The work is directed at the numerical simulation of latent-heat thermal energy storage in a two-dimensional rectangular cavity with partially thermally active parts. The detailed transient computations are performed for the inclination angle varies from 0 to 90 degrees based on horizontal ground, for the aspect ratio of the rectangular cavity varies from 0.5 to 2, and for the number of discrete heat source located in the heated wall varies from 1 to 4. Numerical results indicated that thermally active part heated by discrete heat sources is a promising alternative for high-efficient thermal energy storage, as the vector direction between gravitation and overall heat flux is opposite, and that the aspect ratio has significantly sensitized for the thermal behavior as the inclination angle is 90 degrees. It is demonstrated that the optimized thermal storage behaviors are reached for the inclination angle of 0 degrees, the aspect ratio of 0.5, and the number of discrete heat source of 4, with the requested thermal storage time reduced more than 40%. It is found that the formation of the multicellular flow structure during the early stage of melting process, while a merging of the small recirculating cells into larger ones is observed during the following stage. (C) 2018 Elsevier Ltd. All rights reserved.