Study of Heat Exchange Process in Evaporation of Large Droplets at a High Temperature Flat Surface

About the authors:

Vasiliy Ya. Gubarev, Cand. Sci. (Tech.), Professor, Head of the Department of Industrial Heat Power Engineering, Lipetsk State Technical University; gv_lipetsk@rambler.ru

Aleksey G. Arzamastsev, Cand. Sci. (Phys.-Math.), Associate Professor, Department of Industrial Heat Power Engineering, Lipetsk State Technical University; arzamastcev-ag@mail.ru

Adelina S. Shipulina, Postgraduate Student, Department of Industrial Heat Power Engineering, Lipetsk State Technical University; adelino4ka@inbox.ru

Abstract:

When cooling a high temperature surface with liquid jet dispersed for relatively small values of the irrigation density, the main determinant of the intensity of heat removal is the heat transfer between a single droplet and the cooled surface. The papers on this topic provide solutions for estimating the time of drop evaporation in flat condition, though, in the calculations, they disregard the heat fluxes related to the heat transfer by radiation from the wall to the droplet evaporation and of the diffusion couple with the outer surface of the droplets in the environment.

This article discusses the process of heat exchange in the interaction of large droplets with high temperature flat surface based on the data of heat flow. The authors provide the formulas to calculate the time of evaporation of large drops to flat transition in one half of a spheroid and the average heat transfer coefficient considering heat flow by radiation in the absence of evaporation from the surface of droplets in the environment. Calculations show that accounting for the effects of radiation heat flux for the wall temperature from 300 to 1,200 ˚C leads to an increase in the average heat transfer coefficient from 7-8 to 63-67%, which shows a significant influence of heat flux radiation on the total heat removal at a sufficiently high temperature wall. The dependences for determining parameters of heat exchange considering the radiation heat flux are complemented by the estimate of the maximum possible effect on the heat transfer process of diffusion evaporation from droplet surface to the environment. The authors show that the diffusive heat flux may have a significant impact on the parameters of the heat transfer only when the surface temperature up to 700 ˚C. At higher values of wall temperature, the heat flux will be significantly lower than the radiation heat flux, due to evaporation from the outer surface of the droplet into the environment, and the calculations can be carried out without considering the influence of diffusion and evaporation on the heat transfer intensity.

References:

1. Garber E. A., Goncharskiy A. A., Sharavin M. P. 1991. Tekhnicheskiy progress system okhlazhdeniya prokatnykh stanov [Technical Progress of Cooling Systems of Rolling Mills]. Moscow: Metallurgiya.
2. Gubarev V. Ja., Arzamascev A. G. 2010. “Isparenie kapli na vysokotemperaturnoj poverhnosti” [Heat transfer by gravitational interaction of a drip with a high temperature surface]. Teplovye processy v tehnike, vol. 2, pp. 63-67.
3. Gubarev V. Ja., Efremova A. S. 2014. “Issledovanie processa isparenija kapel' na vysokotemperaturnoj poverhnosti” [Research of Features Evaporation of Large Drops on High Temperature Surface]. Proceedings of the 6th Russian National Conference on Heat Transfer, vol. 2, pp. 127-129. Moscow: Izdatel'skij dom MJeI.
4. Gubarev V. Ja., Shatskikh Yu. V. 2005. “Teploobmen gazokapel'noy sredy s vysokotemperaturnoy poverkhnost'yu” [The Gas-Droplet Heat Transfer Medium with High Temperature Surface]. High Temperature, vol. 5, pp. 774-779.
5. Gubarev V. Ja., Shatskikh Yu. V. 2006. “Teploobmen pri normal'nom soudarenii kapli s vysokotemperaturnoy poverkhnost'yu” [Heat Transfer at Normal Collision of Drops with High Temperature Surface]. Proceedings of the 4th Russian National Conference on Heat Transfer, vol. 5, pp. 101-103. Moscow: Izdatel'skij dom MJeI.
6. Isachenko V. P., Kushnyrev V. I. 1984. Strujnoe ohlazhdenie [Jet Cooling]. Moscow: Jenergoatomizdat.
7. Isachenko V. P., Osipova V. A., Sukomel A. S. 1981. Teploperedacha [Heat Transfer]. Moscow: Jenergoatomizdat.
8. Isachenko V. P., Sidorova I. K. 1982. “Eksperimental'noe issledovanie okhlazhdeniya ploskoy poverkhnosti struey dispergirovannoy zhidkosti” [Experimental Investigation of the Cooling of a Flat Surface by a Jet of Dispersed Liquid]. Teploenergetika, vol. 3, pp. 30-33.
9. Kabakov Z. K. 1977. “Issledovanie usloviy teploobmena v zone vtorichnogo okhlazhdeniya UNRS” [The Study of the Conditions of Heat Transfer in the Secondary Cooling Zone of Continuous Caster]. Izvestiya Vuzov. Chernaya metallurgiya, vol. 11, pp. 184-187.
10. Emmerson G. S. 1975. “The Effect of Pressure and Surface Material on the Leidenfrost Point of Diserete Drops of Water”. International Journal of Heat Mass Transfer, vol. 18, no 3, pp. 381-386. DOI: 10.1016/0017-9310(75)90027-7
11. Wachters L. H. J., Westerling N. A. J. 1966. “The Heat Transfer from a Hot Wall to Impinging Water Drops in the Spheroidal State”. Chemical. Engineering. Science, vol. 21, no 11, pp. 1047-1056. DOI: 10.1016/0009-2509(66)85100-X