In this work the impacts of nanofluids flow on thermal and hydrodynamic behaviors in heat exchangers are studied experimentally. Two nanofluids with similar nanoparticles of ?-Al 2 O 3 and different base fluids are employed. The first nanofluid is provided by inclusion of the nanoparticles in distilled water while the base fluid for the second one is the working fluid of tempered water unit of Isfahan refinery which is distilled water with a low volume concentration of sodium molybdate (with industrial name of energy 110). The tests are performed at three different volume concentrations of 0.05, 0.1 and 0.15%. Two different heat exchangers are employed in this research. The first one is a shell and tube heat exchanger with a single-pass shell and a two-pass tube. The second heat exchanger utilized in this work is a fin-tube one with corrugated flat fins. The effects of many parameters including nanoparticle volume concentration, nanofluid temperature and mass flow rate on overall heat transfer coefficient (U), convective heat transfer coefficient (h) and pressure drop (?P) are investigated. Results show that by increasing the volume concentration of the added nono particles to the bais fluid the thermal behavior of the nono fluid improves. Also increment of nanofluid temperature and mass flow rate have the same effect on the characteristics, qualitatively. As an example, the overall heat transfer coefficient of the distilled water/?-Al 2 O 3 nanofluid with volume concentration of 0.15% for the first and second cases of temperature variation in the shell and tube heat exchanger enhances as 7.2% and 15.5% over those of pure water flow at Re=18,000 and 8,000, respectively. These values for a similar condition in the fin-tube heat exchanger are 12.6% and 17.2%, respectively. The results of sedimentation tests for the tempered water/?-Al 2 O 3 nanofluid at Re=21,000 don’t show any symptoms of precipitation and sediments after three days of the nanofluid circulation. In addition, improvement of the thermal parameters is in an appropriate level in spite of the low volume concentration, whilst pressure drops can be neglected in both heat exchangers. As a summary: utilizing nanofluids results in thermal efficiency enhancement, saving energy carriers consumption, lower investment costs and consequently optimization of energy consumption in industrial applications. Keywords: Nanofluids, Nanoparticles, Heat Transfer, Shell and Tube heat exchanger, Tube-Fin heat exchanger