Pressure altitude and

Conversions for Barometric Pressure and Altitude in Teras of mmHg per each 100 ft. 

Pressure input mode (1 = pressure and altitude) ISPR... 

The exponential relationship between pressure and altitude arises from the compressibility of air. [Recall that for water, which is essentially incompressible, hydrostatic pressure changes linearly with depth (Section 2.2.2).] The exponential relationship can be derived by referring to Fig. 4-3, which shows a sketch of a volume of air located directly above sea level. Pressure at the... 

In Section 4.1.1, Eqs. [4-1] and [4-2] were used to estimate the relationship between air pressure and altitude, assuming temperature to be constant with height. When combined with a third equation, Eqs. [4-1] and [4-2] also can be used to calculate the dry adiabatic lapse rate. The third equation, presented as the following Eq. [4-7], is based on an adiabatic process for air that rises and expands due to a decrease in pressure. By definition for an adiabatic process, heat flow into the rising air is assumed to be zero. Therefore, conser-... 

TABLE 25.3 Vertical Levels, a Coordinates, Pressures, and Altitudes... 

ALTITUDE vs. ATMOSPHERIC PRESSURE AND ALTITUDE VS. CORRECTION FACTOR FOR GAS TURBINE OUTPUT AND FUEL CONSUMPTION... 

Colorado, elevation 3170 m. To do this, use the barometric formula relating pressure and altitude P = 0 X (where P = pressure in... 

Low Density Gases. A fan may have to operate on low density gas because of temperature, altitude, gas composition (high water vapor content of the gas can be a cause of low density), reduced process pressure, or a combination of such causes. To develop a required pressure, the fan has to operate at a considerably higher speed than it would at atmospheric pressure, and hence it must operate much closer to top wheel speed. Bearing life is shorter, and the fan tends to vibrate more or can be overstressed more easily by a slight wheel unbalance. Abrasion of the blades from dust particles is more severe. Therefore, a sturdier fan is needed for low density gas service. 

Life-Support Applications. Exploration of outer space by humans has focused considerable attention on maximum as weU as minimum limits in the oxygen content of life-support atmospheres. Above the earth, both the atmospheric pressure and the partial pressure of oxygen decrease rapidly. The oxygen content of air remains constant at 20.946% to an altitude of ca 20 km, after which it decreases rapidly (1). 

Ground turbine fuels are not subject to the constraints of an aircraft operating at reduced pressures of altitude. The temperature of fuel in ground tanks varies over a limited range, eg, 10—30°C, and the vapor pressure is defined by a safety-handling factor such as flash point temperature. Volatile fuels such as naphtha (No. 0-GT) are normally stored in a ground tank equipped with a vapor recovery system to minimise losses and meet local air quaUty codes on hydrocarbons. 

The theoretical steam rate (sometimes referred to as the water rate) for stream turbines can be determined from Keenan and Keyes or Mollier charts following a constant entropy path. The theoretical steam rate is given as Ib/hr/kw which is easily converted to Ib/hr/hp. One word of caution—in using Keenan and Keyes, steam pressures are given in PSIG. Sea level is the basis. For low steam pressures at high altitudes appropriate coirections must be made. See the section on Pressure Drop Air-Cooled Air Side Heat Exchangers, in this handbook, for the equation to correct atmospheric pressure for altitude. 

As the altitude of an installation increases above sea level, the barometric pressure, and hence p or P decreases for any open vessel condition. This decreases the available NPSH. 

Figure 12-23. Barometric and atmospheric pressure at altitudes. See the appendix for detailed tabular listing.

When an internal combustion engine is to be used at different operating conditions (altitude) other than the standard conditions that the engine was rated at, it is necessary to derate the engine specifications. The brake horsepower H at pressure and temperature conditions other than standard can be obtained from the following ... 

The mechanism of radiative transfer in flares was found to depend on compn, flare diameter and pressure (Ref 69). The flare efficiency calcn is complicated by the drop-off in intensity at increasing altitudes and at very large diameters owing to the lower reaction temps (Ref 11, p 13) and the narrowing of the spectral emittance band (Ref 35). The prediction of the light output in terms of compn and pressure (ie, altitude) is now possible using a computer program which computes the equilibrium thermodynamic properties and the luminance (Ref 104) Flare Formulations... 

Beyer (B8) has recently reported experimental data obtained in small test motors under atmospheric and altitude conditions. At atmospheric pressure, his results showed the observed ignition delay to be a function of the delivery rate, as shown in Fig. 10. Additional data obtained in small test motors by Fullman and Nielsen (F6) are shown for comparison. These latter investigators conducted studies on the effects of various injectors, with delivery from both the head end and the aft end. Their results indicate that the hollow-cone injector is the most efficient. This subject has been treated in more detail by Miller (M7). 

Variations of temperature and pressure with altitude and the consequences for chemistry... 

This simple calculation shows why it is more difficult to breathe when up a mountain than at ground level the pressure term in Equation (8.18) decreases, so the rate at which oxygen enters the blood decreases in proportion to the decrease in the oxygen partial pressure. And the partial pressure is smaller at high altitudes than at sea level. 

Let s look at a situation in which two conditions change. Suppose a balloon has a volume at sea level of 10.0 L at 760.0 torr and 20°C (293 K). The balloon is released and rises to an altitude where the pressure is 450.0 torr and the temperature is -10°C (263 K). You want to calculate the new volume of the balloon. You know that you have to express the temperature in K in the calculations. It is perfectly fine to leave the pressures in torr. It really doesn t matter what pressure and volume units you use, as long as they are consistent in the problem. The pressure is decreasing, so that should cause the volume to increase (Boyle s law). The temperature is decreasing, so that should cause the volume to decrease (Charles s law). Here you have two competing factors, so it is difficult to predict the end result. You ll simply have to do the calculations and see. 

The air-intake used to induce air from the flight-altitude atmosphere plays an important role in determining the overall efficiency of ducted rockets. The air pressure built up by the shock wave determines the pressure in the ramburner. The temperature of the compressed air is also increased by the heating effect of the shock wave. The fuel-rich gaseous products formed in the gas generator burn with the pressurized and shock-wave heated air in the ramburner. The nozzle attached to the rear-end of the ramburner increases the flow velocity of the combustion products through an adiabatic expansion process. This adiabatic expansion process is equivalent to the expansion process of a rocket nozzle described in Section 1.2. 

A significant altitude effect will be shown by these illuminating compositions, especially those containing excess metal. The decreased atmospheric pressure - and therefore less oxygen - at higher altitudes will slow the burning rate as the excess fuel will not be consumed as efficiently. 

This relationship for the variation of pressure with altitude can be converted into that between temperature and altitude as shown in Eq. (N) below for a parcel of dry air that rises without heat exchange occurring between it and the surrounding air this is known as an adiabatic process. 

Gierczak et al. (1998) have also measured the temperature dependence for the absorption cross sections in addition to the quantum yields as a function of pressure and temperature. They have used these data, combined with the kinetics of the OH-acetone reaction, which is the other major removal process, to calculate the contributions of the OH reactions and of photolysis to the loss of acetone in the atmosphere as a function of altitude. Figure 4.31 shows that photolysis is a significant, but not the major, contributor at the... 

Using gas kinetic molecular theory, show that under typical atmospheric conditions of pressure and temperature corresponding to an altitude of 5 km (see Appendix V) collisional deactivation of a C02 molecule will be much faster than reemission of the absorbed radiation. Take the collision diameter to be 0.456 nm and the radiative lifetime of the 15-/rm band of C02 to be 0.74 s (Goody and Yung, 1989). 

---