ABSTRACT

Micro heat exchangers are characterized by their high surface-to-volume ratio of up to 100,000 m²/m³. Due to superior heat transfer performance, their utilization for pure fluids is gaining increased attention. One major drawback though is the unwanted deposition on their surfaces when subject to fluids which tend to foul. To address this, a better understanding of the deposition process in these devices looks imperative. In this study, the crystallization fouling of calcium sulfate on micro-structured surfaces during convective heat transfer has experimentally been studied. The experimental specimens of stainless steel with rectangular micro-channels were subjected to CaSO₄ solution with a concentration of 4 g/L. The impact of channel dimension and direction with respect to fluid flow has also been investigated at a given velocity of 0.17 m/s. In addition, the comparison of finned and grooved structured surfaces was made. The results showed that as the groove’s width increases, the propensity of deposition is expected to decrease as such that fouling rate and fouling resistance decreased as much as 30% and 15%, respectively. Moreover, the crossed grooves increased the turbulence more than the longitudinal ones. It was also attained that the disturbance promoters, i.e. fins, would have positive impact on heat transfer coefficient compared with those of grooves.

摘要

微型热交换器的特点是其高达 100,000 m ² /m ³的高表面体积比。由于优异的传热性能，它们在纯流体中的应用越来越受到关注。然而，一个主要缺点是当遇到容易结垢的流体时，它们的表面会出现不必要的沉积。为了解决这个问题，必须更好地了解这些设备中的沉积过程。在这项研究中，实验研究了对流传热过程中硫酸钙在微结构表面上的结晶结垢。对矩形微通道不锈钢实验试样进行CaSO ₄浓度为 4 g/L 的溶液。在 0.17 m/s 的给定速度下，还研究了通道尺寸和方向对流体流动的影响。此外，还对翅片和凹槽结构表面进行了比较。结果表明，随着凹槽宽度的增加，沉积倾向预计会降低，结垢率和结垢阻力分别降低 30% 和 15%。此外，交叉槽比纵向槽增加了更多的湍流。还发现扰动促进剂，即翅片，与凹槽相比对传热系数有积极影响。