Abstract:

Objective This study aims to investigate the temperature distribution of electrically heated diving suits and human tissues in low-temperature underwater environments， and optimize the diving suit design. Conventional passive diving suits lack sufficient thermal insulation for long deep dives， while underwater tests of heated suits are risky and costly. Thus， it is necessary to establish a reliable simulation model to guide the optimization of heated diving suits， addressing the gap in current research on heated diving suit design and testing.

Method In this study， three simplified three-dimensional heat transfer models of the human arm， torso and thigh were developed using ANSYS. The models consist of a waterproof insulation layer， a heating layer， a skin-friendly layer， an inner liner layer and human tissue layers. A 100 mm × 100 mm graphene heating sheet was embedded， and material properties of chloroprene rubber， nylon and other materials were adopted. The model was validated by comparing the simulated skin temperature with physiological data， and a grid independence test was performed. Steady-state thermal analysis was conducted under various ambient temperatures （0-15 ℃）， inner liner materials （Thinsulate and aerogel fabrics）， and inner liner thicknesses （2-8 mm）.

Results In this study， a three-dimensional simulation model of the human arm， torso， and thigh was established using ANSYS. The skin temperature predicted by the model is in good agreement with the measured data， and the model is verified to be effective and accurate through grid independence tests.The simulation results show that the heating range of the 100 mm × 100 mm graphene heating sheet is limited. The effect of ambient temperature on different body parts varies significantly. When the ambient temperature decreases from 15 ℃ to 0 ℃， the skin temperature of models 1， 2， and 3 with Thinsulate inner liner decreases by 41.85%， 24.25%， and 28.92%， respectively； while for the aerogel inner liner， the corresponding reductions are reduced to 26.5%， 12.89%， and 17.23%.Compared with the Thinsulate inner liner， the aerogel inner liner increases the minimum skin temperature by approximately 7 ℃， 6 ℃， and 6.5 ℃ for the upper arm， torso， and thigh， respectively. However， when the ambient temperature rises to 15 ℃， the temperature difference between the two materials narrows to 3.5-4 ℃.With respect to the inner liner thickness： when the thickness of the Thinsulate inner liner increases from 2 mm to 4 mm， the skin temperature at 100 mm from the center of the heating sheet increases by 41.54%， 29.26%， and 29.5%， respectively； whereas when the thickness increases from 6 mm to 8 mm， the skin temperature rises by only 18.82%， 7.9%， and 8.62%.At an ambient temperature of 0 ℃， even when the thickness of the Thinsulate inner liner is increased to the maximum of 8 mm， the arm skin temperature （19.8 ℃） is still below the safe and comfortable threshold.

Conclusion The ANSYS 3D model constructed in this study can effectively predict the temperature distribution between the electrically heated diving suit and human tissues， determine whether the human body has reached a thermal comfort state， and optimize the clothing design accordingly to enhance the occupational safety of divers in low-temperature environments. The simulation results show that the heating zone of the electric heating sheet is limited， showing a sharp temperature drop beyond 50 mm from the center. Aerogel liners present much better thermal insulation than Thinsulate， especially at 0 ℃. Increasing liner thickness leads to an obvious diminishing marginal gain in skin temperature， as the thermal resistance growth rate declines with thickness.Under cold-induced vasoconstriction， the minimum skin temperature in non-heated regions follows torso > thigh > upper

Key words: electric heating, fabric, heat transfer simulation, human tissue, dry diving suit, cold protection