Contact resistance equal

Electrode pressure on the sample material approximately corresponded to the pressure used in a practical EC in its operational mode and was equal to 8 kgf-cm 2 (this pressure was applied for purposes of minimization of particle contact resistance). 

The electronics of CUORICEMO (see Section 16.6) consists of a complex anticoincidence system. One would hope that signals from all detectors had the same amplitude and shape for the same input. For this reason, all the components for the 56 detectors were carefully selected to be equal. Also the mounting of the components was made with the most reproducible technique. Nevertheless, there are some parameters such as the contact resistances between the thermistors and the absorbers and especially those between the absorbers and the frame which show a wide spread in their values. 

SOLUTION The thickness of the aluminum plate whose thermal resistance is equal to the thermal contact resistance is to be determined. 

Ctinsider two metal plates pres.sed against each other. Other thing / being equal, which of the measures below will cause (he thermal contact resistance to increase ... 

When two large bodies /4 and R, initially at unifonn temperatures and Tgj are brought into contact, they instantly achieve temperature equality at the contact surface (temperature equality is achieved over the entire surface if the contact resistance is negligible). If the two bodies are of the same material with constant properties, thermal symmetry requires the contact surface temperature to be the arithmetic average, + Tbj)12 and to remain... 

Additional parameters specified in the numerical model include the electrode exchange current densities and several gap electrical contact resistances. These quantities were determined empirically by comparing FLUENT predictions with stack performance data. The FLUENT model uses the electrode exchange current densities to quantify the magnitude of the activation overpotentials via a Butler-Volmer equation [1], A radiation heat transfer boundary condition was applied around the periphery of the model to simulate the thermal conditions of our experimental stack, situated in a high-temperature electrically heated radiant furnace. The edges ofthe numerical model are treated as a small surface in a large enclosure with an effective emissivity of 1.0, subjected to a radiant temperature of 1 103 K, equal to the gas-inlet temperatures. 

This equation facilitates understanding of how the channel dimensions (L and W) affect the relative magnitudes of the contact resistance and the channel resistance. Note that the channel resistance scales as LIW but the contact resistance scales as l/W it does not depend on L. Consider two different OFET devices on the same semiconductor/insulator/gate substrate both have the same channel width (equal W), but the length of the channel of the second device is 10 times smaller than that of the first (L2 = Ej/10), as depicted in Figure 2.4.6(a). Both devices have equal contact resistances R because W is the same. But because the channel resistance scales with L/W (the source-drain current scales with W/L), the channel resistance of the second device is 10 times smaller than that of the first device. This means that contact resistance is potentially much more important in the shorter channel device because it contributes a larger fraction of the total resistance. 

Equal contact resistances Device 2 has a lower channel resistance (by lOX)... 

Equal channel resistances Device 4 has a lower contact resistance (by 2X)... 

The difference between the electrolytic ceU potential and the potential (voltage) when the current passes in the external circuit is due to ohmic losses. The main sources of ohmic losses are the resistance of the electrolyte, contact resistances of the leads, and the film formed on the electrode-electrolyte interface. The circuit ohmic resistance decreases the equilibrium potential by an amount equal to iR, where is the current passing between the working and counter electrode and R is the net resistance in the circuit. Current passes through the cell only when the voltage applied to the system consists of thermodynamically controlled equilibrium potential and the potential drop that compensates for the ohmic losses. The potential drop is not thermodynamically controlled and depends on the current density and the resistance in the circuit. It approaches zero when the current is shut off, and increases immediately when the current is switched on [8,9]. The iR drop in volts is equal to i°l/k, where i° is the current density in A/cm, is the thickness of the electrolyte in cm, and k is the specific conductivity of the electrolyte 1/Qcm. Various techniques are employed to measure the ohmic losses in an electrochemical cell. These measurement techniques include current interruption and four probe methods, among others that are discussed later in the book [8-10],... 

According to Sawada et al. [8], the constriction resistance is dominant over film resistance when the loads exceed ION (1kg) and when the film is thin. Due to the mass of electro winning electrodes ( lkg), it can be assumed that the film resistance is negligible, and hence, the contact resistance is equal to the constriction resistance. On this basis, the contact resistance is given by the following equation [9] ... 

The Freeport McMoran and Spool systems have redundancy at the main contact end whereas the Outotec system redundancy is provided on the equalizer bar. This equalizer bar contact will have low contact resistance since it carries full electrode weight but there will be an additional contact resistance and equalizer bar resistance needed to carry the current to that contact. 

