【作者】 方奇；

【导师】 毛佳妮；

【作者基本信息】 中国计量大学 ， 能源计量与测试技术， 2020， 硕士

【摘要】 环路热管(Loop Heat Pipe,LHP)作为一种新型两相热控技术,以其换热能力强、位置布置灵活、可实现热量的远距离传输等独特优点在地面以及太空电子设备冷却中获得了广泛应用。在整个系统中,毛细芯微槽蒸发器作为相变换热核心部件,对系统的性能起着至关重要的作用。本文采用数值模拟的方法研究了毛细芯微槽蒸发器两相换热及极限工况运行特性。首先,本文针对商业软件Fluent采用体积平均法理论求解多孔介质相变传热问题时引起CSF模型无法准确表征毛细力的问题,在两相混合模型基础上进行了修正。同时,根据汽-液交界面附近毛细力的作用特点,对其进行了表征,建立了毛细芯微槽蒸发器计算单元的三维轴对称数学模型,并采用已有文献的实测数据对本文模型的准确性进行了验证。结果表明,仿真趋势与文献实测数据趋势一致,且误差在10%以内。然后,针对无泵辅助的环路热管系统,通过控制变量法,研究了孔隙率、渗透率、有效直径、热流密度载荷与外环路压降对蒸发器传热特性的独立影响。研究结果表明:随着孔隙率、有效直径或外环路压降的增大,计算单元入口流量减小,计算单元最高温度、出口汽相百分数与相变换热比例出现不同程度的增长。而较大的渗透率,会使得入口流量相应增大,计算单元最高温度、出口汽相百分数与相变换热比例则相应减小。虽然热流密度载荷的增大也会引起入口流量增加,但是其对最高温度、出口汽相百分数以及相变换热比例的影响特性则与渗透率相反。最后,针对泵辅助型环路热管系统的驱动条件,以界面热流密度和入口供液流量作为变工况参数,划分得到4种典型工况区间,并且预测分析了蒸发器微型化过程的流动-传热极限特性。结果表明:当热流密度一定时,随着微型化比例减小,3条临界流量线呈交汇趋势,对应的两相安全区流量变化范围不断缩小,且极限控温温度对应的液位相对高度显著降低,液面逼近毛细芯下界面;当入口供液流量一定时,随着微型化比例减小,两相安全区热流密度变化范围几乎不变,且极限控温温度对应的液位相对高度维持在毛细芯2/3高度处。更多还原

【Abstract】 Currently,with the enhancement of electronic equipment integration level and performance,thermal management of electronic components with high heat flux turns out to be a research hotspot.Loop Heat Pipe(LHP),as a novel two-phase thermal control technology,gained its extensive application in the cooling of both electronic devices in spacecraft and communication facilities on ground with its unique advantage in high heat transfer capacity,flexible location layout,and long-distance transmission of heat,ect.In whole system,porous wick micro-channel evaporator is a core component in heat transfer and exerts critical impact on system performance.Numerical simulation method is adopted in this context to investigate two-phase heat transfer and critical working condition characteristics of porous wick micro-channel evaporator.First of all,the volume averaging method is taken in commercial software Fluent to investigate heat transfer process in porous media,and it will cause CSF(Continuum Surface Force)model fail to characterize capillary force.Thus,on the basis of two-phase hybrid model and characteristics of capillary force near vapor-liquid interface,capillary force was characterized,and a three-dimensional axisymmetric model of the calculation element for porous wick micro-channel evaporator was established.The accuracy of the model was verified by the measured data of the existing literature.And the results showed that simulation results are in agreement with experiment ones in trend.Errors of simulation results are about 10%.Then,the driven condition of the loop heat pipe system without pump assistance taken into consideration,the independent effects of porosity,permeability,effective diameter,heat flux load and external loop pressure drop on heat transfer characteristics of the evaporator are investigated through controlling variable method.The research results show that with the increasement of porosity,effective diameter or external loop pressure drop,inlet volume flow rate of the calculation element declines and maximum temperature,outlet vapor volume fraction,external loop pressure drop as well as phase change heat transfer percentage enjoy different degrees of growth.A larger permeability will be beneficial to the increase of inlet volume flow rate,but contribute to a smaller maximum temperature,outlet vapor volume fraction and phase change heat transfer percentage on the contrary.Compared with permeability,although the increase of heat flux load leads to the increase of inlet volume flow rate,too,it exerts opposite impact on maximum temperature,outlet vapor volume fraction and phase change heat transfer percentage.Finally,a pump-assisted loop heat pipe system taken into consideration,with heat flux load on device interface and inlet liquid supply flow rate as variable operating parameters,four kinds of typical operation intervals were obtained.Additionally,the ultimate flow and heat transfer characteristics by the device miniaturization were predicted.The results show that,under the same heat flux condition,with the decrease of miniaturization ratio,three critical flow lines have the trend of convergence,and the flow range in two-phase safety region is shrinking.The relative height of vapor-liquid interface corresponding to the limit control temperature decreases significantly and the interface approaches the lower border of the capillary wick.Under the same liquid supply flow condition,with the decrease of miniaturization ratio,the heat flux range in two-phase safety region is almost unchanged,and the relative height of vapor-liquid interface corresponding to the limit control temperature is maintained at 2/3 height of the capillary wick.The conclusion of the study will provide theoretical reference on the miniaturization design and selection of optimum operating parameters.更多还原