Experimental investigation of flow boiling heat transfer of R-600a/oil/CuO in a plain horizontal tube

• For refrigerant/oil mixture heat transfer coefficient increases for (x < 0.6).
• For refrigerant/oil mixture heat transfer coefficient decreases for higher vapor qualities.
• Adding CuO nanoparticles improves the heat transfer coefficient up to 63%.
• The heat transfer enhancement increases with the increase of nanoparticles weight fraction.
• The maximum enhancement was for G = 77 kg/m2 s x = 0.76 and nanoparticles mass fraction of 1.5 wt.%.

The aim of this paper is to experimentally investigate the effect of CuO nanoparticles on flow boiling of R-600a/Polyester mixture (99/1) inside a horizontal smooth tube. The experimental conditions of this study include mass velocities from 50 to 400 kg/m2 s, inlet vapor qualities from 0 to 0.9, heat fluxes from 3 to 8 kW/m2and mass fractions of CuO nanoparticles from 0 to 1.5 wt%. The well instrumented experimental apparatus including pump, flow meter, preheater, test evaporator, by-pass and condenser was designed, fabricated and installed in order to measure the experimental data on flow boiling heat transfer of refrigerant, refrigerant oil and refrigerant nanooil. Ultrasonic instrument was used to approach to the well dispersed nanooil and then the nanooil was injected with a syringe into the pure refrigerant through the cycle. The solutions were mixed by running them through the system at a high velocity for approximately 3 h. The results show that, nanoparticles cause a maximum heat transfer enhancement up to 63% relative to heat transfer coefficient of R-600a/oil without nanoparticles.