Nano-Fluid: Porous Mixer for Increasing Heat Transfer

Nanofluid Porous Mixer for Enhanced Heat Transfer — ANSYS Fluent CFD Simulation

Description

This project investigates the mixing of hot (303 K) and cold (293 K) nanofluid streams, comparing two configurations: one using 28 mixers and another using 54 mixers, each modeled as a porous medium. The aim is to assess how the mixer arrangement influences the blending of the two streams and the resulting heat transfer.

The geometries were drawn in SpaceClaim and meshed in ANSYS Meshing. Two geometries are considered: the first has 2 rows of mixers, and the second has 4 rows. Both meshes are unstructured, built with the triangular method, comprising 87,501 cells for case 1 and 83,180 cells for case 2. The domain has two inlets, both with a velocity of 0.1 m/s; the upper inlet is at 293 K and the lower inlet at 303 K.

Methodology

A coupled algorithm was used for pressure-velocity coupling, and the Realizable k-epsilon model with standard wall functions was selected as the turbulence model. The nanofluid is treated as a single-phase fluid with modified thermophysical properties — density, viscosity, specific heat, and thermal conductivity — calculated as functions of the nanoparticle volume fraction using the standard nanofluid property correlations. The mixers are represented as aluminum porous media with a permeability of 1.

The porosity is defined as the ratio of the void volume (Vv) to the total volume (Vt). Based on the dimensions of the problem, the porosity is 0.937 for the 2-row case and 0.875 for the 4-row case.

Conclusion

Contours and vectors of velocity, static pressure, and temperature were obtained. As the figures show, the velocity contour is more uniform in the 2-row case. This can be attributed to the smaller number of mixer blocks and, consequently, the smaller variation in velocity gradient caused by the flow striking their sharp edges. The maximum and average velocities are higher in the 4-row case, indicating that although the 4-row case has more separation zones, the separations are more substantial in the 2-row case.

The pressure readings show more negative values in the 2-row case, which is consistent with Bernoulli's principle. Pressure is more positive at the top of the domain, where the temperature is lower than elsewhere. The temperature contours indicate that the maximum and average temperatures are essentially the same for both cases; however, in the 4-row case the geometry produces a wider range of temperature variation with more gradual changes.

Finally, the temperature is plotted along the centerline of each geometry. The diagram shows that in the 4-row case the temperature is higher at the center of the domain, a result of the greater number of separation zones enhancing the local mixing.