Cell 7 heat exchanger

Once testing was completed, the RD was drained to atmosphere through the Cell 7 heat exchanger (HEX) and vent stack. Residual vapors in the flow system were purged using dry GHe. Then both the ST and RD were brought back to ambient pressure. Videos of the LAD screen were transferred to an external hard drive to be analyzed post-test. 

The fuel cell coolant system uses a liquid fluorinated hydrocarbon and transfers the waste heat from the cell stack through the fuel cell heat exchanger of the fuel cell power plant to the Freon-21 coolant loop system in the midfuselage. Internal control of the circulating fluid keeps the cell stack at an operating temperature of approximately 200°F. 

The heat resulting from these irreversibilities must then be removed in order to maintain the fuel cells at a desired operating temperature. Irreversibilities and the resulting quantity of heat produced can be reduced, in general, by increasing the active area of the fuel cells, heat exchangers, and fuel reformer but increased equipment costs result. 

FIGURE 41.16 Artist s concept of full-scale Li-Al /FeS electric van battery with cutaway showing prismatic cells, heat exchanger, and compressed multifoil insulation, (from Chilenskas et al. Courtesy cf Argorme... 

Correlations defined by the flow chart, (i.e. flow relationship between the compressor, turbine, fuel cell, heat exchangers and other components of the system and the order of the working flow direction through system elements)... 

Up to 0.4 g/L of the iodine stays in solution and the rest precipitates as crystallized iodine, which is removed by flotation (qv). This operation does not require a flotation agent, owing to the hydrophobic character of the crystallized element. From the flotation cell a heavy pulp, which is water-washed and submitted to a second flotation step, is obtained. The washed pulp is introduced into a heat exchanger where it is heated under pressure up to 120°C to melt the iodine that flows into a first reactor for decantation. From there the melt flows into a second reactor for sulfuric acid drying. The refined iodine is either flaked or prilled, and packed in 50- and 25-kg plastic-lined fiber dmms. 

Shells, clams, wood fragments, and other biological materials can also produce concentration cell corrosion. Additionally, fragments can lodge in heat exchanger inlets, locally increasing turbulence and erosion-corrosion. If deposits are massive, turbulence, air separation, and associated erosion-corrosion can occur downstream (see Case History 11.5). 

As the (n)th plate of the column acts as the detecting cell, there can be no heat exchanger between the (n-l)th plate and the (n)th plate of the column. As a consequence, there will be a further convective term in the differential equation that must account for the heat brought into the (n)th plate from the (n-l)th plate by the flow of mobile phase (dv). Thus, heat convected from the (n-l)th plate to plate (n) by mobile phase volume (dv) will be... 

In recent years there has been a continued interest in the use of alkali metals, notably sodium and lithium, as heat exchange media in nuclear reactors and fusion systems respectively and as chemical reactants in fuel cells. This interest is reflected in the proceedings of several major conferences which are referenced in the bibliography (see p. 2.109). 

Titanium is the only one of the more common structural metals which is not attacked by wet chlorine gas and it is thus widely used as a heat exchange material for cooling the gas after the electrolysis stage. Preheating of sodium chloride brine is carried out in titanium plate heat exchangers, while titanium butterfly valves, demisters, and precipitators handle the chlorine gas produced in the cell. The most important use of titanium in chlorine production is as anodes in place of graphite in the electrolytic process. This is covered in more detail later. 

Copper-base alloys will corrode in aerated conditions. It is, therefore, sometimes appropriate to consider cathodic protection. It becomes particularly relevant when the flow rates are high or when the design of an item causes the copper to be an anode in a galvanic cell (e.g. a copper alloy tube plate in a titanium-tubed heat exchanger). Corrosion can be controlled by polarisation to approximately — 0-6V (vs. CU/CUSO4) and may be achieved using soft iron sacrificial anodes. 

For an industrial application it is clear that flow cells will be highly advantageous since they allow continuous operation, the use of external heat exchangers and continuous monitoring of quality. In addition the reactant concentration remains invariant with time, allowing the cell to be run under true steady-state conditions, and the lower residence time of the products reduces further reactions. 

With decreasing cell size, the temperature difference between the wall of the cell and the eatalyst partiele in the cell would decrease to zero. For sufficiently small cell dimensions, we may assume the two temperatures are the same. In this case, the heat conduction through the wall becomes dominant and affects the axial temperature profile. As the external heat exchange is absent and the outside of the reactor is normally insulated, the temperature profile is flat along the direction transverse to the reactant flow, and the conditions in all channels are identical to each other. The energy balance is... 

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