Abstract

In this paper, the first experimental results related to fouling taking place at heat exchangers during heat treatment of milk is presented. Instead of milk, simulated milk ultrafiltrate was used and the experiments were conducted in a simplified model geometry consisting of one heating plate (dimensions 32 mm by 40 mm) made of stainless steel in a flat flow channel (height 2.0 mm) in a closed flow loop. The three-dimensional deposit structure was measured in real time with optical coherence tomography (OCT) with ca. 4 μm resolution. Fouling was observed in a flow rate range 300 − 1500 ml/min (Reynolds number 250 − 1250). The largest amount of deposited layer was 70 g/m² in 7.5 hours at the flow rate of 1500 ml/min. The thickness of the deposited layer was ca. 300 μm. In some cases, we observed detachment of deposit flocks, which was seen both in the OCT images and in temporary decrease of the plate temperature (indicating improved heat transfer). The system seemed to be here in a dynamic equilibrium; reflocculation and floc detachment followed each other the plate temperature fluctuating in a range of a few degrees.

摘要

在本文中，介绍了与牛奶热处理过程中换热器处发生结垢有关的第一个实验结果。使用模拟牛奶超滤液代替牛奶，并在一个简化的几何模型中进行实验，该几何模型由一个不锈钢制成的加热板（尺寸为 32 毫米 x 40 毫米）在封闭流中的扁平流道（高度 2.0 毫米）中组成环形。三维沉积结构是通过光学相干断层扫描 (OCT) 实时测量的。4 μm 分辨率。在 300 - 1500 毫升/分钟（雷诺数 250 - 1250）的流速范围内观察到结垢。最大沉积层量为70 g/m ²在 7.5 小时内，流速为 1500 毫升/分钟。沉积层的厚度约为。300 微米。在某些情况下，我们观察到沉积物絮凝物的分离，这在 OCT 图像和板温度的暂时降低中都可以看到（表明传热得到改善）。该系统似乎处于动态平衡状态。再絮凝和絮凝物分离相互跟随，板温度在几度的范围内波动。