Pilot study to improve the heat transfer characteristics of nanofluids

Nanofluid is considered 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.

​​​​​​​​​​​​​​Study: Optimization of the heat transfer characteristics of MWCNTs and TiO2 water-based nanofluids through a new pilot-scale configuration. Image credit: Romix Image/Shutterstock.com

A recent study published in the journal Scientific reports aims to improve the heat transfer properties and thermal efficiency of a multi-walled carbon nanotube (MWCNT) and titanium dioxide (TiO2) nanofluid using a pilot-scale cross-flow cooling tower.

Nanofluid: overview and challenges

The nanofluid is classified as a stable dispersion with a low concentration of nanoparticles in the region of 1-100nm in working fluids such as oil, water, and glycol. Recent research has focused on improving the heat transfer of nanofluids 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, metal oxides, and carbon-based nanostructures are some of the nanoadditives used in the creation of nanofluids.

Despite their exceptional properties such as small size, large surface area and high heat absorption, these materials tend to agglomerate, especially at high concentrations. Therefore, the production of a stable nanofluid remains a significant challenge.

Improving the thermal properties of a nanofluid

Many techniques, such as ultrasonic motion, surface modification approaches, and pH modification, address the widespread problem of nanofluid inefficiency using nanoparticles. TiO2 nanoparticles have been widely used as nanoadditives for increasing the thermal efficiency of nanofluids due to their unique qualities, such as good colloidal and chemical resistance, environmental friendliness, heat transfer enhancement capabilities heat and the tendency to reduce friction.

MWCNTs can significantly improve the thermophysical characteristics of a nanofluid because MWCNTs have about five times the thermal conductance of other common materials. As a result, the increased thermal conductivity of the MWCNT nanofluid provides better heat transfer efficiency in applied systems.

A cooling system to evaluate the performance of nanofluids

Among the classic cooling technologies, the cooling tower has been applied in various sectors where waste heat needs to be removed from the process. Due to the disparity of vapor content between the water and gas phases, the basic principle of the water cooling tower requires a direct interaction between two channels of humidity and unsaturated air.

As a result, the water vaporizes and cools while the air becomes humid and warms. The efficiency of a cooling tower is determined by a variety of factors, including water flow, fluid inlet characteristics, and system behavior. The cooling tower fluid flow is divided into cross flow, parallel flow and counter flow.

So far, most cooling system studies have focused on improving the efficiency of cooling towers by considering various factors such as environmental scenarios, physical elements, and operational parameters. Nevertheless, the impact of using nanoparticles, such as TiO2 nanoparticles, on the production of a system’s working fluid is not fully understood.

Additionally, previous research has focused on counter-flow cooling towers, whereas none of these studies have examined cross-flow towers using TiO2 and MWCNT nanofluids.

Highlights of the current study

This study created two distinct water-based nanofluids using MWCNTs and TiO2 nanoparticles. The influence of nanofluidic fluid velocity and composition on cooling tower efficiency was assessed using an experimental setup of Response Surface Methodology (RSM) based on central composite design ( CCDs).

During the investigation, the efficiency, Merkel numbers and cooling range of MWCNT and TiO2 nanofluids were also examined. Moreover, the optimal and economic optimization for different parameters has been shown. The researchers’ earlier mid-point investigation into the impacts of using the MWCNT nanofluid has been resumed and completed in this research. Earlier results were analyzed with contemporary TiO data2 nanofluid.

Important Findings

The results demonstrated that nanofluids significantly improved the efficiency of cooling towers, especially at lower flow rates. Additionally, MWCNT nanofluids outperformed TiO2 nanofluids to improve the observed characteristics.

MWCNT nanofluid improved cooling tower efficiency, Merkel number, and cooling range by 10.2, 28, and 15.8%, respectively, while TiO2 the nanofluid increased the same parameters by 4.1, 5 and 7.4% at the same concentration.

Based on these results, it is reasonable to infer that MWCNT and TiO2 The nanofluids developed in this work have remarkable potential for future heat transfer applications due to their superior thermal conductivity and heat transfer capabilities.

Reference​​​​​​​

Javadpour, R. et al. (2022). Optimization of the heat transfer characteristics of MWCNT and TiO2 water-based nanofluids with a new pilot-scale setup. Scientific reports. Available at: https://www.nature.com/articles/s41598-022-19196-3

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