Through-plane resistance

Bulk resistivity (through-plane. Q cm) Mercury contacts 0.08 Not available... 

Product Name Thickness (mm) Weight (g/m ) Bulk Density (g/cm ) Porosity (%) Tensile Strength (MPa) Stiffness (Taber) Through-Plane Air Permeability (sec/100 cc) In-Plane Air Permeability (sec/100 cc) Compressibility (%) Through- Plane Resistivity (mohm cm ) In-Plane Resistivity (mohm cm) Comments ... 

Product Thickness Weight Bulk Density Porosity Tensile Strength Stiffness Through-Plane Air Permeability In-Plane Air Permeability Compressibility Through- plane Resistivity In-Plane Resistivity... 

M. Khandelwal and M. M. Mench. Direct measurement of through-plane thermal conductivity and contact resistance in fuel cell materials. Journal of Power Sources 161 (2006) 1106-1115. 

A coaxial probe can also be used to measure the through-plane conductivity of membranes. Figure 5.15 shows the schematic for a coaxial conductivity measurement cell. In this method, the membrane is cut to the same size as the inner conductor, and the measured resistance is the through-plane resistance. The resulting conductivity, 2.4 x 10 2 S/cm, is close to that reported in the literature. 

For the Nafion -based PEM fuel cells, the membrane conductivity decreased with increasing operating temperatures. The resistance points on the Re axis at the high-frequency end in Figure 6.49 can be treated approximately as the membrane through-plane resistance in PEM fuel cells other resistances, including the ionic resistance of the Nation ionomer and the cell contact resistance, may have made... 

Figure 2 shows the basic physical idea of the microstructure of the continuum rheologicS model we proposed earlier (2). The layers can be idealized as separated by porous slabs, which are connected by elastic springs. Liquid crystals may flow parallel to the planes in the usual Newtonian manner, as if the slabs were not there. In the direction normal to the layers, liquid crystals encounter resistance through the porous medium, proportional to the normal pressure gradient, which is known as permeation. The permeation is characterized by a body force which in turn causes elastic compression and splay of the layers. Applied strain from the compression causes dislocations to move into the sample from the side in order to relax the net force on the layers. When the compression stops and the applied stress is relaxed the permeation characteristic has no influence on stress strain field. 

Product Thickness name (mm) Electrical resistivity (mf2 cm) Through plane In plane Thermal conductivity (W/mK) Through In plane plane (room (room In plane temp) temp) (100 °C) Gas permeability (ml mm/ (cm -hr-mmAq) Porosity (%) Bulk density (g/cm ) Surface roughness (pm) Coefficient of thermal expansion (in plane) (25-100 °C) (xl0- /°C) Flexural strength (MPa) Flexural modulus (GPa) Tensile strength (kgf/cm)... 

Overall conductance (overall heat-transfer coefficient) n. In heat-transfer engineering, the reciprocal of the total thermal resistance, for heat flow through plane walls or tube walls. It is defined by the equation U = q/AAT, where q is the rate of heat flow through (and normal to) the surface of area A, and AT is the fall in temperature through the layer in the direction of q. This is a modification of Fomier s law, invented to deal conveniently with heat flow through stagnant fluid films adjacent... 

For a GDM made of carbon fiber (e.g., carbon paper), the in-plane conductivity is normally much higher than the through-plane conductivity because most of the carbon fibers stay in the planar direction. Fortunately, since the thickness of the GDM is around 0.2 mm, the voltage loss caused by the through-plane resistance is not significant. For example, if the through-plane conductivity is 20 S cm then the voltage drop caused by one membrane electrode assembly (MEA) (with two pieces of GDM) will be 2 mV at a current density of 1 A cm. ... 

N. Cunningham, M. Lefevre, G. Lebrun, and J.-P. Dodelet. Measuring the through-plane electrical resistivity of bipolar plates (apparatus and methods). J. Power Sources, 143 93-102, 2005. 

The in-plane as well as the through-plane resistance of the GDM contributes to the ohmic resistance due to their function of evening out the current distribution. As most current GDM s are based upon non-isotropic materials such as paper or woven materials, these differ often by an order of magnitude. The through plane resistance of the material depends strongly upon the compression, a factor that has to be taken into account for application in a fuel cell. In general, the overall ohmic loss through the GDM is quite small, in the order of 2 mV at 1 A cm [44]. 

It must be both electrically and thermally conductive, again in both through-plane and in-plane. Interfacial or contact resistance is typically more important than bulk conductivity. 

The two-probe configuration can also be used to measure the through-plane resistance of a membrane by sandwiching the membrane between two Pt sheets or foils ... 

In the described techniques, the contact resistance-related issues usually are more typical in the through-plane measurements than in the in-plane measurements. However, surface conductivity measurements are also affected by the contact resistance. These types of experiments are sensitive to undesired electric noise (Tong 2011). Also, the qualities of all electric connections are of great importance. Preconditions for reliable results are careful construction of the measuring unit and sample preparation and quality management of testing procedures with reference probes. The environment has effects on the conductivity values and temperature, but humidity in particular may cause inaccurate results (Boudenne et al. 2011). 

The contact resistance in the cell is a major source of error for through-plane measurements, and should be registered for each type of material by a series of measurements with membranes of different thickness. A plot of the measured... 

Fig. 19.8 Through-plane surface resistance (relative test method) results of HT-PEM bipolar plates with different configurations where BPP4 is mature material while PPS and PVDF are development materials. The data show...

FIGURE 5.3 Approximate stress-strain curves for GDL materials calculated from representative, published data. (Reprinted from the Electrochimica Acta, 55, Karimi, G., Li, X., and Teertstra, P. Measurement of through-plane effective thermal conductivity and contact resistance in PEM fuel cell diffusion media, 1619-1625, Copyright (2010) Journal of Power Sources, 196, Corrected proof, Sadeghi, E., Djilali, N., and Bahrami, M. Effective thermal conductivity and thermal contact resistance of gas diffusion layers in PEM fuel cells. Part 1 Effect of compressive load, 246-254, Copyright (2011), with permission from Elsevier.)... 

---