In this work, experimental and numerical studies are carried out to investigate the effect of adding Multi Wall Carbon Nano Tube (MWCNT) nano particles to the base oil on flow heat transfer and pressure drop characteristics. The experiments are done for pure base oil and nano fluid with different mass percent flow inside U-bend tubes. Test sections were heated by an electrical heating coil wrapped around them to produce constant heat flux condition. Base oil (sn-500) and MWCNT- Base Oil nano fluids with weight fraction of 0.23%, 0.46% and 0.69% are considered as the working fluids. ased on these measurements, some correlations are proposed to predict the rheological properties of nano fluids with different weight fraction. The results of the experimental measurements showed that adding nano particles to the base fluid would lead to an increase in density, thermal conductivity and viscosity of the nano fluid and will decrease specific heat of the base liquid. The results obtained for convective heat transfer of flow inside U-bend tubes indicated that by increasing heat flux and flow rate, the convective heat transfer coefficient is increased. Also, it was observed that using nano fluid flow instead of base oil flow and applying U-bend tube will enhance the convective heat transfer.In addition, flow pressure drop results showed that by adding nano particles to the base oil, the flow pressure drop increases. Also, by using the U-bend tube instead of straight tube, pressure drop of the flow is increased considerably. Having the experimental data for heat transfer and pressure drop of flow, two correlations are derived for predicting the Nusselt number and friction factor of nano fluid flow U-bend tube. Furthermore, the performance evaluation of the two enhanced heat transfer techniques studied in this investigation showed that applying U-bend tube instead of the straight tube is a more effective way to enhance the convective heat transfer compared to the second method which is using nano fluids instead of the base liquid. At the end of experimental section, with the aid of work done, it was determined that utilizing stabilizer elements (Oleic Acid) in oil- MWCNT suspension is a more efficient way to increase heat transfer relative to the method of using nano fluid instead of base fluid.Finally U-bend tube were simulated numerically using Fluent software. Fluid properties were extracted from equations derived in thermophysical properties section. Boundary conditions were the same as that of experiment. Eventually by utilizing these data using Fluent software and comparing the outputs of the numerical simulation and experimental results, it was observed that the results are in a good agreement.k eywords : Heat transfer, pressure drop, nano fluid, constant heat flux, U-bend tube.