An experimental apparatus was developed to investigate the thermal performance of a cold storage system utilizing rigid spheres containing an internal element to account for dilatation or contraction of the material during the change of phase. Most of the encapsulated thermal storage devices experiments a variation in its external dimensions due to the expansion or contraction that appear in the freezing or melting processes. If the expansion or contraction is absorbed internally, the external shape remain invariable and accommodation problems in storage tanks can be avoided. In spherical encapsulated systems, the internal element absorbs the volume variation in order to maintain constant the outside diameter. To develop the absorber, different sizes of spheres were investigated, as well, different shapes of absorbers. The sphere is cooled or heated by an external flow controlled by a constant temperature bath. Several situations were investigated for different temperatures and flow regimes. During the changing of phase, the temperature field, the interface position and the convection