Intelligent catalyst carrier concept with additively manufactured structures made of shape memory alloys for the optimization of the wall heat transfer in tubular reactors

蜂窝结构具有良好的热传递特性，是替代传统随机填充床反应器的一种很有前途的选择。在管式反应器中使用蜂窝结构作为催化剂载体的一个关键挑战是结构与管壁的接触，这在许多情况下是不够的，从而降低了整体传热性能。特别是对于强烈的放热或吸热反应，这种对热传递的抑制会导致不希望看到的温度梯度。因此，这一建议的主要目的是对结构-墙体相互作用的科学认识，以便预测最优墙体耦合的设计。从形状记忆合金(NiTi、NiTiNol)中添加制造(选择性电子束熔炼，SEBM)的周期开放蜂窝结构(POC)是实现这一目标的一种特别合适的创新模型系统。通过SEBM添加制造这些POC提供了很大的自由度，几乎不受设计过程中的任何限制。为了确保可交换催化剂载体良好的壁面耦合，我们提出了一种利用伸展效应的系统。采用单轴压缩来减小结构的直径。然而，仅靠伸展效应就需要恒定的压力来保持结构的压缩。这可以通过结合形状记忆合金的伸展效应和单向记忆效应来避免。在这里，结构在插入反应堆之前变形一次，然后通过在反应堆内进行原位热处理重新膨胀到其原始形状。这种方法代表了一种确保蜂窝结构和反应器壁之间的压力配合的优雅方法。通过SEBM使用镍钛醇在文献中没有充分的文献记载，因此代表了一个非常有趣的研究主题。有关POC的知识和有关形状记忆合金添加剂制造的文献相结合，为克服管式反应器中壁面换热限制的问题提供了一条很有前途的途径。机械和反应工程问题的数值模型为改进催化剂载体的良好开发奠定了基础。通过执行几个优化周期，将确定最有希望的设计。最后，将通过一个基于技术相关性反应系统的案例研究来证明这一新概念的可行性和有效性。

Cellular structures represent a promising alternative to classical randomly packed bed reactors owing to their very good heat transport characteristics. A key challenge of using cellular structures as catalyst carriers in tubular reactors is the contact of the structure with the tube wall, which in many cases is not sufficient and thus downgrades the overall heat transfer performance. Especially with strongly exo- or endothermic reactions, this inhibition of heat transfer leads to undesirable temperature gradients. Therefore, the main goal of this proposal is to achieve a scientific understanding for the structure-wall interactions in order to predict the design of an optimal wall coupling. Auxetic POCS (periodic open cellular structures) that are additively manufactured (selective electron beam melting, SEBM) from a shape memory alloy (NiTi, Nitinol) represent a particularly suitable and innovative model system for achieving this goal.The additive manufacturing of these POCS via SEBM offers a great degree of freedom almost without any limitations in the design process. To ensure a good wall coupling for exchangeable catalyst carriers, we propose a system that utilizes the auxetic effect. Uniaxial compression is used to decrease the diameter of the structure. The auxetic effect alone, however, would require a constant pressure to keep the structure compressed. This can be circumvented by combining the auxetic effect with the one-way memory effect of a shape memory alloy. Here, the structure is deformed once before insertion into the reactor and then re-expanded to its original shape by an in situ heat treatment inside the reactor. This method represents an elegant approach for ensuring a press fit between the cellular structure and the reactor wall.The use of Nitinol via SEBM is not sufficiently documented in literature and therefore represents a highly interesting research topic. The combination of knowledge about POCS and literature about additive manufacturing of shape memory alloys offers a promising approach to overcome the problem of wall heat transfer limitations in tubular reactors. Numerical models for mechanical and reaction engineering problems build the framework for the well-founded development of improved catalyst carriers. By performing several optimization cycles the most promising design will be identified. Finally, the feasibility and efficiency of this new concept will be demonstrated in a case study based on a reaction system of technological relevance.