Internal irreversibility

The thermal efficiency, the work output as a fraction of the fuel exergy (the maximum reversible work), is shown as no. 1 in the figure and is 0.368. The internal irreversibility terms, are shown as nos. 2, 3, and 4 in the diagram, for the combustion... 

However, it is important to note that this conclusion becomes invalid if the air for cooling the LP turbine is taken from compressor delivery (as in Fig. 4.3b) and then throttled at constant temperature (T2 = Ty) to the lower pressure before being mixed with the gas leaving the HP turbine. The thermal efficiency drops as another internal irreversibility is introduced it can be shown [5] that... 

Figure 231. Indirect thermal energy storage by the conversion of thermal energy into work (Si entropy production due to internal irreversibilities, Q and S waste heat and entropy of the converter, Ta ambient temperature, W work)...

Does the Carnot heat pump cycle involve any internal irreversibilities ... 

Does the ideal vapor compression refrigeration cycle involve any internal irreversibility ... 

The actual finite-time Rankine cycle is shown in Fig. 7.17. The cycle is an external and internal irreversible cycle that consists of two irreversible internal adiabatic processes (pump and turbine) and two irreversible external isobaric heat-transfer processes. The heat source and heat sink are... 

Wu, C. and Kiang, R.L., Finite time thermodynamic analysis of a Carnot engine with internal irreversibility. Energy The International Journal, 17(12),... 

Chen, L., Sun, F., and Wu, C., Performance analysis of a closed regenerated Brayton heat pump with internal irreversibility. International Journal of Energy Research, 23, 1039-1050, 1999. 

A total of the entropy of any open system in its stationary state is con stant as well dS/dt = dgS/dt + d S/dt = 0. However, terms dgS/dt and diS/dt, which relate to the processes of exchange with the system environment and to internal irreversible processes, may be nonzero. 

Consider an open isothermal system where m internal irreversible processes related to a spontaneous evolution of several thermodynamic parameters a, occur simultaneously. The rate of energy dissipation in the system is given by the positively determined expression (2.5) ... 

The internal irreversible processes in this machine are accompanied by the entropy rise. The value of this rise is determined by variations in the total Gibbs potential of the system components and the components from the environment ... 

We saw in Chapter 2 that in the range of validity of linear nonequilibrium thermodynamics (i.e., in the scope of linear Onsager relations), a system approaching its stationary state is characterized by a monotonous decrease in the rate of entropy production (energy dissipation rate) resulting from the existence of internal irreversible processes dP < 0 and < 0. 

The approach of the entire system towards equilibrium, likely involving internal, irreversible processes, gives rise to a dissipation of energy given by... 

The final term, representing the rate of entropy generation Sq, reflects the second-law requirement that it be positive for irreversible processes. There are two sources of irreversibility (a) those within the control volume, i.e., internal irreversibilities,and (b) those resultingfrom heat transfer across finite temperature differences between system and surroundings, i.e., external thermal irreversibilities. In the limiting case where Sq = 0, the process must be completely reversible, implying ... 

For an adiabatic gas compressor, the efficiency with respect to isentropic operation r] is a measure of internal irreversibilities so is the dimensionless rate of entropy generation Sg/R = Sfi/fiR. Assuming tliat the gas is ideal with constant heat capacities, show that r] and Sg/R are related through the expression ... 

In a previous published chapter by InTech [25], we devoted to analyze the Curzon and Ahlborn cycle under the following conditions without internal irreversibilities and non instantaneous adiabats. We have shown some results in case of the Newton heat transfer law (Newton cooling law) and the Dulong and Petit heat transfer law, namely, heat transfer law like dQ Idt cc (AT)1, k= 5/4. Hence, we begin with a summary of the cited chapter. 

By contrast, in finite time, thermodynamics is usually considered an endoreversible Curzon-Ahlborn cycle, but in nature, there is no endoreversible engine. Thus, some authors have analyzed the non-endoreversible Curzon and Ahlborn cycle. Particularly in [16] has been analyzed the effect of thermal resistances, heat leakage, and internal irreversibility by a non-endoreversibility parameter, advanced in [14],... 

Moreover, in [31] has been applied variational calculus showing that the saving function in [17] and modified ecological criteria are equivalent. In this section, internal irreversibilities are taken into account to obtain Equation (4), replacing (r2 + r)/2f instead (,< 2 +, < )/2 in case of a non-endoreversible Curzon and Ahlbom cycle. The procedure in [5] is combined with the cyclic model in [16] to obtain the form of power output function and of ecological function. 

We know that dS = d S + diS and hence for the organism, the d S term must be negative to compensate for the positive d S. The organism discards matter with greater entropy content than the matter it ingests, thereby losing entropy to compensate for the entropy produced in internal irreversible processes. 

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