Pumping cells

Furan was dimethoxylated to give 2,5-dihydro-2,5-dimethoxyfuran, using electrogenerated bromine molecules generated from bromide salts in electrolyte solutions [71]. This reaction was characterized in classical electrochemical reactors such as pump cells, packed bipolar cells and solid polymer electrolyte cells. In the last type of reactor, no bromide salt or electrolyte was used rather, the furan was oxidized directly at the anode. H owever, high consumption of the order of 5-9 kWh kg (at 8-20 V cell voltage) was needed to reach a current efficiency of 75%. 

Pumps move ions and molecules up their electrochemical gradient. Pumps require energy, usually in the form of ATP hydrolysis. Sodium-potassium ATPase is an example of a pump. Cells maintain a higher concentration of potassium inside the cell than they do outside the cell. Sodium is maintained low inside, high outside. Sodium-potassium ATPase pumps three sodium ions from inside the cell to outside. This is the unfavorable direction—Na+ moves from low concentration to a higher one and against the membrane potential. At the same time, it also... 

Household appliances can also benefit from improvements in other areas. For example, oxygen sensors that measure the 02-concentations in exhaust gas have been developed that combine a Nernst type lambda gauge (which can measure only the ( -concentration at one lambda-point) with an amperometric 02-pumping cell. 

Pumping cell Gap Sensing cell Reference gas (air) Heater... 

Fig. 3 Pumping cells with different diffusion barriers (a)...

Experimental current-voltage characteristic of a pumping cell having the structure shown in Fig. 3b for two different O2 concentrations in N2. The temperature of the device was 750 C. 

It is apparent that the double-cell sensor can be operated in the limiting current mode (which corresponds to large values of Vg, of the order of 600 to 800 mV). The advantage of this mode of operation is that errors associated with the measurement of small values of Vg (e.g, less than 100 mV) are avoided. However, limiting current operation is generally undesirable since the problems associated with complete depletion of oxygen at the cathode of the pump cell can seriously limit the performance of the device. It is... 

Wuytack, F., Raeymaekers, L., and Missiaen, L., 2002, Molecular physiology of the SERCA and SPCA pumps. Cell Calcium, 32 279-305. 

The two differentially pumped cells are joined by a trapping plate containing a small orifice that is capable of supporting a 10 pressure differential. Ions may be detected in either cell. However, if desired, ions formed in the "source" region under higher pressure conditions may be transferred to the "analyzer" cell for detection under lower pressure conditions, as described in the text. 

Pumps Sodium or potassium pumps Cell membranes... 

The effectiveness of RE and PC electrochemical reactors for methoxylation of furan was examined by Thomas et al. (1988). The performance of various types of reactors is compared in Table XXIX. As shown, both RE and PC with cathode spinning gave better performance than a capillary gap cell. For the pump cell, the results differ depending on whether the cathode is spinning or... 

Thomas et al. (1988) also showed that for both CGC and RE, the velocity profiles become fully developed after a certain radial entry length. The fully developed velocity profile has a parabolic shape for the CGC and the shape of two wall jets with a nearly stagnant region in between for the RE. For the pump cell, no asymptotic velocity profile is reached. The fluid continues to accelerate in the radial direction near the spinning electrode, while significant reverse flow is obtained near the stationary electrode. 

Because of the strong effects of plate rotations on the rector performance for both RE and PC electrolyzers, the critical design parameters for these reactors are the Taylor number (a2w/4v)0 5 and the Reynolds number (aVf/v). Here a is the gap width between the plate, w the angular velocity of rotation (in radians per second), v the kinematic viscosity of the fluid, and V the velocity in the feed pipe. Since no asymptotic velocity profile is reached for PC, the length of the cell will be an important design parameter in a pump-cell electrolyzer. Detailed mathematical models for RE and PC electrolyzers are given by Thomas et al. (1988), Jansson (1978), Jansson et al. (1978) and Simek and Rousar (1984). 

Cells with relatively small electrode area but improved mass transport to increase km by setting the electrodes in motion or by applying turbulence promoters. Examples are the pump cell [55, 56], the Chemelec cell [57], the ECO cell [58-60], the beat-rod cell [61, 62], and cells with vibrating electrodes or electrolytes [63]. 

---