Study of Frosting Heat-and Mass-Transfer. Defrosting Mechanisms, and its Control by Impinging Solid Particles.

本研究分为两个部分。首先是在不同凝结和结霜条件下，湿空气在平行板内的传热传质实验研究。另一项是利用极浅流化床对冷却管内霜层的除霜及传热传质的实验研究。所得结果总结如下：1。传热传质与霜层生长的实验研究。i)霜层的厚度、质量和密度的增长取决于气流的速度；由于霜层中水汽的扩散和凝固，密度随时间增加。(2)膜状凝结总热流密度和潜热流密度随湿度差的增大而增大。iii)存在临界质量通量。此时膜状冷凝换热系数最大。流化床冷却管周围结霜层的传热传质与除霜机理实验研究i)设计了一种新型射流分布器，专门用于流化床除霜，并开发了一种可视化技术来研究结霜的形成和流化颗粒的运动。ii)高速视频系统观测显示，分布器产生的气固碰撞射流有效地剥离了管道上的结霜。iii)将冷却液温度降低至-30^ C，测量局部换热系数和霜面积分数；DB温度的影响。阐明了管内温度、颗粒静态床层高度、分布器和稳定剂位置对除霜性能和传热特性的影响。iv)用激光多普勒粒子动力学分析系统测量了剥离霜的尺寸分布。综上所述，本研究的目标已基本实现，本研究和后续研究的成果将对工程和工业做出巨大贡献。少

The present research is divided into two parts. The first is an experimental study on heat-and mass-transfer of humid air flow in a parallel plate under various conditions covering condensation and frost formation. The other is an experimental study on defrosting of frost layers on cooled-tubes using a very shallow fluidized-bed and the heat/mass transfer. The obtained results are summarized as follows :1. Experimental Study on Heat/Mass Transfer and Frost Layer Growth. i) Growing thickness, mass, and density of the frost layer depend on the velocity of air stream ; the density increases with time, owing to the diffusion and solidification of water vapor in the frost layer. ii) Total heat flux and latent-heat flox of filmwise condensation are increased with increasing the humidity difference. iii) There exists a critical mass flux. at which the heat transfer coefficient of filmwise condensation has the maximum value.2. Experimental Study on Heat/Mass Transfer and Defrosting Mechanisms … More of Frost Layers around Cooled-Tubes in a Fluidized Bed. i) A novel jet distributor has been designed specially for defrosting in the fluidized bed, and a visualization technique has been developed to investigate the initiation of frost formation and the motion of fluidizing particles. ii) Observation using a high speed video system revealed that gas-solid impinging jets produced by the distributor strip effectively off the frost on the tubes. iii) The local heat transfer coefficient and frost area fraction were measured lowering the coolant temperature to -30^ﾟ C ; the effects of the DB temperature. tube temperature, static bed height of particles, and position of distributor and stabilizers on the defrosting performance and heat transfer characteristics were clarified. iv) The size distribution of stripped frost was measured with a Laser Doppler Particle Dynamics Analyzer System.In summary, the objectives of the present study have almost been achieved, and the results of present and successive research will make great contributions towards engineering and industries. Less