Enthalpy concentration diagram

Reference states enthalpy ammonia at —77°C = zero enthalpy water at 0°C = zero 

Enthalpy-concentration diagrams greatly facilitate the calculation of energy balances involving concentration and phase changes this is illustrated in Example 3.6. 

Calculate the maximum temperature when liquid ammonia at 40°C is dissolved in water at 20°C to form a 10 per cent solution. 

Himmelbau (1995) or any of the general texts on material and energy balances listed at the end of Chapter 2. The Ponchon-Savarit graphical method used in the design of distillation columns, described in Volume 2, Chapter 11, is a further example of the application of the lever rule, and the use of enthalpy-concentration diagrams. 

2500 kg of 5% w/w solution is required per batch. Calculate the heat removed by the cooling water if the solution is to be discharged at a temperature of 25°C. The temperature of the solutions fed to the vessel can be taken to be 25°C. 

From a plot of the integral heats of solution versus concentration, 

Heat transferred to cooling water, neglecting heat losses, 

In Example 3.5 the temperature of the feeds and final solution have been taken as the same as the standard temperature for the heat of solution, 25°C, to simplify the calculation. Heats of solution are analogous to heats of reaction, and examples of heat balances on processes where the temperatures are different from the standard temperature are given in the discussion of heats of reaction. Section 3.10. 

CHAPTER 3 FUNDAMENTALS OF ENERGY BALANCES AND ENERGY UTILIZATION 

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Figure 1 gives an enthalpy-concentration diagram for ethanol(1)-water(2) at 1 atm. (The reference enthalpy is defined as that of the pure liquid at 0°C and 1 atm.) In this case both components are condensables. The liquid-phase enthalpy of mixing... 

Figure 5-1. Enthalpy concentration diagram for ethanol-water at 1.013 bar.

Enthalpy-Concentration Diagram for Aqueous Sulfuric Acid... 

FIG. 2-10 Enthalpy-concentration diagram for aqueous ethyl alcohol. Reference states Enthalpies of hquid water and ethyl alcohol at 0 C are zero. NOTE In order to interpolate equilihrium compositions, a vertical may he erected from any liquid composition on the hoihug hue and its intersection with the auxihary hue determined. A horizontal from this intersection will estahhsh the equihhrium vapor composition on the dew hue. (Bosnjakovic, Techuische Thermo-dynamik, T. Steinkopff, Leipzig, 1935. )... 

FIG. 2-11 Enthalpy-concentration diagram for aqueous hydrogen chloride at 1 atm. Reference states enthalpy of liquid water at 0 C is zero enthalpy of pure saturated HCl vapor at 1 atm (—85.03 C) is 8000 kcal/moL NOTE It should he observed that the weight basis includes the vapor, which is particularly important in the two-phase region. Saturation values may be read at the ends of the tie lines. [Van Nuys, Trans. Am. Inst. Chem. Eng., 39, 663 (1943).]... 

The maximum temperature will occur if there are no heat losses (adiabatic process). As no heat or material is removed, the problem can be solved graphically in the enthalpy-concentration diagram (Figure 3.3). The mixing operation is represented on the diagram... 

Figure 3.3. Enthalpy-concentration diagram for aqueous ammonia. Reference states enthalpies of liquid water at 0°C and liquid ammonia at —77°C are zero. (Bosniakovic, Technische Thermodynamik, T. Steinkopff,... 

The heat of dilution was calculated from an enthalpy — concentration diagram given in Perry s Chemical Engineers Handbook, 5th edn, p. 3.205, Figure 3.42. 

Taking the datum as 0°C for this calculation, so the enthalpy-concentration diagram can be used directly. 

From enthalpy-concentration diagram, enthalpy of mixed acid... 

Figure 13.9. Combined McCabe-Thiele and Merkel enthalpy-concentration diagrams for binary distillation with heat balances, (a) Showing key lines and location of representative points on the operating lines, (b) Completed construction showing determination of the number of trays by stepping off between the equilibrium and operating lines.

The advantage of taking H = 0 for pure liquid water at its triple point is that this is the base of the steam tables. Enthalpy values from the steam tables can then be used in conjunction with values taken from the enthalpy/concentration diagram. Were some other base used for the diagram, one would have to apply a correction to the steam-table values to put them on the same basis as the diagram. 

For an ideal solution, isotherms on an enthalpy/concentration diagram are straight lines connecting the enthalpy of pure species 2 at x, = 0 with the enthalpy of pure species 1 at Xj — 1. This follows immediately from Eq. (13.10),... 

Figure 13.10 Enthalpy/concentration diagram for H2S

Figure 13.11 Basic relations on an enthalpy/concentration diagram.

The use of enthalpy/concentration diagrams is illustrated in the following examples for the NaOH/H20 system, for which an Hx diagram is shown in Fig. 

Example 13.8 Determine the enthalpy of solid NaOH at 68(°F) on the basis used I the NaOH/HaO enthalpy/concentration diagram of Fig. 13.12. 

Enthalpy/concentration diagram, 440-447 for sodium hydroxide/water, 444 for sulfuric acid/water, 441 Enthalpy/entropy (Mollier diagram), 183, 185 for steam (see back endpapers)... 

A comparison of this example with Example 13.5 shows the simplification introduced by use of an enthalpy/concentration diagram. 

FIGURE 10.5 Enthalpy-concentration diagram for MgSCVEUO system. (Note 1 Btu/lb = 2.326 kJ/kg.) From Perry—Chemical Engineers Handbook, McGraw-Hill, 1963.)... 

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