Soret Effects in Combustion For Power Production or
Chemical Synthesis
DANIEL E. ROSNER*
Chemical Engineering Department , Yale University, New Haven CT USA
ABSTRACT
For the past 25 years I have been fascinated by the phenomenon of thermally-driven mass
transport and its engineering consequences----especially in combustion systems. By about
1980(1) I had already become rather suspicious of the many 'footnotes' I had seen, especially in
ChE textbooks, about the supposed dominance of Fickian (Brownian) mass transport and the
negligibility of Soret(Thermophoretic)mass transport. Moreover, in my consulting and universitybased research I began encountering dramatic examples in which Soret transport and/or its
particulate analogue: 'thermophoresis', were far from 'higher-order' effects [reaching 3.5
decades in some of our experiments on micron-size particle deposition from flames(4)]! The
present talk will survey some of these applications, emphasizing our development of rational
engineering methods to predict/ correlate such effects(1-8). The applications considered here
fall conveniently into two general classes. In the first class are Soret effects in combustion
systems for power production or chemical propulsion(2,3). More recently I have been concerned
with combustion for the purpose of materials synthesis or processing----a still emerging area of
combustion in which one necessarily makes use of a wider variety of 'fuels' and 'oxidizers'(8,1012). In most combustion examples we find the simultaneous conditions which ensure significant
Soret effects---viz., the co-existence of large temperature gradients (often 10^6 K/m) with large
molecular weight disparities. Moreover, even when the fuel itself is a simple hydrocarbon vapor
like CH4(g), higher C-number intermediates or reaction products are often produced locally-----a
dramatic example being multi-ring molecules (PAHs) and 'soot' nano-spherule formation in fuelrich regions of pre-mixed- or (especially) diffusion-flames(7). When the fuel itself is light (H2) or
heavy (>C12H24, as in diesel fuel vapors), then even such a fundamental property as the
adiabatic diffusion flame temperature is appreciably Soret-shifted (7,9), often with important
implications for NOx production and radiative heat transfer. Several recent studies of gaseous
diffusion flames did explicitly consider the consequences of the fuel vapor Fick diffusivity being
significantly different from the local gas thermal diffusivity (ie., non-unity 'Lewis number') but
ignored an important implicit consequence of ideal gas kinetic theory---viz., that appreciable fuel
vapor Soret effects and non-unity Lewis number effects will necessarily 'go-together'(3,7).
These and related fundamental developments will be discussed in the context of the
abovementioned combustion engineering applications(3, 10-12).
____________________________________
L.W. Jones Prof. Chemical Engineering; Director Yale Univ. High Temperature Chemical Reaction Engineering Laboratory;
Revised/Submitted 12/21/05 for Int. Mtg. on Thermodiffusion #7, San Sebastian, Spain , May 29-June 3, 2006(1) Rosner, D.E., Physicochemical Hydrodynamics (Pergamon), vol.1, 159-185 (1980)
(2) Gokoglu, S.A and Rosner, D.E., Int. J. Heat Mass Transfer, vol 27, 639-645(1984); see, also: Rosner, D.E. and Fernandez de la
Mora, ASME,J Engrg. for Power, vol 104, 885-894(October 1982)
(3) Rosner, D.E., Transport Processes in Chemically Reacting Flow Systems, DOVER Publications, New York(2000); See
Supplement 3
(4) Rosner, D.E. and Kim, S.S., Chemical Engineering J. (Elsevier) vol 29(3) 147-157 (1984)
(5) Park, H.M. and Rosner, D.E., Chem. Eng. Sci. , vol 43(10)2689-2704(1988)
(6) Garcia-Ybarra, P. and Rosner, D.E., AIChE J., vol. 35(1) 139-147(1989)
(7) Rosner, D.E., Israel, R.A. and La Mantia, B., Comb. & Flame, vol. 123, 547-560(2000)
(8) Rosner , D.E. and Pyykonen, J.J., AIChE J , vol 48(3) 476-491(2002)
(9).Rosner, D.E., Arias-Zugasti, M., and La Mantia, B., AIChE J, vol 51(10), 2811-2824 (2005); see, also:
Comb.& Flame, vol 135, 271-284(2003)
(10) Rosner, D.E., Ind. & Eng. Chem.-Res(ACS), vol 44(8); pp 6045-6055 (2005)
(11) Rosner, D.E., Chemical Engineering Education (ASEE), Fall 1997, pp 228-235; see, also: Winter '98 issue
(12) Rosner, D.E. , Combustion For The Synthesis or Processing of Valuable Materials, (Treatise-Text in prep.(2005))