Nanofluid is regarded as the heat transfer fluid of the future in a variety of heat transfer applications. A nanofluid provides higher thermal performance than normal fluids due to dispersed nanoparticles with high thermal conductance.
A recent study published in the journal Scientific Reports intends to improve the heat transfer properties and thermal efficiency of a multi-walled carbon nanotube (MWCNTs) and titanium dioxide (TiO2) nanofluid using a pilot-scale cross-flow cooling tower.
Nanofluid: Overview and Challenges
Nanofluid is classified as a stable dispersion with low nanoparticle concentration in the region of 1-100 nm in working fluids such as oil, water, and glycol. Recent research has focused on improving nanofluid heat transfer in many applications, such as cooling and refrigeration devices, manufacturing technology, combustion engines, and mechanical instruments.
A nanofluid can greatly improve heat transmission and thermophysical properties such as viscoelasticity, flash point, heat capacity, and cooling rate. Metals, metallic oxides, and carbon-based nanostructures are some of the nano additives utilized in creating nanofluids.
Despite their outstanding properties like small size, huge surface area, and great heat absorption, these materials tend to agglomerate, particularly at high concentrations. Therefore, producing a stable nanofluid remains a significant challenge.
Enhancing Thermal Properties of a Nanofluid
Many techniques, such as ultrasonic movement, surface modification approaches, and pH modification, address the prevalent issue of nanofluid ineffectiveness by using nanoparticles. TiO2 nanoparticles have been extensively employed as nano additives for the augmentation of nanofluid thermal efficiency because of their unique qualities, such as good colloidal and chemical resistance, environmental friendliness, heat transfer improvement capabilities, and friction-reduction tendency.
MWCNTs can considerably improve the thermophysical characteristics of a nanofluid because MWCNTs have about five times the thermal conductance of other common materials. As a result, MWCNTs nanofluid's increased thermal conductivity provides a better heat transfer efficiency in the applied systems.
A Cooling System for Assessing Nanofluid Performance
Among classic cooling technologies, the cooling tower has been applied in various sectors where waste heat must be removed from the process. Because of the disparity in vapor content between the water and gas phases, the fundamental premise of the water-cooling tower requires direct interaction between two flowing channels of moisture and unsaturated air.
As a result, water vaporizes and cools while air moistens and warms. A cooling tower's effectiveness is determined by various factors, including water flow rate, fluid inflow characteristics, and system behavior. Cooling tower fluid flow is divided into cross-flow, parallel-flow, and counter-flow.
Until now, most studies on cooling systems have concentrated on enhancing cooling tower effectiveness by taking into account various factors such as environmental scenarios, physical elements, and operational parameters. Nevertheless, the impact of employing nanoparticles, such as TiO2 nanoparticles, on producing a system's working fluid is not entirely understood.
Furthermore, previous research has concentrated on counter-flow cooling towers, whereas none of these studies examined cross-flow towers utilizing TiO2 and MWCNTs nanofluids.
Highlights of the Current Study
This study created two distinct water-based nanofluids utilizing MWCNTs and TiO2 nanoparticles. The influence of nanofluid fluid velocity and composition on cooling tower efficiency was assessed using a response surface methodology (RSM) experimental setup based on the central composite design (CCD).
During the investigation, the efficiency, Merkel numbers, and cooling range of MWCNTs and TiO2 nanofluids were also examined. In addition, the optimal and economic optimization for different parameters were shown. The researchers' earlier halfway investigation on the impacts of employing MWCNT nanofluid was resumed and finished in this research. Prior findings were analyzed with the contemporary data of TiO2 nanofluid.
The findings demonstrated that nanofluids significantly improved cooling tower effectiveness, particularly at lower flow rates. Moreover, MWCNTs nanofluids outperformed TiO2 nanofluids to enhance the observed characteristics.
MWCNTs nanofluid enhanced cooling tower effectiveness, Merkel number, and cooling range by 10.2, 28, and 15.8 percent, respectively, while TiO2 nanofluid boosted the same parameters by 4.1, 5, and 7.4 percent at the same concentration.
Based on these results, it is reasonable to infer that the MWCNTs and TiO2 nanofluids developed in this work have remarkable potential for future heat transfer applications owing to their superior thermal conductivity and heat transfer capabilities.
Javadpour, R. et al. (2022). Optimizing the heat transfer characteristics of MWCNTs and TiO2 water-based nanofluids through a novel designed pilot-scale setup. Scientific Reports. Available at: https://www.nature.com/articles/s41598-022-19196-3