Air-standard assumptions

An ideal Diesel cycle with a compression ratio of 17 and a cutoff ratio of 2 has a temperature of 313 K and a pressure of 100 kPa at the beginning of the isentropic compression process. Use the cold air-standard assumptions and assume that k= A. Determine (a) the temperature and pressure of the air at the end of the isentropic compression process and at the end of the combustion process, and (b) the thermal efficiency of the cycle. 

In the gas power cycles, the working fluid remains gas for the entire cycle. Internal combustion cycles of Otto and Diesel engines as well as the gas turbines are some well-known examples of engines that operate on gas cycles. In the analysis of gas power cycles, the following assumptions known as air-standard assumptions are used ... 

When it is assumed that the air has a constant value for the ratio of specific heats y = Cp/Cv) determined at room temperature (25 °C or 77 °F), the air-standard assumptions are called the cold-air-standard assumptions. These assumptions simplify the analysis of gas power cycles without significantly deviating from the actual cycle (Cengel and Boles, 2002). 

Under the cold-air-standard assumptions (constant specific heat values at 25 °C and y = 1.4), the thermal efficiency becomes ... 

Analysis procedures for Brayton cycles are similar to the previous examples of Rankine cycles with the exception that properties are determined from gas fables. The gas turbine in Figure 23.21 is analyzed using air standard assumptions, which consider the working fluid to be air and treat combustion as a heat addition process. A more accurate analysis could employ tables that account for combustion products, such as Keenan and Kay (1960). The heat to the combustion chamber is assumed to be available at 2500°F. In the example, air from the dead state (14.7 psia, 75°F) enters the intake structure. Pressure drops before the turbine inlet in the intake ducting to 14.5 psia. It is compressed in a compressor with a... 

Many preliminary analyses of gas turbines are based on the assumption of a closed air standard cyclic plant, and for such analyses the use of tj as a thermal efficiency is entirely correct (as discussed in the early part of Chapter 3 of this book). But most practical gas turbines are of the open type and the rational efficiency should strictly be used, or at least its approximate form, the arbitrary overall efficiency tjq. We have followed this practice in the latter part of Chapter 3 and subsequent chapters even though some engineers consider this differentiation to be a somewhat pedantic point and many authors refer to tjo as a thermal efficiency (or sometimes the lower heating value thermal efficiency ). 

Toxicity alucs for carcinogenic effects also can be c.xprcsscd in terms of risk per unit concentration of the substance in the medium where human contact occurs. These measures, called unit risks, are calculated by dividing the slope factor by 70 kg and multiplying by the inhalation rate (20 m /day) or the water consumption rate (2 L/day), respecti ely, for risk associated with unit concentration in air or water. Where an absorption fraction less than 1.0 has been applied in deriving the slope factor, an additional conversion factor is necessary in the calculation of unit risk so that the unit risk will be on an administered dose basis. The standardized duration assumption for unit risks is understood to be continuous lifetime c.xposure. Hence, when there is no absorption conversion required ... 

Linear rollback As the name implies, linear rollback is based on the assumption that pollutant concentrations will decrease proportionally to a decrease in the precursor emissions. For a pollutant such as CO, for example, the percentage reduction in emissions required to meet air quality standard for CO (Aco) in a region that currently has observed concentrations as high as Cco is given by linear rollback as ... 

In practice, the gases exiting the fluidized bed reactor contain a certain amount of ash and have to be cleaned. Also, the combustion products of coal are sometimes corrosive, which means that in addition to air being fed into the reactor, various other chemicals are added to ensure "clean" combustion products that will not corrode turbine blades or violate environmental standards. Coal combustion is a very active field of research, and many exciting developments are occurring there. In this analysis, we make certain assumptions that illustrate the thermodynamic concepts as clearly as possible. Therefore, we do not examine the effect of hydrodynamics, heat, and mass transfer, which are very important in the combustion of the coal particle and the distribution of combustion products. We do not expect that this will have a significant impact on the analysis. 

Respiratory exposure assessments place great emphasis on the accurate measurement of enviromnental concentrations in the air breathed by the worker, and normally make simplifying assumptions regarding contact rate (standard respiratory volnme) and absorption (100% absorption). 

In 1998 two units, olf and decipol, were introduced to quantify sensory source emissions and perceived air quality [15]. This theory is based on the assumption that the pollutants in buildings all have the same relation between exposure and response after one factor normalisation based on human bioeffluents. Emission rates are measured in olf, where 1 olf is defined as the emission rate causing the same level of dissatisfaction as bioeffluents from one seated person at any airflow. Concentration or perceived air quality is measured in decipol. One decipol is defined as the concentration of pollution causing the same level of dissatisfaction as emissions from a standard person diluted by a clean airflow of 101/s. In this context perceived air quality is the dissatisfaction with or the acceptability of lAQ. 

The H.U.D. formaldehyde standards of 0.2 ppm and 0.3 ppm for hardwood plywood paneling and particleboard, respectively, were chosen because the combination of these products at their specific loadings and air change rate would result in a chamber concentration of less than 0.4 ppm. This assumption was based on four studies. 

Trasatti [2] has described the methods used to estimate the absolute electrode potential on the basis of suitable extrathermodynamic assumptions. The method presented here is the one which gives an estimate which can be related to the potential scale used by physicists. Moreover, the resulting estimates of the absolute values of the standard electrochemical potential are based on experimentally measured quantities. The analysis is illustrated here for cell (9.3.30), which contains a hydrogen electrode. An air gap is introduced into the cell, so that the solutions surrounding each electrode are separated. The resulting cell is... 

This example shows that, for the assumption of perfect mixing of benzene into the shop air, it is quite straightforward to compute the required dilution air to meet the industrial hygiene standard. We also see that this is an impossibly large airflow rate. If we divide the above flow rate by the cross-sectional area of the shop (4 m x 4 m), we find... 

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