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| Influence of flow fluctuation characteristics on flow and heat transfer in different regions |
| PENG Jinghua1, SHEN Jiehui2, XIE Weian3, ZHAI Shaohua1, XI Guannan1* |
| 1. School of Mechanical Engineering, Nantong University, Nantong, Jiangsu 226019, China; 2. School of Traffic Engineering, Jiangsu Shipping College, Nantong, Jiangsu 226010, China; 3. School of Automotive and Traffic Engineering, Nantong Vocational University, Nantong, Jiangsu 226007, China |
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Abstract To study the enhanced heat transfer mechanism of the cylinder model built into the back step of the heat exchanger, Fluent was used for numerical simulation, and the reliability of the simulation results was verified by particle image velocimetry(PIV). When Reynolds number is 700 and the cylinder(Xc/S=0.6, Yc/S=1, d=6 mm)is inserted, the periodicity of the unsteady flow in the backward step passage and the influence of the periodic fluctuation on the heat transfer in different areas of the passage are studied. The results show that in the transitional flow state, the periodic velocity fluctuation of the flow passage is controlled by the frequency of two fundamental waves, that is, the frequency affected by the step fs(fs=7.25 Hz)and the frequency affected by the cylinder fc(fc=14.10 Hz). fc mainly acts on the upstream of the flow passage, the upstream backflow movement is destroyed and the instantaneous peak value of Nusselt number is increased by 2.52 times; fc promotes the generation of step vibration frequency fs in advance; the downstream temperature gradient decreases and the instantaneous Nusselt number decreases gradually. The combined action of the step separating fluid and the cylinder wake improves the heat transfer effect of the flow passage as a whole, and at the same time, the friction coefficient of the wall increases.
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Received: 24 August 2020
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