## 5 Conclusions  
This study proposes a discharge method to determine the flow characteristics of sintered metal porous media using an isothermal chamber. The pressure in the chamber is measured and then differentiated to calculate the discharged flow rate. Fifteen samples, categorized into three groups, are employed as the test element to perform the experiments. A modified Forchheimer equation is constructed to represent the relationship between flow rate and pressure difference in terms of the permeability and inertial coefficients. First, the coefficients are determined per the steady-state method by determining first the permeability in the Darcy region and then the inertial coefficient in the Forchheimer region. The Darcy and Forchheimer regions were defined with a Reynolds number of 0.1 as the boundary. Then, with the discharge method, the coefficients are simultaneously determined in five uniformly distributed pressure subsections. The results of permeability in comparison with the steady-state results indicate that using a medium-pressure dataset (250 kPa-350 kPa) improves the accuracy. Although the permeability and inertial coefficients determined by the discharge method somewhat deviate from those of the steady-state method, the theoretical calculation can represent the flow rate characteristics within 3% accuracy compared with the experimental results indicating that the traditional method can be replaced by the discharge method, which greatly shortens the measuring time, with only 10% air consumption as in the steady-state method. However, an appropriate volume for the isothermal chamber is necessary to ensure the measuring accuracy because the discharge method requires a reasonable discharging speed.  
The presented results indicate that the discharge method has potential for use in industry. As an example, in air-bearing systems, a large number of porous pads are employed and their flow properties are required to be as consistent as possible. A lot of testing and analysis are needed to help evaluate the manufacturing process. In this case, the discharge method is very useful since it facilitates the procedures and greatly reduces the air consumption under the premise of ensuring the accuracy.  
The limitations of the present study lie in the following aspects:  
1. The test samples are mainly tight porous media, which have a permeability on the order of 10\({}^{-12}\) m\({}^{2}\) and are generally applied in air-bearing systems.
2. An isothermal condition for the chamber is necessary during the discharge process. Otherwise, the calculated flow rate would exhibit large error. This means that a reasonable discharge speed is required.
3. The theoretical model is somewhat realistic since the inner structure of the actual porous media is not uniform. Therefore, the determined coefficients might not reflect the true properties of the media.
4. Only the permeability and inertial coefficients are discussed. The influences of other parameters such as porosity \(\varphi\), cross-sectional area \(A\), and length of the medium \(L\) are not included.  
Conceptualization, W.Z.; Data curation, X.J.; Investigation, J.F.; Methodology, X.J. and C.L.; Resources, C.L.; Validation, J.F.; Writing--original draft, W.Z.; Writing--review & editing, F.L.  
This study was supported by the National Natural Science Foundation of China (Grant No. 51675247).