Thermal-conductivity measurement of nanofluids using 3ω method

An experimental device was developed to measure the thermal conductivity of electrically conducting liquid based on the 3ω method. In this device, a line heater(Au) was patterned on the surface of a substrate(Pyrex glass), then a dielectric film(silicon nitride) was deposited to prevent the electrical leakage from the heater to the surrounding liquid. For the designed geometry, an analytic expression of the temperature oscillation of the heater was derived, and the effect of the dielectric film on the thermal-conductivity measurement was investigated. In the case that the thermal penetration depth was much larger than the heater width, the real part of the oscillating temperature was linearly proportional to the logarithm of frequency, and the sum of the thermal conductivities of liquid and substrate were obtained by the corresponding slope. When the dielectric film was thermally thin, its effect on the thermal-conductivity measurement could be neglected. The effective thermal conductivities of the aqueous suspensions of multi-walled carbon nanotubes with different concentrations were measured, which showed good agreement with the value predicted from the Hamilton-Crosser model. © All Rights Reserved.