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Homogeneous nucleation of DBP vapour in a laminar flow diffusion chamber: the carrier gas effect
J. Aerosol Sci., Vol. 26. Suppl 1, pp. $631-S632, 1995 Elsevier Science Ltd Printed in Great Britain 0021-8502/95 $9.50 + 0.00
Pergamon
Homogeneous nucleation of DBP vapour in a laminar flow diffusion chamber: the carrier gas effect Kaarle Hgmeri, Markku Kulmala and Eija Rantanen University of Helsinki, Department of Physics P. O. Box 9, FIN-00014 University of Helsinki, Finland
KEYWORDS Homogeneous nucleation rate, laminar flow diffusion chamber, DBP vapour, carrier gas effect
Laminar flow d i f f u s i o n c h a m b e r The preliminary tests of a laminar flow diffusion chamber for homogeneous nucleation studies of DBP vapour has performed earlier by Anisimov et al. (1994). The laminar flow, which is initially saturated (S=I) and at temperature of saturator (T~) is cooled by leading the flow to condenser section where the walls are maintained at lower temperature (To). The cooling leads to supersaturation of the flow (S > 1) and consequently homogeneous nucleation of the vapour inside the condenser.
Homogeneous nucleation of D B P vapour Prom the measured homogeneous nucleation rates we have determined the critical saturation ratios Serif corresponding to nucleation rate of 106 cm-3s -1 which is in the middle of our experimental nucleation rate scale. Figure 1 shows the dependence of the critical saturation 10 ~ . . . . . . . . 2
I = l O 6 c r n ' a s -1
10 5 5 2
- Claasical theory
"'"'"'"'"'.., ...
O'~ 1 0 4
..... "-,.
• ""'-....
2
SCC-th
..... .
...
5
M-theory
•
"'°'"'"'" •
2 2 I
lo 240
2~o
~;o
2~o
2;0
2;0
aoo
31o
a2o
T [K]
Figure 1: Critical saturation ratios So,it for a nucleation rate of 10 6 cm-3s -1 for DBP as a function of the various nucleation temperatures T considered. The predictions of the classical nucleation theory, SCC theory and DM theory are shown for comparison. ratio on the nucleation temperature. In figure 1 lines predicted using the different theories are plotted. Similar trend is showed between experimental curve and theoretical ones. However all the theories fail more or less in predicting the experimental values. $631
$632
K. HAMERIet al.
T h e effect o f carrier gas The description of vapour to liquid homogeneous using classical theory do not consider the presence of noncondensable carrier gas in the development of the model and resulting equations. Consequently, it has long been assumed that the presence of a carrier gas can be ignored. Recently, it has been reported that nucleation rate data obtained by using a thermal diffusion exhibited significant dependence on total pressure and the nature of the carrier gas (e.g. Katz et al., 1992; Smolik and Zdimal, 1993; Heist et al., 1994). Interestingly, nucleation rate data obtained by using an expansion cloud chamber suggest no observable dependence of nucleation rate on the carrier gas or the total pressure (see e.g. Strey et al, 1994). Considering the conflicting nature of what few experimental results exist that attempt to address the question of the role of the carrier gas in the nucleation process, it is essential that the role of the carrier gas is investicated more thoroughly. The nucleation rates in the laminar flow diffusion chamber were measured using Nitrogen, Helium or Argon as carrier gas in three different nucleation temperatures. The results of these measurements are shown in fig 2. It is lO s 10 7
@o
~r-~106
Oem
¢0 10 s
~
..,, @O• *em
"=
.2
,%
,,.-
:=
10 4 i0 z 10 2
101102
i • • • 2
.
10 a
2
5
10 4
2
5
i0 ~
Nitrogen Helium Argon z
S
Figure 2: The comparison of the nucleation rates as a function of saturation ratio S in the different carrier gases. The mean nucleation temperatures in different cases were from left to right: Nitrogen: 286.55 K, 276.35 K, 260.65 K; Helium: 286.9 K, 276.3 K, 259.25 K; Argon: 287.0 K, 276.1 K, 259.3 K The accuracy of the measurements is shown for two measurement points as error bars. noted here that there is a slight difference in mean nucleation temperatures with different carrier gases (see figure caption), which is mostly responsible for the difference in the position of the slopes. Considering the various uncertainties both in determining the saturation ratio and also determining the experimental nucleation rate, it is concluded here that no carrier gas effect can be observed even though there is a significant difference in the properties of the carrier gases.
References Anisimov M.P., H~meri K. and Kulmala M. (1994) J. Aerosol Sci. 25, 23-32. Heist R.H., Janjua M. and Ahmed J. (1994) Effects of Background Gases on the Homogeneous Nucleation of Vapors. 1. J. Phys. Chem. 98, 4443-4453. Katz J.L., Fisk J.A. and Chakarov V. (1992) in Nucleation and Atmospheric Aerosols; Proceedings of the 13th International Conference on Nucleation and Atmospheric Aerosols, Eds. by Fukuta, N , Wagner P.E., A. Deepak; Hampton, VA, pp. 11-18. Smolik J. and Zdimal V. (1993) J. Aerosol Sci. 24, 589-596. Strey R., Wagner P.E. and Viisanen Y. (1994) J. Phys. Chem. 98, 7748-7758.
