Department of Mechanical Engineering, Technion, Israel Institute of Technology, Haifa, Israel.
Int J Biometeorol. 2012 Jul;56(4):639-51. doi: 10.1007/s00484-011-0463-0. Epub 2011 Jul 4.
Facial heat exchange convection coefficients were estimated from experimental data in cold and windy ambient conditions applicable to wind chill calculations. Measured facial temperature datasets, that were made available to this study, originated from 3 separate studies involving 18 male and 6 female subjects. Most of these data were for a -10°C ambient environment and wind speeds in the range of 0.2 to 6 m s(-1). Additional single experiments were for -5°C, 0°C and 10°C environments and wind speeds in the same range. Convection coefficients were estimated for all these conditions by means of a numerical facial heat exchange model, applying properties of biological tissues and a typical facial diameter of 0.18 m. Estimation was performed by adjusting the guessed convection coefficients in the computed facial temperatures, while comparing them to measured data, to obtain a satisfactory fit (r(2) > 0.98, in most cases). In one of the studies, heat flux meters were additionally used. Convection coefficients derived from these meters closely approached the estimated values for only the male subjects. They differed significantly, by about 50%, when compared to the estimated female subjects' data. Regression analysis was performed for just the -10°C ambient temperature, and the range of experimental wind speeds, due to the limited availability of data for other ambient temperatures. The regressed equation was assumed in the form of the equation underlying the "new" wind chill chart. Regressed convection coefficients, which closely duplicated the measured data, were consistently higher than those calculated by this equation, except for one single case. The estimated and currently used convection coefficients are shown to diverge exponentially from each other, as wind speed increases. This finding casts considerable doubts on the validity of the convection coefficients that are used in the computation of the "new" wind chill chart and their applicability to humans in cold and windy environments.
面部的热交换对流系数是根据寒冷和多风环境下的实验数据估算出来的，这些数据可用于计算风寒指数。本研究中使用的测量面部温度数据集来自 3 项独立研究，涉及 18 名男性和 6 名女性受试者。这些数据大多数来自环境温度为-10°C、风速范围为 0.2 至 6 m/s 的情况。另外还有一些单一实验的环境温度为-5°C、0°C 和 10°C，风速范围相同。通过应用生物组织的特性和典型的 0.18 米面部直径，使用数值面部热交换模型估算了所有这些条件下的对流系数。通过调整计算出的面部温度中的猜测对流系数，同时将其与测量数据进行比较，以获得令人满意的拟合（大多数情况下 r(2) > 0.98）。在其中一项研究中，还使用了热通量计。这些热通量计得出的对流系数仅非常接近男性受试者的估计值。当与估计的女性受试者数据进行比较时，它们存在显著差异，约为 50%。由于其他环境温度下的数据有限，仅对-10°C 环境温度和实验风速范围进行了回归分析。回归方程的形式假设为“新”风寒图表所依据的方程。回归得到的对流系数与测量数据非常吻合，除了一个单一情况外，都高于该方程计算出的对流系数。研究发现，随着风速的增加，估计的和当前使用的对流系数呈指数式发散。这一发现对“新”风寒图表计算中使用的对流系数的有效性以及它们在寒冷和多风环境中对人类的适用性产生了相当大的怀疑。
