Process parameters thermodynamics

Adiabatic flame temperatures agree with values measured by optical techniques, when the combustion is essentially complete and when losses are known to be relatively small. Calculated temperatures and gas compositions are thus extremely useful and essential for assessing the combustion process and predicting the effects of variations in process parameters (4). Advances in computational techniques have made flame temperature and equifibrium gas composition calculations, and the prediction of thermodynamic properties, routine for any fuel-oxidizer system for which the enthalpies and heats of formation are available or can be estimated. 

One of the most important SOFC behaviors considered today is thermal dynamics. In this section we analyze the fuel cell via one of the most simplified methods thermodynamic analysis. While we sacrifice some details, one key strength to this simplified approach is how, as we will see below, it brings clarity to how the various process parameters affect the thermal behavior of a fuel cell. We will arrive at a single analytic equation that relates key problem variables to the thermal behavior of the cell. Another strength of the model is the speed of solution, which may be required for some applications that are focused on the thermal response of a system. 

In real reactive absorption processes, the thermodynamic equilibrium can seldom be reached. Therefore, some correlation parameters such as tray efficiencies or HETP-values (Height Equivalent to One Theoretical Plate) are introduced to adjust the equilibrium-based theoretical description to the reality. However, reactive absorption always occurs in multicomponent mixtures, for which this simplified concept often fails [16, 23, 24]. 

CVD phase diagrams constructed using the SOLGAS-MIX-PV/FACT program have been shown to be powerful tools in the systematic development of CVD coatings. Their primary benefit is to initially establish the feasibility of a particular system and establish initial process parameters to obtain a particular deposit. Since equilibrium thermodynamics is used to generate CVD phase diagrams, they can only be used to establish trends because CVD process are typically non-equilibrium. With sufficient... 

Marcus [12-14] provided a simple approach allowing the prediction of the kinetics of the process, using thermodynamic parameters and spectroscopic measurements. Marcus theory assumes that bimolecular electron transfer, as shown in Scheme 1, occurs in three stages ... 

The second approach to coating scale-up involves an understanding of thermodynamic and mass transfer processes. A robust process can be demonstrated by establishing a coating procedure that identifies critical process parameters and their effect on the equilibrium between mass flow (the coating solids applied) and heat transfer (the solvent removed). This approach allows one to evaluate air temperature, air flow, and spray rate as applied to a known mass of tablets, and then scale these conditions into a larger coater. A thermodynamic model for aqueous film coating as described by Ebey is shown in Eq. (9). 

This short review shows that it is rather difficult at present to connect the process parameters to of micronization to the efficiency of the undertaking. This is due to the strong interrelation between the kinetic and thermodynamic phenomena involved in the particle production. 

The selection of process parameters is limited by the potential for carbon formation. The curve shows the thermodynamic carbon limit considering the deviation of the carbon structure from ideal graphite observed on catalysts (ref. 1). For 0/C and H/C ratios below the values indicated by the curve, there is thermodynamic potential for the formation of carbon. Hence, the position of the carbon limit curve depends on the type of catalyst. 

Wunderlich [270,271] succeeded in depositing CNTs on nickel sheets by plasma-enhanced CVD. Different morphologies of the nanotube layer on the nickel sheets could be achieved by variation of the process parameters such as the partial pressures of acetylene and ammonia in the inlet gas mixture, the total gas pressure, and the temperature. The authors summarized their results by formulating a detailed growth model, which included thermodynamic considerations. 

These achievements still come at a price. The reactants used are expensive and generally highly toxic, highly flammable and sometimes explosive. The great diversity of process parameters requires initial detailed optimization of a wide variety of often conflicting constraints. Fortunately, the thermodynamics and hydrodynamics have been well studied and process variables are fairly well understood. Further, modeling advances have connected theory and experiment to, in somecases, develop well proven processes with minimal effort. 

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