Experimental Investigation Of Heat Transfer And Flow Resistance Characteristics Of Air In Three-dimensional Internally Finned Tubes With Staggered Arrangement Finns

Single-phase forced convective heat transfer inside tube is an important research realm in the technology of heat transfer augmentation. It plays an important part in saving energy and decreasing the volume and weight of heat exchanger. In our studies, three-dimensional internally finned tube (3-D IFT) can be used to enhance single-phase forced convective heat transfer inside tube. The new type tube can be called a revolution in heat transfer augmentation. Compares the 3-D IFT with smooth tube, the result shows that heat transfer augments, volume decreases, metallic material reduces and energy saves. So the tube with three dimensional internally extended surface have very wide engineering application background. Few studies have been carried out on the enhanced heat transfer mechanism of 3-D IFT due to the complex and irregual external shape. The effects of various structure parameters and fins arrangement of the three dimensional extended surface on heat transfer performance in the 3-D IFT have not been studied systematically .3-D IFT have three fin arrangements: staggered arrangement fins, in-line arrangement fins and spiral arrangement fins. The former experimental study regressed the experimental data of all three fin arrangements and obtained the heat transfer criterion equation of 3-D IFT, while the paper sets apart the three mixed fin arrangements and applies Othorgonal Testing Method to the 3-D IFT with staggered arrangement fins which is wide used in the engineering. Through the conventional analysis of the Othorgonal Testing results, we can initially determine that the best structure parameter of 3-D IFT with staggered arrangement fins .In this paper, the working fluid is air. Experimental study of the nine different structure parameters of 3-D IFT with staggered arrangement fins in the Reynolds number range of 250 to 30000 is performed to investigate the characteristics of heat transfer and flow friction behavior. Analyses and reduces the experimental data by the least square method, obtains the Nusselt and Fanning friction fitting criterion equations. The experimental results of air heat transfer show that the relative fin height, relative fin width, relative fin pitch and density of 3-D IFT with staggered arrangement fins all have an effect on heat transfer and flow friction. Especially, the effect of fin density is bigger. The highest heat transfer coefficient for air flowing in the nine 3-D IFT with staggered arrangement fins is No9 tube. In the turbulent region, the heat transfercoefficient of No9 tube is a factor of 10.36 compared with smooth tube, and its thermodynamic performance coefficient is as high as 6.49; The average Nusselt number in the most superior 3-D IFT with staggered arrangement can be increased by about 1.04 times in the laminar flow, and 6.38 times in the transitional flow as compared with that in the smooth tube. The friction factor between fluid and tube wall can be 0.96 times in laminar flow, and 12.68 times in transitional flow as compared with that inside the smooth tube. The thermodynamic performance coefficient in the laminar region and transitional region is individually 1.06 and 2.74.In this paper, increase with Reynolds number, we first find that 3-D IFT with staggered arrangement fins and smooth tube's heat transfer characteristic curve will have a point of intersection. That is heat transfer valid fold point. At the same time, we regress experimental data and obtain the critical Reynolds number judge of this heat transfer valid fold point.The fitting criterion equations and important results which are obtained by the experimental data can be used in the design field of heat exchanger. The research provides some theory bases for engineering use.