Abstract In this work, a phenomenological model that considers the interaction of nanoparticles of a Al 2 O 3 /water nanofluid within a cylindrical mesh wick heat pipe has been developed. The model is based on Navier-Stokes equations and it uses population balance as a method to account for the interaction of nanoparticles. The model predicted values of capillary limit with nanofluids up to 32% higher than that of the heat pipe using DI water. Those values were in agreement with the values found experimentally. Although the better performance of the capillary limit in the model was a consequence of the reduction of the pore radius which increases the capillary pressure, that was not the main cause for better capillary limit in experimental conditions at lower nanofluid concentrations. On the other hand, it was found that exists an optimum concentration of nanoparticles which decreases the effective thermal resistance of the heat pipes. In this work, that concentration was 0.5% w/w.