【作者】 曹滨斌；

【导师】 李惟毅；

【作者基本信息】 天津大学 ， 动力工程与工程热物理， 2010， 博士

【摘要】 本课题以近年国际传热领域研究热点——单环路脉动热管（CLPHP）为研究对象,以开发新结构、试用新工质为目的,运用可视化实验与混沌动力学方法进行分析,所得结论为其在实际工程领域的应用提供了实验与理论基础。通过对实验现象的观察,传热性能的计算,并与CLPHP启动运行时测得时间—温度曲线的比较,得到特征温度曲线,其能够体现管内工质运行状态,反应传热情况,为实际应用中快速判断脉动热管运行情况提供方便。在分析传统型CLPHP蒸发段缓慢受热时启动失败的原因基础上,以增强管内压力波动为目的,通过顶部设置扩容室,提出新型扩容型CLPHP,实验证明可有效提高脉动热管启动性能。通过对新型扩容型CLPHP传热性能影响因素的研究表明:提高加热功率,可以降低启动温度,但加热功率过高,则导致干烧;重力对运行起促进作用,所以脉动热管竖直底加热时传热性能最佳;低充液率时,需对脉动热管进行局部点加热才能启动并维持运行,定性说明了运行过程具有混沌动力学的“蝴蝶效应”特征;增大扩容室容积可进一步降低脉动热管启动温度,提高传热性能,但加热功率较高时,扩容室内工质存液增加,导致传热性能下降。采用酒精为脉动热管工质,研究表明:工质表面张力决定充液初始分布状态,工质汽化潜热与饱和温度决定启动温度,工质汽化潜热与比热决定传热性能,因此,应选择汽化潜热较小,饱和温度较低且比热较大的流体作为扩容型CLPHP的工质。以近年国际传热领域另一研究热点——纳米流体为工质（TiO₂-水）,研究表明:利用分散剂所得纳米流体更加均匀稳定;纳米流体强化传热作用明显,加热水60℃-65℃范围内,1.5%TiO₂-水纳米流体提高传热功率20%左右,提高当量导热系数50%左右;加热水70℃-75℃范围内,0.7%TiO₂-水纳米流体提高传热功率20%左右,提高当量导热系数50%左右;纳米颗粒在基流体中的分散性,是强化作用实现的关键,一旦发生团聚沉降,则强化作用消失,并导致传热恶化。应用混沌动力学对扩容型CLPHP的运行传热过程进行分析,通过相空间重构表明:当CLPHP处于稳定运行阶段时,吸引子呈结构紧凑的团状分布;处于启动阶段时,吸引子均匀分布于相空间;处于干烧阶段时,吸引子呈狭长的带状分布。通过混沌动力学特征参数的计算,从定量角度判断CLPHP传热过程具有混沌动力学特征,且随着当量导热系数的增大,最大Lyapunov指数减小,最佳维数升高,最佳时间延迟减小。更多还原

【Abstract】 Closed-loop pulsating heat pipe （CLPHP）, which is a research hot spot at present in heat transfer area, is investigated and researched in this dissertation. By carrying out visualization experiments and chaotic dynamic calculations on CLPHP, new structures are developed and new working fluids are tested. The conclusions gained in this dissertation can provide directions for engineering applications of the CLPHP.Characteristic temperature curve is gained by experimental phenomena observation and heat transfer calculation, and then, it is compared with the time-temperature curve which is measured during its start-up. The characteristic temperature curve embodies the states of the working fluids and the heat transfer status inside the heat pipes, which can be used to judge the operation situation of CLPHP in practical application.The causes of failure in start-up of the traditional CLPHP when its evaporating section was slowly heated are analyzed. In order to enhance the pressure fluctuation inside the pipe, the dilatant closed-loop pulsating heat pipe is introduced and investigated. And the experiment results show that this new kind of CLPHP possesses better starting performance than the common type.The heat transfer performances of the dilatant closed-loop pulsating heat pipe are researched in this dissertation and some important conclusions are gained. When the heating power increases, the starting temperature decreases. But when the heating power is too high, dry burning occurs. There is obvious promotion of the gravity to its operation. When the charging ratio is low, spot heating is necessary to its starting and operation, which qualitatively proves that the Butterfly Effect exists in the operation of CLPHP. By enlarging the dilatant room, the heat transfer performances of the dilatant closed-loop pulsating heat pipe could be improved, meanwhile, the starting temperature could be further decreased. But when the heating power is too high, more working fluids appear in the dilatant room, which leads to the heat transfer deterioration.By using alcohol as the working fluid, it is found that the initial charging distribution is determined by the surface tension of the working fluid while the starting temperature are determined by the working fluid’s latent heat of vaporization and its saturation temperature. And the latent heat of vaporization and the specific heat of the working fluid affect the heat transfer performances greatly. Based on these conclusions, it is believed that the working fluids with low latent heat of vaporization, low vaporization temperature and high specific heat are fit for the dilatant closed-loop pulsating heat pipe.By using nano-fluids （TiO₂-water） as the working fluids, it is found that, the nano-fluid is much more stable when the dispersant is added in, and the heat transfer performance is improved greatly. In the temperature range 60℃-65℃, by using TiO₂-water of 1.5%, the heat transfer rate increases about 20% and the equivalent thermal conductivity increases about 50%. In the temperature range 70℃-75℃, by using TiO₂-water of 0.7%, the heat transfer rate increases about 20% and the equivalent thermal conductivity increases about 50%. A good dispersion of the nano-particles in the based fluid is the key to improve the heat transfer. When the agglomeration and sedimentation occur, the heat transfer enhancement turns to the heat transfer deteriorationThe heat transfer process of the dilatant closed-loop pulsating heat pipe is analyzed by using chaotic dynamic method and phase space reconstruction. It is found that, when the operation of CLPHP is stable, the attractor morphology is a compactly spherical distribution. When the CLPHP is at the start-up stage, the attractor distributes symmetrically in the phase space. When the CLPHP is at the dry burning stage, the attractor morphology is a long-narrow zonal distribution. By calculating the characteristic parameters, the heat transfer process of the CLPHP is found to be chaotic dynamic. With the increase of the equivalent thermal conductivity, the maximum Lyapunov index and the optimum delay time decrease while the optimum dimension increases.更多还原