Evaluation of Hydrodynamic and Thermal Behaviour of Non-Newtonian-Nanofluid Mixing in a Chaotic Micromixer

Abstract

Three-dimensional numerical investigations of a novel passive micromixer were carried out to analyze the hydrodynamic and thermal behaviors of Nano-Non-Newtonian fluids. Mass and heat transfer characteristics of two heated fluids have been investigated to understand the quantitative and qualitative fluid faction distributions with temperature homogenization. The effect of fluid behavior and different Al₂O₃ nanoparticles concentrations on the pressure drop and thermal mixing performances were studied for different Reynolds number (from 0.1 to 25). The performance improvement simulation was conducted in intervals of various Nanoparticles concentrations (φ = 0 to 5%) with Power-law index (n) using CFD. The proposed micromixer displayed a mixing energy cost of 50-60 comparable to that achieved for a recent micromixer (2021y) in terms of fluid homogenization. The analysis exhibited that for high nanofluid concentrations, having a strong chaotic flow enhances significantly the hydrodynamic and thermal performances for all Reynolds numbers. The visualization of vortex core region of mass fraction and path lines presents that the proposed design exhibits a rapid thermal mixing rate that tends to 0.99%, and a mass fraction mixing rate of more than 0.93% with very low pressure losses, thus the proposed micromixer can be utilized to enhance homogenization in different Nano-Non-Newtonian mechanism with minimum energy.

Keywords: Nano-Non-Newtonian fluid; chaotic micromixer; low generalized Reynolds number; mass mixing index; minimal mixing energy cost; thermal mixing index.

Figure 1

(a): 3-D view design of the proposed micromixers, (b): geometric parameters.

Figure 2

Evolutions of outlet velocities at the exit mid-line of X coordinates.

Figure 3

Structure of the generated mesh grid.

Figure 4

Quantitative validation for mixing efficiency index (a), and quantitative validation of local mass fraction contours for various planes (b) With the results of Xia et al., reproduced with permission from [15] and Hossain et al. reproduced with permission from [16].

Figure 5

Heat transfer coefficient Vs Reynolds number for non-Newtonian case with Li et al. reproduced with permission from [43].

Figure 6

Evolution of mixing rates Vs Reynolds number with Jibo et al. [44].

Figure 7

Mass fraction contours at various Reynolds numbers with different fluid concentrations (φ = 0.5 to 5%).

Figure 8

Development of mass mixing performance for different Reynolds numbers with variation cases of nanofluid concentration (φ = 0.5 to 5%).

Figure 9

Evolution of the mass standard deviation along the (a): exit X-line and (b) exit Y-line of different cases of nano-fluid concentration (φ = 0.5 to 5%) at fixed Re_g = 25.

Figure 10

Streamlines and vectors of the mass fraction with vortex core region.

Figure 11

Qualitative representation of Temperature contours for different generalized Reynolds number at the horizontal middle section of each nano-fluid concentrations (φ = 0.5 to 5%).

Figure 12

Evolutions of heat transfer coefficient for different generalized Reynolds numbers with various nanofluid concentrations (φ = 0.5 to 5%).

Figure 13

Evolutions of local heat transfer coefficient as a function along the geometry with φ = 1 and 5%.

Figure 14

Improvement of thermal mixing performance for different generalized Reynolds numbers for variation cases of nanofluid concentrations (φ = 0.5 to 5%).

Figure 15

Development of Mixing Energy Cost for several generalized Reynolds numbers (Re_g = 0.1 to 25) for various nanofluid concentrations (φ = 0.5 to 5%).