Convection Heat Transfer of Nanofluids in Commercial Electronic Cooling Systems N.A. Roberts and D.G. Walker Department of Mechanical Engineering Vanderbilt University InterPACK 09 San Francisco, California, USA July 23, 2009 Sponsor: Oak Ridge National Laboratory 1/10
Introduction Nanofluids are colloidal suspensions of nanoparticles in a base fluid Typical nanofluid properties particles are metals, metal oxides or carbon in various forms particles range in size between 1 and 100 nm base fluid usually water and organic liquids Effects of nanofluids have shown an enhancement in thermal conductivity have shown enhancement in convective heat transfer in well controlled systems - can they be used in real systems Benefits of nanofluids reduced sedimentation and viscosity reduced damage to internal system components http://www.anl.gov/media Center/News/2004/nanofluidsbig.html 2/10
Why do nanofluids exhibit enhancement of thermal conductivity over effective medium theories? 1. Brownian motion results in micro/nanoconvection around particles 2. Ordering of liquid near the liquid/solid interface 3. Near field radiation between particles 4. No actual enhancement over theory, but a clustering into spherical or linear chains of particles while models assume well dispersed solutions 1. 2. http://www.mae.ncsu.edu/research/ck CM-P Lab/nanoflow.htm T 1 T 2 3. 4. 3/10
Experimental Setup Heat Exchanger O scope Straight Tube Setup Flow Meter Constant Temperature Bath Multimeter 15 Volt 15 Volt Power Supply Power Supply Differential Pressure Transducer Heated Test Section w/ Wall TC s Thermocouple Bank Key measurements pressure drop along test section Parastaltic Pump Nanofluid Reservoir temperature profile along outside of test section inlet and outlet fluid temperatures heat dissipation from heater wire volumetric flow rate Test section properties d i (mm) d o (mm) l (m) 1.07 1.47 0.91 d d o i Commercial System Setup Water block Heater Insulation 4/10
Nanoparticles and Preparation http://miam.physics.mcgill.ca/miam/images/research/self assembly/lennox nanoparticle.jpg Lai et al., 2008 Nanoparticles (Al 2 O 3 ) γ 10 nm γ 20-30 nm Preparation Nanoparticles are weighed and added to de-ionized water for different particle loadings Nanoparticles are ultrasonicated for 1 hour to break up agglomerates Results from DLS Particle (nm) 10 20-30 Ave. Part. Size (nm) 148.7 253.8 poly disp. 0.783 0.277 5/10
Results: Pressure and Temperature Drop/Increase temperature gain (K) Nearly equal pressure drop across the tube for all fluids Deviation from theoretical pressure drop for DI-water due to entrance effects and surface roughness 50 40 30 20 10 0 0 5 10 15 20 25 30 flow rate (ml/min) di-water 0.1% nanofluid 0.5% nanofluid 1.5% nanofluid theoretical pressure drop (kpa) 16 14 12 10 8 6 4 2 0 di-water 0.1% nanofluid 0.5% nanofluid 1.5% nanofluid theoretical -2 0 5 10 15 20 25 30 flow rate (ml/min) Nearly equal temperature gain across the heated tube for the DI-water and the 0.5% nanofluid Greater temperature gain in the 1.5% nanofluid due to enhanced convective heat transfer 6/10
Results: Average Convection Heat Transfer Coefficients convection coefficient (W/m 2 K) 3800 3600 3400 3200 3000 2800 2600 2400 0 5 10 15 20 25 30 flow rate (ml/min) di-water 0.1% nanofluid 0.5% nanofluid 1.5% nanofluid theoretical 7/10
Results: Calculated Thermal Conductivity thermal conductivity (W/mK) 0.9 0.85 0.8 0.75 0.7 0.65 0.6 0.55 0.5 0.45 0 0.5 1 1.5 2 volume loading (%) calculated di-water Maxwell s model H-S bounds 8/10
Results: Commercial System temperature gain (K) 30 25 20 15 10 5 0 0 5 10 15 20 25 30 35 40 flow rate (ml/min) di-water 1% nanofluid 0.5% nanofluid 9/10
Conclusions/Future Work Observed enhancement in convective performance without an increase in viscosity Calculated enhancement thermal conductivity with increasing volume loading within the Hashin-Shtrickman Bounds Keblinski s recent theory is supported by our results 10/10