Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Process enthalpy descriptions

The specific heat capacity of an ideal gas is the basic quantity for the enthalpy calculation, as it is independent from molecular interactions. It is also possible to define a real gas heat capacity, but for process calculations it is more convenient to account for the real gas effects with the enthalpy description of the equation of state used (see Section 6.2). In process calculations, the specific heat capacity of ideal gases mainly determines the duty of gas heat exchangers, and it has an influence on the heat transfer coefficient as well. [Pg.102]

For the handling of enthalpies in a process simulation program, the change of a model between two blocks is often critical. This problem has much to do with the enthalpy description. Between the two blocks, the simulation program hands over the values for P and h to describe the state of the stream. According to the particular models used in the two blocks, the stream is assigned with two different temperatures that may differ significantly. [Pg.347]

A number of attempts have been made [11,21-33] however, none of them fulfills the particular demands of a process simulator, that is, extension to multicomponent mbctures, proved enthalpy description, and derivation of a fugacity coefficient. [Pg.583]

The terms enthalpy of fusion, enthalpy of vaporization, enthalpy of combustion, and many more cause some students to believe that there are many different kinds of enthalpies. There are not. These names merely identify the processes with which the enthalpy term is associated. Thus, there are processes called fusion (melting), vaporization, sublimation, combustion, and so forth. The corresponding enthalpy changes are called by names that include these descriptions. [Pg.276]

For a possible quantitative description of typical polymer effects we made the assumption that the values of AH and AS found for the low molecular weight catalysts stand for the activation process of the naked catalyst-substrate complex and are independent of cx. So, after subtracting these values the separate polymer effects are found. Then we have to explain why more entropy is gained and more enthalpy is needed for adaptation of the intermediate chains to... [Pg.20]

Reaction characterisation by calorimetry generally involves construction of a model complete with kinetic and thermodynamic parameters (e.g. rate constants and reaction enthalpies) for the steps which together comprise the overall process. Experimental calorimetric measurements are then compared with those simulated on the basis of the reaction model and particular values for the various parameters. The measurements could be of heat evolution measured as a function of time for the reaction carried out isothermally under specified conditions. Congruence between the experimental measurements and simulated values is taken as the support for the model and the reliability of the parameters, which may then be used for the design of a manufacturing process, for example. A reaction modelin this sense should not be confused with a mechanism in the sense used by most organic chemists-they are different but equally valid descriptions of the reaction. The model is empirical and comprises a set of chemical equations and associated kinetic and thermodynamic parameters. The mechanism comprises a description of how at the molecular level reactants become products. Whilst there is no necessary connection between a useful model and the mechanism (known or otherwise), the application of sound mechanistic principles is likely to provide the most effective route to a good model. [Pg.11]

The first and the second law of thermodynamics allow the description of a reversible fuel cell, whereas in particular the second law of thermodynamics governs the reversibility of the transport processes. The fuel and the air are separated within the fuel cell as non-mixed gases consisting of the different components. The assumption of a reversible operating fuel cell presupposes that the chemical potentials of the fluids at the anode and the cathode are converted into electrical potentials at each specific gas composition. This implies that no diffusion occurs in the gaseous phases. The reactants deliver the total enthalpy J2 ni Hi to the fuel cell and the total enthalpy J2 ni Hj leaves the cell (Figure 2.1). [Pg.16]

Elements 108 - 116 are homologues of Os through Po and are expected to be partially very noble metals. Thus it is obvious that their electrochemical deposition could be an attractive method for their separation from aqueous solutions. It is known that the potential associated with the electrochemical deposition of radionuclides in metallic form from solutions of extremely small concentration is strongly influenced by the electrode material. This is reproduced in a macroscopic model [70], in which the interaction between the microcomponent A and the electrode material B is described by the partial molar adsorption enthalpy and adsorption entropy. By combination with the thermodynamic description of the electrode process, a potential is calculated that characterizes the process at 50% deposition ... [Pg.196]

Define the terms flow work, shaft work, specific internal energy, specific volume, and specific enthalpy. Write the energy balance for an open process system in terms of enthalpy and shaft work and state the conditions under which each of the five terms can be neglected. Given a description of an open process system, simplify the energy balance and solve it for whichever term is not specified in the process description. [Pg.314]

Given a description of any nonreactive process for which tabulated specific internal energies or specific enthalpies are available at all input and output states for all process species, (a) draw and completely label a flowchart, including Q and W (or Q and for an open system) if their values are either specified or called for in a problem statement (b) perform a degree-of-freedom analysis and (c) write the necessary equations (including the appropriately simplified energy balance) to determine all requested variables. [Pg.315]

SR (sum-rates) method. The new liquid flow rates are taken proportional to the nonnormalized sums of mol fractions, the vapor rates by subsequent material balances, and the new temperatures by enthalpy balances. A flowsketch of the calculation process is in Figure 13.17, and a brief description also is given subsequently. This method is particularly suited to separations involving substances with widely differing volatilities, as in absorbers and strippers, where the bubblepoint method breaks down. [Pg.432]

Adsorption (desorption) energies or enthalpies of molecules and atoms on various surfaces are of primary and major interest in the experimental gas-phase radiochemical studies of the heaviest elements. In practice, pertinent data can be obtained almost exclusively in the experiments based on chromatographic principles. In the pioneering works [1-3] the required values were derived using the simplest description of the processes in columns in terms of molecular kinetics (see Sect. 4.2). Later [4] the task of finding the adsorption enthalpies was examined using a thermodynamic approach. It revealed that the molecular-kinetic treatment... [Pg.120]


See other pages where Process enthalpy descriptions is mentioned: [Pg.240]    [Pg.339]    [Pg.339]    [Pg.341]    [Pg.343]    [Pg.345]    [Pg.347]    [Pg.349]    [Pg.351]    [Pg.353]    [Pg.367]    [Pg.2841]    [Pg.304]    [Pg.149]    [Pg.502]    [Pg.291]    [Pg.408]    [Pg.12]    [Pg.9]    [Pg.486]    [Pg.207]    [Pg.67]    [Pg.429]    [Pg.212]    [Pg.221]    [Pg.202]    [Pg.82]    [Pg.501]    [Pg.408]    [Pg.103]    [Pg.115]    [Pg.58]    [Pg.408]    [Pg.651]    [Pg.408]    [Pg.456]   
See also in sourсe #XX -- [ Pg.339 ]




SEARCH



Enthalpy Description in Process Simulation Programs

Enthalpy description

Enthalpy descriptions, in process simulation

Enthalpy processes

Process description

© 2024 chempedia.info