Study On Vibration Enhanced Heat Transfer Mechanism Of A Bundle Of Hot And Cold Microtubes

Equipment miniaturization in national defense, aviation, biomedicine, bio mimicry technology, precision machinery and microelectronics industry etc. reflects and influences the scientific and technological level of the whole industry. On one hand, Equipment miniaturization economizes materials and space with light weight; what's more, it can significantly reduce energy consumption in achieving the same goal compared with the conventional ones.Micro heat-exchanger is small in size, large in specific surface area with a high rate of heat exchange. Besides, the fluid circulation in the heat-exchanger may cause its vibration and thus produce noise which would shorter its lifespan. As a result, it is significant to develop a new micro heat-exchanger which could strengthen heat transfer with vibration.A new micro heat-exchanger with hot and cold tubes staggered arrangement is put forward in the paper. Natural-convection heat transfer between the hot and cold microtubes plus the mechanism of heat transfer reinforcement with periodic small transverse vibration exerted on the microtubes has been mainly discussed. In order to grasp the effect law of different influencing parameters towards the heat-exchanger so as to lay a theoretical basis and guidance for the development of the new heat-exchanger, experimental methods and numerical simulation has been applied in achieving the result. On the experimental part, after setting up the experiment table, the natural convection heat transfer between two pairs of tubes was studied through controlling the tube arrangement, amplitude and frequency, temperature of the hot and cold water and flux etc. respectively. The main conclusions listed as following: with the increase of vibration intensity, Nu number of the tube increases gradually and the heat transfer enhances gradually. Heat transfer reaches lowest when the cold tube sits below the hot one in line arrangement while heat transfer reaches highest when the hot and cold tube in staggered arrangement with hot tube horizontal and cold vertical. When analyzing from the general view, heat exchange with four tubes is better than two and two tubes better than single which means heat transfer enhancement with vibration is much better with more microtubes in the enclosure.Direct-forcing immersed boundary LBM method was applied in numerical simulation and heat exchange with two tubes in the enclosure was mainly numerically simulated and the corresponding flow chart and temperature chart was obtained. The main conclusions are as follows: the average Nu number is the lowest when the cold tube is directly below the hot one and the overall heat exchange is the worst while the maximum can be achieved while the cold tube is above the hot one but with a 60° inclination angle from the upward direction. At the same time, the heat exchange of the four tubes was calculated in order to make comparison and supplement with the fourtube experiment.In the end, based on the course of this study, a few advises has been put forward towards the subsequent research and made some prospects as well.