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Correlations Between Spray Properties and Heat Transfer Dynamics During Cryogen Spray Cooling

[+] Author Affiliations
Odette Ma, G. Aguilar, J. S. Nelson

University of California at Irvine, Irvine, CA

G.-X. Wang

University of Akron, Akron, OH

Paper No. IMECE2003-42178, pp. 451-457; 7 pages
doi:10.1115/IMECE2003-42178
From:
  • ASME 2003 International Mechanical Engineering Congress and Exposition
  • Heat Transfer, Volume 4
  • Washington, DC, USA, November 15–21, 2003
  • Conference Sponsors: Heat Transfer Division
  • ISBN: 0-7918-3718-1 | eISBN: 0-7918-4663-6, 0-7918-4664-4, 0-7918-4665-2
  • Copyright © 2003 by ASME

abstract

Cryogen spray cooling (CSC) has been used along with pulsed lasers for nearly a decade to irreversibly photocoagulate a variety of vascular lesions. However, the fundamental mechanisms that take place at the skin surface are still incompletely understood. In this work, we built a fast-response temperature sensor with the objective to determine the time in which liquid cryogen remains on the skin surface during and after a short spurt of cryogen—the residence time (tr ). Measurements are conducted systematically at various distances from the nozzle (z) and various spurt durations (Δt) for two nozzles that produce completely different spray characteristics. It was found that for each nozzle, there is a critical spray distance (zc ) where an abrupt increase in tr occurs and another critical distance (zmax ) that can be related to maximal cryogen deposition. Furthermore, using experimentally measured average droplet diameter (d) and velocity (v) for sprays produced by each nozzle, we defined a spray characteristic time τ(z) as the ratio of d to v. This parameter allows us to represent our experimental data on a single curve for each nozzle, by plotting the dimensionless residence time (tr /τ) and a function of the product of dimensionless spurt duration (Δt/τ) and a dimensionless factor (m/mmax ). The factor m/mmax is envisioned as an effective mass deposition which, due to the evaporation of cryogen droplets in-flight and the spray-surface interactions, is a strong function of z. These results represent a step towards a more complete understanding and quantification of the physics involved in CSC.

Copyright © 2003 by ASME

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