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Register a new userHeat Transfer in Underground Rail Tunnels
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Added by
Jean-Luc Thiffeault
Publication date
2007
fields
Physics
and research's language is
English
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The transfer of heat between the air and surrounding soil in underground tunnels ins investigated, as part of the analysis of environmental conditions in underground rail systems. Using standard turbulent modelling assumptions, flow profiles are obtained in both open tunnels and in the annulus between a tunnel wall and a moving train, from which the heat transfer coefficient between the air and tunnel wall is computed. The radial conduction of heat through the surrounding soil resulting from changes in the temperature of air in the tunnel are determined. An impulse change and an oscillating tunnel air temperature are considered separately. The correlations between fluctuations in heat transfer coefficient and air temperature are found to increase the mean soil temperature. Finally, a model for the coupled evolution of the air and surrounding soil temperature along a tunnel of finite length is given.
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We present results of interface-resolved simulations of heat transfer in suspensions of finite-size neutrally-buoyant spherical particles for solid volume fractions up to 35% and bulk Reynolds numbers from 500 to 5600. An Immersed Boundary-Volume of Fluid method is used to solve the energy equation in the fluid and solid phase. We relate the heat transfer to the regimes of particle motion previously identified, i.e. a viscous regime at low volume fractions and low Reynolds number, particle-laden turbulence at high Reynolds and moderate volume fraction and particulate regime at high volume fractions. We show that in the viscous dominated regime, the heat transfer is mainly due to thermal diffusion with enhancement due to the particle-induced fluctuations. In the turbulent-like regime, we observe the largest enhancement of the global heat transfer, dominated by the turbulent heat flux. In the particulate shear-thickening regime, however, the heat transfer enhancement decreases as mixing is quenched by the particle migration towards the channel core. As a result, a compact loosely-packed core region forms and the contribution of thermal diffusion to the total heat transfer becomes significant once again. The global heat transfer becomes, in these flows at volume fractions larger than 25%, lower than in single-phase turbulence.
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