Transient effect of soil thermal conductivity and duration of operation on performance of Earth Air Tunnel Heat Exchanger

Effect of soil thermal conductivity and time period of continuous operation of EATHE on thermal performance has been carried out for different pipe length of EATHE using experimentally validated CFD simulation. In this paper, the authors aim to study the underground temperature characteristics of the soil surrounding the EATHE pipe and the effect of duration of operation of EATHE on its thermal performance. Maximum air temperature drop of 15.6, 17.0 and 17.3 K are observed for soil thermal conductivities of 0.52, 2 and 4 W m−1 K−1 respectively. Maximum deterioration in the performance in terms of temperature drop obtained during continuous operation of 24 h is recorded as 2.9 K for soil with thermal conductivity of 0.52 W m−1 K−1. Thickness of soil annulus surrounding the pipe up to which the thermal influence is observed depends on the thermal conductivity of the soil and period of continuous running of EATHE system. The thickness of the soil annulus beyond which no significant rise in temperature of soil is observed is equal to the pipe diameter.