Heat transfer irreversible

The power versus efficiency characteristics of the endoreversible Carnot heat engine is a parabolic curve. The endoreversible heat engine is a simple model, which considers the external heat-transfer irreversibility between the heat engine and its surrounding heat reservoirs only. 

In a waste heat recovery system, we might reduce the heat transfer irreversibility by designing a heat recovery steam generator with a smaller stream-to-stream temperature difference, and/or reduce friction by designing a turbine with a higher efficiency. 

In the case of thermodynamics, the designer can investigate the nature of the reaction heat and whether the reaction is reversible. If these exothermic reactions are irreversible, attention may be focused on the influence of reactor design on conversion and with heat transfer control. An objective of reactor design is to determine the size and type of reactor and mode of operation for the required job. The choice... 

For any method of heat transfer to take place, a temperature difference is necessary between two faces of a solid body, or at the boundaries of a gas or vapor. Flear transfer will take place only from a high-temperature source to a lower-temperature sink and is an irreversible process unless acted upon by another agency, as is the case with the refrigeration process. 

If the heat transferred from the control volume is not used externally to create work, but is simply lost to the atmosphere in which further entropy is created, then Equj can be said to be equal to /quj, a lost work term, due to external irreversibility. Another form of Eq. (2.23) is thus... 

J. C., Irreversibility phenomena associated with heat transfer and fluid friction in laminar flows through singly connected ducts, Int. J. Heat Mass Transfer 40 (1997) 905-914. 

That is, the total increase in entropy (which is a measure of disorder ) comes from heat transferred across the system boundary (Sq). However, a flowing fluid is in a dynamic, or irreversible, state. Because entropy is proportional to the degree of departure from the most stable (equilibrium) conditions, this means that the further the system is from equilibrium, the greater the entropy, so for a dynamic (flow) system... 

Finite-time thermodynamics is an extension to traditional thermodynamics in order to obtain more realistic limits to the performance of real processes, and to deal with processes or devices with finitetime characteristics. Finite-time thermodynamics is a method for the modeling and optimization of real devices that owe their thermodynamic imperfection to heat transfer, mass transfer, and fluid flow irreversibility. 

The ideal finite-time Rankine cycle and its T-s diagram are shown in Figs. 7.14 and 7.15, respectively. The cycle is an endoreversible cycle that consists of two isentropic processes and two isobaric heat-transfer processes. The cycle exchanges heats with its surroundings in the two isobaric external irreversible heat-transfer processes. The heat source and heat sink are infinitely large. Therefore, the temperature of the heat source and heat sink are unchanged during the heat-transfer processes. 

Chen, L. and Wu, C., Effect of heat transfer law on the performance of generalized irreversible Carnot refrigerator. Journal of Engineering Thermophysics, 20(2), 10-13, 1999. 

Truly isothermal operation of a tubular reactor may not be feasible in practice because of large enthalpies of reaction or poor heat transfer characteristics. Nor is it always desirable, as, for example, in the case of a reversible exothermic reaction (see Sect. 3.2.4). In an exothermic catalytic reaction, it may be necessary to provide adequate means for heat transfer to prevent the development of local hot-spots on which coking may occur and reduce the catalyst activity. An excessive temperature rise may also cause the catalyst particles to sinter, thereby reducing their surface area and causing an irreversible decrease in catalytic activity. 

The third idealized process, illustrated in Figure 8, is a modification of the first to include irreversible heat transfer across finite temperature differences, and discharge of... 

Numerous industrial operations involve a heat transfer between a liquid phase and a gaseous phase, with an important mass transfer effect, either as desorption-evaporation or as absorption-condensation. Here are some examples reconcentration, by evaporation, of solvents, toxic industrial effluents production, by absorption, of industrial aqueous acid solutions reversible or irreversible chemical reactions (oxidation, hydrogenation, sulfonation) purification of permanent gases (air, smoke) by scrubbing of soluble vapors desorbers and absorbers for heat pumps, where these two operations occur simultaneously. 

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