Shitzer Avraham
Department of Mechanical Engineering, Technion, Israel Institute of Technology, Haifa, 32000, Israel.
Eur J Appl Physiol. 2008 Sep;104(2):215-20. doi: 10.1007/s00421-007-0624-3. Epub 2007 Nov 30.
Combinations of wind-driven convection and environmental radiation in cold weather, make the environment "feel" colder. The relative contributions of these mechanisms, which form the basis for estimating wind chill equivalent temperatures (WCETs), are studied over a wide range of environmental conditions. Distinction is made between direct solar radiation and environmental radiation. Solar radiation, which is not included in the analysis, has beneficial effects, as it counters and offsets some of the effects due to wind and low air temperatures. Environmental radiation effects, which are included, have detrimental effects in enhancing heat loss from the human body, thus affecting the overall thermal sensation due to the environment. The analysis is performed by a simple, steady-state analytical model of human-environment thermal interaction using upper and lower bounds of environmental radiation heat exchange. It is shown that, over a wide range of relevant air temperatures and reported wind speeds, convection heat losses dominate over environmental radiation. At low wind speeds radiation contributes up to about 23% of the overall heat loss from exposed skin areas. Its relative contributions reduce considerably as the time of the exposure prolongs and exposed skin temperatures drop. At still higher wind speeds, environmental radiation effects become much smaller contributing about 5% of the total heat loss. These values fall well within the uncertainties associated with the parameter values assumed in the computation of WCETs. It is also shown that environmental radiation effects may be accommodated by adjusting reported wind speeds slightly above their reported values.
在寒冷天气中，风驱动对流与环境辐射的组合会使环境“感觉”更冷。在广泛的环境条件下，对构成估算风寒等效温度（WCETs）基础的这些机制的相对贡献进行了研究。区分了直接太阳辐射和环境辐射。未纳入分析的太阳辐射具有有益作用，因为它能抵消和补偿一些因风和低温产生的影响。纳入分析的环境辐射效应在增强人体热损失方面具有有害作用，从而影响整体环境热感觉。该分析通过一个简单的人体 - 环境热相互作用稳态分析模型进行，使用环境辐射热交换的上下限。结果表明，在广泛的相关气温和报告风速范围内，对流热损失比环境辐射占主导。在低风速下，辐射对暴露皮肤区域总热损失的贡献高达约23%。随着暴露时间延长和暴露皮肤温度下降，其相对贡献大幅降低。在更高风速下，环境辐射效应变得更小，占总热损失的约5%。这些值完全在计算WCETs时所假设参数值的不确定性范围内。研究还表明，通过将报告风速略微调整至高于其报告值，可以考虑环境辐射效应。
