Heat transfer between moving beds of solids and a vertical tube

Graduation date: 1989Heat transfer to moving packed beds of solids has been studied\ud extensively but predictions are usually specific to the experimenter's\ud own equipment. In order to obtain a more general predictive equation,\ud the heat transfer coefficient was measured for a single vertical tube\ud immersed in a moving packed bed of glass beads, sand, or copper in air\ud at atmospheric pressure and compared to measurements performed by\ud independent researchers with various experimental configurations.\ud High speed photography was used to observe the motion of the\ud particles as they flowed past the heated wall. The particle separation\ud from the wall could not be determined. There was little interchange of\ud the wall particles with the particles in the bulk beyond the wall\ud layer. Likewise, the particles in the layer adjacent to the wall\ud showed very little rotational or cross-flow motion.\ud A numerical method, based on the unsteady state conduction\ud equation, was developed to predict the heat transfer coefficient\ud between the wall and the flowing bed of solid particles. This method\ud could be used to predict the experimental heat transfer coefficients\ud obtained provided the correct value of the particle separation from\ud the wall was used in the numerical solution. This separation cannot be\ud predicted a priori so that the numerical method is, therefore, not\ud suitable for predicting the heat transfer coefficient.\ud The experimental data showed good agreement with the analytic\ud solution obtained by Mickley and Fairbanks (1) at long contact times.\ud At short contact times, the data do not agree with the Mickley and\ud Fairbanks solution but the heat transfer coefficient tends to level\ud off at an asymptotic value.\ud An empirical correlation was obtained by which the contact time\ud at which the data depart from the Mickley and Fairbanks solution may\ud be predicted. The following equation, was found to be valid for the\ud data of the present work and for data of other researchers who used\ud different geometries in their work.\ud \ud tcr/dpρs= 0.3622 + 9.691 L.\ud \ud This equation may be used in conjunction with the Mickley and\ud Fairbanks solution to predict the heat transfer coefficient for a\ud given flowing packed bed over a wide range of contact times