Abstract
The present work investigates forced convective heat transfer characteristics of alumina-water nanofluids in a turbulent flow regime. Nanofluids are dilute colloidal suspensions with nano-sized particles ( < 100 nm) dispersed in a basefluid. The thermal conductivity values are measured by a steady state method, using a guarded hot plate (GHP) apparatus customized for liquids. The forced convective heat transfer characteristics are evaluated with the help of a test loop maintained in a constant heat flux condition. Controlled experiments under a turbulent flow regime are carried out using four particle concentrations (0.5vol%, 1vol%, 2vol% and 4vol %). The experimental results show that, the thermal conductivity of nanofluids increases with an increase in particle concentration and closely follow effective medium theories. However, the enhancement of heat transfer coefficients in the turbulent regime is observed to be within the measurement uncertainty.
Highlights
Cooling of thermal equipment has been one of the vital problems faced since the dawn of industrialization
There exists a vertical heat flow between the main heater and the top guard heater, and a horizontal heat flow between heater plate and the guard ring plate. These losses have to be accounted and corrected for. After accounting for these losses along with corrections for thermo-elements, it was observed that the apparatus was able to measure thermal conductivity with a maximum uncertainty of 1%
Since indirect electrical heating is applied in present guarded hot plate (GHP) apparatus, the electrical conductivity of fluids will not influence the thermal conductivity measurements
Summary
Cooling of thermal equipment has been one of the vital problems faced since the dawn of industrialization. Similar to observations of thermal conductivity enhancement, forced convective heat transfer characteristics of nanofluids showed mixed performances. They referred it as “dispersed fluid with sub-micron particles.” It was observed that in the turbulent flow regime the convective heat transfer coefficient of nanofluid was about 3–12 % lower than that of pure water (when compared at the same average velocity of fluid in the pipe).
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