Heat Generation and Transport

So as / tot increased, the RH increases, decreases, and condensation occurs in pores above the normal bulk condensation temperature due to increased pore-level vapor pressure. This is not a signihcant effect in most fuel cells and does not matter for any species besides water. For example, for a 50-nm (typical of a catalyst layer) pore at 80°C, water will condense at approximately 100.5°C. So capillary condensation is not a major effect in DM or catalyst layers but can be significant for vapor dissolving and condensing into solid polymer electrolytes with nanometer-size holes. 

In a typical combustion engine, around 80% of the waste heat is removed by the exhaust gas flow. In a larger PEFC stack, the waste heat is primarily removed by the fuel cell coolant, and relatively little heat is removed by the exhaust flow. This puts additional heat rejection burdens on the system. 

Due to the low operating temperature, the heat rejection rate to the environment is reduced compared to a combustion engine, since the heat transferrate is proportional to the temperature difference between the heated source and the ambient. 

In Chapter 4, the heat generation flux in a fuel cell was shown to be related to the current and the departure of the cell voltage from the thermal voltage  

This entropy-generated heat is known as Peltier heating. The irreversible heat generated by activation, ohmic, and concentration polarizations is 

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Chemical manufacture Fluid transport Handling of bulk solids Size reduction and enlargement Heat generation and transport Distillation Gas absorption Bioreactions... 

K. Fushinobu, A. Majumdar, and K. Hijikata, Heat Generation and Transport in Submicron Semiconductor Devices, / Heat Transfer (117) 25-31,1995. 

Reaction calorimetry aims to measure heat released from a polymerization in order to infer monomer conversion and polymerization rate (as reviewed, for example, in Refs. 8, 38, and 39). Careful measurement and balancing of mass and energy flows are necessary for success of this technique. For example, the commercial Metder-Toledo RCl jacketed reactor acts as a calorimeter supplying mass balance, polymerization heat generation, and transport data. 

Generation and transport of heat within the core, including boiloff of water from the reactor vessel. 

The other notation for the material and energy balances is identical to that of Chaps. 2 and 4 note that the work, heat, generation, and mass transport are now all expressed as rate terms (mass or energy per unit time). 

There is the prospect of wind farms, wave and tidal power facilities being linked to hydrogen generation, as well as nuclear plants, which nevertheless pose other challenges related to security and radioactive waste disposal. In one form or other and with the right leadership and entrepreneurship, these could meet, potentially, all our heating, power and transportation needs. 

As shown in Table 4.2, large break LOCA events involve the most physical phenomena and, therefore, require the most extensive analysis methods and tools. Typically, 3D reactor space-time kinetics physics calculation of the power transient is coupled with a system thermal hydraulics code to predict the response of the heat transport circuit, individual channel thermal-hydraulic behavior, and the transient power distribution in the fuel. Detailed analysis of fuel channel behavior is required to characterize fuel heat-up, thermochemical heat generation and hydrogen production, and possible pressure tube deformation by thermal creep strain mechanisms. Pressure tubes can deform into contact with the calandria tubes, in which case the heat transfer from the outside of the calandria tube is of interest. This analysis requires a calculation of moderator circulation and local temperatures, which are obtained from computational fluid dynamics (CFD) codes. A further level of analysis detail provides estimates of fuel sheath temperatures, fuel failures, and fission product releases. These are inputs to containment, thermal-hydraulic, and related fission product transport calculations to determine how much activity leaks outside containment. Finally, the dispersion and dilution of this material before it reaches the public is evaluated by an atmospheric dispersion/public dose calculation. The public dose is the end point of the calculation. 

No limits are established for these radionuclides in Class B or C wastes. Practical considerations such as the effects of external radiation and internal heat generation on transportation, handling, and disposal will limit the concentrations for these wastes. These wastes shall be Class B unless the concentrations of other nuclides in Table 16.6 determine the waste to the Class C independent of these nudides. 

Hydrocarbons derived from fossil fuel are the main source of energy and raw material for petrochemicals in the industrial world. When not used in combustion to generate power and heat, fossil fuels are refined in various petrochemical transformation processes into purer and higher-valued products. This chapter continues the discussion by Leo Manzer to address opportunities for research in chemical sciences to reduce carbon (dioxide) emission. Although the large majority of carbon emission is from power generation and transportation, the discussion here focuses on hydrocarbon conversion in the chemical processing industry, with only a brief discussion of hydrocarbon conversion in fuel cell applications. 

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