Experimental study on mixed convective heat transfer over human body under low-speed turbulent wind

The acceleration of global urbanisation is creating urban wind environments characterised by low-speed and turbulence. In such conditions, a high skin-to-ambient temperature difference (ΔT) may shift the dominant transfer mode from forced convection to mixed convection. Nevertheless, the mixed convective heat transfer over the human body remains poorly understood. To address this issue, an experiment was conducted in a multi-fan wind tunnel equipped with a passive grid and a perforated plate to generate low wind speeds across multiple turbulence-intensity levels. A thermal manikin was used to measure the convective heat transfer coefficient (h_c) under different ΔT conditions. The results show that under low wind speed (< 1 m/s) and low turbulence intensity (< 8%) conditions, increasing ΔT significantly enhances the h_c of the lower body, by over 10% at ΔT = 12°C, whereas the upper body's h_c exhibits a negligible change. Conversely, when turbulence intensity (TI) exceeds 14%, high turbulence can suppress the influence of ΔT on h_c. In prevailing thermal comfort models, the Fiala model is among the few that explicitly account for mixed convection when predicting convective and evaporative heat loss. However, it substantially overestimates the whole-body h_c by more than 35%. Therefore, this study proposes a new set of h_c prediction formulas for local body segments to improve prediction accuracy in outdoor mixed convection conditions.