This present work studies the effect of single nanoparticle diameter on a nanochannel fluid flow and convective heat transfer using the molecular dynamics simulation code LAMMPS. The channel dimensions are 95 Å in length, 40 Å in depth, and 60 Å in height. Channel wall temperatures are fixed at 200 K whereas inlet bulk fluid temperature is set as 300 K. Two regions (force region and thermostat region) are considered before the channel inlet to create a flow and apply the quasi-periodic boundary condition to the system. Fluid and solid (walls and nanoparticle) materials are argon and copper, respectively. Surface wettability are modeled by setting the energy scale to be 1.67 × 10−21 J and the input force is imposed at 0.002 eV/Å. Both velocity and temperature profiles across the channel height will be plotted at 12.5, 22.5, and 32.5 Å away from the inlet. Effect of single nanoparticle diameter of 0.8, 1.0, 1.25, 1.5, 1.75, and 2 nm on the convective heat transfer enhancement will be studied. Nusselt number will be used to quantify the convective heat transfer enhancement with the presence of a nanoparticle size in the nanochannel flow. Nusselt number of a base nanochannel fluid flow without any nanoparticle will be included as a benchmark comparison.