Physical changes common fuels

In general, there are three common ways of preparing nano-thermites these include arrested reactive milling, physical mixing, and sol-gel methodology. Changing from the microscale to the nano, these methods provide accessibility and use of different particle sizes, as well as materials with different degrees of contact between oxidizer and fuel. 

All the above mentioned fuels have certain factors in common (i.e., variable and often unstable chemical composition). This means changing physical-chemical properties and possible presence of large amounts of solid particles. Often there are also dissolved inorganic compounds present. A comparison of selected properties of ELFO, LFO, HFO, rapeseed oil, and its corresponding transesterification products with methanol and ethanol is shown in Table 20.2. 

Note that calculation based on HHV or LHV is an arbitrary decision and does not necessarily correspond to the actual physical state of the product water at the fuel cell electrode. The terms HHV and LHV are used in combustion calculations as well, where the product water is nearly always in the gas phase. The difference between the two values is proportional to the latent heat of vaporization of the liquid. Use of the LHV (gas-phase vapor product) will result in a lower calculated thermal voltage, since some energy is used for the latent heat of vaporization of the liquid. In practice, the LHV is completely appropriate for high-temperature fuel cells, but the HHV is also commonly used. An important point regarding low-temperature fuel cells that is often confusing is that the choice of HHV or LHV is arbitrary and 100°C is not a point of demarcation between the two. Often 100°C is thought of as a natural boundary between the HHV and LHV because it is the phase change temperature of water at 1 atm pressure. The delineation between liquid and gas, however, is more complex and is related to the local vapor pressure and total pressure, as discussed in Section 3.5. 

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