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TBAB包络化合物浆的管内流动和传热特性研究
其他题名Study on Flow and Heat Transfer Characteristics of TBAB Clathrate Hydrate Slurry in Pipes
肖睿
导师冯自平
2008-06-02
学位授予单位中国科学院广州能源研究所
学位授予地点广州能源研究所
学位名称博士
关键词四丁基溴化铵 包络化合物 潜热输送 流动 传热
摘要四丁基溴化铵(TBAB)包络化合物浆(CHS)是由TBAB水溶液在常压下被冷却到0~12 ℃时生成的一种固-液混和浆状流体,是一种适用于中央空调、区域供冷等领域的高密度潜热输送冷媒材料。CHS具有良好的流动性,可以像普通流体一样方便的通过泵和管道系统输送。由于存在固-液相变,CHS的冷量输送密度远高于相同温差下的冷水,因此可以使冷媒循环流量大幅降低,从而降低循环能耗,实现节能。 首先在整理和归纳国内外已有研究成果的基础上,通过实验补充,全面的掌握了TBAB及TBAB包络化合物浆的相关基础热物理性质;其次系统介绍了非牛顿流体的基本本构关系以及几种经典的非牛顿流体模型;然后是对CHS在水平管内的流动阻力和对流换热特性的实验研究,分别在A型和B型、层流和湍流、不同管径、以及定热流密度等条件下进行了实验,获得了大量实验数据;最后对管内流动和传热分别建立了理论分析模型并进行数值求解,数值计算结果与实验结果进行了对比。 根据不同管径下的层流流动实验数据确定了在固相含量χ < 30%时A型和B型CHS都属于Bingham流体的结论,而当χ > 30%后则表现出比较明显的Herschel- Bulkley流体特性,不能再按Bingham流体进行处理。由实验数据确定了A型和B型CHS的重要流变参数——塑性粘度η和屈服应力τ0——与固相含量χ之间的变化关系。 对于流动阻力实验,分别研究了定固相含量和定流速等条件下的阻力变化规律。发现了定固相含量流动下的“阻力降低区”,以及定流速条件下的“再层流化”现象。在定流速条件下,除了过渡区以外,在层流区和湍流区CHS的流动阻力都随固相含量χ的增加而增加。按Metzner-Reed通用雷诺数ReM定义的层流-湍流转变临界雷诺数ReMc与固相含量χ之间大体上呈单调递增的变化关系。最后得到了CHS的阻力系数f与通用雷诺数ReM之间的对数坐标图,在层流区有f•ReM = 16,与经典牛顿流体在形式相统一,在湍流区则通过数据拟合得到了阻力系数关联式,A型和B型CHS的湍流阻力关联式相同。 对于管内对流换热实验,热边界条件为定热流密度,分别研究了定固相含量(定Pr数)和定流速等条件下的对流换热系数变化规律。发现了在定固相含量条件下存在与流动中的“阻力降低区”相似的“换热系数降低区”。在定流速条件下,除了过渡区以外,在层流区和湍流区CHS的对流换热系数α基本上都随固相含量χ的增加而增加。最后通过数据拟合,分别得到A型和B型CHS在层流和湍流下的Nu数关联式,由关联式计算的结果与实验结果之间的相对偏差为±20%。 最后,对管内流动和传热分别建立了层流和湍流条件下的理论分析模型并进行了数值求解。其中层流流动模型基于Bingham流体理论,湍流流动模型基于RNG k-ε湍流理论。对流换热理论模型则在流动模型的基础上,通过引入用以描述相变对对流换热特性的影响的“焓-多孔介质法”(Enthalpy-Porosity)而建立。通过与实验对比发现流动模型计算得到的阻力偏高,而对流换热模型计算得到的换热系数则偏低。
其他摘要The Tetra-n-Butyl-Ammonium Bromide (TBAB) Clathrate Hydrate Slurry (CHS) is one kind of solid-liquid suspension slurry, which is produced from TBAB aqueous solution in the temperature 0-12 ℃ under normal atmosphere. It can be used as a secondary refrigerant for high-density latent heat transportation in central air conditioning and district cooling, etc. CHS has good fluidity and so can be transferred conveniently by pumps and pipes like normal liquid. Because phase change happens between solid and liquid, the density of cold transportation of CHS is much higher than that of the cold water under the same temperature differences, then the circulating flux of refrigerant decreases dramatically, which results in the decrease of pump power consumptions, so the energy saving can be achieved. Firstly, based on the current researches throughout the world, the comprehensive thermophysical properties of TBAB and CHS have been obtained through some experimental supplements. Secondly, the general constitutive relationship of non-Newtonian fluid and several classical rheological models have been introduced. Then, the flow and heat transfer about CHS in the horizontal pipes have been studied through experiments. Data were obtained under conditions of type A or type B, laminar or turbulent, pipes with different diameter, and constant heat fluxs, etc. At last, the theoretic models of flow and heat transfer in the horizontal pipes have been established and simulated, and the results were compared between calculations and experiments. Based on the experimental data of laminar flows, the CHS of both type A and type B are confirmed as Bingham fluid when solid fraction χ < 30%. When χ >30%, however, it is