Session: 12-21-01: Multiphase Flow

Paper Number: 166510

Heat Exchange of a SiO2/Water Nanofluid in 3D Printed Lattice Channels With Differently Staggered Kagome Structures 

In this study, a lattice channel crossed by a nanofluid is proposed as a composite technique to enhance heat transfer processes. Possible applications are related to heat exchangers in civil and industrial applications. In detail, with reference to sustainability and environmental aspects, special attention is dedicated to improving the efficiency of the heating or cooling system in Nearly Zero Energy Buildings (nZEB), for example, by using waste heat to be transferred to other parts of the systems or even in closed-circuit solar plants.

A nanofluid is composed of a base fluid with a suspension of nanoparticles that improves the thermophysical properties of the base fluid. The authors conducted experimental tests on a silica-based nanofluid (SiO2/H2O) moving inside an aluminium 3D-printed lattice channel. The test channel is 80 mm long and has a cross-sectional area, without internal lattice, with the dimensions H=5 mm in height and W=15 mm in width. The channel is heated by an electrical resistance wrapped on its external surface so that a constant heat flux is applied.

The reticular shape of the unit cell is of the double tetrahedron Kagome type. Three different configurations have been studied, identified by how the base cell repeats in the main direction of the duct. The Kagome K4 proposes the base cell perfectly aligned with the first; the Kagome K1 is characterized along the duct by a cell offset equal to 1/2, while for the K2, the deviation is equal to 1/4. A final configuration, K5, presents a more interconnected base cell that constantly repeats itself. All configurations have the same porosity, equal to 87%, and the same diameter of the pillars, equal to 0.8mm.

The heat exchange in the presence of nanofluid and Kagome lattices is compared both with the case of the smooth duct alone and with other fluids, such as water and a mixture of water and glycol (Agal E6733, 67% by volume of ethylene glycol, 33% water).

The volume flow rates range from 0.2 to 4.0 l/min. The flow regime corresponds to the Reynolds ranges Re_D(hydr)=200-5500 for the nanofluid, Re_D(hydr)=500-7500 for the water and Re_D(hydr)=100-1200 for the Agal. The tests were conducted with the fluids at 20°C at the inlet to the test channel.

Considering also the pressure drops in the overall evaluation of the reticular duct performance, the cooling efficiency is calculated by introducing the thermal efficiency index Nu/f^(1/3), where Nu is the Nusselt number and f is the friction factor coefficient.

The results of the experimental investigation regarding the thermal performances show that the nanofluid-reticular duct combination is a novel and valid solution, especially for low values of the evolving flow rates. If compared with water alone, it allows average increases in heat exchange of 15-20% for flow rates up to 1 l/min.

In terms of energy efficiency, the K1 and K4 geometries are comparable with the smooth duct at low flow rates, but with a significant increase in heat rejection (more than 60%).

Presenting Author: Ivano Petracci University of Rome "Tor Vergata"

Presenting Author Biography: Ivano Petracci, PhD, is an Associate Professor at the Department of Industrial Engineering of "Tor Vergata" University of Rome. He currently teaches "Thermodynamics and Heat Transfer 1" and "Energetics" for the Bachelor's and Master's degrees in Mechanical Engineering, the course "Thermodynamics and Heat Transfer" for the Degree in Energy Engineering and for the Master's Degree in Medical Engineering. His experimental activity focuses on methods for enhancing convective heat transfer with active and passive techniques (extended and treated surfaces, lattice ducts, acoustic fields applied to fluids and composite solutions). The research is supported by thermodynamic and fluid dynamic investigations (hot wire anemometry and flow visualization techniques such as Particle Image Velocimetry) and by CFD studies in thermo-fluid dynamic applications.

Authors:

Giacomo Tosatti University of Rome "Tor Vergata"
Sandra Corasaniti University of Rome "Tor Vergata"
Michele Potenza University of Rome "Tor Vergata"
Ivano Petracci University of Rome "Tor Vergata"