In physics and chemical engineering, the term Pouillet effect refers to an exothermic reaction that takes place when a liquid is added to a powder. Strictly speaking, the heat generated is caused by adhesion of the liquid to the surface of the particles rather than by a chemical reaction.[1] It was first observed in 1802 by Leslie, who noted that heat was evolved when dry sawdust was wetted with water.[2] Claude Pouillet later described this phenomenon in 1822, and it subsequently became known as the "Pouillet effect" in France, and then elsewhere.[3][4]

Negative Pouillet effect

Under certain conditions, a negative Pouillet effect is possible, i.e., heat can be absorbed instead of being released. G. Schwalbe showed that in the case of water below 4 degrees Celsius, the temperature of the system decreases.[5] Joseph Mellor argued that this is due to the negative thermal expansion coefficient of water between 0 and 4 degrees Celsius,[6] with the temperature change given by

where is the thermal expansion coefficient, is the specific heat, is the specific gravity, and is the applied pressure due to the addition of the liquid. According to this formula, any liquid with a negative thermal expansion coefficient would be expected to exhibit a drop in temperature.

References

  1. Taggart, Arthur F.; Beach, Frederick E. (November 1, 1916). "An Explanation of the Flotation Process". Metallurgical and Chemical Engineering. 15 (9): 518–523. Retrieved 19 February 2022.
  2. Leslie, John (1802). "On capillary action". Philosophical Magazine. 1st series. 14 (55): 193–205. doi:10.1080/14786440208676183. From p. 201: Upon wetting paper or linen with water or oil, and " … applying a delicate thermometer, I perceived a very sensible extrication of heat invariably to take place during such combinations. And this effect was the greater in proportion to the previous dryness of the solid. Thus I have sometimes produced a heat of ten degrees by moistening saw-dust which had been parched before the fire."
  3. Pouillet (1822). "Mémoire sur de nouveaux phénomènes de production de chaleur" [Memoir on new phenomena of heat production]. Annales de Chimie et de Physique. 2nd series (in French). 20: 141–162. From p. 142: "À l'instant où un liquide mouille un solide, il y a dégagement de chaleur." (At the instant when a liquid wets a solid, there is a release of heat.)
  4. 'Adsorption by powders & porous solids: principles, methodology and applications' Academic Press, 1999.
  5. Schwalbe, G. (1905). "Über die beim Benetzen pulverförmiger Körper, insbesondere von Sand, mit Wasser auftretende Wärmetönung, sowie Untersuchungen über das Verhalten von Wasser unter 4° bei diesem Vorgange". Annalen der Physik. 321 (1): 32–45. Bibcode:1905AnP...321...32S. doi:10.1002/andp.19053210105. Retrieved 19 February 2022.
  6. Mellor, J.W. (1922). A Comprehensive Treatise on Inorganic and Theoretical Chemistry, Volume 1. London: Longmans, Green and Co. pp. 495–496. Retrieved 19 February 2022.
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