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Technical Note (National Research Council of Canada. Division of Building Research), 1961-12-01
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Moisture Sorption Isotherms for Two Desiccants
Hedlin, C. P.
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ｾＭＭDIVISION OF BUILDING RESEARCH
NATIONAL RESEARCH COUNCIL OF CANADA
'fE
C
1HIN II CAlL
NOTlE
No.
354
NOT FOR PUBLICATION
PREPARED BY C. P. Hedlin CHECKED BY G. O. H.
FOR INTERNAL USE
APPROVED BY N. B. H.
DATE December 1961
PREPARED FOR Building Services Section, DBR/NRC
SUBJECT MOISTURE SORPTION ISOTHERMS FOR TWO DESICCANTS
One of the problems associated with studies on the per-formance of sealed, double-glazed window units is the interpretation of internal dew point measurement in relation to moisture gain to the
sealed space. One factor of interest in this regard is the equilibrium
moisture content vs dew point relationship for the desiccant involved.
In order to check the accuracy of published information, and to provide
additional data on the characteristics of one commonly used desiccant and one potentially usable material, a series of measurements were made using the special humidity facilities at Saskatoon.
Davison silica gel, Grade 408, mesh size 12-28, was obtained from the McArthur Chemical Company, Limited, and Type
l3X, 1/16-inch pellet, molecular sieve material was also procured for these tests.
Samples of both were dried to equilibrium in a vacuum oven
at 260 - 265"F. This treatment reduced the moisture content of the
silica gel received from the manufacturer by O. 5 to 0.6% (dry weight
basis).
Samples were weighed, exposed to air of known dew point
at 70of until they were substantially at equilibrium, then reweighed
to find the increase in moisture content. The "atmosphere producer"
and a controlled atmosphere chamber were used in these tests to provide the required air conditions.
Several moisture content - dew point values for silica gel, taken from the Chemical Engineers Handbook, third edition, page 912,
2
-are included in the attached Table. These values differ considerably
from our experimental values at low dew point temperatures. The
di screpancy cannot be entirely attributed to a difference in initial dryness because the absolute difference between the two sets of data
is substantially less at higher dew point temperatures. The Prairie
Regional Station values were all obtained by a process of ｡､ｳｯｲｰｴｩｯｮｾ
Although adsorption values lie below desorption values, it seems unlikely that hysteresis would account for such large differences.
TABLE I
Dew Point Dry Bulb %Weight increase - dry basis
Temp. Temp.
Silica gel Molec. sieves
1
2
3
1
2
3
-20. 1
69.6
3.2
3.2
13.5
14.3
-12. 1
69.6
3.5
3.7
16.4
17.4
-10. 1
69.7
4. 1
4. 1
16.7
17.6
-0.2
69.4
5.7
5.6
17.6
18.6
+6.5
70. 1
7.2
7.2
7.2
19. 1
19. 1
19.2
+9.6
70. 1
7.3
7.4
7.4
19.2
19.2
19.3
+28.3
70.2
15. 1
15. 1
15.1
21. 1
21. 1
21. 1
+44.7
70. 1
24.2
23.8
23.8
22.4
22.4
Moistur e content - dew point values for silica gel, taken from the Chemical Engineers Handbook:
Dew Point Dry Bulb Temp.
0/0
Moisture contentdry basis
