【作者】 朱蒙生；

【导师】 邹平华；

【作者基本信息】 哈尔滨工业大学 ， 供热、供燃气、通风及空调工程， 2009， 博士

【摘要】 暖通空调系统中泵的能耗在整个建筑能耗中所占比例非常大,以往围绕其进行的节能降耗研究多集中在输配系统的设计及运行调节等方面。由于在液体中加入少量的高分子聚合物或表面活性剂可导致其流动阻力大幅度减少,即出现添加剂减阻现象,此时不但流体输送过程的摩阻系数显著下降,而且会因传热性能降低而减少沿程输送的热量(或冷量)损耗。如果能够将添加剂减阻技术应用于暖通空调系统,不仅能够大大降低输配系统中水泵的能耗,而且能够相应地提高水输送热量(或冷量)的能力并有助于减少输配管网的初投资,因此在我国开展此项技术的研究对暖通空调领域的节能减排工作具有重要的意义。本文将从应用基础的角度研究添加剂减阻技术在暖通空调水系统中实际工程应用的可行性。本文针对暖通空调水系统的专业技术特点,设计并建立了温度可控、实验管段管径可变、具有循环剪切功能的添加剂减阻实验台。该实验台的水温可控制在8℃至80℃之间、雷诺数可控制在500~100000范围内,来模拟暖通系统运行中的大多数常见的流动状态;减阻实验在循环系统中进行,便于研究不同减阻剂的抗剪切特性;实验管段部分可拆卸,以实现对常见管材不同管径的减阻效果研究。在进行减阻实验之前先进行清水实验,即在层流区以Hagen-Poiseuille定律为标准,湍流区以Prandtl-Karman定律为标准,对实验段管径进行了率定。采用高分子聚合物聚丙烯酰胺(PAM)和表面活性剂十六烷基三甲基氯化铵(CTAC)的水溶液分别在塑料管(PVC管)和紫铜管中进行减阻实验来研究减阻液的减阻起始点、浓度效应、温度效应、管径效应及抗剪切性能等特性。实验结果显示,浓度为200ppm的PAM水溶液在紫铜管中最大减阻百分比在温度10℃时为65%,减阻效果非常突出,而在高温条件下存在明显降解现象,故PAM减阻剂在区域供冷系统中应该具有一定的应用潜力。浓度为300 ppm的表面活性剂CTAC水溶液在温度为60℃的紫铜管中其最大减阻百分比就可达到65%,同时表面活性剂CTAC水溶液的临界雷诺数随着溶液浓度的增加而增加,但是在低温下表现出一种饱和的行为,当20℃时,100ppm的表面活性剂CTAC溶液临界雷诺数约为12000,而400、500和600ppm下临界雷诺数几乎恒定在22500。实验结果显示表面活性剂CTAC具有一定的耐高温抗剪切特性,其在区域供冷及地板采暖等系统中应该具有较好的应用前景。暖通空调系统中大多数管道内的流动都处在湍流(紊流)状态下,其中20~30%的能量损失是由湍流中心区内大尺度旋涡的高次分叉所引起的,而70~80%的湍流能量损失却是由边界层附近的湍流猝发所引起的。通过对湍流拟序结构的研究发现,湍流猝发虽然在空间上是随机的,但却是一种带有概周期性和具有确定性结构的拟序性结构,会在边界层内形成一个振荡流场,因此在研究添加剂减阻机理时就必须观察添加剂中的大分子(可将其看做微尺度球形粒子)在此振荡流场中的动力行为。本文提出了含悬浮粒子流体振荡粘度的概念,建立了粒子与振荡流场之间相互作用的数学物理模型,推导出了微尺度球形粒子在振荡流场中运动规律及含有大分子的含悬浮粒子流体振荡粘度的解析表达式。这部分工作是对经典颗粒悬浮液粘度理论的有益扩展,同时为本文随后的添加剂减阻机理的研究奠定了基础。本文的研究结果表明添加剂中的粒子进入边界层附近时,会受到湍流猝发所引起的振荡流场的作用,产生振荡响应。该过程有利于减弱流场的振荡强度,更为重要的是该能量损耗会引起局部流场动态振荡粘度附加,由于粘度附加将阻碍涡管的形成和已形成涡管的发育,从而降低湍流猝发的频率和强度,抑制在湍流阻力中起着最主要贡献的湍流猝发,最终达到宏观减阻效果。利用本文得到的振荡粘度解析表达式就可以计算粒子尺寸、密度、圆频率等对含悬浮粒子流体粘度的影响,例如10wppmPEO(WSR-301)溶液在能谱峰值频率时动态振荡粘度将比纯水粘度约增加7.14%,此时可获得接近于最大的宏观减阻效果。含悬浮粒子流体局部动态振荡粘度是时空的函数,在边界层附近其值越大,对湍流猝发的抑制能力越强,减阻效果就越显著。这就是本文提出的关于减阻机理新的解释。更多还原

