Barometric example

For each mol of urea produced in a total-recycle urea process, one mol of water is formed. It is usually discharged from the urea concentration and evaporation section of the plant. For example, a 1200 t/d plant discharges a minimum of 360 t/d of wastewater. With a barometric condenser in the vacuum section of the evaporation unit, the amount of wastewater is even higher. Small amounts of urea are usually found in wastewaters because of entrainment carry-over. 

There are problems to be considered and avoided when using Hquid-in-glass thermometers. One type of these is pressure errors. The change in height of the mercury column is a function of the volume of the bulb compared to the volume of the capillary. An external pressure (positive or negative) which tends to alter the bulb volume causes an error of indication, which may be small for normal barometric pressure variations but large when, for example, using the thermometer in an autoclave or pressure vessel. 

Example At a barometric pressure of 25.92 with 220 F dry-bulb and 100 F wet-bulb temperatures, determine H, h, andi . Ap = —4, and from table AH = 50.4. From note. 

Example 8 Determination of Air Properties For a barometric pressure of 25.92 inHg (Ap = —4), a dry-bulb temperature of 90 F, and a wet-bulb temperature of 70 F determine the following absolute humidity, enthalpy, dew point, relative humidity, and specific volume. 

Example 6-11 Size Selection and Utilities For Two-Stage Ejector With Barometric Intercondenser... 

Example 6-12 Temperatures at Barometric Condenser on Ejector System... 

The amount of water in dry air required to saturate the air (specific humidity, Wsat) is dependent on the temperature and certain other factors. Some examples of Wsat are shown here (for a barometric pressure of29.92 in. Hg) ... 

When laying out the diagram, it is only necessary to show the relative elevation of the process connections to the equipment where these affect the process operation for example, the net positive suction head (NPSH) of pumps, barometric legs, syphons and the operation of thermosyphon reboilers. 

EXAMPLE 11.26. How many moles of oxygen is contained in a l.OO-L vessel over water at 25°C and a barometric pressure of 1.00 atm ... 

Ventilation rates are generally sub-physiological to prevent excess barometric pressure on the lung, for example 1.5-2 ml volume at a rate of 30-80 min-1 for the rat. Periodic hyperinflation (sometimes described as a sigh ... 

As many as six stages are represented on Figure 7.30, combined with interstage condensers in several ways. Barometric condensers are feasible only if the temperature of the water is below its bubblepoint at the prevailing pressure in a particular stage. Common practice requires the temperature to be about 5°F below the bubblepoint. Example 7.13 examines the feasibility of installing intercondensers in that process. 

The term (z - 2i) may be called a static pressure head, and it can be expressed in feet or inches of water, or some height of any liquid. For example, barometric pressure can be expressed in inches of mercury. 

C. Dry Ice Baths. In contrast to the fixed temperature of slush baths, a Dry Ice bath is somewhat less reliable because the equilibrium temperature is a strong function of the partial pressure of C02 above the bath. For example, one test in which Dry Ice was freshly powdered in air had a temperature 8°C below the normal sublimation temperature of —78.5°C. In another test, 40-h standing was required for a Dewar of Dry Ice to attain —78.5°C.1 However, a small electric heater buried in the Dry Ice produced enough C02 to expel the air and attain the normal sublimation temperature in a matter of minutes. The temperature of an equilibrated Dry Ice bath at any barometric pressure may be found using the expression for sublimation pressure ... 

Now, let s try a more complex example. What is the partial pressure of oxygen in air when the air temperature is 20°C, the barometric pressure is 740 torr, and the relative humidity is 45% The vapor pressure of water at this temperature is 17.54 torr and the mole fraction of oxygen in air is 0.21. 

As an example of the calculations involved in computing permeability, let us assume that a volume of 750 cc of air is moved through a packing 10 sq cm in area and 30 cm long in 50 sec, and that the pressure at entrance is 5 cm H20. The outlet pressure is taken as zero, the air temperature 0 deg C, and the barometric pressure 755 mm Hg. We then have... 

Example 1.3 A dead-weight gauge with a 1-cm-diameter piston is used to measure pressures very accurately. In a particular instance a mass of 6.14 kg (including piston and pan) brings it into balance. If the local acceleration of gravity is 9.82 m s 2, what is the gauge pressure being measured If the barometric pressure is 748(torr), what is the absolute pressure ... 

Example 9.5 Extremely fine polonium-210 particles (0.01-p.m diameter, p = 9.4 g/cm3) are spilled on a laboratory bench. Assuming a barometric distribution is established, at what height will c/c0 = 0.1 ... 

There are a number of units that can be used to measure barometric pressure. For example, millimeters can be converted into inches thus, a standard pressure of 760 mm Hg can also be recorded as 30.0 inches of mercury. Inches of mercury are the units used for weather reports in the United States. Three other very common units that correspond to 760 mm Hg are ... 

A number of units are used to express a pressure measurement. Some are based on a force per unit area for example, pound (force) per square inch (psi) or dyne per square centimeter (dyne/cnr). Otliers are based on a fluid height, such as inches of water (in H2O) or millimeters of mercury (imiiHg) units such as tliese are convenient when tlie pressure is indicated by a difference between two levels of a liquid, as in a mmiometer or barometer. Barometric pressure is a measure of the ambient air pressure. Standard barometric pressure is 1 atm and is equivalent to 14.696 psi and 29.921 in Hg. 

---