Adiabatic heating and cooling

The more trivial effect of temperature is the immediate disturbance of rates and equilibria due to adiabatic heating and cooling during compression and decompression. The maximum temperature increase that can be obtained in water by reversible compression is... 

It was noted in Section ILC that departures from zonal-mean radiative equilibrium in the stratosphere are balanced mainly by adiabatic heating and cooling due to vertical motions. This fact can be used to deduce the vertical zonal-mean vertical motion of the stratosphere from its net heating rate the zonal-mean meridional velocity can then by obtained by continuity. 

Furthermore, because the net radiative drive is balanced primarily by adiabatic heating and cooling (see Section II. C), it follows that arty departures of the zonal-mean temperature fleld from radiative equilibrittm are also wave driven. This can be expressed analytically by writing the net radiative drive as a relaxation toward radiative equilibrium,... 

The oscillating wind regimes depicted schematically in Fig. 16 (and from observations in Figs. 10 and 11) are accompanied by secondary circulations in the meridional plane, and by temperature anomalies in balance with the adiabatic heating and cooling associated with the secondary circulations. The magnitude of these anomalies can be estimated because, even in the tropics, the zonal-mean zonal wind and temperature are in thermal wind balance. Near the equator, Eq. (13) can be written as follows ... 

The second part of the first law of thermodynamics arises when the requirement that the process be adiabatic is dropped recall that this means the system is not insulated, and processes can be caused by heating and cooling. In a general process (the only assumption is that matter is not added or removed from the system), if an amount of work W is done on the system and the energy changes by DE then the heat supplied to the system Q is defined by... 

USA in 1872. Thermodynamically, the cooling version consists of an adiabatic (isentropic) compression followed by heat transfer to the surroundings, then adiabatic expansion and cooling. 

Figure 4.3 Reversible Camot cycle, showing steps (1) reversible isothermal expansion at th (2) reversible adiabatic expansion and cooling from th to tc (3) reversible isothermal compression at tc (4) reversible adiabatic compression and heating back to the original starting point. The total area of the Camot cycle, P dV, is the net useful work w performed in the cyclic process (see text).

The specific heating and cooling power is an often-underestimated source of error. It is physically possible for a large production extruder to require less heating and/or cooling power than a small laboratory extruder in terms of drive power (Fig. 11.15). Therefore, laboratory extruders are often operated adiabatically or only moderately heated in order to ensure comparability with a large extruder. 

HEATING AND COOLING REQUIREMENTS. Heat loss from a large insulated column is relatively small, and the column itself is essentially adiabatic. The heat effects of the entire unit are confined to the condenser and the reboiler. If the average molal latent heat is X and the total sensible heat change in the liquid streams is small, the heat added in the reboiler is VX, either in watts or Btu per hour. When the feed is liquid at the bubble point (q 1), the heat supplied in the reboiler is approximately equal to that removed in the condenser, but for other values of q this is not true. (See page 554.)... 

A number of three-dimensional adiabatic reactor network synthesis problems were described in Chapter 7. A paper by Nicol et al. (1997) looks at extending these principles to include heating and cooling utilities. In effect, heat transfer equipment may be incorporated into the optimal reactor structure on the AR boundary. The results are dependent on a number of ideas developed by Godorr et al.(1994). Aspects of this work also involve finding conditions for optimality in four-dimensional space. Further details may be found in the PhD theses of Love (1995) and Nicol (1998). 

They are heated by adiabatic elongation, and cooled by adiabatic compression. 

Studies were carried out by ICI many years ago into using a gas turbine as a hydrocarbon cracker for ethylene production. The aim was to use the rapid heating and cooling available in a gas turbine to carry out a chemical reaction. The heat for an endothermic reaction is provided by adiabatic compression and rapid expansion in the turbine gives the rapid cooling necessary to maintain high selectivity. The concept was revisited three years ago, and it was concluded that for a 600 000 tonne/ annum cracker, ethylene costs could be significantly reduced. 

In many of the direct driers to be described, the solid is moved through a drier while in contact with a moving gas stream. The gas and solid may flow in parallel or in countercurrent, or the gas may flow across the path of the solid. If heat is neither supplied within the drier nor lost to the surroundings, operation is adiabatic and the gas will lose sensible heat and cool down as the evaporated moisture absorbs latent heat of vaporization. By supplying heat within the drier, the gas can be maintained at constant temperature. 

Adiabatic operation. If adiabatic operation leads to an acceptable temperature rise for exothermic reactors or an acceptable fall for endothermic reactors, then this is the option normally chosen. If this is the case, then the feed stream to the reactor requires heating and the efiluent stream requires cooling. The heat integration characteristics are thus a cold stream (the reactor feed) and a hot stream (the reactor efiluent). The heat of reaction appears as elevated temperature of the efiluent stream in the case of exothermic reaction or reduced temperature in the case of endothermic reaction. 

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