扩缩方孔蜂窝蓄热体强化传热的数值模拟

Numerical simulation of heat transfer enhancement in honeycomb regenerators with expansion and contraction square channels

为提高烟气余热回收率,提出一种扩缩方孔蜂窝蓄热体,通过用户自定义函数(UDF)实现烟气和空气周期切换时流体种类和进口速度、温度等参数的改变,基于ANSYS Fluent软件建立了新型蓄热体的三维非稳态传热数值模型。通过比较模型预测值与文献实验值进行了模型验证。利用模型研究了新型蓄热体方孔扩缩角、扩缩节距和总长度对其传热和流阻性能的影响。通过温度云图分析了扩缩通道强化蓄热体性能的机理。结果表明,缩放通道能有效提高蜂窝蓄热体的传热性能,在压力损失增加不多的前提下,蓄热体效能最多提高约5个百分点。扩缩方孔蜂窝蓄热体长度越长,其传热性能越好;对于一定长度的新型蓄热体,扩缩节距(或扩缩角)不变时,蓄热体传热性能随扩缩角(或节距)增大而增强。扩缩角过大时,新型蓄热体流动阻力很大,综合性能不佳。

In this work,expansion and contraction square channels were presented for honeycomb regenerators to recover more waste heat from flue gas.A 3D numerical model of unsteady heat transfer was built with ANSYS Fluent for the new type of regenerators and user-defined functions(UDFs)were compiled to express the changes of fluid type,inlet velocity and temperature,etc.due to the switch between the flue gas and air blows.The current numerical model was validated by comparing its predicted results to experimental data in the literature.With the present model,the effects of expansion and contraction angle(θ),pitch(S)and regenerator length(L)on the performances of heat transfer and flow resistance were investigated for the novel regenerators.Temperature contours were presented to discuss the physical mechanism for the performance enhancement of regenerators with the expansion and contraction square channels.Numerical results confirmed that the expansion and contraction channels can improve the performance of honeycomb regenerators effectively,and regenerator effectiveness was improved by about 5 percentage under the premise of a limited increment of pressure loss.Besides,it was found that the longer the new regenerator,the better heat transfer performance it had.For the regenerators with a constant L,when theθ(or S)was fixed,the heat transfer performance can become better with the increment of S(orθ).However,the overall performance of the regenerator with a bigθcan be undesirable because of its large flow resistance.The current numerical study on the heat transfer enhancement of honeycomb regenerators via the secondary development of CFD software presented a new way for the optimal design and performance improvement of regenerative heat exchangers.