Flow resistance measurement

The flow resistance of a sample of porous material may be measured using an apparatus that meets the requirements of ISO 9053-1991 or ASTM C522-03, such as that illustrated in Fig. 5.1. Small flow rates from 5x 10 to 5x 10 m/s are recommended to avoid introduction of undamping effects and nonlinear relationships between the pressure drop and the velocity (Dies and Hansen, 2009 Cox and D Antonio, 2009). 

The flow resistivity of the test specimen shown in Fig. 5.1 is calculated from the measured quantities as follows  

In the alternating airflow method, a piston is used to generate a low frequency alternating airflow through the test specimen and a condenser microphone is used to obtain the root mean square (rms) value of the pressure change in front of the porous material. Fig. 5.2 shows the basic principle of the experiment setup. 

The frequency of the alternating airflow generated by the piston displacement is recommended to be around 2 Hz, and the rms value of the airflow velocity is recommend to be between 0.5 and 4mm/s, which can be calculated by 

There are many acoustical methods proposed for measuring flow resistivity (Delany and Bazley, 1971 Smith and Parott, 1983). A method that uses a standard impedance tube directly to measure the static flow resistivity without any additional requirements to tube modification or sensor location change is described in ISO Standard, 10534-2 (1998) and by Tao et al. (2015). In the method, the specific acoustic impedance on the front surface of the test specimen is measured first by using the traditional transfer function method with the test specimen being placed against and with a known interval to the rigid termination, and then the characteristic impedance, the propagation constant, and the static flow resistivity are calculated based on the obtained impedance transfer functions. 

---

Jones, D.P., Krier, H., 1982. Gas flow resistance measurements through packed beds at high Reynolds numbers. J. Fluid Eng. 105, 168-172. 

To ensure maximum continuity of the tin-iron compound layer between tin and steel. This layer is itself corrosion resistant and appears to act as a nearly inert screen limiting the area of steel exposed as tin is removed by corrosion. Its effectiveness is measured by the Alloy-Tin Couple (A.T.C.) test, in which the current flowing is measured between a sample of tinplate from which the unalloyed tin layer has been removed, and a relatively large tin electrode immersed in an anaerobic fruit juice. ... 

Hardness is determined by hardness tests which involve the measurement of a material s resistance to surface penetration by an indentor with a force applied to it The indentation process occurs by plastic deformation of metals and alloys. Hardness is therefore inherently related to plastic flow resistance of these materials. Brittle materials, such as glass and ceramics at room temperature, can also be subjected to hardness testing by indentation. This implies that these materials are capable of plastic flow, at least at the microscopic level. However, hardness testing of brittle materials is frequently accompanied by unicrack formation, and this fact makes the relationship between hardness and flow strength less direct than it is for metals. 

Results from constant differential pressure filtration tests have been analyzed according to traditional filtration science techniques with some modifications to account for the cross-flow filter arrangement.11 Resistivity of the filter medium may vary over time due to the infiltration of the ultrafine catalyst particles within the media matrix. Flow resistance through the filter cake can be measured and correlated to changes in the activation procedure and to the chemical and physical properties of the catalyst particles. The clean medium permeability must be determined before the slurries are filtered. The general filtration equation or the Darcy equation for the clean medium is defined as... 

The water vapor flows from the sublimation front into the chamber and to the connection between chamber and condenser with a favorable small pressure drop there are no measurable flow resistances, e. g. between the shelves or the shelves and the chamber walls. 

Resistance to electron flow is measured in ohm units and is symbolized by the letter R. The ohm unit is symbolized by the Greek letter omega (Q). A resistance slows the movement of electrons in a circuit much like a smaller-diameter pipe would slow the movement of water. While all electronic circuit components have a certain resistance, components known as resistors—components that have a certain defined resistance in ohms, kilohms (kO, or 103 Q), or megaohms (MQ, or 106 Q) and are inserted into circuits for their resistance values—are available. These usually are small, cylindrical epoxy or plastic packages with leads (short wires) protruding from each end and small granules of carbon or resistance wire inside to slow the electrons. Resistors are manufactured with different degrees of accuracy. One percent... 

If we know the resistance of the leads and cell, and we also know the current passing through them, we can then use Ohm s law (equation (2.2)) to determine the IR drop (i.e. the additional potential induced by current flow during measurement). 

Konstandopoulos, A. G. Flow resistance descriptors for diesel particulate filters Definitions, measurements and testing. SAE Technical Paper No. 2003-01-0846 (SP-1755) (2003). 

---