Biological tissue, pharmaceutical tablets, wood, porous rocks, catalytic reactors, concrete, and foams are examples of heterogeneous systems that may contain one or several fluid phases. Fluids in such systems carry chemical species that may participate in chemical reactions in the bulk of a fluid, as homogeneous reactions, or at the fluid/fluid or fluid/solid interfaces, as heterogeneous reactions. Magnetic resonance relaxation measures the return of ¹H nuclear magnetization in chemical species of these fluids to an equilibrium state in a static magnetic field. Despite the perceived difference between reaction–diffusion and relaxation–diffusion in heterogeneous systems, similarities between the two are remarkable. This work draws a close parallel between magnetic resonance relaxation–diffusion and chemical reaction–diffusion for elementary unitary reaction \({\text{A}}\to {\text{B}}\) in a dilute solution—both in heterogeneous systems. A striking similarity between the dimensionless numbers that characterize their relevant behavior is observed: the Damköhler number of the second kind \({{\text{Da}}}^{{\text{II}}}\) for reaction and the Brownstein–Tarr number \({{\text{BT}}}_{i}\) for relaxation. The new vision of analogy between reaction- and magnetic resonance relaxation–diffusion in heterogeneous systems encourages the exploitation of similarities between reaction and relaxation processes to noninvasively investigate the dynamics of chemical species and reactions. One such example of importance in chemical engineering is provided for solid–fluid reaction in packed beds.

生物组织、药片、木材、多孔岩石、催化反应器、混凝土和泡沫是可能包含一种或多种流体相的异质系统的例子。此类系统中的流体携带化学物质，这些化学物质可以参与流体本体中的化学反应（作为均相反应），或者参与流体/流体或流体/固体界面处的化学反应（作为非均相反应）。磁共振弛豫测量这些流体的化学物质中¹ H 核磁化强度在静磁场中恢复到平衡状态的情况。尽管异质系统中的反应扩散和弛豫扩散之间存在明显的差异，但两者之间的相似之处是显着的。这项工作在稀溶液中的基本酉反应\({\text{A}}\to {\text{B}}\)中的磁共振弛豫扩散和化学反应扩散之间建立了密切的相似性——两者都在异质系统中。观察到表征其相关行为的无量纲数之间惊人的相似性：反应的第二类 Damköhler 数\({{\text{Da}}}^{{\text{II}}}\)和 Brownstein –Tarr 数\({{\text{BT}}}_{i}\)用于放松。异质系统中反应和磁共振弛豫扩散之间类比的新愿景鼓励利用反应和弛豫过程之间的相似性来非侵入性地研究化学物质和反应的动力学。化学工程中一个重要的例子是填充床中的固液反应。