Process entropy

The Carnot cycle is formulated directly from the second law of thermodynamics. It is a perfectly reversible, adiabatic cycle consisting of two constant entropy processes and two constant temperature processes. It defines the ultimate efficiency for any process operating between two temperatures. The coefficient of performance (COP) of the reverse Carnot cycle (refrigerator) is expressed as... 

Polytropic compression is characterized by being neither adiabatic nor isothermal but is a variable entropy process. Its relation is expressed... 

In a constant pressure and entropy process, p — pexts and dp and dS are equal to zero so that equation (5.54) becomes... 

Figure 4.19 Electrospray spectra of a protein (a) after transformation, and (b) after maximum entropy processing. From applications literature published by Micromass UK Ltd, Manchester, UK, and reproduced with permission.

The raw electrospray spectrum obtained is shown in Figure 5.14. Maximum entropy processing of these data yielded the spectrum shown in Figure 5.15, which shows the presence of two species with molecular masses of 14293.6 and 14 309.6 Da, with the latter being attributed to partial oxidation of the parent protein. 

Green B.N., Hutton T., and Vinogradov S.N. (1996), Analysis of complex protein and glycoprotein mixtures by electrospray ionization mass spectrometry with maximum entropy processing, Method. Mol. Biol. 61, 279-294. 

Adiabatic expansion or compression of an air mass maintains a constant potential temperature. From the definition of entropy, S, as dS = dqKV/T, these processes are also constant-entropy processes since no heat is exchanged between the system (i.e., the air parcel) and its surroundings. Hence the term isen-tropic is used to describe processes that occur without a change in potential temperature. 

The h-S diagram becomes most convenient in following rocket motor processes and this is the reason for its introduction. The conveniences obtained are generally hidden by machine computation programs which essentially deal with the enthalpy-entropy process for the expansion process, h is the sensible enthalpy only. Theoretical performance calculations are performed in terms of the total enthalpy which is here defined as the sum of the sensible and chemical enthalpies only. 

Q = 0 Btu. (By definition, there is no transfer of heat in a constant-entropy process.) Nonflow W2 = AE = 4236 Btu (4469.2 kJ). Steady flow W2 = AH = 4902 Btu (5171.9 kJ). Note In a constant-entropy process, the nonflow work depends on the change in internal energy. The steady-flow work depends on the change in enthalpy and is larger than the nonflow work by the amount of the change in the flow work. 

Another interesting development in natural gas fueled fuel cell area is the Direct Fuel Cell developed by Energy Research Corporation (ERC Danbury, CT). This is a carbonate fuel cell which could use directly either natural gas or coal gas without the necessity of external supply (usually by steam reforming of hydrocarbon fuel) of hydrogen. Since the galvanic combustion of methane is essentially a zero entropy process, the maximum theoretical efficiency could be 100%. A carbonate fuel cell was chosen because ... 

Fig. 11.3. The Z-contrast image of the YBCO asymmetric 30° [001] tilt boundary shown in Fig. 11.2 after maximum entropy processing.

The most efficient way to use this index is to look for the pertinent property (e.g., vapor pressure, entropy),/process (e.g., disposal of chemicals, calibration), ov general concept (e.g., units, radiation). Most primary entries are subdivided into several secondary entries, e.g., under heat capacity there are 17 secondary entries such as air, metals, water, etc. Primary entries will be found for certain classes of substances, such as alloys, elements, organic compounds, refrigerants, semiconductors, etc. Primary entries are also given for the individual chemical elements and for a few compounds such as water and carbon dioxide. However, only the most important tables are listed under these substances. Therefore, the user will find in most cases that it is best to look first for the property of interest, then examine the table or tables that are referenced. 

This is true for any substance— solid, liquid, or gas.) For a constant-entropy process (i.e., an isentropic process), the first term on the right of the equals sign is zero. We then substitute for dh from Eq, D.3 and substitute for Cp from Eq. D.IO to find... 

The basic premise of supercritical storage is that the contained fluid exists in a single phase. Thus, during operation, the stored fluid is not allowed to go subcritical, in which case it would exist as both vapor and liquid, in the fixed volume. Therefore, the operative process to maintain the fluid in a single phase is as follows The vessel is initially filled with liquid at atmospheric pressure, state point 1. After the vessel is filled and closed, heat is introduced to the contents, increasing vessel pressure. Since very little vapor initially exists in the vessel, the pressure increase can be considered essentially as a constant-entropy process. At the saturated liquid line, state point 2, the slope of the curve will increase slightly to reflect hydrostatic pressure build-up. A relatively small increase in heat input under this... 

Example. The normal boiling point of saturated NaCl brine is 108.7°C. If we are to provide a temperature differential of 10°C, the steam must condense at 118.7°C, or at 190.3 kPa. Taking compression to be a constant-entropy process, we can follow its course on a Mollier diagram or in the steam tables. Increasing the pressure of the cogenerated steam from atmospheric requires an increase in enthalpy of 118 kJ kg and produces a vapor temperature of 196.5°C (78° superheat). We can perform similar calculations for... 

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