The kinetics of water sorption by a bed of powder was modeled in order to estimate the characteristic time of caking under real (similar to storage conditions) and test (accelerated) environmental conditions. In combination with the model, the kinetics of water sorption by henna powder was experimentally measured in the devices of “humidity chamber” and “caking device” as the environments representing real and test processes, respectively. According to the results, the water uptake by the powder was faster in caking device in comparison with humidity chamber whereas the equilibrium amount of water uptake was expectedly the same. The diffusion–convection and convection–convection were considered as the governing mechanisms of mass transfer in humidity chamber and caking device, respectively. Model equations were solved by applying the finite difference method (FDM) to track the water uptake amounts by the powder over the time. By matching the experimental data and the model results, the mass diffusion coefficient (D) and the total mass transfer coefficient (K) of henna were predicted. Extending the model, a dimensional analysis came up in order to understand the effects of the Stanton and Sherwood numbers on the time of equilibrium of sorption for both mentioned mechanisms. These findings will lead to a better prediction of characteristic time of caking in different conditions. Moreover, the results of this study define a protocol for performing accelerated laboratory tests of caking so that their results can be generalized to real conditions. The generalization procedure was also explained.

对粉末床的吸水动力学进行建模，以估计在真实（类似于储存条件）和测试（加速）环境条件下结块的特征时间。结合模型，分别在“加湿室”和“结块装置”作为代表真实和测试过程的环境，对指甲花粉的吸水动力学进行了实验测量。根据结果​​，与湿度室相比，结块装置中粉末的吸水速度更快，而平衡吸水量预期相同。扩散-对流和对流-对流分别被认为是湿度室和结块装置中传质的控制机制。通过应用有限差分法 (FDM) 来跟踪粉末随时间的吸水量来求解模型方程。通过匹配实验数据和模型结果，得到质量扩散系数（D ) 和指甲花的总传质系数 ( K ) 进行了预测。扩展模型，进行量纲分析以了解斯坦顿数和舍伍德数对上述两种机制的吸附平衡时间的影响。这些发现将导致更好地预测不同条件下结块的特征时间。此外，这项研究的结果定义了执行结块加速实验室测试的协议，以便他们的结果可以推广到实际条件。还解释了泛化过程。