Ageing of fouling layers

结垢，即在传热和/或传质表面上不希望的绝缘层的形成，是随空间和时间变化的现象。这导致沉积物的随时间变化的材料变化（老化），从而影响其热性能和机械性能。通过了解这些过程，可以更详细地描述热传递和清洁行为。这项研究建议建立在这样的假设上，即随着时间的推移，可以通过温度依赖的动力学方法来定量地描述对老化过程的透彻理解。这可以从导热系数、强度、结构和成分等方面进行计算。为此目的，在层流通道中以变化的工艺参数（例如本体和壁温度、流速和组成）产生来自食品加工的含有矿物质和蛋白质的沉积物。首先，老化速率与沉积和去除速率解耦，并且确定污垢层的横截面积内的离散子层中的热导率。为了实现后者，设计了一个实验程序，结合联合收割机热阻和层厚度。此外，内聚力和粘附力，剪切强度，耐磨性和抗渗透性定量表征的机械性能。为了能够以一种简化和分离的方式研究老化机制和动力学，之前提到的材料特性也是在均匀的模型层上确定的。除了将现有的热老化模型转移到两个新的材料系统之外，还将根据结构和机械特性的信息对沉积物内的结合力进行新的定义。这可以集成到一个经典的污垢模型。老化过程的进展和由此产生的材料变化可以根据先前阐明的热、机械和结构参数的相互作用来预测。

Fouling, i.e. the unwanted formation of insulating layers on heat and/or mass transfer surfaces, is a phenomenon varying in space and time. This leads to a time-dependent material change (ageing) of the deposits, which influences their thermal and mechanical properties. With the knowledge of such processes the heat transfer and the cleaning behavior can be described more detailed. This research proposal builds on the hypothesis that a thorough understanding of the ageing processes over time can be described quantitatively by means of a temperature dependent kinetic approach. This can be figured out for thermal conductivity, strength and the structure and composition re-spectively. For this purpose, mineral and protein containing deposits from food processing are produced in a laminar flow channel at varying process parameters such as bulk and wall temperature, flow velocity and composition. First, the ageing rate is decoupled from the deposition and removal rate and the thermal conductivity in discrete sublayers within the cross-sectional area of the fouling layer is determined. In order to achieve the latter, an experimental procedure was designed to combine thermal fouling resistance and layer thickness. Furthermore, cohesion and adhesion, shear strength, wear and penetration resistance are quantified to characterize the mechanical properties. In order to be able to examine ageing mechanisms and kinetics in a simplified and sepa-rated manner, the material properties mentioned before are also determined on homogeneous model layers.In addition to the transfer of existing models of thermal ageing to two new material systems, a new definition of binding forces within deposits will be undertaken based on the information on structure and mechanical properties. This can be integrated into a classical fouling model. The progression of the ageing process and the resulting material changes can then be predicted on the basis of the previously elucidated interaction of thermal, mechanical and structural parameters.