Study On Heat Transfer Of Laminar Oscillatory Flow In Circular Channnel

Pulse tube cryocoolers utilize an oscillatory flow to realize cryogenic refrigeration. The oscillatory flow is characterized by the cyclic reversion of its fluid velocity direction, which results in quite different flow and heat transfer features, compared with the unidirectional steady flow. Better understanding these features is of great importance for the research and development of pulse tube cryocoolers, and for precise design. Based on the analysis of reported work, present research focuses on laminar oscillatory pipe flow, and specifies in the following three aspects:1. Quantitative analysis of temperature annular effect of laminar oscillatory pipe flow:When discrete fourier series is used to reprensent the heat transfer characteristics of oscillatory flow, there exists phase difference between the heat flux at wall and the center-wall temperature difference. To demostrate this phase difference, numeicial computations are conducted to analyze the characteristics of temperature profile on the channel’s cross section. The phase at which the temperature annular effect is most visible is discussed, and Coefficient of Temperature Annular Effect (CTAE) is proposed as an index parameter to quantitatively evaluate the temperature annular effect. Also numerical computations with the index parameter CTAE are conducted to analyze the impacts of dimensionless parameters, i.e., maximum Reynolds number and Peclet number, on temperature annular effect of the oscillatory flow in the circular channel.2. Applicabiity analysis of hot-wire anemometer for velocity measurement of oscillatory flow:For high-frequency and low-velocity oscillatory flows, there are relatively larger errors of the velocity measurement with the hot-wire anemometer. Numerical computations are conducted on the the hot-wire anemometer to model the calibration process in the unidirectional steady flow and the velocity measurement process in the oscillatory flow. According to the numerical results, analysis focuses on the differences between the so-called real values and measured values of the velocity under various operating conditions of the oscillatory flow. An index of reliability of ξ is proposed to quantitatively evaluate, the applicability of velocity measurement with the hot-wire anemometer for the oscillatory flow in pulse tube cryocoolers. Additionally, the applicability of velocity measurement with the hot-wire anemometer for the oscillatory flow conditions of our experimental apparatus is also discussed with the index of reliability ξ.3. Investigation on heat transfer characteristics of laminar oscillatory pipe flow:An experimental apparatus has been designed and built to investigate the on heat transfer of laminar oscillatory flow in circular channel. Discrete Fourier series is used to represent the heat transfer characteristics, and the emphasis focuses on the impact of the dimensionless criterions (e.g., maximum Reynolds number and Peclet number), on the time-averaged Nusslet number (i.e.,0th Nusselt number). By fitting the experimental data, a correlation of the time-averaged Nusslet number with respect to the Peclet number is achieved.