| Under the background of vigorously promoting the scientific development of energy-saving and emission-reduction,additive drag reduction is widely used in various fields as an effective way to save energy and reduce emissions and reduce transportation costs,such as oil extraction,flood discharge and storm drainage,ship navigation,HVAC engineering,farm irrigation and medical engineering and many other fields.As a kind of drag reducer with environmental friendliness,renewability and strong anti-degradability,natural polymers have very important significance for further research on their drag reduction characteristics.The xanthan gum(XG),an important natural polysaccharide biological polymer,has high relative molecular weight and molecular chain mainly composed of the main chain with a small number of large side chains.Compared with most of flexible synthetic polymers,XG has better temperature resistance and salt resistance.These characteristics make it a good drag reducer.Therefore,the original design of the drag reduction experimental device designed by the research group was revised and upgraded,and the pipe diameter was calibrated to ensure accurate experimental data.Afterwards,the drag reduction and anti-shearing of XG solution with NaCl(XG/NaCl solution)were investigated experimentally by using two kinds of drag reduction methods: homogenous solution and pseudo-homogeneous solution.In order to the comparative analysis,the relevant experimental researches of XG aqueous solution has also been carried out simultaneously.The variable parameters are as follows:(1)pipe diameters: 5,10,and 20 mm,respectively;(2)the concentration of XG solutions with and without NaCl(XG solutions): ranging from 100 ppm to 600 ppm;(3)experimental temperature: 20°C,25°C,and 35°C,respectively;(4)flow rate: being characterized by the average Reynolds number(Re)from 0 to 75,000.Based on the experimental results,the onset phenomenon of drag reduction,the concentration effect,the temperature effect,the diameter effect,the effect of the polymer entanglement and the anti-shearing characteristic for XG solutions.The main conclusions are as follows:(1)For the drag reduction of homogeneous solution,(a)XG solutions began to reduce drag after the Re number exceeded 2,000,but the drag reduction start of XG/NaCl solution slightly lags behind that of XG aqueous solution;(b)XG aqueous solution shows obvious diameter effect,but the relationship between drag reduction and diameter of XG/NaCl solution varies with Re,ie,there is the diameter effect in the low Re regime and no such phenomenon in high Re regime;(c)the friction factor of XG solutions at different temperatures decreased with the increase of Re to stabilize,and showed a strong temperature resistance after reaching stability.(2)For the drag reduction of the pseudo-homogenous solution,the drag reduction effectiveness of XG solutions are better than that of the homogeneous solution,indicating that the polymer entanglement can increase the drag reduction effectiveness.(3)Regardless of the drag reduction method,there exist the concentration effect for XG solutions.The optimum drag reduction concentrations for both 10 mm and 20 mm are 500 ppm;after the drag reduction is stabilized,the different concentrations XG/NaCl solution are only better than that of XG aqueous solution in the diameter of20 mm.(4)The concentration,temperature and pipe diameter all have little effect on the anti-shearing characteristic of the XG solutions,and the anti-shearing characteristic of the XG aqueous solution is better than that of the XG/NaCl solution.The above comprehensive analysis of the XG solutions shows that the drag reduction of the XG solutions has good temperature resistance and salt resistance as well as anti-shearing characteristic,which have certain reference value for the application of XG in practical engineering.The study will also deepen the understanding of the additive turbulence drag reduction mechanism. |
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