Dry adiabatic process

Thus air cools as it rises and warms as it descends. Since we have assumed an adiabatic process, -ATIAz defines the dry adiabatic process lapse rate, a constant equal to 0.0098 K/m, is nearly 1 K/lOO m or 5.4°F/1000 ft. 

Comparing the temperature of this parcel to that of the surrounding environment (Fig. 17-6), it is seen that in rising from 100 to 300 m, the parcel undergoes the temperature change of the dry adiabatic process lapse rate. The dashed line is a dry adiabatic line or dry adiabat. Suppose that... 

It is possible for an environmental lapse rate to be both stable and unstable, depending on whether or not the air parcel is saturated. Profile CC is said to be conditionally unstable because it is stable for dry adiabatic processes but unstable for moist adiabatic processes. 

Solution. Figure 12-8 shows the path on a psychrometric chart. The leaving dry-bulb temperature is obtained directly from Fig. 12-2 as 72.2 F. Since the spray water enters at the wet-bulb temperature of 70 F and there is no heat added to or removed from it, this is by definition an adiabatic process and there will be no change in wet-bulb temperature. The only change in enthalpy is that from the heat content of the makeup water. This can be demonstrated as follows ... 

However, away from the surface, processes frequently are adiabatic. For example, if a volume (parcel) of air is forced upward over a ridge, the upward-moving air will encounter decreased atmospheric pressure and will expand and cool. If the air is not saturated with water vapor, the process is called dry adiabatic. Since no heat is added or subtracted. Ah in Eq. (17-13) can be set equal to zero, and introducing the hydrostatic equation... 

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. 

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-... 

It is important not to confuse this dry adiabatic lapse rate with the rate of change in temperature with height in a Standard Atmosphere. The latter represents average conditions in Earth s atmosphere, where heating, mixing, and wet adiabatic processes also are occurring. 

Drying methods have been evolved around every product s specific requirement. The process takes many forms and uses many different kinds of equipment. In general, drying is performed by two basic methods (1) adiabatic processes and (2) non-adiabatic processes. In adiabatic processes, the heat of vaporization is supplied by the sensible heat of air in contact with the material to be dried. In non-adiabatic processes, the heat of evaporation is supplied by radiant heat or by heat transferred through walls in contact with the... 

If an isothermal drying process can be achieved by supplying extra heat to the fluidized bed of a dried material, a substantial increase in water content can be reached. Because of the large drying potential, an isothermal process provides several-fold larger water uptake compared to the adiabatic process in the humidity range from 30% to 90%. 

FIGURE 4 Examples of absolutely stable, conditionally unstable, and absolutely unstable environmental lapse rates (solid lines) relative to the dry and moist adiabatic process lapse rates (dashed lines) experienced by parcels of air displaced vertically from point A. Parcels follow the dry (DD) and moist (MM) adiabatic process curves. 

When the parcel of air originally located at point A in Fig. 4 is displaced upward along either curves DD or MM (representing dry and moist adiabatic processes, respectively), the air becomes increasingly colder than the surrounding temperatures indicated by the SS curve. By virtue of its negative buoyancy, the parcel descends back to equilibrium point A. When the parcel is displaced downward, it becomes increasingly warmer than profile SS and positive buoyancy returns it to point A. Environmental lapse rate SS is said to be absolutely stable because a parcel of air displaced either dry or moist adiabatically returns to its equilibrium level. 

The Dravo hydrate addition at low temperature process involves a two-step injection of water and dry sorbent in a rectangular 19.8-m duct having a cross section of 2 m. In one step water is injected through atomization nozzles to cool the flue gas from 150°C to approximately a 15°C approach to adiabatic saturation. The other step involves the dry injection of hydrated lime, either downstream or upstream of the humidifica tion nozzles. Typical SO2 removals were 50—60% at a Ca S ratio of 2. 

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