Trane TRG-TRC011-EN manual Crystallization

period three

Capacity Control

notes

out of the condition called crystallization—a solidification of the bromide salt. Crystallization will be discussed next.

In the past, absorption water chillers would vary the heat input to the generator as the primary means of maintaining the desired leaving-chilled-water temperature. Because the absorption refrigeration cycle has the capability to store energy, using the energy valve as the sole method of control would cause the chiller to react very slowly to a change in capacity. By varying the flow rate of solution to the generator and absorber sprays, especially with the use of adjustable-frequency drives, recent chiller designs are now able to react very quickly to ever-changing load and cooling-water conditions.

15 psia

[103.4 kPa]

								re
							su
						s		5 psia
					re
				p
			r
		o						[34.5 kPa]
	p
a
v

1psia

[6.9 kPa]

0.1 psia				crystallization
[0.69 kPa]		123°F		line
50°F	100°F	[50.6°C]		150°F	200°F
[10°C]	[37.8°C]		[65.6°C]		[93.3°C]
	solution temperature

5	concentration
0
0
5
5
5
0
6

LiBr solution

Figure 44

Crystallization

Lithium bromide is chemically classified as a salt. In its solid state, it has a crystalline structure and, like most salts, is soluble in water. With any salt solution, there is a “saturation” temperature for a given concentration, below which the salt begins to leave the solution as a solid. This is called crystallization.

The saturation temperature for various solution concentrations is represented by the crystallization line on the equilibrium chart. For example, consider a lithium bromide solution of 65% concentration. Above 123°F [50.6°C], all salt remains dissolved in the solution. If, however, the solution concentration remains the same and the temperature falls below 123°F [50.6°C], the solution becomes saturated—meaning that the solution contains more salt than it can hold at that temperature—and the salt begins to leave the solution in a solid crystalline form.

TRG-TRC011-EN 37