Influence of an obstruction on fluid-particle heat-transfer in a packed bed

The influence of a local obstruction on heat transfer between one particle in a packed bed and the coolant gas which is forced through it is presented. A method is developed, giving average as well as local heat transfer coefficients in the case of a packed bed containing spherical particles of constant diameter. Typical obstructions which can form inside a packed bed are then defined and heat transfer perturbations in the vicinity of such obstructions are measured. The results show (1) an important decrease of the average cooling of a sphere near the obstruction. The measurements are correlated by an expression such as Nu = A.Re superscript B where Nu is the Nusselt number, Re the Reynolds number and A, B constants depending upon the type and the amount of obstruction; (2) important local variations of the heat transfer coefficient over the surface of a sphere; and (3) rapid attenuation of the perturbation in the upward and downward directions.