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Thermal and Hydraulic Performance of Metal Oxide - Based Nanofluids in Heat Exchangers
Keywords: Cooling, Nanofluid, Cold plate
Nanofluids (suspensions of nanoparticles in base fluids) were investigated for potential coolant use in heat exchangers. The thermal and hydraulic performance of three kinds of metal oxide - water nanofluids (Aluminum Oxide, Copper Oxide and Silicon Dioxide) was studied in round straight tubes with/without enhancement features (Twisted Tape Inserts and Internal Fins) using volume concentration (0 – 6%), flowrate (0.01 - 2GPM, Re=200 - 10,000) and working temperature (30 - 70C) as variables. Nanofluids were also tested in cold plates having two separate designs (tube-embedded and minichannel based architectures) where the thermal resistance, maximum temperature, pressure drop and other performance metrics were compared with baseline values measured for water. Within the bounds of experimental uncertainty, the heat transfer coefficients measured in experiments match the predicted values from conventional theories, when the thermophysical properties of the nanofluids (specific heat, viscosity, thermal conductivity and density) are properly accounted for (Figure 1a). In other words, no abnormalities were observed in the heat transfer performance of nanofluids (at least for low concentrations, ≤2%). Viscosity of nanofluids is generally higher compared to the base fluid and increases with increasing particle concentration; as expected, the flow of nanofluids requires larger pump pressure (power) for a given flow rate and fixed working temperature. A similar trend was observed when nanofluids were used as coolants in actual heat exchangers (cold plates). For example, at fixed conditions (coolant flow, inlet temperature and heat load), the maximum surface temperature was lowest for water in both cold plate designs, and increased as the particle volume fraction was increased; this also indicates an increase in thermal resistance. Tests conducted at various working temperatures (in the range of 30 - 70˚C) did not result in any significant change in the cooling performance of alumina nanofluids compared to the base fluid water. Results for copper oxide and silica-based nanofluids will also be presented at the conference.
Sanjida Tamanna, Research and Development Engineer
Advanced Cooling Technologies
Lancaster, PA
USA


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