【Abstract】 In the building HVAC system, the pumps consume a large proportion of the total building energy, and the former energy saving research was mainly focused on the design of the distribution system and operation adjustments. Because the additive drag-reduction phenomenon, which can lead to great reduction of friction drag by adding a little high polymer or surfactant into the fluid, could not only significantly reduce the friction coefficient during the fluid distribution process, but also decrease the heat loss (or cold loss) along the distribution network due to the reduction of the heat transfer. Applying additive drag-reduction to HVAC systems could largely reduce the pump power in the distribution systems, meanwhile increase the capability of water carrying on the heat and as a result, the initial cost of the distribution network drops. So it is of great significance for energy conservation in HVAC field to investigate additive drag-reduction. This paper studies on the feasibility of applying the additive drag-reduction technology to practical engineering project in water system of HVAC.Based on the characteristics of water distribution system in HVAC, we design and set up an experiment-table for additive drag-reduction with controlled temperature, alternative pipe diameters and circulation mechanical degradation. The temperature is controlled from 10℃to 80℃and the Reynolds number alters in the range of 500~100,000 so as to simulate the majority of flow regimes in HVAC systems. We conduct drag-reduction experiments in circulation system convenient for researching the performance of withstanding mechanical degradation of different drag-reduction additives. Parts of the pipes are dismountable so that we could investigate the drag-reduction effect of different pipe diameters. Before starting the drag-reduction experiments we experimentize with water to calibrate inner diameter of the experiment pipes, using Hagen-Poiseuille law for laminar flow and Prandtl-Karman law for turbulence as standard.To explore the characteristics of drag-reduction solution, such as drag-reduction onset、concentration effect、temperature effect、diameter effect and performance of withstanding mechanical degradation, the drag-reduction experiments conducted in the PVC and copper pipes with PAM and CTAC solution are designed and implemented. The experiment results show that the maximum percentage of drag-reduction of 10℃,200ppm PAM solution flowing in copper pipes could be 65%,which indicates significant effect of drag-reduction, but degradation is observed under high temperature condition. Therefore, PAM drag-reduction additive can be potentially applied in the chilled water delivery systems. The experiment results also demonstrate that the maximum percentage of drag-reduction of 60℃,300ppm CTAC solution flowing in copper pipes could be 65% and meanwhile, the critical Reynolds number of CTAC solution increases with the increasing of the solution concentration, however, saturation behaviour is observed when the CTAC solution is under low-temperature condition. For instance, the critical Reynolds number of 100ppm CTAC solution is about 12000 while the critical Re number of 400,500 and 600 ppm CTAC solution is almost a constant at 22500. Since it shows that CTAC has a certain characteristics of withstanding high temperature and mechanical degradation, its promising application in district cooling and under-floor heating systems is expected.Most of the pipe flows in the HVAC systems are turbulent flow, in which 20~30% of the energy loss is caused by the high order bifurcation of large scale vortex in turbulence central area while 70~80% energy loss is caused by turbulent bursting near boundary layer. Based on the research of turbulent coherent structure, we find that although the turbulent bursting is stochastic in space, it is a coherent structure with probable periodicity and determinacy structure, which could form an oscillation flow field in the boundary layer. So it is necessary to observe the dynamic behavior of macromolecule, viewed as microscale globose particles, in oscillation flow field when we research on mechanism of drag-reduction. This paper brings forward the conception of“oscillation viscosity of particle suspended fluid”, constructs a mathematical physics model of the interaction between globose particles and oscillation flow field, and deduces the analytical expression of movement laws of microscale globose particles in oscillation flow field and oscillation viscosity of particle suspended fluid. This part of work is a good extension for the classic theory of viscosity of particle suspended fluid, meanwhile establishes a solid base for succeeding research on mechanism of drag-reduction in this paper.The results of this research demonstrate that the particles of drag-reduction additive will generate oscillation response when they come to boundary layer and effected by oscillation flow field caused by turbulent bursting. This process is able to lower the oscillation intensity of the flow field, and what is more important, the energy loss will result in an addition in dynamic oscillation viscosity in local field. The addition viscosity can obstruct formation of vortex tube and development of formed vortex tube to reduce the frequency and intensity of turbulent bursting, and restrain the turbulent bursting which is of significant contribution in turbulence friction, finally achieves macroscopical drag-reduction effect. The influences on the viscosity of particle suspended fluid by size, density and frequency of the suspended particles could be calculated with the analytical expression of oscillation viscosity deduced in this paper. For instance, the dynamic oscillation viscosity of 10wppmPEO(WSR-301)solution at peak frequency of energy spectrum increases 7.14% compared with the pure water and the maximum macroscopical drag-reduction effect could be achieved at the same time. The local dynamic oscillation viscosity of particle suspended fluid is a function of space and time, the larger the value near the boundary layer, the more ability of restraining the turbulent bursting could be obtained, as a result, the more significant effect of drag-reduction can be achieved. This is the new explanation to mechanism of drag-reduction raised in this paper.更多还原