Question

Why is dry ice more effective for cooling purpose than ordinary ice?

Answer 1

Its advantages include lower temperature than that of water ice and not leaving any residue (other than incidental frost from moisture in the atmosphere). It is useful for preserving frozen foods where mechanical cooling is unavailable.

Answer 2

The cooling of a drink with a cube of ice is more effective than using cold water because of the energy extracted from the drink to melt the ice (heat of fusion). The cooling of a container of water with a mass of ice at 0 C illustrates the energy of the phase change and the approach to thermal equilibrium.