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91.
Thermoacoustic oscillation is a significant problem in ducted domestic heating systems fitted with fully premixing burners as well as in combustion systems of industrial scale. This paper reports experiments using a burner closely representative of practical designs in which high-intensity free-field sound has been used to simulate the feedback which may be excited naturally in installations with different acoustic properties. This experimental approach facilitates study of the non-linear response of the burner/flame sub-system to feedback of different frequencies and direct measurement of the acoustic impedance of the burner under operational conditions. A function proportional to the Rayleigh integral has been evaluated directly from the experimental results. It is found that the head of this type of burner divides the typical installation into a quarter-wave tube and a Helmholtz resonator which must couple unstably for thermoacoustic oscillations to be autoexciting. It is further found that there is a strong interaction between the acoustic field and the mean flow which modifies significantly the behaviour of the burner as a Helmholtz resonator and thus the stability of the whole system. 相似文献
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This paper establishes a model of a nonlinear diode refrigerator consisting of two diodes switched in the opposite directions and located in two heat reservoirs with different temperatures. Based on the theory of thermal fluctuations, the expressions of the heat flux absorbed from the heat reservoirs are derived. After the heat leak between the two reservoirs is considered, the cooling rate and the coefficient of performance are obtained analytically. The influence of the heat leak and the temperature ratio on the performance characteristics of the refrigerator is analysed in detail. 相似文献
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An entangled quantum refrigerator working with a three-qubit one-dimensional isotropic Heisenberg XX model in a constant external magnetic field is constructed in this paper. Based on the quantum first law of thermodynamics, the expressions for several basic thermodynamic quantities such as the heat transferred, the net work and the coefficient of performance are derived. Moreover, the influence of the thermal entanglement on the basic thermodynamic
quantities is investigated. Several interesting features of the variation of the basic thermodynamic quantities with the thermal entanglement in zero and nonzero magnetic field are obtained. 相似文献
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介观体系输运过程中载流子的离散性导致了散粒噪声.通过测量散粒噪声可以得到传统的基于时间平均值的电导测量无法得到的随时间涨落信息,因而作为一种重要手段在极低温量子输运研究中得到了一定的应用.极低温环境下的噪声测量是一种难度很大的极端条件下的微弱信号测量,通常需要在低温端安装前置放大器并且尽量靠近待测器件以提高测量信噪比和带宽,因此对放大器的噪声水平和功耗都有严格的要求.提出了在稀释制冷机内搭建的散粒噪声测量系统,以及利用此套系统得到了在mK温区超导隧道结散粒噪声的测量结果.自行研制的高电子迁移率晶体管低温前置放大器采用整体封装,便于安装在商用干式稀释制冷机的4 K温区,本底电压噪声为0.25 nV/√Hz,功耗仅为0.754 mW.通过对隧道结进行散粒噪声测量,得到的Fano因子和理论计算吻合. 相似文献
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如何优化工作在有限尺寸的热源与冷源之间的热设备的性能是有限时间热力学领域的一个重要课题.本文在线性不可热力学框架下,结合有限时间热力学理论,研究了一个无限尺寸热源而有限尺寸冷源的制冷机的工作过程,解析性地推导了紧耦合条件下平均输入功率以及制冷系数表达式,并且进一步讨论了该制冷机的性能.发现平均输入功率与制冷时间不存在明确的优化关系,而且输入功率的增加导致制冷系数单调减小,但辐射能的增加致使制冷系数增强.研究结果对于深入理解实际的热力学过程具有一定的工程实践性价值. 相似文献