Local fouling investigations as basis for describing the integral fouling behavior

污垢，即在换热和/或传质表面形成绝缘层，是一种在空间和时间上变化的现象。然而，污垢效应，如换热的减少和/或压降的增加，通常是用给定设备的单个恒定积分值来量化的，例如热垢阻力。这项研究建议建立在一个假设的基础上，即对局部污垢过程的透彻了解可以预测整体污垢效应。为此，对流体加热双管换热器中逆溶盐硫酸钙和碳酸钙结晶结垢的局部结垢过程进行了实验和理论研究。在两台平行且运行相同的换热器上，将对污垢的局部分布和结构特征进行互补和独立的调查。局部热垢阻力是根据局部能量平衡结合传热学计算确定的。体积位移法显示了污垢沉积的轴向分布。两根管子中的一根将被切割成十个管段，以便进行光学检查和确定管段压降。第一种方法可以区分紧凑的基层和顶部的粗糙生长层。结合分段压降，可以分离收缩效应和粗糙度效应，并可以提取等效的粗糙度。最后，确定污垢层的孔隙率、密度和导热系数与位置和时间的关系。根据流体动力学和传热学计算，可以计算局部速度、壁面剪应力和温度。结合处理过的盐溶液的溶解度，可以确定过饱和度的位置，从而可以确定晶体的形成。基于对组分、热力学和流体动力学参数相互作用的透彻了解，可以预测污垢过程的进展，从而可以预测开始的积分效应。

Fouling, i.e. the formation of insulating layers on heat and/or mass transfer surfaces, is a phenomenon varying in space and time. However, fouling effects, such as the reduction of heat transfer and/or a pressure drop increase, are typically quantified in a single constant integral value, such as the thermal fouling resistance, for a given equipment. This research proposal builds on the hypothesis that a thorough understanding of local fouling processes allows for a prediction of integral fouling effects. Therefor local fouling processes for the crystallization fouling of the inverse soluble salts calcium sulfate and calcium carbonate in a fluid-heated double-pipe heat exchanger are investigated experimentally as well as theoretically. At two parallel and identically operated heat exchangers complementary and independent investigations on the local distribution and structural characteristics of the fouling layer will be carried out. Local thermal fouling resistances are determined based on local energy balances in combination with heat transfer calculations. A volumetric displacement method reveals the axial distribution of the fouling deposit. One of the two tubes will be cut into ten segments thus allowing for the optical inspection and the determination of segmental pressure drop. The first one allows to distinguish between a compact base layer and a rough growth layer on top. In combination with the segmental pressure drops, constriction and roughness effects may be separated and an equivalent roughness can be extracted. Finally, porosity, density and thermal conductivity of the fouling layer with respect to location and time shall be determined.Based on fluiddynamic as well as heat transfer calculations local velocities, wall shear stresses and temperatures may be calculated. In combination with the solubility of the treated salt solutions loci of supersaturation and thus crystal formation may be identified. Based on a thorough understanding of the interaction of component-related, thermal and fluiddynamic parameters the progress of the fouling process and thus the initiated integral effects may then be predicted.