Development of heat transfer coefficient model for external heated rotary kiln with low filling large particles

On the basis of heat transfer mechanism analysis, this paper regards the heat transfer process between the kiln's surface and large particles as consisting of heat conduction between the kiln's surface and gas film, heat convection between the gas film and particles, and heat radiation between the kiln's surface and particles. To validate the developed model, a series of experimental tests are performed. Alumina spherical grains with a diameter of 6 mm are used as testing particles. The tests find that the heat transfer coefficient only slightly increases with rotary speed increase. Comparisons of the experimental results and predictions show that the maximum relative error (e sub(max)) is about 9.8 percent, and the average error (e sub(ave)) is 5.86 percent. The results also show that, for the testing material in this paper, the fraction of radiation heat transferred from kiln's surface to particles is more than 75 percent of the total heat transfer when the surface temperature is higher than 220[degrees]C.