Heat transfer can be enhanced when fluid oscillates axially within pipes. A numerical analysis is given using the finite difference method. The relationship derived from differential equations and unambiguous conditions is written in theform ofwhere ae- the effective thermal diffusivity

a-the thermal diffusivity

AS-the tidal displacement of oscillation

R-the radius and L-the length of the pipe. The results obtained show that ae/a is independent of L/R as L>>ΔS and proportional to the square of AS/R

and its value increases with an increase in Wom or Pr. The numerical solution is in good agreement with the data of experiments.