Whenever there is a temperature difference, heat transfer occurs. Heat transfer happens in several ways in rail tunnels, for instance, when trains accelerate or brake, they produce heat that warms the surrounding air. That hot air is then mixed with other air in the tunnel and with heat radiating from the ground. Until now, engineers have been unable to accurately calculate the amount of heat present in the air of the tunnel.
Now, a team of researchers at the Soil Mechanics Laboratory (LMS) of Ecole polytechnique fédérale de Lausanne (EPFL) has found a solution for this. They have precisely estimated the convection heat transfer coefficient, and this could pave the way for innovative applications involving so-called energy tunnels that can supply energy to build environments.
The geothermal heat-recovery system would be cheap and energy-efficient to install, according to the researchers. It has a lifespan of between 50 and 100 years, with only the heat pumps having to be replaced every 25 years. Once equipped, heat from the tunnel would cover up to 80% of the heating needs of local apartments throughout winter, with the shortfall preferably coming from other renewable sources.
But what makes geothermal systems like these unique is that they work in summer too. “The tunnel would act like a highly reliable, year-round heating and air-conditioning system,” says Margaux Peltier, a scientific assistant at the LMS, whose Master’s research forms the basis of the article.
Numerical investigation of the convection heat transfer driven by airflows in underground tunnels, by Margaux Peltiera, et al. Applied Thermal Engineering, Volume 159, August 2019, https://doi.org/10.1016/j.applthermaleng.2019.113844
