弱结霜对翅片管传热的影响,提高气化器换热效率。

Experimental study on heat transfer characteristics of air-heating cryogenic finned-tube vaporizer under frosting conditions

A gasification test on the cryogenic liquid in the air-heated finned-tube vaporizer was conducted with liquid nitrogen as working medium to investigate the interaction effect between the gasification of cryogenic liquid in the vaporizer and the growth of frost thickness on the surface of the finned tube.The temperature and frost thickness of the finned tube at different position were measured by thermocouples and scale belts,and the growth rule of frost layer on the surface of the finned tube and the flow characteristics of cryogenic liquid in the finned tube were analyzed.It is shown that the cold surface temperature has a great influence on the frosting process on the surface of the vaporizer.The lower the cold surface temperature is,the higher the frosting rate is and the greater the frost thickness is.The operation of the vaporizer under frosting conditions consists of two states:pre-cooling state and stable state.The former is that the cryogenic liquid gasifies rapidly when entering into the vaporizer and contains two heat transfer sections of gas-liquid two phase and single gas phase;the latter is that the cryogenic liquid gasifying in the vaporizer goes through three heat transfer sections of single liquid phase,gas-liquid two phase and single gas phase.The frosting is relatively serious on the surface of the finned tube of single liquid phase while there is no frost at the finned tube of single gas phase.It is concluded that the air-heated finned-tube vaporizer can be designed according to states and sections to weaken the effect of frosting on the heat transfer of finned tube and improve the heat transfer efficiency of vaporizer.