Research on Helmholtz self-excited oscillating jets enhanced heat transfer in horizontal tubes

The self-excited oscillating jets have several advantages, including simple structures, environmental friendliness, and high efficiency. It has become a prominent research focus in the heat transfer field. This study focuses on analyzing the influence of the self-excited oscillation chamber structural parameters on the interaction between coherent structures and heat transfer. Combining the heat transfer enhancement of the pulsating backflow vortex with boundary layer theory, a self-excited oscillation horizontal tube model is constructed. The Large Eddy Simulation (LES) method simulates the self-excited oscillation in horizontal tubes. The heat transfer and flow resistance mechanisms in the tube are investigated. The results indicate that backflow vortices in the downstream pipe alternate near the shear layer. As the flow approaches the oscillator outlet, discrete vortices decrease, the pulsation effect weakens, the temperature gradient diminishes in the tube, and the heat transfer boundary layer thickens. The pressure drops and resistance coefficient in the horizontal tubes exhibit periodic pulsations. The optimal structural parameters of the Helmholtz horizontal tubes are obtained through comprehensive analysis: diameter ratio of the chamber to the upstream pipe DT/d1 = 9.5, ratio of the chamber length to the upstream pipe diameter LT/d1 = 4.3, collision wall angle α = 100°. The relationship between the structural parameters of the oscillator and the heat transfer factors has been established, guiding the application of the Helmholtz oscillating jets in the field of enhanced heat transfer.