Experimental comparison of specific heat capacity of three different metal oxides with MWCNT/ water-based hybrid nanofluids: proposing a new correlation

The main objective of this study is to investigate three distinct non-commonly used metal oxide-based nanoparticles, i.e., CuO + MWCNT, MgO + MWCNT, and SnO₂ + MWCNT with a weight mixture ratio of 80:20 each (by weight ratio) and DI water as a base fluid along with the addition of the CTAB surfactant at 3:2. The study incorporates the effect of varying size, d_p (20–50 nm), different temperature range (25–50 °C), and volume concentration range of 0.25–1.5%. After examining the stability of prepared HNF over the 30th day from the preparation day and some of the meticulous experimentation on isobaric heat capacity, a new correlation is developed to predict the specific heat of hybrid nanofluid. Considering various parameters like various volume concentration (φ = 0.25–1.50%) and temperature range (T = 25–50 ℃), specific heat of nanofluid, specific heat of base fluid, density of nanofluid, density of base fluid, and average diameter of used nanoparticles. The developed correlation was with 2.93% and 0.903% maximum and average absolute deviation, respectively. Experimental results show the maximum decrement in specific heat value is about 15.09% compared to base fluid DI water at 25 ℃ and 1.50% volume concentration with an average particle diameter of 20 nm for the MgO + MWCNT (80:20)/water HNF. However, it is found that the rate of decrement decreases with the increase of d_p from 20 to 50 nm. From the current experimental results, it is concluded that the usage of HNF on relatively higher temperature significantly influences the overall thermophysical properties such as enhancement in thermal conductivity and decrement in viscosity of the working fluid, by paying the marginal loss in specific heat capacity. Therefore, it recommended that the usage of HNF on higher temperature is more beneficial for critical heat transfer application such as HVAC, effective thermal management of the system, natural and forced convection phenomenon.