Heat-transfer dynamics during cryogen spray cooling of substrate at different initial temperatures

Jia, Wangcun; Aguilar, Guillermo; Wang, Guoxiang; Nelson, J. Stuart

doi:10.1088/0031-9155/49/23/007

Cited by 23 publications

(13 citation statements)

References 29 publications

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“…Temperatures recorded by the thermal sensor are assumed to be surface temperatures because the silver disc Biot number (hL/k) for a heat transfer coefficient h ¼ 20,000 W/m 2 K [12], characteristic length L ¼ 0.09Â10 À3 m and thermal conductivity k ¼ 429 W/m K is %0.004; that is, the disc temperature is spatially uniform, hL/k << 1. The following analytical expression based on Fourier's law and Duhamel's theorem is used to compute the surface heat flux q c from temperature measurements y:…”

Section: Methodsmentioning

confidence: 99%

Extent of lateral epidermal protection afforded by a cryogen spray against laser irradiation

et al. 2007

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Accumulation of heat within the epidermis is always greater at the laser beam periphery, away from the CSC nozzle tip, where heat extraction is lowest. Therefore, there is risk of thermal injury at the beam periphery when there is a mismatch between the skin protected by CSC and that exposed to laser irradiation. For the cooling and irradiation sequences considered herein, heat extraction provided by a 60 milliseconds spurt/30 milliseconds delay correctly matches the heating profile of a 10 mm diameter beam.

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Section: Methodsmentioning

confidence: 99%

Extent of lateral epidermal protection afforded by a cryogen spray against laser irradiation

et al. 2007

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“…The use of ex vivo human skin specimens serves as a model that closely approximates in vivo human skin as compared to other previously used models such as an epoxy phantom [13], Plexiglas 1 [12,14], and skin-equivalent engineered tissue [23,24]. Furthermore, use of ex vivo human skin allowed insertion of the thermocouple at the epidermal-dermal junction, which is very difficult to accomplish in vivo.…”

Section: Ex Vivo Human Skin Specimenmentioning

confidence: 99%

“…Fast-response temperature sensors, such as thermocouples, have been used to measure temperature changes and estimate the total heat removed from the surface during CSC [11][12][13][14][15]. When the thermocouple time constant is much shorter than the thermal relaxation time of the surrounding tissue, artifacts induced by direct absorption of laser irradiation by the thermocouple can be removed by applying exponential and linear fits to measured temperature curves [16].…”

Section: Introductionmentioning

confidence: 99%

Thermal responses of ex vivo human skin during multiple cryogen spurts and 1,450 nm laser pulses

et al. 2006

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Background and Objective: Although cryogen spray cooling (CSC) is used to minimize the risk of epidermal damage during laser dermatologic surgery, concern has been expressed that CSC may induce cryo-injury. The objective of this study is to measure temperature variations at the epidermal-dermal junction in ex vivo human skin during three clinically relevant multiple cryogen spurt-laser pulse sequences (MCS-LPS). Study Design/Materials and Methods: The epidermis of ex vivo human skin was separated from the dermis and a thin-foil thermocouple (13 mm thickness) was inserted between the two layers. Thermocouple depth and epidermal thickness were measured using optical coherence tomography (OCT). Skin specimens were preheated to 308C before the MCS-LPS were initiated. Three MCS-LPS patterns, with total cryogen spray times of 38, 30, and 25 milliseconds respectively, were applied to the specimens in combination with laser fluences of 10 and 14 J/cm 2 , while the thermocouple recorded the temperature changes at the epidermal-dermal junction. Results: The thermocouple effectively recorded fast temperature changes during three MCS-LPS patterns. The lowest temperatures measured corresponded to the sequences with longer pre-cooling cryogen spurts. No subzero temperatures were measured for any of the MCS-LPS patterns under study. Conclusions: The three clinically relevant MCS-LPS patterns evaluated in this study do not cause sub-zero temperatures in ex vivo human skin at the epidermal-dermal junction and, therefore, are unlikely to cause significant cryogen induced epidermal injury.

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“…Adiabatic boundary conditions are applied at z ¼ 1 and r ¼ AE 1. The thermal boundary condition at the skin surface (z ¼ 0) is as follows: a heat transfer coefficient of 200 W/(m 2 Á K) [27] and an ambient temperature of 608C during hot air jet preheating; CSC heat flux determined in the proposed experiment during an effective CSC cooling period (spurt duration plus cryogen residence time [12]); a natural convection heat transfer coefficient of 10 W/(m 2 Á K); and an ambient temperature of 258C after laser irradiation. The period of preheating is 40 seconds, the cooling period of CSC is 60-100 milliseconds depending on vessel depth, and the laser pulse duration is 1.5 millisecond.…”

Section: Numerical Modelsmentioning

confidence: 99%

“…Skin temperature can be increased by 10-158C higher than normal body temperature by preheating using a hot air jet, infrared irradiation, etc. Since CSC heat flux increases with initial skin temperature [12], the epidermis can be cooled more effectively while higher temperatures within the PWS vessels induced during the preheating period can be preserved. Because the PWS blood vessel temperature is raised from baseline while keeping the epidermis selectively cooled, two advantageous effects would be attained.…”

Section: Introductionmentioning

confidence: 99%

Improvement of port wine stain laser therapy by skin preheating prior to cryogen spray cooling: A numerical simulation

Jia¹,

Aguilar²,

Verkruysse³

et al. 2006

Lasers Surg Med

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Background and Objectives: Although cryogen spray cooling (CSC) in conjunction with laser therapy has become the clinical standard for treatment of port wine stain (PWS) birthmarks, the current approach does not produce complete lesion blanching in the vast majority of patients. The objectives of this study are to: (1) experimentally determine the dynamic CSC heat flux when a skin phantom is preheated, and (2) numerically study the feasibility of using skin preheating prior to CSC to improve PWS laser therapeutic outcome. Study Design/Materials and Methods: A fast-response thin-foil thermocouple was used to measure the surface temperature and thus heat flux of an epoxy skin phantom during CSC. Using the heat flux as a boundary condition, PWS laser therapy was simulated with finite element heat diffusion and Monte Carlo light distribution models. Epidermal and PWS blood vessel thermal damage were calculated with an Arrhenius-type kinetic model. Results: Experimental results show that the skin phantom surface can be cooled to a similar minimum temperature regardless of the initial temperature. Numerical simulation indicates that upon laser irradiation, the epidermal temperature increase is virtually unaffected by preheating, while higher PWS blood vessel temperatures can be achieved. Based on the damage criterion we assumed, the depth and maximum diameter of PWS vessels that can be destroyed irreversibly with skin preheating are greater than those without. Conclusions: Skin preheating prior to CSC can maintain epidermal cooling while increasing PWS blood vessel temperature before laser irradiation. Numerical models have been developed to show that patients may benefit from the skin preheating approach, depending on PWS vessel diameter and depth.

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Heat-transfer dynamics during cryogen spray cooling of substrate at different initial temperatures

Cited by 23 publications

References 29 publications

Extent of lateral epidermal protection afforded by a cryogen spray against laser irradiation

Extent of lateral epidermal protection afforded by a cryogen spray against laser irradiation

Thermal responses of ex vivo human skin during multiple cryogen spurts and 1,450 nm laser pulses

Improvement of port wine stain laser therapy by skin preheating prior to cryogen spray cooling: A numerical simulation

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