Numerical study of heat transfer in laminar and turbulent pipe flow with finite-size spherical particles

•We investigate heat transfer in laminar and turbulent pipe flows with different volume fraction of finite-size spherical particles.•We show that a considerable heat transfer enhancement (up to 330%) can be achieved in the laminar regime by increasing the volume fraction of spherical particles.•The heat transfer is observed to increase significantly in the laminar regime as the pipe to particle diameter ratio decreases for the parameter range considered here.•In the turbulent regime, only a transient increase in the heat transfer is observed before the process decelerates in time below the values in single-phase flows.•A heat transfer enhancement, measured with respect to the single phase flow, is only achieved at volume fractions as low as 5% in a turbulent flow. Controlling heat and mass transfer in particulate suspensions has many applications in fuel combustion, food industry, pollution control and life science. We perform direct numerical simulations (DNS) to study the heat transfer within a suspension of neutrally buoyant, finite-size spherical particles in laminar and turbulent pipe flows, using the immersed boundary method (IBM) to account for the solid fluid interactions and a volume of fluid (VoF) method to resolve the temperature equation both inside and outside the particles. Particle volume fractions up to 40% are simulated for different pipe to particle diameter ratios. We show that a considerable heat transfer enhancement (up to 330%) can be achieved in the laminar regime by adding spherical particles. The heat transfer is observed to increase significantly as the pipe to particle diameter ratio decreases for the parameter range considered here. Larger particles are found to have a greater impact on the heat transfer enhancement than on the wall-drag increase. In the turbulent regime, however, only a transient increase in the heat transfer is observed and the process decelerates in time below the values in single-phase flows as high volume fractions of particles laminarize the core region of the pipe. A heat transfer enhancement, measured with respect to the single phase flow, is only achieved at volume fractions as low as 5% in a turbulent flow.