Study On Enhanced Heat Transfer And Flow Characteristics Of Self-excited Oscillation Pulse Jet

The self-excited oscillation pulsation effect can effectively improve the turbulence intensity of the fluid without external excitation.The self-excited oscillation chamber structure and parameter adjustment can achieve continuous and efficient pulsation without additional reconstruction system,which reduces the control difficulty of the whole system.In this paper,the advantages of the existing pulsation-enhanced heat transfer technology and the self-excited oscillation pulse effect are combined.To solve the bottleneck problem in the scientific research and application research of using pulsating flow to achieve efficient heat transfer enhancement,it is proposed to introduce self-excited oscillation instantaneous vorticity pulsation.The effect realizes the precise scientific explanation of the pulsation-enhanced heat transfer mechanism and innovatively establishes its hot runner design method.The main work of this paper is as follows:(1)Based on the experimental results of predecessors,the current research status of pulsation-enhanced heat transfer is analyzed,and the mechanism of pulsation heat transfer is theoretically analyzed.The influencing factors of turbulent flow enhancement heat transfer are studied,and the principle of pulsating jet generated by self-excited oscillation chamber and the principle of enhanced heat transfer are analyzed in combination with previous research results.(2)The study of self-excited oscillating pulse jet heat transfer characteristics based on eddy current of pulsating shear layer is analyzed.The large eddy simulation numerical calculation method is used to pulsate shear vorticity in one cycle at the outlet of the downstream flow passage of the self-excited oscillation chamber.Field and flow field analysis reveals the root cause of self-excited oscillating pulse jet to enhance heat transfer.It is proposed that the ratio of pulse jet diameter to heat exchanger tube diameter plays a decisive role in enhancing heat transfer.The effect of flow state on heat transfer characteristics and resistance characteristics.(3)Using the numerical calculation method of large eddy simulation,the flow state and pressure field of the fluid in the heat exchange tube are discussed in detail.By analyzing the non-dimensional structure parameters of different chambers,the effects of pulsating jet flow and cavitation are compared and different.The dimensionless structural parameters of the chamber are used to analyze the heat transfer performance and the resistance performance.The comprehensive performance evaluation system is used to evaluate the heat transfer performance.A self-excited oscillation chamber structure design method is proposed.(4)Based on the generation principle of secondary vortex,the boundary point of the secondary vortex and the central large vortex ring is used to design the new chamber wall structure to eliminate the secondary vortex,and the flow state in the chamber,the jet exit speed,and the change Thermal characteristics are calculated and analyzed.