no longer true because the Herschel-Bulkley rheological characteristics prevail gradually. The relationship between plastic viscosity η and solid fraction χ is verified by experimental data, so is done between yield stress τ0 and χ. In the flow experiments, the flow resistance was investigated under the conditions of constant solid fractions and constant flow velocities, respectively. A region of weakened flow resistance at constant solid fractions and a phenomenon of relaminarization at constant flow velocities were observed. Except the region of transition flow, the flow resistance increases monotonically with the solid fraction χ in the regions of both laminar and turbulent flow under the constant flow velocities. By and large, the relationship between the critical Reynolds number ReMc and solid fraction χ shows as a monotone increasing function, in which ReMc is defined according to Metzner-Reed Reynolds number ReM. At last, the logarithmic plot between the Fanning resistance coefficient f and the universal Reynolds ReM was obtained accoding to experimental data. From which the relationship of f•ReM =16 was confirmed for CHS in the region of laminar flow, which has the same form with the classical Newtonian fluids. And in the region of turbulent flow, the same correlation between f and ReM was fitted for CHS of the Type A and Type B. In the convectional heat transfer experiments, the thermal boundary conditions of constant heat flux were imposed on. The convectional heat transfer coefficient was investigated under the conditions of constant solid fractions (i.e. constant Prandtl number Pr) and constant flow velocities, respectively. A region of weakened heat transfer coefficient at constant solid fractions, similar with the region of weakened flow resistance in flow experiments, was observed. Other than in the region of transition flow, the convectional heat transfer coefficient α increases monotonically with the solid fraction χ in the regions of both laminar and turbulent flow under the constant flow velocities. At last, the correlations of Nusselt number Nu for both type A and type B were fitted according to the experimental data in the regions of laminar flow and turbulent flow, respectively. These correlations were compared with experimental results and show a maxmum error equal to ±20%. Lastly, the analytical models of flow and convectional heat transfer in the horizontal pipes were established and simulated. The model of laminar flow is based on the theoretics of Bingham fluid, and the model of turbulent flow is derived from the RNG k-ε turbulent theoretics. Based on the flow models mentioned above, the convectional heat transfer model was founded through introducing the technique of Enthalpy-Porosity, which is used to describe the effects of phase change. Through the comparisons between calculations and experiments, it was found that the flow resistance was overestimated, while the convectional heat transfer coefficient was underestimated consistently by the analytical models.
页数142
语种中文
文献类型学位论文
条目标识符http://ir.giec.ac.cn/handle/344007/3997
专题中国科学院广州能源研究所
推荐引用方式
GB/T 7714
肖睿. TBAB包络化合物浆的管内流动和传热特性研究[D]. 广州能源研究所. 中国科学院广州能源研究所,2008.
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