Ideal-gas properties of air

The foregoing equations are based on flow coefficients determined by calibration with air. For application with other gases, the difference between the properties of air and those of the other gas must be considered. The gas density is incorporated into the equations, but a correction must be made for the specific heat ratio (k = cp/cv) as well. This can be done by considering the expression for the ideal (isentropic) flow of a gas through a nozzle, which can be written (in engineering units ) as follows ... 

SOLUTION Plastic sheets are cooled as they leave the forming section of a plastics plant. The rate of heat loss from the plastic sheet by convection and radiation and the exit temperature of the plastic sheet are to be determined. Assumptions 1 Steady operating conditions exist. 2 The critical Reynolds number is Re, = 5 X 10. 3 Air is an ideal gas. 4 The local atmospheric pressure is 1 atm. 5 The surrounding surfaces are at the temperature of the room air. Properties The properties of the plastic sheet are given in the problem statement. The. properties of air at the film temperature oi T, = [T, + T-rV2 -(95 + 25)/ . = 60°C and 1 atm pressure are (Table A-15)... 

Assumptions 1 Steady operating conditions exist. 2 The tube and its cover are isothermal. 3 Air is an ideal gas. 4 Heat loss by radiation is negligible. Properties The properties of air should be evaluated at the average temperature. But we do not know the exit temperature of the air in the duct, and thus we cannot determine the bulk fluid and glass cover temperatures at this point, and we cannot evaluate the average temperatures. Therefore, we assume the gla.ss temperature to be dO C, and use properties at an anticipated average temperature of (20 + 40)/2 = SOT (Table A-15),... 

As we are primarily interested in blast effects in air, the properties of air that affect the blast wave are also considered in this section. For our purposes, air can be treated as an ideal gas. The speed of sound in an ideal gas is... 

What are the desirable properties of air in an air mattress used by a camper Show which part of the ideal gas model is related to each property. 

List some properties of air that make it suitable for use in automobile tires. Explain how each property relates to the ideal gas model. 

To extend our model, we should note that, at low pressures at least, all gases respond in the same way to changes in pressure, volume, and temperature. Therefore, for calculations of the type that we are doing in this chapter, it does not matter whether all the molecules in a sample are the same. A mixture of gases that do not react with one another behaves like a single pure gas. For instance, we can treat air as a single gas when we want to use the ideal gas law to predict its properties. 

Fhosphoric acid does not have all the properties of an ideal fuel cell electrolyte. Because it is chemically stable, relatively nonvolatile at temperatures above 200 C, and rejects carbon dioxide, it is useful in electric utility fuel cell power plants that use fuel cell waste heat to raise steam for reforming natural gas and liquid fuels. Although phosphoric acid is the only common acid combining the above properties, it does exhibit a deleterious effect on air electrode kinetics when compared with other electrolytes ( ) including such materials as sulfuric and perchloric acids, whose chemical instability at T > 120 C render them unsuitable for utility fuel cell use. In the second part of this paper, we will review progress towards the development of new acid electrolytes for fuel cells. 

A surface effect (air cushion) vehicle measures 10 ft by 20 ft and weighs 6000 lbf. The air is supplied by a blower mounted on top of the vehicle, which must supply sufficient power to lift the vehicle 1 in. off the ground. Calculate the required blower capacity in scfm (standard cubic feet per minute), and the horsepower of the motor required to drive the blower if it is 80% efficient. Neglect friction, and assume that the air is an ideal gas at 80°F with properties evaluated at an average pressure. 

Solubility in water and vapor pressure are both saturation properties, i.e., they are measurements of the maximum capacity that a solvent phase has for dissolved chemical. Vapor pressure P (Pa) can be viewed as a solubility in air, the corresponding concentration C (mol/m3) being P/RT where R is the ideal gas constant (8.314 J/mol.K) and T is absolute temperature (K). Although most chemicals are present in the environment at concentrations well below saturation, these concentrations are useful for estimating air-water partition coefficients as ratios of saturation values. It is usually assumed... 

Argon, an inert gas, has the useful property of being heavier than air, thus making it the ideal medium in which to work anaerobically (keep everything at the bottom of your argon-flushed glove box ). 

An ideal gas is a relatively low-density gas. The pressure p, temperature T, and specific volume v of an ideal gas are related by an equation of state, pv = RT, where i is a constant for a particular gas and is called the gas constant. Air, helium, and carbon dioxide are ideal gases. The properties of an ideal gas can be found in tables such as air tables. 

A sample calculation was given in Ref 29b for shock waves in air employing the general equation of state (See eq 23) for the expln products and the ideal gas adiabatic eq of state for air. Employing the method of calculation based on the hydrodynamic theory, good agreement was obtd for expls investigated (PETN Tetryl) between calculated and experimentally detd explosive properties... 

For all calculations, we need the characteristic properties of the gas phase. The air density can be evaluated by using the ideal gas law ... 

In this case, the free energy of transfer of i from the pure liquid to an ideal gas phase (i.e., air) AaLG and thus the corresponding gas (air)-liquid equilibrium partition constant, Ki lL (see Eq. 3-16 below), are direct measures of the attractive forces between like molecules in the liquid (recall we assume no interactions among gas phase molecules). Note that for the following discussion we use a subscript a (air) to denote the ideal gas phase. Furthermore a capital L is used to describe the pure liquid in order to distinguish from other liquid phases (subscript ). Finally, the superscript indicates that we are dealing with a property of a pure compound. 

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