Study On Compressible Oscillatory Flow And Heat Transfer In Circular Channel

Oscillatory flow is one of primary features of thermoacoustic engines and pulse tube refrigerators. In oscillatory flow, the fluid velocity direction reverses periodically, and as a result, the fluid flows over the heat transfer surface and exchanges heat periodically. Accordingly, oscillatory flow has quite different flow and heat transfer characteristics, compared with conventional unidirectional flow. These characteristics are important foundations for better understanding the working principles of thermoacoustic engines and pulse tube refrigerators, and for precise design. Based on the analysis of reported work, present research focuses on compressible oscillatory pipe flow, specifies in the following aspects:1. Analysis of similarity criterion system for heat transfer of compressible oscillatory pipe flow A similarity criterion system for describing the flow and heat transfer characteristics of oscillatory pipe flow, is deduced based on the general governing equations for unsteady compressible viscous flow.2. Analysis and verification of mathematical model Numerical computations are conducted to analyze the flow and heat transfer characteristics of oscillatory pipe flow. Accordingly, mathematical model is proposed and analyzed, which are verified to be effective.3. Numerical analysis on hydrodynamic and thermal entrance lengths of compressible oscillatory pipe flow Based on the temporal-spatial profile characteristics of compressible oscillatory pipe flow and heat transfer, present work proposes two index parameters, i.e., coefficient of hydrodynamic development (CHD) and coefficient of thermal development (CTD), to describe the hydrodynamic and thermal developing phenomena, respectively. Numerical computations are conducted to validate the effectiveness of the index parameters in determining the entrance lengths.4. Quantitative analysis of velocity annular effect of compressible oscillatory pipe flow A redefinition of velocity annular effect is given, based on the slope variation of velocity profile, and then the phase, at which the velocity annular effect appears most visible, is analyzed and concluded. Additionally, an index parameter CVAE is proposed to evaluate the velocity annular effect. Quantitative analysis with the index parameter focuses on the impacts of dimensionless parameters on the velocity annular effect of laminar oscillatory pipe flow.5. Investigation on heat transfer characterization of compressible oscillatory pipe flow Multiple-order Nusselt number is used to represent heat transfer characteristics of oscillatory pipe flow. And close attention is paid to the 0th Nusselt number (time-averaged Nusselt number), to analyze the impacts of similarity criterions on heat transfer processes.6. Construction of experimental system of oscillatory pipe flow and heat transfer Based on the similarity principle, an experimental system is constructed at ambient temperature and atmosphere pressure. Present work proposed an experimental scheme, and finished the related construction designment. Nowadays, the construction of oscillatory flow generation apparatus has completed.