The purpose of this study is to find the influence of a local Obstruction on heat transfer between one particle in a-p packed bed and the coolant gas which is forced through it. A method is chosen and developed, giving average as well as local heat transfer coefficients in the case of a packed bed containing spherical particles of constant diameter. The results show: -an important decrease of the average cooling of a sphere near the obstruction. The measurements can be correlated by an expression such as: Nu = A.ReB where Nu is the Nusselt number, Re the Reynolds number and A, B constants depending upon the type and the amount of obstruction. -important local variations of the heat transfer coefficient over the surface of a sphere. This work was conducted for the “gas cooled breeder reactor association” and presented at the Thermohydraulics Specialist Meeting at Windscale on May 17-19, 1972, in connection with the ENEA GCFR Programme.