Exergy, kinetic

Other forms of exergy can be those associated with kinetic and potential energy, which we have neglected in this treatment. 

Liquid-gas or solid-gas separation exergy loss can usually be neglected as long as the saturation vapour pressure of the liquid (solid) phase is low (and kinetics fast enough). 

When the transport rates of independent commodities are known (given or determined from kinetic relations), then the exergy transport terms can be evaluated using transport relationships like those presented in the next section. Then, the balance can be used to evaluate the one remaining quantity, the consumption. 

The detailed analysis of the different sub-processes of the boiler, as summarized in Figure 3, shows that the two largest dissipations are due to the uncontrolled kinetics of combustion (26.2% of the total exergy input), and heat transfer (34.5%) as heat passes from hot products at a high average (1 - Tq/T) to liquid and gaseous H2O with a relative low average (1 - Tq/T). 

A general thrust of the chapter will be SIMPLICITY. Differences in terminology have been eliminated wherever possible. In this analysis Availability, Available Energy, Exergy, and Work will be used as equivalent. This means that kinetic and potential energy effects and the potential work to be derived from the diffusion of chemical species into equilibrium with the environment have been ignored. This simplification may introduce significant inaccuracies in some studies, but is not important here. The intent is to demonstrate that simplified - perhaps even approximate - analysis can have valuable practical applications. 

Total exergy Ex of a multicomponent material stream consists of physical, chemical, and mixing parts. Disregarding kinetic and potential exergy contributions, the rate of exergy of a stream is Ex // T0S, Ex = hEx, where h is the molar flow rate of a stream and Ex the molar exergy. Similarly, H and W, are the stream enthalpy and entropy rates, respectively, and are based on reference conditions. T0 is the environmental temperature usually assumed as 298.15 K. 

Michaelis-Menten equation shows that the enzyme reactions in certain regions can be approximated by linear kinetics. Stucki (1984) demonstrated that variation of the phosphate potential at constant oxidation potential yields linear flow-force relationships in the mitochondria. Through linear flow-force relationships, cells may optimize their free energy production and utilization by lowering their entropy production and hence exergy losses at stationary states. 

Calculation of the efficiency of the practical air-breathing fuel cell, based on the fuel calorific value, involves ignoring or not realising that combustion is irreversible, with destruction of the kinetic exergy of high-speed product molecules. 

In the absence of nuclear, magnetic, electrical, and sirr-face tension effects, the total exergy of a system Esys can be divided into four components physical exergy Ef, kinetic exergy E , potential exergy E, and chemical exergy E ... 

Kinetic and potential exergy are equal to kinetic and poterrtial energy, respectively. 

Second law analysis results are shown in Figure 23.13. The flow exergy (vj/) of each point is calculated using Equation 23.52 where potential and kinetic energy are ignored. 

In this study, the two components, which are kinetic and potential exergy, are assumed to be negligible as the elevation and speed have negligible changes. The chemical exergy is associated with the departure of the chemical composition of a system from its chemical equilibrium. For a multi component mixture, chemical exergy can be written as [12] ... 

Exergy flows are identical to power in the case of the change of potential, kinetic, or electric energies. To evaluate the flow i of a fluid mixture, specific exergies e, in kj/kg for every mass flow w, in kg/s must be calculated. 

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