## 1 Introduction  
The most typical pressure swing adsorption (PSA) process is a two-bed four-step Skarstrom cycle, the schematic is shown in Figure 1[1]. The cyclic process consists of pressurization, adsorption, countercurrent blow down and purge. It is the basis for designing more complex PSA processes [2]. Currently there are two-bed PSA, three-bed PSA, four-bed PSA and vacuum pressure swing adsorption processes. The PSA oxygen production system has been widely used in industrial production due to its low energy consumption, simple equipment, and convenient operation. However, with the continuous increase of air processing capacity and the decrease of the utilization efficiency of adsorbent, oxygen production system is seriously restricted by the development of large-scale and low energy consumption. Conventional large-scale axial flow adsorbers have large void volume percentages, and uneven flow distribution, which will seriously affect the oxygen production [3]. In contrast,radial flow adsorber (RFA) has the characteristics of large cross-sectional area, large flow capacity, gas distribution uniformity, small flow resistance and large feed flowrate [4; 5]. It has been widely used in chemical industry, petrochemical and gas production industry [6; 7]. However, due to the extremely complex variable mass flow caused by the internal structure of RFA, one of the most important issues to be solved for heat and mass transfer in two-phase flow in RFA is model verification [8]. [PERSON] et al. [9] pointed out RFA designs were becoming more popular because of high velocities and short mass-transfer zones. [PERSON] et al. [10] studied the flow distribution of radial-flow beds using computational fluid dynamics and showed that the centrifugal-\(\pi\) type had a significant uniform flow. [PERSON] [11] proposed to improve the uniform distribution of airflow by using the non-uniform opening distribution of the inner and outer cylinders. [PERSON] et al. [12] developed a differential equation for the Z-flow type RFA by pressure drop analysis considering the change in the flow area of central pipe. The ideal shape of the central pipe along the axis was obtained by solving the differential equation, which could be realized by inserting a cone with a variable cross-sectional radius along the axis in the middle of the central pipe. [PERSON] [13] investigated one and two-stage spherical reactors through a mathematical model. To verify the accuracy of the considered model, the simulation results of a conventional reactor were compared with the plant data and found that DME (Dimethyl ether) production was improved by about 2.8% and 3.7% in the one and two-stage membrane configurations against conventional tubular reactor. [PERSON] et al. [14] measured the pressure profiles in the flow channels and layers of a three-layer RFA and investigated the properties of the fluids in flow channels of a three-layer RFA. [PERSON] et al. [15] established a two-dimensional model for studying the transport phenomena during the PSA process in consideration of the heat effect, gas compressibility, radial porosity, and dead volumes. [PERSON] et al. [16] established a 3D hydrodynamic and mathematical model for the RFA in consideration of cross section ratio of central channel to outer channel, and the opening ratios of the central channel and the outer channel. They found that radial inward flow was proved to have a better performance than radial outward flow, and the \(\pi\)-type of inward flow is a little better than that of the z-type of inward flow. [PERSON] et al. [17] found a novel radical flow reactor with lower pressure drop, and compared the optimized reactor with an optimized conventional axial flow reactor to ascertain the superiority of the proposed reactor configuration. [PERSON] et al. [18] performed a numerical simulation of a PSA oxygen production process based on radial-flow adsorber and found that the centripetal \(\pi\)-flow radial adsorber has the best flow characteristics for the PSA process.