【作者】 曾尚春；

【导师】 李友荣；

【作者基本信息】 重庆大学 ， 工程热物理， 2003， 硕士

【摘要】 流体流动中的换热现象普遍存在于工业的各个领域中，因此如何强化换热、节约能源是一个重要的研究领域。在当今能源严重短缺的时代，这方面的研究更具有紧迫性。随着我国工业的不断发展，对能源开发、利用和节约的要求不断提高，因而对换热器的技术要求也日益增强了，换热器的优化就越来越重要。正是在这种迫切要求下，基于自激振荡能产生脉冲流动而影响流动边界层从而提高对流换热系数来强化换热的考虑，需要开展对自激振荡的机理及其应用的研究。将Helmholtz共振腔应用于换热器来增强换热是一种新的强化换热方法。我们设计了一种换热效果较好的Helmholtz共振腔，并通过实验研究了Helmholtz共振腔对换热器的换热强化效果，分析了水力参数和结构参数对换热效果的影响，得出了对流换热系数及换热强化比随流量的变化规律，同时得到了如下重要结论：①对一定结构的共振腔，配以适当的水力参数，就可以产生自激振荡，对于同一结构的共振腔，水力参数不同，产生的自激振荡的强弱也不同，随着压力的增加，自激振荡的强度也增加；②将共振腔产生的自激振荡流引入换热器后，当自激振荡达到一定的强度时，能够破坏层流底层，从而可以强化换热，Helmholtz共振腔在绝大多数工况下能将管内换热系数提高10%—30%；③对同一结构的共振腔，后喷嘴结构尺寸对换热有一定影响，这是由于后喷嘴长度的变化会引起共振腔固有频率的改变，从而改变共振腔出口射流的脉动频率；④共振腔不是在所有的工况下都能强化换热。当流量及压差降低至一定程度时，共振腔还可能削弱换热；⑤加热功率的提高会增加流体（水）的温度，流体的粘度会随着降低，这会减少对流体脉动的阻碍，使脉动衰减得更慢，而脉动幅度的增加会增强换热，故加热功率对有脉动的对流换热是有影响的；⑥自振腔产生的流体脉动频率是自振腔固有频率或其整数倍,流体脉动频率过高或过低都不利于对流换热，存在一有利于强化换热的频率范围。上述结论对进一步的研究具有重要的指导意义。更多还原

【Abstract】 The phenomenon of convective heat transfer in a pipe flow exits universally in many industrial areas, therefore, how to enhance heat transfer and how to save energy sources are an important investigation domain. Nowadays because of the deficiency of energy sources, the research in this field is more critical. Accompanied with the continuous industrial development in our country, the demand in exploiting, using and thrift with energy sources gets higher and higher increasingly. Accordingly, the technology for improving heat exchanger performance absorbed wide attention of the scientists, the optimize of heat transfer is more important. Just under this urgent consideration, based on the fact that self-oscillation can produce pulsation of flow, to influence the flow boundary layer, thus to increase convective heat transfer coefficient, it is necessary to devote to the mechanism of self-oscillation and apply it to a heat exchanger.It is a new heat transfer enhancement method to apply Helmholtz resonance chamber to convective heat transfer in a pipe. We design a kind of Helmholtz resonance chamber with better convective heat transfer effect. The convective heat transfer characteristics of water in a pipe with the Helmholtz resonance chamber is investigated experimentally. The influence of various waterpower and configuration parameters on heat transfer is analysed and the rules of convective heat transfer coefficient and the ratio of heat transfer enhancement with mass flux are obtained. At the same time, we gain important results as below: ①as for resonance chamber with certain configuration, self-oscillation can be generated under suitable configuration and waterpower parameters. For the same configuration resonance chamber, the intensity of the self-oscillation is changed by the waterpower parameters. When the pressure increases, self-oscillation intensity will increase. ②By applying the self-oscillation generated by the resonance chamber to the heat exchanger, and when the self-oscillation intensity achieves a certain degree, laminar flow layer would be destroyed, then heat transfer will be enhanced. At the most condition the heat transfer coefficient will be increased by about<WP=5>10%-30% when Helmholtz resonance chamber is used. ③For the same configuration resonance chamber, configuration and size of back nozzle have some influences on heat transfer. This is because the change of size of back nozzle would alter the inherent frequency of resonance chamber, thus alter the pulsation frequency of fluid spurting out from back nozzle. ④Resonance chamber can enhance heat transfer not under any working conditions, as flux and pressure difference fall to certain degree, resonance chamber maybe weaken heat transfer. ⑤the increase of wall temperature may improve the fluid (water) temperature, fluid viscosity may decrease at the same time, this may decrease the block of pulsation of fluid, compel pulsation attenuate more slowly, moreover, the increase of pulsation amplitude may enhance heat transfer, therefore, in the region of pulsating convective heat transfer, the heating power has some influences to heat transfer. ⑥The pulsation frequency produced by resonance chamber is its inherent frequency or integral multiple of inherent frequency, excessive high or low fluid pulsation frequency can both weaken convective heat transfer, so there is a certain region for enhancing heat transfer. The results mentioned above are of important significance for engineering design and the further investigation.更多还原