Effect of rheokinetics on convective heat transfer of microalgae slurry in tube during hydrothermal conversion

摘要

Hydrothermal pretreatment is a suitable technique to release microalgae biomass into liquid phase, which prepared for further biofuel production. During the hydrothermal treatment process, the dynamic rheo-logical behavior leads to the complex convective heat transfer performance of microalgae slurries in tube, which increased the difficulty in designing the heat exchanger. Herein, we experimentally investigated the temperature-dependent rheokinetics in a rheometer and convective heat transfer characteristics of the microalgae slurry in tube flow. The results revealed that the theological index varied with the reaction time in hydrothermal pretreatment processing, and the variation tendency was affected by temperature. Besides, the variation of Nusselt number (Nu) with temperature appears a peak Nu at 363 K, which was affected by the rheological index of microalgae slurry in stable state. Considering the effects of the rhe-ological index, volume fraction, and Peclet number, an empirical equation was proposed to describe the Nu of the microalgae slurry in tube flow from 293 to 423 K. It is a guidance to design the large scaled tubular heat exchanger for microalgae hydrothermal conversion.