Experimental and Analytical Studies on Nanofluids Vertical Tube Bundle Pool Boiling

Description

Nanofluids, which are nanoparticle dispersions in a liquid, have already seen much interest due to their heat transfer enhancements with low particle concentrations compared to the base pure fluids. Pool boiling is one of the most efficient heat transfer modes. However, the complexity of two-phase flow boiling on tube bundles presents many challenges understanding of physical phenomena taking place, especially for vertical tube bundle pool boiling, about which very few research has been done.It is important to quantify these numerous two-phase flow, heat transfer and bubble dynamics mechanisms in order to better describe tube bundle pool boiling performance with different operational conditions. A tube bundle pool boiling facility is designed and constructed with three vertical tubes bundle submerged in a water pool. This specific tube position design can allow us to use a two phase flow particle image velocimetry (PIV) system for simultaneous measurement of bubble geometry and liquid flow velocity field, and a high speed camera for bubble image capture.To better understand different nanoparticles’ performance with tube bundle pool boiling, two-step method will be used to produce Al2O3-water, SiC-water and copper-water nanofluids with different nano-particle concentrations, which are oxide, carbide, and metal, respectively. The nanofluids will then be characterized, including TEM images of nanofluids and tube surfaces before and after boiling as well, particle size distribution, surface tension, thermal conductivity and etc. Tube bundle pool boiling experiments will then be conducted with pure water and water-based nanofluids. Through the experiments under different operational conditions, different sets of data and images of temperature profiles, full velocity field measurements and bubble geometries will be obtained using the instrumentation, DAS system on the experimental loop, including PIV system and high speed camera. Analyses and comparisons will be conducted to see the tube bundle effects, nanofluids effects and other factors affecting tube bundle pool boiling.Using the experimental results obtained, bubble dynamics and tube bundle effect analysis will be conducted with and without the introduction of nanoparticles of different types and concentrations. The bubble breakup and coalescence models due to bubble dynamics and turbulent mixing effect will be developed and implemented into a commercial CFD code, ANSYS CFX. As a result of this study, a simulation tool will be developed to predict the bubble dynamics, two-phase flow and heat transfer in a vertical tube bundle pool boiling with tube bundle turbulent mixing effect considered for both pure-water and water-based nanofluids.