The basic measure of effectiveness of an earth electrode system is called earth electrode resistance. Earth electrode resistance is the resistance, in ohms, between the point of connection and a distant point on the earth called remote earth. Remote earth, about 25 ft from the driven electrode, is the point where earth electrode resistance does not increase appreciably when this distance is increased. Earth electrode resistance consists of the sum of the resistance of the metal electrode (negligible) plus the contact resistance between the electrode and the soil (negligible) plus the soil resistance itself Thus, for all practical purposes, earth electrode resistance equals the soil resistance. The soil resistance is nonhnear, with most of the earth resistance contained within several feet of the electrode. Furthermore, current flows only through the electrolyte portion of the soil, not the soil itself Thus, soil resistance varies as the electrolyte content (moisture and salts) of the soil varies. Without electrolyte, soil resistance would be infinite. 

Until today, this method has undergone shght change in setup and a diversification of measured and calculated resistances. Mostly, this measurement is conducted as illustrated in Figure 6.13b where one sample (equal properties on both surfaces assumed, here nitrided chromium on 316L stainless steel) is sandwiched between two carbon papers which are clamped between two gold-plated current collectors which are adjustable in compaction force. In order to calculate the contact resistance between carbon paper and coating, two different measurements have to be performed is the measurement of the... 

In summary, the electrical conductivity of adhesive joints is dominated by the physical contact between the two unmelted conductive materials and, therefore, the resistance of the joint seems to be nearly equal to the contact resistance. Among the various adhesives, ACAs are considered to be the least-conductive materials and the resistance is controlled by the joint... 

If the contact resistance is assumed to be independent of sample thickness, an assumption supported by experimental results (20), equation 10 implies a plot of AT/Q vs Ax should 3ueld a straight line with slope 1/kA and intercept equal to contact resistance. In Figure 3 precautions have been taken in curve A to reduce contact resistance, whereas in curve B no precautions have been taken. Contact resistance was, as expected, smaller in curve A. However, both cases jdelded straight lines and an identical, and uniequivocal, value of thermal conductivity. This method should probably be preferred for the most accurate work, but it requires three or more specimens of varying thickness, adding enormously to the cost or time of measurement. 

A fuel cell operates at 0.6 V and 1 Acm . Calculate the temperature distribution through a gas diffusion layer-bipolar plate sandwich on the cathode side. Assume a constant heat flux at the gas diffusion-catalyst layer interface equal to all the fuel cell losses, except those due to ionic and electrical resistance. Assume that half of the resistive losses apply to the anode side and half to the cathode. Ionic resistance through the membrane is O.lOhm-cm. At the outer edge of the bipolar plate assume that heat is removed by a cooling fluid at 60°C, with heat transfer coefficient, h = 1600Wm K. Electrical resistivity of the gas diffusion layer and bipolar plate is 0.080hm-cm and 0.060hm-cm, respectively. There is a contact resistance of 0.005 Ohm-cm between the gas diffusion layer and bipolar plate. Effective thermal conductivity of GDL and bipolar plate is 1.7 Wm K and 20 Wm" K , respectively. There is a thermal contact resistance between these two layers equal to 1°C/W Thickness of GDL and bipolar plate is 0.38 mm and 3.3 mm, respectively. 

F (A0I + A0ii). The term in the braces is Uqs- and refers exclusively to the sample, while A0i + A0II refers to the potential drops over the two ion conductor samples. If contact resistances also occur at other phase boundaries the drop in electrochemical potential does not equal zero in the stationary state it is given by the product of current and contact resistance. Since, on the time scale of the stoichiometry polarization, electrical bulk processes and charge transfer processes actually behave in a quasi stationary manner, we may write that U =. .. + SilRi, whereby i refers to all parts outside the sample. 

A reasonable power density expectation for a (planar) fuel cell is about 500 mW cm at 0.7 V, which corresponds to about 0.7 A cm and so a total cell resistance of about 0.5 ohm cm . Spreading this resistance equally among the cell components gives a maximum of about 0.15 ohm cm as targets for each of the cathode, anode and electrolyte [3-5]. with a little leftover for interconnects and contact resistances. This specific resistance, however, does give a good upper limit for any one component in a stack and so this value will be used for the rest of this work. 

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