An Experimental Study On The Self-oscillation Impulse Convective Heat Transfer

The phenomenon of convective heat transfer in a pipe flow exits universally in many industrial areas, therefore, how to enhance heat transfer and how to save energy sources are an important investigation domain. Nowadays because of the deficiency of energy sources, the research in this field is more critical. Accompanied with the continuous industrial development in our country, the demand in exploiting, using and thrift with energy sources gets higher and higher increasingly. Accordingly, the technology for improving heat exchanger performance absorbed wide attention of the scientists, the optimize of heat transfer is more important. Just under this urgent consideration, based on the fact that self-oscillation can produce pulsation of flow, to influence the flow boundary layer, thus to increase convective heat transfer coefficient, it is necessary to devote to the mechanism of self-oscillation and apply it to a heat exchanger.It is a new heat transfer enhancement method to apply Helmholtz resonance chamber to convective heat transfer in a pipe. We design a kind of Helmholtz resonance chamber with better convective heat transfer effect. The convective heat transfer characteristics of water in a pipe with the Helmholtz resonance chamber is investigated experimentally. The influence of various waterpower and configuration parameters on heat transfer is analysed and the rules of convective heat transfer coefficient and the ratio of heat transfer enhancement with mass flux are obtained. At the same time, we gain important results as below: ①as for resonance chamber with certain configuration, self-oscillation can be generated under suitable configuration and waterpower parameters. For the same configuration resonance chamber, the intensity of the self-oscillation is changed by the waterpower parameters. When the pressure increases, self-oscillation intensity will increase. ②By applying the self-oscillation generated by the resonance chamber to the heat exchanger, and when the self-oscillation intensity achieves a certain degree, laminar flow layer would be destroyed, then heat transfer will be enhanced. At the most condition the heat transfer coefficient will be increased by about10%-30% when Helmholtz resonance chamber is used. ③For the same configuration resonance chamber, configuration and size of back nozzle have some influences on heat transfer. This is because the change of size of back nozzle would alter the inherent frequency of resonance chamber, thus alter the pulsation frequency of fluid spurting out from back nozzle. ④Resonance chamber can enhance heat transfer not under any working conditions, as flux and pressure difference fall to certain degree, resonance chamber maybe weaken heat transfer. ⑤the increase of wall temperature may improve the fluid (water) temperature, fluid viscosity may decrease at the same time, this may decrease the block of pulsation of fluid, compel pulsation attenuate more slowly, moreover, the increase of pulsation amplitude may enhance heat transfer, therefore, in the region of pulsating convective heat transfer, the heating power has some influences to heat transfer. ⑥The pulsation frequency produced by resonance chamber is its inherent frequency or integral multiple of inherent frequency, excessive high or low fluid pulsation frequency can both weaken convective heat transfer, so there is a certain region for enhancing heat transfer. The results mentioned above are of important significance for engineering design and the further investigation.