The current work uses a novel fundamental heat transfer experiment to understand the morphological and thermal performance effects of nanoparticle deposition processes on heating surfaces under high heat fluxes. This is a unique fundamental study of nanosuspension induced nanoparticle coated boiling surfaces under realistic fusion relevant conditions. Al2O3-H2O nanosuspensions have been used under forced convection and boiling. The experiments were performed on a test bed able to simulate realistic fusion reactor heat flux. Nanosuspensions are found to deteriorate the cooling performance due to the formation of a complex self-assembled porous nanoparticle layer on the heating surfaces. This negative effect on thermal performance is irrespective of operation in nanoparticulate latent or pure coolants modes. For heat transfer in nanosuspensions, the increase of nanoparticle concentration reduced the observed negative thermal performance effects. Improvement of thermal performance beyond the break-even point, as witnessed for some conditions in the current work, could be potentially achieved by increasing the concentration of nanoparticles in the coolant. When the nanosuspension is removed and the heat transfer surfaces with the nanolayer deposit are washed and operated with pure liquids, it was discovered that the deposited layers survived and still affected (negatively) their heat transfer performance. The deposited layers are porous and are expected to extend the critical heat flux of surfaces in relevant industrial processes. The deposition process and the final thermal properties could be affected by several controlled parameters providing design opportunities for new or retrofitted applications that were otherwise inaccessible or unfeasible.