Study On Heat Transfer Enhancement Of Alumina Nanofluids In Engine Oil Cooler

The vehicle engine coolant is the main heat transfer medium for Vehicle Thermal Management System (VTMS). As engine power density and key components'heat load increase, it becomes essential to improve coolant's property and performance so as to make more efficient, compact and light-weighted cooling system, raise engine heat efficiency, reduce fuel consumption and exhaust gas. Nanofluid is a brand-new coolant based on nanotechnology. With higher thermal conductivity than pure liquid, better suspension stability than millimeter and micrometer particle suspensions, as well as improved boiling point and corrosion resistant, nanofluid has many advantages in new generation VTMS.This thesis investigated heat transfer enhancement of nanofluids in engine oil cooler. The main contents are as follows:Preparation method and thermo-physical properties:a new type nanofluid with alumina nanoparticles dispersed in mixed base-fluid was prepared by stabilizer and supersonic dispersion technology. The thermal conductivity, specific heat, thermal diffusivity and viscosity were measured respectively by various test methods.Fluid flow and heat transfer experiment in heat transfer unit of engine oil cooler:a convection heat transfer system was built, and flow and heat characteristics of nanofluids were tested and analyzed under different particle volume concentration, Reynolds number and flow velocity.Fluid flow and heat transfer numerical simulation in heat transfer unit of engine oil cooler:based on standard turbulence model, flow and heat transfer properties of nanofluids in heat transfer unit of engine oil cooler were numerically studied and compared by both continuous phase and dispersed phase models, and the mechanism of nanofluids'heat transfer enhancement was then analysed.Heat transfer enhancement of nanofluids in engine oil cooler:a heat transfer experiment system for engine oil cooler was built and the heat transfer performance of alumina nanofluids were measured and compared with mixed base-fluid, water and antifreeze.The main conclusions were as follows: 1. The addition of nanoparticles can improve the heat transfer ability of the mixed base-fluid. The thermal conductivity, specific heat and heat diffusivity of nanofluids increase with temperature, and the viscosity rises with particle volume concentration but falls rapidly with elevated temperature.2. The heat transfer capability of nanofluids in the heat transfer unit can be enhanced by adding more nanoparticles into the mixed base-fluid. Under the same flow resistance, nanofluids can transfer much more heat than the mixed base-fluid.3. Compared to the continuous phase model, the dispersed phase model can better numerically simulate the flow and heat transfer characteristcs of nanofluids. Adding nanoparticles can both change the thermo-physical and flow properties of mixed base-fluid, and improve the coordination between velocity and temperature field, leading to heat transfer enhancement.4. The heat flow and heat transfer coefficient of nanofluids increase with nanoparticle volume concentration, mass flow rate and temperature difference between hot and cool fluids, which are significantly higher than the mixed base-fluid and antifreeze (with concentration above 3%). Under higher working temperature, nanofluids show greater heat transfer enhancement but with much lower flow resistance.The new type vehicle nanofluid coolant was prepared and its thermo-physical properties, fluid flow and heat transfer performance were studied in this thesis, which would provide theory and experiment basis for nanofluids' practical application in new generation Vehicle Thermal Management Systems.