In present study the effect of electric field on thermal performance of two-phase closed thermosyphon as external modifications has experimentally investigated. Internal modifications applied by using two different water based nanofluids as working fluids. Nanofluids prepared by adding Al2O3 and CuO nanoparticles into the pure water using ultrasonic vibration system without adding any dispersant or stabilizer to prevent any possible change of chemical properties of the nanofluid. Results show that the thermal performance, and the Nusselt number ratio of thermosyphon gradually increase by increase in electric field intensity and nanofluids concentration. These values decrease by increasing in input power. Results also show that Al2O3/water nanofluid improves thermal performance of thermosyphon more than CuO/water nanofluid. Also, the experimental results indicate that the effect of nanoparticles on thermosyphon thermal performance is higher than the electric field. Maximum enhancement of Nusselt number ratio is about 43% that observed at 60 W input power and 2.5% by volume of Al2O3 nanoparticles in the work fluid under 20 V electrical field strength. Enhancement value is 39% for CuO/water nanofluid.

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