Temperature-enthalpy diagram

It is supposed that water is to be cooled at a mass rate L per unit area from a temperature 0L2 to Ql - The air will be assumed to have a temperature 6G, a humidity Jf ], and an enthalpy Hoi (which can be calculated from the temperature and humidity), at the inlet point at the bottom of the tower, and its mass flow per unit area will be taken as G. The change in the condition of the liquid and gas phases will now be followed on an enthalpy-temperature diagram (Figure 13.16). The enthalpy-temperature curve PQ for saturated air is plotted either using calculated data or from the humidity chart (Figure 13.4). The region below this line relates to unsaturated air and the region above it to supersaturated air. If it is assumed that the air in contact with the liquid surface... 

Hence on an enthalpy-temperature diagram, the operaling line of slope 1.33 is drawn through the point... 

On an enthalpy temperature diagram (Figure 13.20) the enthalpy of saturated gas is plotted against its temperature. If equilibrium between the liquid and gas exists at the interface, this curve PQ represents the relation between gas enthalpy and temperature at the interface H/ v. 0/). The modified enthalpy of saturated gas is then plotted against temperature (curve RS) to give the relation between H f and Of. Since b is greater than unity. RS will lie below PQ. By combining equations 13.35. 13.70, and 13.72, H[ is obtained in terms of Ha-... 

The answer to question (2) raised above is more easily seen if we translate Figure 14.5 into an enthalpy-temperature diagram, and then consider the stationary-states as those resulting from balancing the rate of enthalpy generation by reaction with the rate of enthalpy removal by flow (we are still considering adiabatic operation for an exothermic reaction). 

Figure 14.7 Representation of multiple stationary-states on an enthalpy-temperature diagram corresponding to (b) in Figure 14.5...

If we decrease the air rate (i.e., increase L G), then in effect the driving force is decreased and a greater degree of difficulty is reflected in the form of a larger value for Ntu(. This is illustrated by the enthalpy-temperature diagram of Figure 6.1. The plot reflects a counterflow cooling tower at constant conditions but variable L G ratios. 

Prepare an enthalpy-temperature diagram. Select the exit air enthalpy so that the slope of the line for the air enthalpy is equal to the slope of the curve for the enthalpy of saturated air at the water outlet temperature. 

Figure 9.16, the enthalpy-temperature diagram, shows the relationship between the water and air as they exist in a counterflow cooling tower. The vertical difference at any given water temperature between the water operating line and the air operating line is the enthalpy driving force. 

Fig. 8.4. (a) Dimensionless enthalpy - temperature diagram showing three crystallization paths, (b) Schematic diagram of solid fraction with time... 

Enthalpy-temperature diagram for the complete combustion of methane with air. 

FIGURE 1.2 Typical enthalpy-temperature diagram for apure substance. 

A process for separating nitrogen from natural gas is shown in Fig. 5.1-10. The separation is performed by partial condensation and partial evaporation The feed is cooled down and partially liquefied against the cold products. The two-phase system is flashed in a nozzle and, in turn, further cooled down. The two fractions after the nozzle are split in a vessel and heated up in separate product lines. The whole process can be simnlated with the eqnations presented before. Especially complex is the evalnation of the cooling down and heating np cnrves in the enthalpy/temperature diagram of Fig. 5.1-10. 

Figure A4 shows the enthalpy-temperature diagram for carbon dioxide. Plotting in this manner is a little imconventional. It is more common to make pressure-enthalpy plots. One look at Figure A4 and you can see why - it is very complicated.

Figure A4 Enthalpy-Temperature Diagram for Carbon Dioxide.

FIGURE 3.23 (See color insert.) Enthalpy-temperature diagram. 

J. Sestak Use of phenomenological kinetics and the enthalpy-temperature diagrams (and its derivative DTA) for a better understanding of transition processes in glasses Thermochim. Acta 280/281(1996)175... 

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