Water system, ammonia

Ammonia—water systems are more complex than water—Hthium bromide systems, but can be used at temperatures down to —40° C. 

Ammonia—water systems operate under moderate pressures and care must be taken to avoid leaks of the irritating and toxic ammonia (qv). Sometimes a third material with a widely different density, eg, hydrogen, is added to the cycle in order to eliminate the need for mechanical pumping. 

Fig. 2. Vapor—hquid equiUbrium of ammonia—water system. Numbers represent the weight percent of ammonia ia the Hquid (1).

Absorption Refrigeration Systems Two main absorption systems are used in industrial application lithium bromide-water and ammonia-water. Lithium bromide-water systems are hmited to evaporation temperatures above freezing because water is used as the refrigerant, while the refrigerant in an ammonia-water system is ammonia and consequently it can be applied for the lower-temperature requirements. 

The ammonia-water absorption system was extensively used until the fifties when the LiBr-water combination became popular. Figure 11-103 shows a simplified ammonia-water absorption cycle. The refrigerant is ammonia, and the absorbent is dilute aqueous solution of ammonia. Ammonia-water systems differ from water-lithium bromide equipment to accommodate major differences Water (here absorbent) is also volatile, so the regeneration of weak water solution to strong water solution is a fractional distillation. Different refrigerant (ammonia) causes different, much higher pressures about 1100-2100 kPa absolute in condenser. 

Figure 8-45. McCabe-Thiele diagram for ammonia-water system.

Figure 9-73. Fellinger s overall gas film mass transfer data for ammonia-water system. Used by permission of Leva, M. Tower Packings and Packed Tower Design, 2nd Ed. U.S. Stoneware Co. (now, Norton Chemical Process Products Corp.) (1953).

Ammonia - Water System. Interaction parameter for the ammonia - water system was obtained using the data of Clifford and Hunter (1 4) and of Macriss et al. (15). A single - valued parameter was capable of representing the composition of the liquid phase reasonably well at all temperatures, however, the calculated amount of water in the vapor phase in the very high ammonia concentration region was somewhat lower than the data of Clifford and Hunter and Macriss et al. Edwards et al. (16) have applied a new thermodynamic consistency test to the data of Macriss et al and have concluded that the data appear to be inconsistent and that the reported water content of the vapor phase is too high. 

Pour 2 ml of a dilute ammonia solution into a test tube and heat it. How does equilibrium shift in the ammonia-water system when the temperature is changed ... 

Construct the equilibrium line. The equilibrium line relates the mole fraction of ammonia in the gas phase to that in the liquid phase when the two phases are at equilibrium. Equilibrium is assumed to exist between the two phases only at the gas-hquid interface. For dilute systems, Henry s law will apply. It applies for liquid mole fractions less than 0.01 in systems in general, and, as can be seen in Example 11.5, for the ammonia-water system it applies to liquid mole fractions as high as... 

Enthalpy-concentration charts are particularly useful for two-component systems in which vapor and liquid phases are in equilibrium. The Gibbs phase rule (Equation 6.2-1) specifies that such a system has (2 -I- 2 - 2) = 2 degrees of freedom. If as before we fix the system pressure, then specifying only one more intensive variable—the system temperature, or the mass or mole fraction of either component in either phase—fixes the values of all other intensive variables in both phases. An H-x diagram for the ammonia-water system at 1 atm is shown in Figure 8.5-2. 

Figure 8 -2 Enthalpy-concentration diagram for the ammonia-water system at 1 atm. (From G. G. Brown el al.. Unit Operations, 1950. Figure 551. Reprinted by permission of John Wiley Sons.)...

Van Blaaderen and Vrij s chapter (Chapter 4) constitutes an excellent contribution to the understanding of the mechanisms of nucleation and growth of silica spheres in the alcohol-ammonia-water system to achieve particle sizes much larger than those of the classic silica sols synthesized in water. Kozuka and Sakka (Chapter 6) provide detailed conditions and the mechanism of formation of micrometer-sized particles of gels synthesized in highly acidic solutions of tetramethoxysilane (TMOS). 

As discussed in the section on absorbers (Section 7.7.4), falling films used in microchannels have shown potential for ammonia-water systems [279]. The military has shown interest in these absorption systems due to their inherently low electrical requirements and low noise. However, military application requires orientation independence, even more restrictive size requirements, and a heat rejection temperature of 50 °C (120 °F). To address this need, wicking and fractal microchannel technology has been developed that allows orientation independence and control of the liquid film thickness, which in turn controls the majority of mass... 

Surface Tension. King, Hall, and Ware, in studying the properties of the ammonia-water system, concluded that It is evident from the surface... 

In their studies on the properties of ammonia-water systems, King et al. found that theoretical and observed surface tensions were in good agreement (Fig. 8-3) except in the middle region. In this connection it is to be... 

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