The effect of solid particles on crossflow heat transfer in a tube array

Abstract

An experimental investigation was made into the effects of particles on heat transfer in a staggered tube array at the third row where high heat transfer rates are due to high levels of turbulence. Systematic experiments were conducted with and without particles to determine the effects of particle size and concentration and of airflow rate on local heat transfer coefficients for tubes in an array. For all cases, the addition of the particles reduced the local Nusselt number at every measurement point. The suspension heat transfer is shown to be determined by a combination of thermal capacity effects and changes in the flow structure and turbulence levels within the array. The greatest reduction in Nusselt number was measured for the larger particles at the higher Reynolds number, but when potential enhancement due to increased thermal capacity is taken into account, the reduction in heat transfer due to turbulent suppression effects is more significant for the smaller particles. A preliminary analysis of the effect of the particles on the carrier-phase turbulence using a relative time hypothesis gives reasonable agreement with the observed variations in heat transfer when account is taken of the local thermal capacity effects.