# A High Thermal Conductivity of MgO-H\({}_{2}\)O Nanofluid Prepared by Two-Step Technique
###### Abstract  
In this paper, the main goal is to study the impact of nanopowder volume concentration and ultrasonication treatment time on the stability and thermophysical properties of MgO-DW nanofluid at room temperature. The co-precipitation method was utilized to prepare pure MgO nanoparticles with an average particle size of 33 nm. The prepared MgO nanopowder was characterized by using XRD, SEM, and EDX analyses. Then, MgO-DW nanofluid was obtained with different volume concentrations (i.e., 0.05, 0.1, 0.15, 0.2, and 0.25 vol.%) and different ultrasonication time periods (i.e., 45, 90, 135, and 180 min) by using a novel two-step technique. With volume concentration and ultrasonication time of 0.15 vol.% and 180 min, respectively, good stability was achieved, according to the zeta potential analysis. With increasing volume concentration and ultrasonication time period of the nanofluid samples, the thermal conductivity measurements showed significant increases. As a result, the maximum enhancement was found to be 25.08% at a concentration ratio of 0.25 vol.% and agitation time of 180 min. Dynamic viscosity measurements revealed two contrasting trends with volume concentration and ultrasonication time. The lowest value of relative viscosity was gained by 0.05 vol.% MgO-DW nanofluid. The chemical and physical interactions between MgO nanoparticles and DW molecules play an important function in determining the thermal conductivity and dynamic viscosity of MgO-DW nanofluid. These findings exhibit that MgO-DW nanofluid has the potential to be used as an advanced heat transfer fluid in cooling systems and heat exchangers. M 20  
suggested the concept of blending nanoparticles into traditional working fluids to enhance the thermophysical properties and heat transfer characteristics of the working fluids. [PERSON] formulated the idiom \"nanofluid\" at the Argonne National Laboratory in the United States of America in 1995 [12]. Nanofluids have unique and effective features such as larger specific surface area (SSA) nanoparticles, high suspension stability (longer suspension time), reduced erosion of ducts, significant energy saving, minimal viscosity increase, and higher heat transfer rate as compared with the milli- and micro-sized suspension fluids proposed by [PERSON] [13; 14]. Therefore, different aspects of nanofluids have been studied such as synthesis techniques [15; 16; 17], thermophysical properties such as thermal conductivity and dynamic viscosity [18; 19; 20; 21; 22; 23], and nanofluid applications [16; 24]. Because of its clear influence on heat transfer, thermal conductivity is worth investigating. Accordingly, researchers have worked hard to investigate aspects that have an impact on thermal conductivity, such as the shape (morphology) and size of the dispersed phase (nanopowder), type of the base fluid, temperature, synthesis technique, using or not using and type of surfactant (additives), pH, nanopowder concentration, and ultrasonication time [25; 26; 27; 28; 29; 30]. Metal oxide nanopowders are widely used in nanofluid preparation due to their chemical stability as compared with metals, as well as their good thermal conductivity, abundance, and cheapness [31; 32]. Metal oxide nanoparticles such as MgO, CuO, Al\({}_{2}\)O\({}_{3}\), ZnO, TiO\({}_{2}\), Fe\({}_{2}\)O\({}_{3}\), and SiO\({}_{2}\) are suitable candidates for the development of effective heat transfer fluids due to their significant properties. Among these particles, MgO has played a critical role in improving the thermal properties of traditional fluids. In addition, MgO nanofluid has been employed in various applications including catalysis, catalyst supports, nuclear reactors, storage materials, and boiling processes [33; 34; 35; 36; 37]. Subsequently, investigators have extensively examined MgO nano oxides.