Nucleate boiling heat transfer characteristics of non-azeotropic refrigerant on micro-nano composite structured surfaces

The study on enhanced boiling heat transfer of non-azeotropic refrigerant is of great significance for its application in thermal management systems. Researches have shown that composite surface is an effective surface modification technique for enhancing nucleate boiling heat transfer of water. In order to study the effect of composite surface on nucleate boiling heat transfer of non-azeotropic refrigerant, first, the heat transfer performances of R32, R1234yf, R454B (R32/R1234yf = 0.689/0.311), R454C (R32/R1234yf = 0.215/0.785), and Mixture 1 (R32/R1234yf = 0.5/0.5) on smooth surface (SS) were tested. Second, R32 and R454B were selected as measured fluids to test the boiling heat transfer on different composite surfaces. The composite surfaces used in the experiment include the mechanical machining-femtosecond laser processing (MM-FLP) composite surface, the mechanical machining-femtosecond laser processing-oxidation etching (MM-FLP-OE) composite surface, the MM-FLP-OE composite surface with low surface energy material modification. All above surfaces are prepared based on the microcolumn surface (MS). The results show that for SS, the values of critical heat flux (CHF) in descending order are R32, R454B, R32/R1234yf (0.5/0.5), R454C, and R1234yf, with values of 658 kW/m2, 624 kW/m2, 537 kW/m2, 270 kW/m2, and 228 kW/m2, respectively. Compared to the MS, the CHF and the maximum heat transfer coefficient (HTC) of R454B on MM-FLP composite surface increase by up to 9.5 % and 105.7 %, respectively. While for R32, the increase in CHF and the maximum HTC on MM-FLP composite surface is 8.8 % and 390.8 %, respectively. For MM-FLP composite surface, laser power, laser spacing, and the number of laser scans all have a great influence on the boiling heat transfer of refrigerants. MM-FLP-OE composite surfaces are detrimental to nucleate boiling heat transfer of refrigerants compared with MM-FLP, especially the MM-FLP-OE composite surface with low surface energy material modification, which is different from the results of water. However, compare with the heat transfer of refrigerants on SS, all composite surfaces in this study are beneficial to the boiling heat transfer performance of the refrigerants.