The governing equations, the boundary and connective conditions of the helical flow of non-newtonian fluids in eccentric annuli, which are the 4th order nonlinear nonhomogeneous partial differential equations with varible coefficients expressed by the stream function and axial velocity in the bipolar coordinate system, are established theoretically and calculated numerically by using the finite difference method.

The calculation steps of the above mentioned equations are given and, being as the examples of the experimental data of the aqueous solution of CMC in the laboratory, the helical flow of the non-newtonian fluid in eccenric annuli are calculated and analysed practically. The results are as follows:

  1. There is a secondary flow, which is very important for analysing cuttings carrying capacity of drilling muds in the annuli and for preventing drill pipe from being suck, in the helical flow of the non-newtonian fluid in eccentric annuli.

  2. The flow rate of the helical flow is enhanced by the rotation of the inner cylinder of eccentric annulus.

  3. The results of comparison between the numerically calculated flow rates and the flow rates meassured in the experiments show that the governing equations and the method of the numerical calculation of the helical flow of the non-newtonian fluids in eccentric annuli in the paper are correct.

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