Experimental investigation of a two-phase closed thermosyphon with Al2O3/R134a nanorefrigerant

Nanorefrigerants are mixtures of refrigerant and nanoparticles, which enhance the heat transfer in both air-conditioning and refrigeration systems. In the present work, the nanorefrigerant Al2O3/R134a is applied in a two-phase closed thermosyphon in order to investigate its thermal performance. More specifically, the influence of the Al2O3/R134a on the thermal resistance and heat transfer coefficient for various heat inputs in a two-phase closed thermosyphon were investigated experimentally. The two-phase closed thermosyphon was tested by varying the concentration of Al2O3 nanoparticles from 0.5% up to 1.5% by weight basis in the usual refrigerant R134a. The results of the experimental investigations indicate that there is a significant enhancement in heat transfer by 93.2% when the nanoparticle concentration of 1.0% was used in R134a when compared to the thermosyphon tested with pure R134a. The nanorefrigerant in thermosyphon has reduced its thermal resistance significantly by 59%. The heat transfer coefficient obtained for nanorefrigerants in two-phase closed thermosyphon is validated by Cooper correlation. It is inferred from the study that the depositions of nanoparticles in the thermosyphon enhance heat transfer. A new correlation to predict the rate of heat transfer is also proposed for employing the nanorefrigerants in a two-phase closed thermosyphon. The predicted correlation, heat transfer coefficient and thermal resistance are optimized by using Grey Relation analysis by computing the grade between the minimum and maximum values obtained from the experimental results.