Naphthalene thermosyphons are efficient heat transfer devices that operate within 250 and 400 degrees C. There is a lack of literature about naphthalene thermosyphons, especially with the presence of non-condensable gases (NCG). Thermal circuit resistance models, considering or not NCG, are developed. NCG-vapor flat front hypothesis is adopted. Condensation and evaporation heat transfer coefficients are obtained from literature correlations. Thermal resistance data provided from naphthalene thermosyphon charged with argon, is obtained using especial experimental setup. Two combinations of correlations provided good comparison with data, for thermosyphons with and without NCG. These models are successfully applied for heat exchanger design. (C) 2010 Elsevier Ltd. All rights reserved.