2.3.2. Mesh Sensitivity Study

A mesh sensitivity analysis has been carried out to optimize the numerical model results. Four different mesh sizes between 1.44 <sup>×</sup> <sup>10</sup><sup>6</sup> and 3.47 <sup>×</sup> <sup>10</sup><sup>6</sup> cells were used to simulate the air compression process from the ambient conditions to 8 MPa using FRP as sealing layer. The thermal energy balance through the sealing layer was analyzed for the first cycle of compression.

The results for the four scenarios are indicated in Table 2. Finally, a mesh model with 2.69 <sup>×</sup> <sup>10</sup><sup>6</sup> cells was selected to simulate the air charge and discharge periods in the underground reservoir. When a model with 3.47 <sup>×</sup> <sup>10</sup><sup>6</sup> cells is considered, an increase in the computational time of 26.72% is obtained regarding the selected mesh size.


**Table 2.** Mesh sensitivity analysis.
