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Oscillating flow heat pipes are also known as pulsating heat pipes. The working principle of this new type of heat pipe is very different from that of a traditional heat pipe, and its heat transfer performance is much better than that of a traditional heat pipe. This oscillating flow heat pipe has the following outstanding advantages: no capillary core is required in the heat pipe, which is conducive to miniaturization, heat transfer performance is not affected by the heating position (top, bottom or horizontal heating can be), can be freely bent and start quickly . Therefore, the oscillating flow heat pipe has a huge application prospect in the drying system.
Obviously, the efficiency of waste heat recovery is closely linked with the performance of heat exchangers. For this reason, it is necessary to carry out research on the heat transfer enhancement of the oscillating heat pipe. According to the operating mechanism of the oscillating flow heat pipe, two ways can be used to enhance the heat transfer of the oscillating flow heat pipe: one is to enhance the heat exchange between the working fluid inside the pipe and the wall surface of the heat pipe, and the second is to increase the oscillation frequency and the circulating power within the pipe. The author used the following two methods in the study: (1) using pulse heating instead of traditional continuous heating; (2) replacing the usual uniform cross section with a non-uniform heat pipe channel cross section. The experimental results of these two methods were compared and compared with the traditional heat pipes. Derive the following experimental results:
(1) In the experiment, heat transfer performance was compared between pulse heating and continuous heating under the same heating power conditions. The temperature oscillation frequency and amplitude of the oscillating flow heat pipe during pulse heating are higher than those of continuous heating. The heat transfer heat flux and equivalent thermal conductivity of the pulse heating oscillating flow heat pipe can be significantly enhanced. At the same heating power, the heat flow of heat transfer by the pulse-heated oscillating flow heat pipe is 15%~38% higher than continuous heating, and the equivalent heat conductivity is 12%~63% higher. At the same time, the pulsating conditions of the wall temperature of the evaporation section and the condensing section in different heating modes were studied. It was concluded that the pulse heating can enhance the oscillating flow in the oscillating flow heat pipe.
(2) Experiments show that the heat transfer of the oscillating heat pipe can be enhanced by increasing the oscillating flow pulsation frequency and amplitude. Because the heat transfer enhancement effect of the pulsed heating oscillating flow heat pipe is related to the pulse width and pause time, there may be a more effective optimal pulse width and pause time, and it is necessary to further carry out the research on the enhanced coupling between the external and internal fields of the heat pipe.
(3) The author also compares the heat transfer performance and uniform section heat transfer performance of an oscillating flow heat pipe with non-uniform flow through the experiment. When the heating power is greater than 100W, the heat transfer heat flux and the equivalent thermal conductivity of the non-uniform cross-section oscillating flow heat pipe are significantly higher than that of the uniform cross-section heat pipe, and will increase as the heating power increases. Therefore, under certain conditions, its heat transfer performance can be improved by changing the flow section of the oscillating flow heat pipe. The experimental results show that the heat transfer performance of oscillating flow heat pipe is much higher than that of pure copper conductor.
As the energy consumption of drying equipment occupies a high proportion in industrial energy consumption, energy saving in the drying process is of great significance. Generally, energy efficiency can be improved or the energy consumption of the drying system can be reduced by improving heat and mass transfer in the drying process to achieve energy saving. In a common convective drying system, on the one hand, the heat transfer efficiency of the heat exchanger or hot blast stove can be increased, and on the other hand, the residual heat discharged by the drying system can be recovered.