Laboratory, comparative and statistical investigations of MWCNT and ZnO (15:85)/ethylene–glycol hybrid nanorefrigerant for improving thermal conductivity of ethylene glycol

In this study, thermophysical properties of MWCNT (15%)-ZnO (85%)/ethylene glycol hybrid nanofluid (HNF) have been investigated statistically and experimentally. Understanding thermal behavior of nanofluid (NF) in different laboratory conditions and also determining the correlation between process factors and how the factors affect the thermal behavior are the most important objectives of this study. This study is performed under laboratory conditions (T = 28–55 °C, SVF = 0.05–1.85%). Experimental results show with increasing SVF and temperature; thermal conductivity (TC) of NF increases due to increasing collisions number, increasing kinetic energy and increasing energy transfer between fluid layers. The Maximum increase and minimum increase in TC occur in laboratory conditions of SVF_max = 1.85% and SVF_min = 0.055 % which was equal to 27% and 2.5%, respectively. To predict and determine the correlation between process variables, RSM is used with a second-order model with R-squared = 0.9854 and − 1.5% < MOD <  + 1.5%. Also, the price performance factor (PPF) has been studied for two different HNFs.