The results of study of heal carrier mixing for different types of hydrodynamic unsteadiness in helical tube bundles are generalized and analyzed. New generalizing relations are proposed for calculation of unsteady effective turbulent transfer coefficients that can be used to close the initial systems of equations. Deviations of the numerical values of unsteady transfer coefficients from their quasi-steady values are found and explained by the disturbance of the balance among the energy supplied to the flow, turbulent diffusion and turbulence energy dissipation that cause the turbulent flow structure to vary with lime. (C) 1997 Elsevier Science Ltd.