Pergamon
Homogeneous nucleation of DBP vapour in a laminar flow diffusion chamber: the carrier gas effect Kaarle Hgmeri, Markku Kulmala and Eija Rantanen University of Helsinki, Department of Physics P. O. Box 9, FIN-00014 University of Helsinki, Finland
KEYWORDS Homogeneous nucleation rate, laminar flow diffusion chamber, DBP vapour, carrier gas effect
Laminar flow d i f f u s i o n c h a m b e r The preliminary tests of a laminar flow diffusion chamber for homogeneous nucleation studies of DBP vapour has performed earlier by Anisimov et al. (1994). The laminar flow, which is initially saturated (S=I) and at temperature of saturator (T~) is cooled by leading the flow to condenser section where the walls are maintained at lower temperature (To). The cooling leads to supersaturation of the flow (S > 1) and consequently homogeneous nucleation of the vapour inside the condenser.
Homogeneous nucleation of D B P vapour Prom the measured homogeneous nucleation rates we have determined the critical saturation ratios Serif corresponding to nucleation rate of 106 cm-3s -1 which is in the middle of our experimental nucleation rate scale. Figure 1 shows the dependence of the critical saturation 10 ~ . . . . . . . . 2
I = l O 6 c r n ' a s -1
10 5 5 2
- Claasical theory
"'"'"'"'"'.., ...
O'~ 1 0 4
..... "-,.
• ""'-....
2
SCC-th
..... .
...
5
M-theory
•
"'°'"'"'" •
2 2 I
lo 240
2~o
~;o
2~o
2;0
2;0
aoo
31o
a2o
T [K]
Figure 1: Critical saturation ratios So,it for a nucleation rate of 10 6 cm-3s -1 for DBP as a function of the various nucleation temperatures T considered. The predictions of the classical nucleation theory, SCC theory and DM theory are shown for comparison. ratio on the nucleation temperature. In figure 1 lines predicted using the different theories are plotted. Similar trend is showed between experimental curve and theoretical ones. However all the theories fail more or less in predicting the experimental values. $631
$632
K. HAMERIet al.
T h e effect o f carrier gas The description of vapour to liquid homogeneous using classical theory do not consider the presence of noncondensable carrier gas in the development of the model and resulting equations. Consequently, it has long been assumed that the presence of a carrier gas can be ignored. Recently, it has been reported that nucleation rate data obtained by using a thermal diffusion exhibited significant dependence on total pressure and the nature of the carrier gas (e.g. Katz et al., 1992; Smolik and Zdimal, 1993; Heist et al., 1994). Interestingly, nucleation rate data obtained by using an expansion cloud chamber suggest no observable dependence of nucleation rate on the carrier gas or the total pressure (see e.g. Strey et al, 1994). Considering the conflicting nature of what few experimental results exist that attempt to address the question of the role of the carrier gas in the nucleation process, it is essential that the role of the carrier gas is investicated more thoroughly. The nucleation rates in the laminar flow diffusion chamber were measured using Nitrogen, Helium or Argon as carrier gas in three different nucleation temperatures. The results of these measurements are shown in fig 2. It is lO s 10 7
@o
~r-~106
Oem
¢0 10 s
~
..,, @O• *em
"=
.2
,%
,,.-
:=
10 4 i0 z 10 2
101102
i • • • 2
.
10 a
2
5
10 4
2
5
i0 ~
Nitrogen Helium Argon z
S
Figure 2: The comparison of the nucleation rates as a function of saturation ratio S in the different carrier gases. The mean nucleation temperatures in different cases were from left to right: Nitrogen: 286.55 K, 276.35 K, 260.65 K; Helium: 286.9 K, 276.3 K, 259.25 K; Argon: 287.0 K, 276.1 K, 259.3 K The accuracy of the measurements is shown for two measurement points as error bars. noted here that there is a slight difference in mean nucleation temperatures with different carrier gases (see figure caption), which is mostly responsible for the difference in the position of the slopes. Considering the various uncertainties both in determining the saturation ratio and also determining the experimental nucleation rate, it is concluded here that no carrier gas effect can be observed even though there is a significant difference in the properties of the carrier gases.
References Anisimov M.P., H~meri K. and Kulmala M. (1994) J. Aerosol Sci. 25, 23-32. Heist R.H., Janjua M. and Ahmed J. (1994) Effects of Background Gases on the Homogeneous Nucleation of Vapors. 1. J. Phys. Chem. 98, 4443-4453. Katz J.L., Fisk J.A. and Chakarov V. (1992) in Nucleation and Atmospheric Aerosols; Proceedings of the 13th International Conference on Nucleation and Atmospheric Aerosols, Eds. by Fukuta, N , Wagner P.E., A. Deepak; Hampton, VA, pp. 11-18. Smolik J. and Zdimal V. (1993) J. Aerosol Sci. 24, 589-596. Strey R., Wagner P.E. and Viisanen Y. (1994) J. Phys. Chem. 98, 7748-7758.