Air flow thermal behavior along LHC sector 3-4

The heat flow released to the air along the LHC sector 3-4 will be removed by the ventilation system, which will operate at 45000 m3/h. The present study aims at evaluating the thermal contribution, in the heat removal, of the rock cold mass surrounding the tunnel wall. A thermal model of the tunnel is built in that purpose. This model is run in two configurations, one assuming the tunnel walls to be adiabatic and the other one taking into account the heat transfer through the walls to the surrounding rock. The comparison of the results given in both configurations allows the contribution of the rock cooling effect to be estimated. This contribution turns out to be about 10% of the total heat released in the tunnel. Nevertheless, such a figure needs to be taken with caution as it strongly depends on the heat transfer coefficients across the wall and surrounding rocks, which are assumed in the model. These coefficients are taken from the literature and are not confirmed by any experimental measurements.