Effects of surface functionalization on the flow boiling heat transfer characteristics of MWCNT/R141b nanorefrigerants in smooth tube

This paper presents an experimental method to study the flow boiling heat transfer characteristics of two functionalized multi-walled carbon nanotube nanorefrigerants (MWCNT-COOH/R141b and MWCNT-OH/R141b). The experimental conditions are as follows: the nanoparticles volume fraction are individually set at 0.059%, 0.117% and 0.176%; the mass flow rate ranges from 100 to 350 kg·m−2·s−1; the inlet vapor quality ranges from 0.2 to 0.7. Results showed that both functionalized MWCNT/R141b nanorefrigerants can enhance the flow boiling heat transfer coefficient of a refrigerant in a tube, and the enhancement was increased with an increase in volume fraction. The heat transfer characteristics of the MWCNT-COOH/R141b nanorefrigerants were better than MWCNT-OH/R141b nanorefrigerants. At the condition of G = 120 kg·m−2·s−1 and a volume fraction 0.176%, the heat transfer coefficient of the MWCNT-COOH/R141b nanorefrigerant and MWCNT-OH/R141b nanorefrigerant increased up to 23.4% and 15.18%, respectively.