Nanofluid optimum concentration for Heat Transfer enhancement, Paper Validation

Description

The nanofluid optimum concentration for Heat Transfer enhancement, Paper Numerical Validation, CFD Simulation by ANSYS Fluent

Nanofluids, solid-liquid composites, have higher thermal conductivity and convection heat transfer performance than base fluid without nanoparticles. Therefore, using nanotechnology, the heat transfer process can be optimized.

Nanoparticle concentration is an important parameter in increasing heat transfer under free convection, as many studies show that heat transfer is proportional to the nanoparticle concentration.

It is also important to understand the mechanism of increasing heat transfer at the optimum concentration of nanoparticles. In addition, many researchers still focus on developing mathematical formulas for the various properties of nanofluids and using those models in natural convection analysis.

The present study aimed to identify the optimal concentration of nanoparticles when using TiO2 nanoparticles with water to discover the possible mechanism of increased heat transfer.

This project simulates the process of combining water and nanofluid in a laboratory chamber by ANSYS Fluent software.

This work is based on the paper “Optimal Concentration of Nanofluids to Increase Heat Transfer under Natural Convection Cavity Flow with TiO2 – Water,” The quasi-simulation results are compared with the results of the paper.

In experimental research, a mixture of titanium dioxide and water is used as a nanofluid. The nanofluid is composed of nanoparticles with an average size of 50 nanometers. We change the temperature of the heat and cool walls and the nanofluid’s volume fraction to investigate their effects on heat transfer.

The volume fraction of nanofluids varies from 0.05 vol% to 0.8 vol%, and Ra in this study varies from 4.9 * 108 to 1.47 * 109. First, the geometry of the test chamber was designed in Design Modeler software and prepared for meshing.

The geometry file was implemented in ANSYS Meshing software to create mesh and boundary conditions name selection. The dimensions of this problem are 120 * 96 * 103 mm as a cube. The mesh type is hexahedral. The element number is 40000.

Nanofluid Methodology

As the number of elements in the mesh increases, the Nusselt number changes, but with increasing more than a certain value, these changes become very small.

As shown in the diagram and table above, the difference between the results of the two grids of 40,000 and 80,000 elements is less than 2%. Therefore, the mesh independence is done at elements number equal to 40000.

Nanofluid Conclusion

This study aimed to identify the optimum nanofluid concentration during the free convection process using a square chamber with hot and cold opposite walls, and all other walls were insulated. The Nusselt numbers reported in the paper with their corresponding numbers in the current CFD simulation are validated as follows.

Experiment result (based on paper)		Numerical result (based on simulation)
RA	NU	RA	NU
5.76E+08	5.34E+01	5.76E+08	53.43
8.65E+08	5.97E+01	8.65E+08	59.88
1.16E+09	6.53E+01	1.16E+09	6.48E+01
1.46E+09	6.81E+01	1.46E+09	6.82E+01

This comparison shows that the present numerical results are comparable to the theoretical and experimental results. At different temperature differences between the walls, the Nusselt number is reported. Numerical CFD Simulation and experimental values in different temperature differences are as follows.

	dT	Nu-exp	Nu-num	E%
1	20	44.99	45.43434	0.987642
2	30	51.83	51.03283	-1.53805
3	40	55.68	55.45027	-0.41259
4	50	65.22	63.4676	-2.68691

The figure above shows the change in the Nusselt number in terms of the Rayleigh number for a concentration of 0.8% nanofluid. The Nusselt number increases with increasing Riley number and concentration of nanofluid.

This study focuses on free convection in a water-based titanium dioxide nanofluid. The effects of a temperature change, as well as volume concentration, were investigated. When investigating the effect of volume concentration on heat transfer, it was found that there is an optimal volume concentration.

From this study, it can be seen that the addition of titanium dioxide nanoparticles increases heat transfer. The maximum increase in heat transfer is 8.2% at a volume concentration of 0.05% and a temperature difference of 50 °C.

This study also shows the correlation between the simulation and experimental and theoretical results. Therefore, this research supports the idea that any nanofluid with a higher thermal conductivity than its base fluid may increase heat transfer under the same conditions.