Investigation on effective thermal conductivity of microalgae suspensions in a shear flow

Abstract

To enhance the production efficiency of microalgae products, heat transfer equipment deserves to be specifically designed to regulate the temperature field during the processing of microalgae. The effective thermal conductivity of microalgae suspension in shear flow fields varied with shear rate, which is one of an important property affecting the temperature fields of microalgae suspensions in reactors. Here we investigate the effective thermal conductivity of microalgae suspension in shear flow, which shows a significant difference with the static thermal conductivity. At low shear rates (<236 s−1), the effective thermal conductivity of microalgae suspensions is lower than the static thermal conductivity. In addition, the effective thermal conductivity of microalgae suspension increases with the increasing shear rate (236–471 s−1), while the static thermal conductivity keeps constant at different shear rates. The phenomena are probably because of the micro-motion of suspended microalgae cells in the shear flow field. Considering the effects of the volume fraction and thermal conductivity of microalgae cells, the shear rate, and particle Peclet number, an empirical formula correlation is proposed to predict the effective thermal conductivity of microalgae suspensions in shear flow.