论文部分内容阅读
为了揭示周期性热作用下相变材料内部相变传热特征,为建筑外表相变隔热设计和计算提供支撑,本文设计制作了能模拟太阳运行、提供周期性加热的装置,并将正18烷封装于塑料圆桶容器中,使容器底部和侧面绝热,制作了测试试件。利用热电偶和巡检仪自动记录了周期性热作用下相变材料内部各层温度的变化。测试结果表明,在稳定周期性热作用下,材料内部相变传热特征主要可表述为:1)材料在非稳态周期性相变传热阶段,各层温度在达到相变温度点之前,温度变化明显;相界面会随着周期性加热次数的增加间断性地向内部扩展;温度平均值和振幅值向稳态周期性相变传热时的平均值和振幅值靠近。2)材料在稳态周期性相变传热阶段,内部各点温度也表现出与外界热作用等周期性变化,温度振幅从外到内依次减小。这与发生在固体中的周期性传热特性类似。但材料内温度变化呈现折转现象,在温度明显升高前出现等温滞后,在温度降低时会出现等温冷却。这与发生在固体中的传热现象有很大的区别。3)材料在稳定周期性热作用下,内部不会出现多个相界面共存现象。4)空气流速对相变材料中温度振幅和相界面移动速率都有较大影响,提高空气流速可以降低温度振幅和减慢相变进程。这意味着当相变材料用于建筑外表进行相变隔热时,可以通过组织自然通风减少其用量。
In order to reveal the internal heat transfer characteristics of phase change material under cyclic thermal effect and provide support for the design and calculation of phase change thermal insulation of building exterior, this paper designs a device capable of simulating solar operation and providing periodic heating, Alkaline encapsulated in plastic drum containers, so that the bottom of the container and the side of the insulation, the production of test specimens. The thermocouple and the inspection device automatically record the temperature change of the inner layers of the phase change material under the cyclic thermal action. The test results show that the heat transfer characteristics within the material can be expressed as follows: 1) The material in the unsteady periodic phase transition heat transfer phase, the temperature of each layer in the phase transition temperature before the point, The temperature changes obviously; the phase interface expands to the inside intermittently with the increase of the number of periodic heating; the mean value and amplitude value of temperature average value and amplitude value are close to the steady state periodic heat transfer. 2) In the steady-state periodic phase change heat transfer phase, the internal temperature also shows periodic changes with the outside heat, and the temperature amplitude decreases from the outside to the inside. This is similar to the periodic heat transfer characteristics that occur in solids. However, the temperature changes within the material showed a turnaround phenomenon, the temperature was significantly increased before the onset of isothermal lag, when the temperature decreases will be isothermal cooling. This is very different from the heat transfer phenomenon that occurs in solids. 3) The materials do not coexist in multiple phases at the interface due to the stable periodic thermal effect. 4) The air velocity has a great influence on the temperature amplitude and the phase velocity in the phase change material. Increasing the air velocity can decrease the temperature amplitude and slow the phase transition. This means that when the phase change material is used for phase change insulation of the building’s exterior, it can be used to reduce the amount of tissue through natural ventilation.