Trane TRG-TRC011-EN manual 10C 37.8C

period three

Capacity Control

notes

15 psia

5

concentration

[103.4 kPa]

0

e

0

r

u

5

s

s

5 psia

5

re

p

5

r

o

[34.5 kPa]

p

a

0

v

&

%

6

1 psia

'

[6.9 kPa]

0.1 psia	$		crystallization
[0.69 kPa]	)	(	line
50°F	100°F		150°F	200°F	LiBr solution
[10°C]	[37.8°C]		[65.6°C]	[93.3°C]	Figure 45
	solution temperature

By plotting the single-effect absorption refrigeration cycle on the equilibrium chart, it is apparent that crystallization is most likely to occur in the heat exchanger. At this particular condition, the 65% concentrated solution (') is cooled to 135°F [57.2°C] (() as it passes through the heat exchanger. As noted previously, the saturation temperature of 65% solution is 123°F [50.6°C] so there is no danger of crystallization.

Consider, however, if the solution was instead 66% concentrated and cooled to the same 135°F [57.2°C] temperature. The saturation temperature for 66% concentrated solution is approximately 143°F [61.7°C]. The result would be a deposit of salt crystals inside the heat exchanger. Prolonged operation at this condition could result in a buildup of salt that would eventually block the passages through the heat exchanger, interrupting the operation of the chiller.

Once a chiller is crystallized, operation can only be resumed after the solution temperature is raised above its saturation temperature, above 143°F [61.7°C] in this example. At this higher temperature, the salt crystals would return to the solution, allowing the chiller to operate again.

With the advent of microelectronic controls, modern absorption water chillers are designed to monitor and control solution concentrations and temperatures, allowing the chiller to operate over a broad range of conditions without danger of crystallization. In addition, safety controls are available to avoid crystallization and even to de-crystallize the chiller if necessary. Therefore, crystallization is not the serious problem that it once was with absorption chillers.

38 TRG-TRC011-EN