Droplet collisions and interaction with turbulent flows for powder manufacturing

以下可能是喷雾干燥机中粉末更快生长的关键：-控制液滴和颗粒的碰撞和适当的结果{例如；液滴聚结（与分离或反弹相反），-产生适当的液滴或粒子浓度“模式”-增加空间和时间上的“聚类”-增加碰撞的可能性，-在更大范围的操作条件下保持这些品质。尽管喷雾干燥是一项古老的技术——“干燥”包括液滴碰撞和团聚的过程，半干燥和干燥的颗粒彼此之间——非常少的基础知识存在，可以可靠地回答一个简单的问题：给定喷雾干燥塔的这种几何形状，我应该生产什么样的喷雾和气流，以生产以下质量的粉末（例如湿度，平均尺寸，尺寸分布，形态）？答案必须包括对雾化器位置和流动条件的微小改变如何以及为什么会彻底改变粉末质量的解释。为了找到答案，我们需要对“基本”过程进行比目前更好、更广泛的测量：我们必须产生新的理解和想法，以提高我们计算实际液体（最初的原料通常具有寒冷天气里牙膏的稠度）和几何形状中湍流碰撞的位置、数量和结果（弹跳、聚结/凝聚、粘滞）的能力，并根据基本的、简单的但具有代表性的流动几何形状来检查进展。该提案的总体目标是通过提高对湍流中液滴或颗粒碰撞的概率以及液滴-液滴，颗粒-颗粒或液滴-颗粒碰撞的结果的理解来创新喷雾干燥机中的粉末制造，重点是通过喷雾干燥或其他类似工艺生产粉末时使用的液体特性和几何形状。研究假设，在喷雾干燥过程中，粉末的生长可以发生比目前认为的要快得多，通过同时多液滴碰撞，由二元液滴碰撞引发。这是因为碰撞的持续时间相对较长，并导致变形的瞬时形状（韧带，椎间盘等）与相对较大的“目标”表面积。在液滴对碰撞过程中形成的韧带可以在碰撞事件中与流动湍流相互作用而破裂，而不是合并成更大的液滴。目前在工业喷雾干燥机的设计和用于预测的液滴碰撞计算模型中都没有考虑到这两个事件。我们的方法将是使用光学仪器在流动配置中对液体、喷雾和气体的运动进行新颖的时间和空间分辨测量，从而可以研究液滴碰撞的微观物理，并在模型喷雾干燥器中研究宏观过程。我们将利用这些结果建立新的“碰撞核”和湍流中液滴碰撞结果的独特半经验相关性和非球形韧带的破裂，并提出控制粉末制造的新方法，以及用于预测喷雾干燥机的新计算模型。

The following may be a key to the faster growth of powders in spray dryers: - control of droplet and particle collisions and appropriate outcomes {e.g. droplet coalescence as opposed to separation or bounce-off}, - generation of appropriate droplet or particle concentration 'patterns' - increased 'clustering' in space and time - to increase probability of collisions, - maintaining these qualities over a wider range of operating conditions. Although spray drying is an old technology - 'drying' including the process of collision and agglomeration of droplets, semidried and dried particles amongst each other - remarkably little fundamental knowledge exists which would reliably answer the simple question: given this geometry of spray drying tower, what kind of spray(s) and air flow(s) should I produce in order to manufacture powder of the following quality (e.g. humidity, mean size, size distribution, morphology)? The answer must include an explanation of how and why small modifications to the location of atomisers and flow conditions radically changes powder quality. To formulate the answer, we need better and more extensive measurements of the 'fundamental' processes than hitherto: and we must generate new understanding and ideas that will advance our ability to calculate the location, number and outcome (bouncing, coalescence/agglomeration, sticking) of collisions in turbulent flows for realistic liquids (initially feedstock frequently has the consistency of toothpaste on a cold day) and geometries - and check the advance against fundamental, simple yet representative flow geometries.The overall aim of the proposal is to innovate powder manufacturing in spray dryers by improving the understanding of the probability of droplet or particle collisions in turbulent flows and of the outcome of droplet-droplet, particle-particle or droplet-particle collisions with emphasis on liquid properties and geometries used in powder production through spray drying or other similar processes. The research hypothesis is that the growth of powders in spray drying processes can occur much faster than currently believed through simultaneous multiple droplet collisions, initiated by binary droplet collisions. This is because collisions have a relatively long duration and result in deformed transient shapes (ligaments, discs, etc.) with relatively large 'target' surface area. The ligaments formed during droplet pair collisions can interact with the flow turbulence during a collision event and break up, instead of coalescing into larger droplets. Both these events are not currently taken into account in the design of industrial spray dryers nor in computational models of droplet collisions used for predictions. Our approach will be to make novel time- and spatially- resolved measurements of the liquid, spray and gas motions using optical instrumentation in flow configurations that allow the study of the microscale physics of droplet collisions and in model spray dryers that allow the study of macroscale processes. We will use these results to establish new 'collision kernels' and unique semi-empirical correlations of droplet collision outcomes in turbulent flows and breakup of non-spherical ligaments and propose novel methods for control of powder manufacturing in, and new computational models for predictions of, spray dryers.