This work presents experimental and numerical results concerning heat transfer for Herschel-Bulkley fluids, the consistency of which depends on temperature. We have considered the flow through a horizontal cylindrical duct submitted to a wall cooling by an external counter current flow. According to the experimental conditions, the wall temperature may fall below the freezing temperature of the non-Newtonian fluid, for some locations. The numerical model shows that the Nusselt number, which characterizes the internal heat transfer, may be written as constant (Pe＇/Z*)1/3. Z* corresponds to a dimensionless abscissa, Pe＇ being a particular Peclet number. This last parameter depends on the wall shear rate, determined for the inlet section, which indirectly takes into account the rheological properties. A very simple model predicting the wall temperature distribution has been developed. The evolution of this quantity allows us to distinguish roughly two zones along the duct. For the first zone, the temperature drop is abrupt and is mainly affected by the internal heat transfer coefficient. For the second zone, the evolution is smoother, the external condition being prevalent.