Aguilar Guillermo, Wang Guo-Xiang, Nelson J Stuart
Department of Biomedical Engineering, University of California, Irvine, CA 92697, USA.
Phys Med Biol. 2003 Jul 21;48(14):2169-81. doi: 10.1088/0031-9155/48/14/309.
Although cryogen spray cooling (CSC) is used to minimize the risk of epidermal damage during laser dermatologic surgery, optimization of the current cooling approach is needed to permit the safe use of higher light doses, which should improve the therapeutic outcome in many patients. The objective of this study was to measure the effect of spurt duration (delta t) on the heat transfer dynamics during CSC using a model skin phantom. A fast-response temperature sensor was constructed to record the changes in surface temperature during CSC. Temperature measurements as a function of delta t at two nozzle-to-skin distances (z = 50 and 20 mm) were performed. The average surface heat fluxes (q) and heat transfer coefficients (h) for each delta t were computed using an inverse heat conduction problem algorithm. It was observed that q undergoes a marked dynamic variation during the entire delta t, with a maximum heat flux (qc) occurring early in the spurt (5-15 ms), followed by a quick decrease. The estimated qc vary from 450 to 600 kW m(-2), corresponding to h maxima of 10 and 17-22 kW m(-2) K(-1) for z = 50 and 20 mm, respectively. For z = 50 mm, spurts longer than 40 ms do not increase the total heat removal (Q) within the first 200 ms. However, for z = 20 mm, delta t longer than 100 ms are required to achieve the same Q. It is shown that the heat transfer dynamics and the time it takes to reach qc during CSC can be understood through classic boiling theory as a transition from transient to nucleate boiling. Based on the results of this model skin phantom, it is shown that spurts longer than 40 ms have a negligible impact on both q and Q within clinically relevant cooling times (10-100 ms).
尽管在激光皮肤科手术中使用冷冻喷雾冷却（CSC）可将表皮损伤风险降至最低，但仍需要优化当前的冷却方法，以允许安全使用更高的光剂量，这有望改善许多患者的治疗效果。本研究的目的是使用皮肤模型来测量喷射持续时间（δt）对CSC过程中传热动力学的影响。构建了一个快速响应温度传感器，以记录CSC过程中的表面温度变化。在两个喷嘴到皮肤的距离（z = 50和20 mm）下，进行了温度随δt变化的测量。使用逆热传导问题算法计算每个δt的平均表面热通量（q）和传热系数（h）。观察到在整个δt期间，q经历了显著的动态变化，在喷射早期（5 - 15 ms）出现最大热通量（qc），随后迅速下降。估计的qc在450至600 kW m(-2)之间变化，对应于z = 50和20 mm时h的最大值分别为10和17 - 22 kW m(-2) K(-1)。对于z = 50 mm，超过40 ms的喷射在最初200 ms内不会增加总散热量（Q）。然而，对于z = 20 mm，则需要超过100 ms的δt才能达到相同的Q。结果表明，通过经典沸腾理论可以理解CSC过程中的传热动力学以及达到qc所需的时间，这是一个从瞬态沸腾到核态沸腾的转变。基于该皮肤模型的结果表明，在临床相关的冷却时间（10 - 100 ms）内，超过40 ms的喷射对q和Q的影响可忽略不计。
