variavel0=<b>José F. Branco</b> - jfiuza@demgi.estv.ipv.pt Instituto Politécnico de Viseu
<b>Carlos T. Pinho</b> - ctp@fe.up.pt Universidade do Porto
<b>Rui A. Figueiredo</b> - rui.figueiredo@mail.dem.uc.pt Universidade de Coimbra
<b>Abstract.</b> The usefulness of the graphical representation of the thermodynamical laws is widely recognized. In this paper the Bejan- Bucher diagram is used in conjunction with a new graphical technique, which allows the deduction of the efficiency of an endoreversible Carnot engine at maximum power conditions, using simple geometrical considerations. The present approach, unlike others available in the literature, may be directly applied to a Curzon-Ahlborn engine with different thermal resistances connecting to its thermal reservoirs.
<b>Keywords.</b> Bejan-Bucher diagram, Thermodynamics laws, endoreversible engines, graphical techniques, thermal efficiency.