Abstract
The necessity of measuring permeability is encountered in number of applications and some of them have adequate measurement techniques available. However, in the fields of freeze drying, composite scaffolds, 3D printed materials, etc., the sample materials have unique shapes and sizes, which disables the use of standardized equipment. Hence, a novel method was developed to determine the permeability of a sample material by analyzing a high frequency unsteady state pressure measurement acquired during the permeation of a working fluid. The method is also suitable for in-line measurements due to the rapid acquisition and analysis. The developed method is novel, hence a comparison of the acquired results and the permeabilities measured with a standard device designed for measuring air permeability of fabric materials was made. Air was the permeating fluid in the novel unsteady state as well as in the referential steady state measurements. The measured permeabilities ranged from approximately 8 Da to 50 Da for the analyzed five fabric materials. The comparative analysis yielded an encouraging linear fit with a R2 = 0.98 by including only one unsteady state measurement of each fabric sample. In addition, the presented method was capable of detecting the difference in permeability of the freeze-dried 5 wt% and 12 wt% aqueous mannitol solutions, which exhibit different permeabilities due to the different porosities after the same process of lyophilization. The possibility of determining permeabilities of freeze-dried pharmaceuticals is essential for lyophilization process optimization.
Highlights
The technics of permeability determination are commonly divided into two categories: steady state and unsteady state methods
Additional rise of the initial upstream pressure, which would lower the noise to signal ratio was omitted in an attempt not to deviate even further from the pressures maintained in the referential steady state measurements, which were performed at a pressure difference of 100 Pa
The presented novel unsteady state method of measuring permeability was successfully evaluated with referential standardized steady state measurements performed on five different fabric materials
Summary
The technics of permeability determination are commonly divided into two categories: steady state and unsteady state methods. Both are most thoroughly studied in the field of geology due to the importance of rock permeability in the oil and gas industry. Compared to the steady state experiments, the unsteady state measurements are more rapid, as shown by Zhong et al [6], and more frequently applied for determining lower permeabilities, whereas the analysis of the results is generally much more complex and requires a profound theoretical background [7] as well as additional parameters: material and fluid compressibility, porosity, viscosity, etc. Compared to the steady state experiments, the unsteady state measurements are more rapid, as shown by Zhong et al [6], and more frequently applied for determining lower permeabilities, whereas the analysis of the results is generally much more complex and requires a profound theoretical background [7] as well as additional parameters: material and fluid compressibility, porosity, viscosity, etc. [8] and [9], which are often difficult to acquire
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