含尘气流掠过干湿交变表面过程中粉尘的时变沉积机制及定量描述

The efficiency of air-conditioners will decrease with the increase of service time, mainly due to the dust particle deposition when ambient air flowing through the heat exchanger. The key factor affecting the particle deposition is wet-dry alternating condition of heat exchanger surface. To inhibit the dust deposition for overcoming its negative effect on the long-term performance of air-conditioner, the quantitive description method for the influence of wet-dry alternating surface on dust deposition characteristics should be obtained. The project will develop the microcosmic predicting models of dust deposition characteristics on dry surface, wet surface and wet-dry alternating surface, respectively, and reveal the time-varying deposition mechanisms of dust particles during the alternating process of droplets condensation and evaporation. Firstly, the dust deposition characteristics on dry surface are investigated and the predicting model is developed based on the observation of dust fouling layer and the measurement of dust quantity. Then, the effects of condensate water droplets on dust deposition carriers are investigated, and the model of dust fouling characteristics on wet surface is established based on the classic nucleation theory, the binary mixture diffusion theory, and the particle capture theory. Finally, the mechanisms of the time-varying dust fouling, including resuspension and separation of the dust particle as the surface alternatively becomes dry or wet are revealed, and the quantitive description method of dust time-varying deposition characteristics on wet-dry alternating surface is developed. The research achievements can provide theoretical basis for developing dust suppression method for heat exchangers, and enrich the migration and deposition theory of suspended particle.

空调器的能效会随着使用年限增加而下降，主要原因是环境空气流过换热器时引起的粉尘沉积，而影响沉积的关键因素是换热器表面的干湿交替变化状态。为抑制粉尘沉积以克服其对空调长效性的不利影响，必须掌握表面干湿交变对粉尘沉积特性的影响规律并加以定量描述。本项目拟从细微观角度分别建立干表面、湿表面及干湿交变表面粉尘沉积过程的预测模型，揭示液滴间歇凝析和蒸干对粉尘时变沉积特性的影响机制。通过干表面沉积层的观测与沉积量测定，研究粉尘沉积特性并开发预测模型；考察凝析的液滴对粉尘沉积载体的影响，并结合经典成核理论、二元混合物扩散理论和颗粒捕集理论，提出粉尘被液滴吸附、随液滴运动的湿表面粉尘沉积特性的模型；在此基础上探究表面由干变湿时已沉积粉尘再悬浮、由湿变干时已吸附粉尘析出的沉积层时变机制，建立干湿交变表面粉尘时变沉积特性的定量描述方法。项目成果为开发换热器抑尘措施提供理论依据，并丰富悬浮颗粒物迁移与沉积理论。

空调器的能效会随着使用年限增加而下降，主要原因是含尘空气流过换热器表面时引起的粉尘沉积，而粉尘沉积量受到换热器表面干湿交替变化的影响。为了抑制换热器表面的粉尘沉积以克服其对空调长效性的不利影响，必须掌握换热器表面干湿交替变化对粉尘沉积的影响规律并提出定量描述方法。本项目从细微观角度分别建立干表面、湿表面及干湿交变表面粉尘沉积机理的预测模型，揭示液滴间歇凝析和蒸干对粉尘沉积层的影响机制，并采用实验来验证和修正模型。首先通过干表面沉积层形成的观测与沉积量测定，研究干表面粉尘沉积特性并开发预测模型；然后考察表面凝析的液滴对粉尘沉积目标载体的影响规律，并结合经典成核理论、二元混合物扩散理论和颗粒捕集理论，开发粉尘被液滴吸附、随液滴运动的湿表面粉尘沉积特性的预测模型；在此基础上揭示表面由干变湿时已沉积粉尘再悬浮、由湿变干时已吸附粉尘析出的沉积层时变机制，建立干湿交变表面粉尘沉积特性的定量描述方法。项目成果为开发抑制换热器积灰的措施、保证换热器及空调长期高效运行提供了理论依据，并丰富了悬浮颗粒物迁移与沉积理论。