Experimental study on pipe flow transition of XG solution and drag reduction characteristics with different mass fractions of NaCl

The Reynolds experiment was conducted to study the transition characteristics of Xanthan Gum (XG) solution (mass fraction: (0-400)×10^–6) in a horizontal smooth circular pipe flow. The influence of different mass fractions of the salt (NaCl) environment on the drag reduction characteristics of XG solution was also investigated experimentally. The relationships of the drag reduction efficiency of XG solution (mass fraction: (100-300)×10^–6) with the flow Reynolds number (Re) and the shearing time in different NaCl mass fractions (0、250×10^–6、500×10^–6和1000×10^–6) were measured. Characterized by the generalized Reynolds number, the flow transition lower critical Reynolds number is delayed in an approximately linear mode with the increase of XG mass fraction, while the value of the upper critical Reynolds number rapidly drops to about 3000. The saturated drag reduction efficiency of XG solution decreases significantly with the dissolution of NaCl under the high Reynolds number condition. Nevertheless, a better drag reduction effect appears under the low Reynolds number condition. The shearing resistance of XG solution shows mass fraction effect, while the addition of an appropriate amount of salt can slightly improve the shearing resistance.