Some comments on “Poiseuille flow of a fluid with couple stress with applications to blood flow”

Recently Valanis and Sun, Biorheology 6, (1969), 85 have studied the Poiseuille flow with couple stress. While obtaining velocity profiles for various values of non-dimensional couple stress parameters α ¯ and η ¯ , they somehow find that for η ¯ = 0.5 the critical value of α ¯ , for which flow velocity is identically zero, is 0.45. Our numerical computations show that the flow velocity is not identically zero for these values of α ¯ and η ¯ . Figures 4 and 7 of (Valanis, K.C. and Sun, C.T. Biorheology 6, (1969), 85) clearly indicate that the critical value of α ¯ depends on η ¯ . In the present note, it is analytically shown that the critical value of α ¯ is zero and it is independent of η ¯ . Due to this almost all the figures of (Valanis, K.C. and Sun, C.T. Biorheology 6, (1969), 85) will change; the corresponding correct figures are given and the conclusions are accordingly modified.