In general, the enhancement techniques are divided into two groups: active and passive techniques. The active techniques require external forces, e.g. electric field, acoustic, surface vibration. The passive techniques require special surface geometries or fluid additives. Both techniques have been used for improving heat transfer in heat exchangers In this work, an experimental study is carried out to investigate the effect of adding multi wall nanotubes to the Heat-Transfer oil (HT-B oil) on flow heat transfer and pressure drop characteristics. Measurements of heat transfer for nanofuil flowing in u-type wavy configuration on constant wall temperature boundary condition are presented. The inner diameters of the test copper tube (d) are 15.1mm with dimensionless spacer length (L/d)=4.375 between sequence u-bends, whereas The effect of nanoparticles concentratio and the dimensionless curvature radius (2R/d) and number of sequence u-bends on the heat transfer was investigated in the range of the laminar regime, Reynolds number from about 100 to 2000 and for the dimensionless pipe curvature radiuses (2R/d)=2.375, 4.0625, 7.1875 and 9.25 in (n)=8 and for number of sequence u-bends (n)=4, 8 and 12 in (2R/d)=2.375. The test results indicated enhancement of heat transfer with increasing of nanoparticles concentrations and decreasing dimensionless curvature radius and increasing number of sequence u-bends. The experiments are done for pure HT-B oil and nanofluid flow inside U-type wavy tubes. To reach constant water temperature, entire test section is surrounded by saturated vapor. Heat-Transfer oil (HT-B oil) and MWCNT-HT-B Oil nanofluids with weight concentrations of 0.1, 0.2 and 0.4% are considered as the working fluids. The Rheological characteristics of nanofluids including density, thermal conductivity, viscosity and specific heat are measured experimentally. Based on these measurements, some correlations are proposed to predict the rheological properties of nanofluids with different weight concentrations. The results of the experimental measurements showed that adding nanoparticles to the base fluid would lead to an increase in density, thermal conductivity and viscosity of the nanofluid and will decrease specific heat of the base liquid. The results obtained for convective heat transfer of flow inside U-type wavy tubes indicated that by decreasing dimensionless curvature ratio (2R/d), the convective heat transfer coefficient is increased. For 0.4% weight concentration and dimensionless curvature ratio at 2.375 this enhancement observed 42%. The applied range of Reynolds number, results indicated that for U-type wavy tube the addition of nanoparticles to the base fluid augmented heat transfer remarkably. This augmentation relate to pure oil was about 51% at maximum. Also, the increasing at number of U-bend leads to enhancement of heat transfer coefficient. In addition, flow pressure drop results showed that for U-type wavy tube, by adding nanotubes to the HT-B oil, the flow pressure drop increases. This was for 0.4% weight concentration in (2R/d=) 2.375 about 180% at Re=136. With Having the experimental data for heat transfer and pressure drop of flow, two correlations are derived for predicting the Nusselt number and pressure drop ratio of nanofluid flow for U-type wavy tube. Keywords : convective heat transfer, nanofluid, U-type wavy tube, U-bend, enhancement.