Chen Jingjing, Risberg Mikael, Westerlund Lars, Jansson Urban, Wang Changsong, Lu Xiaohua, Ji Xiaoyan
Energy Engineering, Division of Energy Science, Luleå University of Technology, 97187, Luleå, Sweden.
State Key Laboratory of Material-Oriented Chemical Engineering, Nanjing Tech University, 210009, Nanjing, People's Republic of China.
Biotechnol Biofuels Bioprod. 2022 Jul 6;15(1):74. doi: 10.1186/s13068-022-02156-4.
The use of food waste as feedstock shows high production of biogas via anaerobic digestion, but requires efficient heat transfer in food waste slurry at heating and cooling processes. The lack of rheological properties hampered the research on the heat-transfer process for food waste slurry. Referentially, the twisted hexagonal and elliptical rubes have been proved as the optimal enhanced geometry for heat transfer of medium viscous slurries with non-Newtonian behavior and Newtonian fluids, respectively. It remains unknown whether improvements can be achieved by using twisted geometries in combination with food waste slurry in processes including heating and cooling.
Food waste slurry was observed to exhibit highly viscous, significant temperature-dependence, and strongly shear-thinning rheological characteristics. Experiments confirmed the heat-transfer enhancement of twisted hexagonal tubes for food waste slurry and validated the computational fluid dynamics-based simulations with an average deviation of 14.2%. Twisted hexagonal tubes were observed to be more effective at low-temperature differences and possess an enhancement factor of up to 2.75; while twisted elliptical tubes only exhibited limited heat-transfer enhancement at high Reynolds numbers. The heat-transfer enhancement achieved by twisted hexagonal tubes was attributed to the low dynamic viscosity in the boundary layer induced by the strong and continuous shear effect near the walls of the tube.
This study determined the rheological properties of food waste slurry, confirmed the heat-transfer enhancement of the twisted hexagonal tubes experimentally and numerically, and revealed the mechanism of heat-transfer enhancement based on shear rate distributions.
将食物垃圾用作原料通过厌氧消化可产生大量沼气，但在食物垃圾浆液的加热和冷却过程中需要高效的热传递。缺乏流变特性阻碍了对食物垃圾浆液热传递过程的研究。作为参考，扭曲六边形管和椭圆管已分别被证明是具有非牛顿行为的中等粘性浆液和牛顿流体热传递的最佳强化几何形状。在包括加热和冷却的过程中，将扭曲几何形状与食物垃圾浆液结合使用是否能实现改进仍不清楚。
观察到食物垃圾浆液具有高粘性、显著的温度依赖性和强烈的剪切变稀流变特性。实验证实了扭曲六边形管对食物垃圾浆液的传热增强作用，并验证了基于计算流体动力学的模拟，平均偏差为14.2%。观察到扭曲六边形管在低温差下更有效，增强因子高达2.75；而扭曲椭圆管仅在高雷诺数下表现出有限的传热增强。扭曲六边形管实现的传热增强归因于管壁附近强烈且持续的剪切效应在边界层中引起的低动态粘度。
本研究确定了食物垃圾浆液的流变特性，通过实验和数值方法证实了扭曲六边形管的传热增强作用，并基于剪切速率分布揭示了传热增强的机制。
