Abstract 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 rheological 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 rheological 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 rheological 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.

中文翻译：

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流变动力学对水热转化过程中管内微藻浆液对流传热的影响

摘要 水热预处理是一种将微藻生物质释放到液相中的合适技术，为进一步生产生物燃料做好准备。在水热处理过程中，动态流变行为导致管内微藻浆的对流换热性能复杂，增加了换热器的设计难度。在此，我们通过实验研究了流变仪中温度相关的流变动力学和管流中微藻浆的对流热传递特性。结果表明，水热预处理工艺中流变指标随反应时间变化，变化趋势受温度影响。此外，努塞尔数 (Nu) 随温度的变化在 363 K 处出现一个峰值 Nu，受稳定状态微藻浆流变指标的影响。考虑流变指数、体积分数和Peclet数的影响，提出了一个经验方程来描述293-423 K管流中微藻浆的Nu。微藻水热转化。