蓄热式管壳换热器传热特性研究

针对热电联产机组供热期发电负荷受供热量限制,机组调峰能力下降、电力系统弃风弃光现象严重的问题,设计了一种新型蓄热式管壳换热器。利用相变材料蓄/放热过程中温度接近恒定、释放潜热量大等优点,选取石蜡为相变材料,换热器相变区作为换热单元,采用控制变量法,针对传热流体流速、相变材料导热系数及相变层厚度等关键因素,对换热单元的蓄/放热过程进行数值模拟。结果表明:提高传热流体流速可增强换热单元蓄热能力,缩短相变材料完全熔化时间,放热过程中为保证换热器输出端热量,应适当选取传热流体流速;使用复合材料提高相变材料导热系数能够增强换热单元的换热能力,在相同传热流体流速下使换热单元平均传热系数较纯石蜡工况提升2倍以上;增加相变层厚度在放热过程中可延长传热流体出口温度维持的时间。

Heat transfer research on regenerative shell-and-tube heat exchanger

The power load of heat and power cogeneration units in heating season is generally limited by the heat supply, as a result, the peak load regulation capacity of generating unit decreases, the curtailment of wind and solar power is severe. To solve this problem, a new type of regenerative shell-and-tube heat exchanger is designed. Phase change materials have the ability of maintaining constant temperature and releasing latent heat during charging/discharging process. Paraffin is selected as the phase change material and the phase change region of the exchanger as the regenerative heat transfer unit. Numerical simulation is carried out to discover the heat transfer characteristics of regenerative heat transfer unit by using control variable method. Key factors such as heat transfer fluid velocity, thermal conductivity of the phase change material and the thickness of the phase change layer are discussed. The simulation results show that increasing heat transfer fluid velocity benefits the heat storage performance of the unit and reduces the melting time of phase change material. Proper heat transfer fluid velocity should be selected in the discharging process to guarantee the output heat quantity of the unit. Using composites with high thermal conductivity enhances the heat transfer performance of the unit and doubled the average heat transfer coefficient compared to the pure paraffin condition under the same heat transfer fluid velocity. Increasing the phase change layer thickness can prolong the time of maintaining the outlet temperature of the heat transfer fluid during exothermic process.