UN METODO INTEGRALE PER LO STUDIO DELLA TRANSMISSIONE DEL CALORE NEL MODELLO ″AXIAL-TRAIN FLOW

Developed for the more general case of heat flux at the wall as a polynomial function of the axial coordinate, the method is applied to the specific case of constant heat flux and compared to the available exact solutions for several values of the thermal conductivities and capacities of the two layers at various interface positions between the layers. As far as the temperature distribution in the cross section is concerned, it is shown that for interface positions close to the pipe axis the temperature profile is not well approximated, but for elastic layer having a diameter not less than half pipe diameter the percent error is negligible. The Nusselt number approximation is far better; in fact, being (for a given heat flux at the wall) related to the bulk temperature, the deviation of the temperature profile in the vicinity of the pipe axis has a small influence in the Nusselt number evaluation.