Abstract:
:Fast heat extraction is critically important to obtain the maximal benefit of cryogen spray cooling (CSC) during laser therapy of shallow skin lesions, such as port wine stain birthmarks. However, a film of liquid cryogen can build up on the skin surface, impairing heat transfer due to the relatively low thermal conductivity and higher temperature of the film as compared to the impinging spray droplets. In an attempt to optimize the cryogen mass flux, while minimally affecting other spray characteristics, we apply a series of 10 ms spurts with variable duty cycles. Heat extraction dynamics during such intermittent cryogen sprays were measured using a custom-made metal-disc detector. The highest cooling rates were observed at moderate duty cycle levels. This confirms the presence, and offers a practical way to eliminate the adverse effect of liquid cryogen build-up on the sprayed surface. On the other hand, lower duty cycles allow a substantial reduction in the average rate of heat extraction, enabling less aggressive and more efficient CSC for treatment of deeper targets, such as hair follicles.
journal_name
Phys Med Bioljournal_title
Physics in medicine and biologyauthors
Majaron B,Svaasand LO,Aguilar G,Nelson JSdoi
10.1088/0031-9155/47/18/301subject
Has Abstractpub_date
2002-09-21 00:00:00pages
3275-88issue
18eissn
0031-9155issn
1361-6560journal_volume
47pub_type
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