A comparative study of the thermal conductivities of nanofluids measured via a modified guarded hot plate method

Abstract

In the current debate surrounding nanofluids, more experimental studies are required for comparison to clarify much of the ambiguity surrounding the thermal conductivity of nanofluids. In recent years the development of nanofluids has come to a relatively slow crawl due to disagreements in results reported from different testing methods. The following study explores designing and constructing a guarded hot plate (GHP) apparatus. The apparatus was calibrated using deionized water. The GHP was then used to test the ethylene glycol and a Cobalt Oxide nanofluid's thermal conductivity, which was compared to existing reported results and numerical models of nanofluids. Ethylene glycol is a base fluid used for the nanofluids and will be used to establish a baseline. A finite element analysis(FEA) analysis was performed to validate numerical models of the device and to guide engineering choices of the selection of components; The GHP uses Fourier’s law of thermal conduction to extract the sample’s thermal conductivity. The GHP uses an embedded system that replicates steady-state conditions. The thermal conductivity is computed using the temperature readings from the two parallel plates and the voltage drop and current measurements across the 120W resistive heat elements embedded in the hot plate. The embedded system uses a PI controller to maintain the cold plate temperature at 20˚C through a 154W Peltier element. The Guard heater will maintain parity between the hot plate and the guard heater to ensure heat flux through the sample. The system was designed for a temperature differential of 40˚C. The research has led to the successful measurement of Cobalt Oxide nanofluids And their comparison to similar fluids and numerical models. The research endeavours to address if there is an increase in thermal conductivity using a methodology not frequently employed in the existing literature.