Abstract:

Paraffin wax in the partition wall type heat exchanger encumbers the heat transfer rate of the system because of its low thermal conductivity. The heat exchange rate of the heat storage system can be greatly improved by direct heat exchange between paraffin and air. Paraffin wax and air were used to study the heat transfer characteristics of air-paraffin direct contact heat transfer. The air at room temperature was injected into high-temperature (100-150℃) liquid paraffin through a distributor. This work examines the effects of superficial gas velocity, static liquid height and heat exchange temperature difference on the volumetric heat transfer coefficient and gas holdup rate in paraffin-air bubble heat transfer system. The results show that the volumetric heat transfer coefficient and the gas hold up increase by increasing the superficial gas velocity, and, for gas holdup, the growth rate is faster at lower superficial gas velocity. Increasing the height of the static liquid height will only lead to a decrease in the volumetric heat transfer coefficient and the gas holdup in the experimental conditions, and the effects of changing the gas liquid temperature difference on the volumetric heat transfer coefficient is not obvious. In addition, these effects are formulated in forms of empirical equations.

Key words: bubble column reactor, gas-liquid flow, bubble, direct contact heat transfer, heat transfer temperature difference, volumetric heat transfer coefficient, volumetric Nusselt number

摘要：

在间壁式换热器中石蜡因为其热导率低影响了蓄热系统的换热速率，采用石蜡与空气直接接触换热可大幅提高蓄热系统的换热速率。把常温的空气通过气体分布器注入熔融状态的石蜡（100~150℃）中，具体考察了表观气速、静液位高度和传热温差等参数对石蜡-空气鼓泡换热中体积传热系数与气含率的影响。实验结果表明，随着表观气速的增大，体积传热系数与气含率随之增大，并且对于气含率，在较低的表观气速下的增长速率更快；在实验条件下，增加静液位高度都只会导致体积传热系数与气含率的降低，而改变气液温差对体积传热系数的影响不甚明显。根据实验结果获得了石蜡与空气直接接触换热的体积Nusselt数经验关联式。

关键词: 鼓泡塔, 气液两相流, 气泡, 直接接触换热, 传热温差, 体积传热系数, 体积Nusselt数