冷凝式燃气热水器二次换热器数值模拟研究

Study on Numerical Simulation of Secondary Heat Exchanger of Condensing Gas Water Heater

二次换热器是冷凝式燃气热水器的重要部件,对提升燃气热水器的热效率具有关键作用。采用数值模拟的方法对冷凝式燃气热水器二次换热器进行研究,对实际设备进行合理简化,采用ANSYS ICEM CFD对几何模型进行网格划分,运用Fluent软件建立湍流模型和冷凝模型对二次换热器对流换热进行模拟。将实验测得的温度与模拟结果进行比较,验证模拟结果的准确性。通过对模拟结果的分析,找出二次换热器烟气流动和温度分布的规律,分析当前换热效果不理想的原因,提出3条改进措施:将烟气导流板从换热管束左侧移至中间位置,以改善烟气气流组织;增加一段导流板,使烟气进口与导流板连接,去除直角区域,以消除烟气气流在烟气进口侧上部的旋涡区;减少底部换热管束数量。

As an important part of condensing gas water heater, secondary heat exchanger plays a crit- ical role in increasing the thermal efficiency of gas water heater. The performance of secondary heat exchanger of condensing gas water heater is studied by numerical simulation method. The actual equipment is reasonably simplified, and the geometric model is meshed by ANSYS ICEM CFD software. The turbulence model and condensing model are built by Fluent software to simulate the convection heat transfer of secondary heat exchanger. The temperature measured by experiments is compared with the simulation results to verify the accuracy of the simulation results. The rules of flue gas flow and temperature distribution of secondary heat exchanger are found by analyzing the simula- tion results. The reasons for current non-ideal heat ex- change efficiency are analyzed, and three improvement measures are proposed, namely moving the guide plate of flue gas from left to middle to improve the flue gas flow distribution, adding a length of guide plate for con necting the flue gas inlet to the guide plate and removing the right angle area to eliminate the vortex region of flue gas stream in the upper part of the flue gas inlet side, and reducing the heat exchange pipe bundle at the bottom.