In this study, effect of electrical field on heat transfer of Al2O3/water and CuO/water in thermosyphon has been investigated experimentally. The length and diameter of thermosyphon that is used in these experiments were 40 and 4 cm, respectively. Thermosyphon is consist of three sections: condenser, adiabatic, evaporator. 40 volume percent of evaporator is filled of fluid. Water, Al2O3/water and CuO/water nano-fluid with different concentration have been used as operating fluid. Electrical field with various intensities has been imposed on the thermosyphon. Evaporator and condenser are the electrodes of electrical field. Water has been used as coolant fluid on condenser. At the time of steady state of the system in any stage, temperature of inlet and outlet coolant water, evaporator and condenser were measured by thermometer. The aim of this study is investigation of thermal resistance of thermosyphon. Recently, was plotted the experimental charts versus applied voltage. Results show that using of nano-fluid and electrical field reduce thermal resistance of thermosyphon. Finally, Maximum reduction percent of thermal resistance is equal to 35% for CuO/water nano-fluid. It’s for Al2O3 Development of new technology and increased industrial processes requires systems and heat exchangers with more efficiency [1]. Improve of heat exchangers due to lower time and high intensity of heat transfer [2]. Heat transfer improving is done by two ways: active and passive methods. Nano-fluid as an internal and passive factor and electrical field as a outlet and active factor are effective in heat transfer [3]. In addition to thermal conductivity, due to easy movement of nanoparticles in base fluid, heat transfer increases by nano-fluid [2]. Li [4] used copper nanoparticles and water flow in pipes with constant heat load on the walls. He observed that the nusselt number of 1 volumetric percentage of copper particles increases compared with water 12 percent. Ding et al.[5] have been studied performance of nano-fluid that contain carbon /water nano-fluid is equal to 45.6%.

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