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Second Thermal and Fluids Engineering  Conference

ISSN: 2379-1748
ISBN: 978-1-56700-430-4

INVESTIGATION ON LAMINAR FLOW AND HEAT TRANSFER CHARACTERISTICS OF MICROALGAE SLURRIES WITH RHEOLIGICAL PROPERTIES

Hao Chen
Key laboratory of Low-grade Energy Utilization Technologies and Systems, MOE, Chongqing, China; Institute of Engineering Thermophysics, Chongqing University, Chongqing, China

Qian Fu
Key laboratory of Low-grade Energy Utilization Technologies and Systems, MOE, Chongqing, China; Institute of Engineering Thermophysics, Chongqing University, Chongqing, China

Yun Huang
Key laboratory of Low-grade Energy Utilization Technologies and Systems, MOE, Chongqing, China; Institute of Engineering Thermophysics, Chongqing University, Chongqing, China

Ao Xia
Key laboratory of Low-grade Energy Utilization Technologies and Systems, MOE, Chongqing, China; Institute of Engineering Thermophysics, Chongqing University, Chongqing, China

Qiang Liao
Chongqing University

Xun Zhu
Key Laboratory of Low-grade Energy Utilization Technologies and Systems, Ministry of Education, Chongqing University, Chongqing 400030, China; Institute of Engineering Thermophysics, Chongqing University, Chongqing 400030, China

Abstract

Hydrothermal hydrolysis is a cost-effective method to pretreat microalgae biomass for further biofuel conversion. In the continuous hydrothermal hydrolysis reactor, the pre-heating process is hard to control due to the complex rheological properties of microalgae slurries with high mass fraction and temperature. In this study, we investigated the rheological properties of microalgae slurries with different mass fraction (10wt.%, 15wt.% and 20wt.%) under different temperature and shear rate (21.5s-1-1000s-1). The results showed that microalgae slurries exhibited non-Newtonian fluid behavior with shear-thinning behavior, and the viscosity of microalgae slurries increased with the increasing temperature from 70 to 100°. Meanwhile, the numerical simulation was performed to investigate the flow and heat transfer characteristics of microalgae slurry flowing through a tubular reactor with homogeneous heat flux. The microalgae slurries are assumed as homogeneous fluid, and the Reynolds numbers were assumed between 300 to 1600. Non-Newtonian viscosity for the microalgae slurries flow was calculated considering shear rate and temperature. The density, specific heat, and thermal conductivity of microalgae slurries are temperature dependent. The predicted Nusselt numbers and friction factors were confirmed by previous experiment data. The flow field and temperature distribution under different heat flux and flow rate were simulated, and the flow resistance and convective heat transfer coefficient were compared to the results of experiment results. On this basis, the effects of variable thermophysical properties and flow behavior index of microalgae slurries with different temperature on flow and heat transfer are discussed in details.

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