Simulation of the influence of wind velocities and direction on heat exchange in local segments of the human body in disaster environments

Heat strain and skin burn injuries severely affect the health of emergency rescue personnel and reduce their rescue efficiency in disaster environments. Predicting these injuries is thus a crucial aspect of early warning approaches. Furthermore, the heat transfer coefficient, influenced by factors such as wind velocity and wind direction, is a critical input for simulations of heat transfer, heat strain, and skin burn injuries. To improve the health and safety of emergency rescue personnel, a comprehensive understanding of the effects of wind velocity and wind direction on the heat transfer coefficient across different body segments is essential.

First, a three-dimensional body scanning technique was applied to obtain a numerical thermal manikin, based on a 20-zone thermal manikin named "Newton" (including the head, face, chest, stomach, shoulders, back, thighs, calves, feet, forearms, hands, hips, and upper arms). Subsequently, a numerical climate chamber measuring 5 m × 2.7 m × 3 m was developed, with the numerical thermal manikin placed at the center. Second, the angle between the numerical manikin and the inlet was adjusted to set five wind directions (0°, 45°, 90°, 135°, and 180°), and eight wind velocities (0.2, 1.0, 2.0, 4.0, 8.0, 12.0, 16.0, and 20.0 m/s) were used in the numerical simulation. Third, heat transfer and airflow were simulated using software based on the finite volume method, and the whole-body and local convective heat transfer coefficients were calculated under various wind directions and wind velocities. Finally, the simulation performance for heat transfer and the convective heat transfer coefficient was validated against experimental measurements and simulations in the literature.

The results indicated that dry heat transfer increased with wind velocity, with total heat transfer increasing by 17.74 times when wind velocity rose from 0.2 to 20.0 m/s. Moreover, the corresponding ratio of convection to dry heat transfer increased by 42.6%. By contrast, wind direction had a negligible effect on whole-body convective heat transfer but showed large differences among body segments. Specifically, the convective heat transfer coefficient at the torso was considerably higher than that at the four limbs (upper arms, forearms, thighs, and calves). At a wind direction of 0° and an wind velocity of 16.0 m/s, compared with the right limb, the convective heat transfer coefficient at the left upper arm, left forearm, left thigh, and left lower leg decreased by 21.1, 25.1, 9.1, and 10.8 W/(m²·℃), respectively.

The convective heat transfer varied greatly across body segments, with the hands exhibiting the highest convective heat transfer coefficient in all cases. Specifically, the difference in convective heat transfer coefficient among body segments was amplified by wind velocity. The simulated convective heat transfer coefficients under different wind velocities and wind directions can serve as inputs for human thermoregulation models, heat strain evaluations, and skin burn injury assessments. Subsequently, these outputs can provide fundamental knowledge for developing early safety warning systems, high-performance personal protective clothing, and decision-making tools for rescue personnel during rescue operations.