Particle contact dynamics on tubes in the freeboard region of fluidized beds

Gas-fluidized beds are operated with a wide particle size range, and the entrainment of particles into the freeboard region above the dense bed is of practical importance. For example, heat transfer coefficients in the freeboard region are a strong function of void fraction and solid holdup. As a result the heat transfer coefficient is reduced an order of magnitude in the freeboard region as compared to in-bed values. The objective of this investigation was to determine the local and average void fractions that may be experienced by a heat transfer tube located in the freeboard region of gas-fluidized beds