Dissipative particle dynamics with energy conservation (eDPD) is a potentially effective mesoscopic approach in simulating complex convection heat transfer phenomena. The eDPD is applied to model mixed convection heat transfer in eccentric annulus. We propose a numerical strategy for dealing with irregular geometries in DPD system and by which the application of DPD (or any other particle simulation method) can be extended to mimic hydrodynamics in arbitrarily complex geometries like ones with moving surface or free surface which cannot be defined by mathematical functions. The eDPD results for convective heat transfer are compared to the finite volume solutions and the experimental data, and a good agreement is achieved. The results by eDPD are also compared well with those by lattice Boltzmann method (LBM). From the comparisons we find that the forced, natural and mixed convection flow and heat transfer in complex geometries are correctly predicted using eDPD model. Finally, the effect of eccentricity on heat transfer at various locations is examined at Ra = 2 x 10(4) and Re = 200, and the streamlines and temperature distributions as well as Nusselt number are obtained. The results show that the average Nusselt number increases when the inner cylinder moves downward regardless of the radial position. (C) 2014 Elsevier Ltd. All rights reserved.