Thermodynamic efficiency The

Distillation is a unit operation that has been around for a long time and continues to be the primary method of separation in processing plants, in spite of its inherently low thermodynamic efficiency, The preeminence of distillation for the separation of fluid mixtures is not accidental, but fundamental, and therefore unlikely to be displaced. The reasons are both kinetic and thermodynamic. 

THERMODYNAMIC EFFICIENCY THE CARNOT, OTTO, DIESEL, AND RANKINE CYCLES... 

Polymer electrolyte fuel cells (PEFCs) have attracted much interest as one of the most promising nonpolluting power sources capable of producing electrical energy with high thermodynamic efficiencies. The key element of PEFCs is a polymer electrolyte membrane (PEM) that serves as proton conductor and gas separator [1, 2, 3,4], The membrane commonly employed in most PEFC developments is based on Nafion, which represents a family of comb-shaped ionomers with a perfiuorinated polymeric backbone and short pendant (side) chains having sulfonic acid end groups... 

Thermodynamic Efficiency. The net amount of work is -J lnjc(TH - Tl). This is negative (why ), which means that it is produced by the cycle. The amount of heat that enters the cycle is QaB = RTh ivc. The thermod)mamic efficiency is... 

Thermodynamic efficiency The net output of a gas turbine divided by the input. It is the reciprocal of heat rate after normalizing units. For example ... 

One of the rich aspects of finite-time thermodynamics is the way it opens options for optimizing any of several objective functions. In traditional equi-librimn thermodynamics, efficiency, the network delivered per unit of heat taken in from the high-temperatme reservoir, is the only objective one has. The other useful objectives such as power and cost have meaning only for systems operating in finite time. It is useful to get some sense of the differences of operating conditions for a chosen process optimized for different... 

Cycle type and thermodynamic efficiency The energy conversion cycle is not applied. 

Stea.m-Ra.ising Converter. There are a variety of tubular steam-raising converters (Fig. 7d) available, which feature radial or axial flow, with the catalyst on either shell or tube side. The near-isothermal operation of this reactor type is the most thermodynamically efficient of the types used, requiring the least catalyst volume. Lower catalyst peak temperatures also result in reduced by-product formation and longer catalyst life. 

Other Separation Techniques. Under some circumstances, distillation is not the best method of separation. Among these instances are the following when relative volatiHty is <1.05 when <1% of a stream is removed, as in gas drying (adsorption or absorption) or C2H2 removal (reaction or absorption) when thermodynamic efficiency of distillation is <5% and when a high boiling point pushes thermal stabiHty limits. A variety of other... 

Thermodynamic efficiency is hurt by the large ATbetween the temperatures of melting and freezing. In an analogy to distillation, the high a comes at the expense of a big spread in reboiler and condenser temperature. Erom a theoretical standpoint, this penalty is smallest when freezing a high concentration (ca 90%) material. 

Electrolysis. Electrowinning of zirconium has long been considered as an alternative to the KroU process, and at one time zirconium was produced electrolyticaHy in a prototype production cell (70). Electrolysis of an aH-chloride molten-salt system is inefficient because of the stabiUty of lower chlorides in these melts. The presence of fluoride salts in the melt increases the stabiUty of in solution, decreasing the concentration of lower valence zirconium ions, and results in much higher current efficiencies. The chloride—electrolyte systems and electrolysis approaches are reviewed in References 71 and 72. The recovery of zirconium metal by electrolysis of aqueous solutions in not thermodynamically feasible, although efforts in this direction persist. 

Because batteries direcdy convert chemical energy to electrical energy ia an isothermal process, they are not limited by the Carnot efficiency. The thermodynamic efficiency S for electrochemical processes is given by ... 

Whenever energy is transformed from one form to another, an iaefficiency of conversion occurs. Electrochemical reactions having efficiencies of 90% or greater are common. In contrast, Carnot heat engine conversions operate at about 40% efficiency. The operation of practical cells always results ia less than theoretical thermodynamic prediction for release of useful energy because of irreversible (polarization) losses of the electrode reactions. The overall electrochemical efficiency is, therefore, defined by ... 

Real irreversible processes can be subjected to thermodynamic analysis. The goal is to calciilate the efficiency of energy use or production and to show how energy loss is apportioned among the steps of a process. The treatment here is limited to steady-state, steady-flow processes, because of their predominance in chemical technology. 

The thermodynamic efficiency of this process as given by Eq. (4-363) is only 3.9 percent. Significant inefficiencies reside with each of the primary units of the process. 

Thermocompression Evaporators Thermocompression-evap-orator calculations [Pridgeon, Chem. Metall. Eng., 28, 1109 (1923) Peter, Chimin Switzerland), 3, II4 (1949) Petzold, Chem. Ing. Tech., 22, 147 (1950) and Weimer, Dolf, and Austin, Chem. Eng. Prog., 76(11), 78 (1980)] are much the same as single-effect calculations with the added comphcation that the heat suppied to the evaporator from compressed vapor and other sources must exactly balance the heat requirements. Some knowledge of compressor efficiency is also required. Large axial-flow machines on the order of 236-mVs (500,000-ftVmin) capacity may have efficiencies of 80 to 85 percent. Efficiency drops to about 75 percent for a I4-mVs (30,000-ftVmin) centrifugal compressor. Steam-jet compressors have thermodynamic efficiencies on the order of only 25 to 30 percent. 

This expansion of a condensing vapor is highly desirable thermodynamically, but the hquid must not bombard and erode the rotor blades, and, in particular, it must not accumulate in the rotor, since that would cause efficiency loss. 

As you may know, the ideal thermodynamic efficiency of a heat engine is given by... 

Although the Westinghouse s PWR Shippingport reactor was the first LW R to generate electricity in the U.S., GE s BWR Dresden 1 reactor followed within a year. Operating power reactors range from 600 to 1,200 MWe (million watts of electric power). Since the thermodynamic efficiency is -33%, the thermal heat production is 1,800 to 3,600 MWt. Both types of reactor operate at about the same temperature (-bOOT),... 

In defining the thermal efficiency of the closed gas turbine cycle, such as the one shown in Fig. 1.2, we employed the first law of thermodynamics (in the form of the steady-flow energy equation round the cycle), which states that the heat supplied is equal to the work output plus the heat rejected, i.e. 

Lloyd carried out a range of similar calculations, for differing thermodynamic parameters the results are presented in Fig. 8.12 in comparison with those for a basic STIG cycle with the same parameters of pressure ratio and maximum temperature. There is indeed similarity between the two sets, with the TCR plant having a higher efficiency. It is noteworthy that both cycles obtain high thermal efficiency at quite low pressure ratios as one would expect for what are essentially CBTX recuperative gas turbine cycles. 

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