Synergistic improvement of melting rate and heat storage capacity by a rotation-based method for shell-and-tube latent thermal energy storage

Abstract

• Convection is enhanced with the lower-half PCM rotated to the top. • Low-speed rotation can’t avoid deterioration of uniformity caused by reverse flow. • High-speed rotation could be equivalent to the single rotation when f R =0.5. • Liquid fraction is chosen for judging the moment of executing single rotation. • Effects of single rotation enhance with the increase of LTES size. Rotation is emerging as a novel heat transfer enhancement technique for latent thermal energy storage (LTES) due to its superiority in concise control of rotation conditions and significant effects of heat transfer enhancement. However, the detailed mechanism of heat transfer enhancement triggered by rotation and optimization of rotation conditions have been hardly concerned and explained in previous studies. This study aims to illustrate the effects of rotation on the total melting time, heat transfer rate as well as temperature uniformity of LTES during the heat storage process. Firstly, the effects of constant rotation on the heat storage process are investigated. Then the single rotation of 180° is proposed and effects of the moment to implement the rotation are discussed. Finally, the effects of the single rotation of 180° are examined under different sizes of LTES. Results indicate that convection caused by rotation inside the LTES enhances the melting process, and the effects enhance with the increase of rotation speed. It is also found that the 180° inversion of LTES significantly improves the intensity and range of convection, which has similar effects to the constant rotation. Quantitively, applying the single rotation when f R =0.5 leads to the maximum reduction in total melting time of 533.7%, which is close to the 610.3% for the case with the highest rotation speed of 1 rpm. The positive effects of single rotation on enhancing the melting rate and heat storage density become much more obvious under the larger size of LTES.