optimum diameter and location of pipes containing phase change materials in a channel in latent and sensible heat transfer

In this paper, two pipes containing phase change materials, located perpendicular to the flow direction in a channel, are simulated numerically to find out their best diameter and location (their distances from the walls) in the convective heat transfer behavior. the governing equations have been solved by the semi-implicit method for pressure linked equations. in the first part, the phase change material is in the phase change (isothermal state) process, and the best location and diameter of the pipes are defined. in the second part, for obtained best size and location obtained in the first part, depending on the phase change material to the fluid special heat capacity ratio, the duration of the after-melting process, and reaching the final equilibrium state of the phase change material has been determined. the results of the first part show the best geometrical parameter depends on the reynolds and the prandtl numbers. results of the second part show, the time at which the temperature of the pipes (phase change material) reaches 99% of the temperature of the inlet flow, depends on the special heat capacity ratio. also, the best non-dimensional diameter of pipes is 0.153 for re=500 and 0.165 for re=700 in different prandtl numbers and the best non-dimensional distance of the pipes from the wall is between 0.15-0.175 for different reynolds and prandtl numbers.