On the suitability of the volume-averaging approximation for the description of thermal expansion coefficient of nanofluids

Abstract

Currently, volume-averaging approximation is in common use for the description of thermal expansion coefficient of nanofluids in terms of expansion coefficients of their constituents. The accuracy of this method is not, however, so clear since it ignores the dependence of density on temperature in the prediction of thermal expansion coefficient that may not be true in natural convection circumstances.

In the current contribution, attention is focused to clarify how predictions of flow and thermal fields as well as heat transfer and entropy generation characteristics during natural convection of nanofluids may be influenced if one adopts the volume-averaging approximation for the description of thermal expansion coefficient. For this purpose, a porous enclosure saturated with several water-based nanofluids is simulated and results of the volume-averaged thermal expansion coefficient are compared with those of a recent correlation that takes into account the dependence of density on temperature.