Rheological and heat transfer behaviour of the ionic liquid, [C₄mim][NTf₂]

Systematic experiments have been carried out on the thermal and rheological behaviour of the ionic liquid, 1-butyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}imide, [C₄mim][NTf₂], and, for the first time, on the forced convective heat transfer of an ionic liquid under the laminar flow conditions. The results show that the thermal conductivity of the ionic liquid is ∼0.13 W m^-1 K^-1, which is almost independent of temperature between 25 and 40 °C. Rheological measurements show that the [C₄mim][NTf₂] liquid is a Newtonian fluid with its shear viscosity decreasing with increasing temperature according to the exponential law over a temperature range of 20-90 °C. The convective heat transfer experiments demonstrate that the thermal entrance length of the ionic liquid is very large due to its high viscosity and low thermal conductivity. The convective heat transfer coefficient is observed to be much lower than that of distilled water under the same conditions. The convective heat transfer data are also found to fit well to the convectional Shah's equation under the conditions of this work.