Effects of solar radiation on cabin temperature inside special vehicles and human heat transfer

Abstract

BackgroundDue to the strong sunlight in summer, the temperature on the vehicle deck rises significantly under solar radiation and the internal structures are heated, resulting in prominent heat stress problems in the cabin and seriously affecting the training performance of staff.ObjectiveTo study temperature variation patterns inside special vehicle cabins after being exposed to solar radiation, and the quantitative relationship of convection and radiative heat transfer between the vehicle interior environment and the human body, which will provide design reference for further cabin temperature control.MethodsUsing a solar radiation simulation experimental system, a 6 h exposure experiment was conducted on a special vehicle. The solar radiation intensity from 9:00 to 15:00 on a summer day at an open testing field site was used as the experimental conditions. The tested parameters included temperature on the surface of the vehicle deck (10 points), ambient temperature in the cabin (2 points), near body ambient temperature of testees, radiative heat flux, and total heat flux.ResultsThe temperature of vehicle deck, cabin, and near body increased with the rising solar radiation intensity before 13:30, and then gradually stabilized. The highest temperatures on the vehicle deck and inside the cabin reached 60.5 ℃ and 39.3 ℃, respectively. The highest ambient temperatures of near body for the 4 testees were 41.4 ℃, 41.1 ℃, 41.3 ℃, and 40.8 ℃, respectively, when the humidity inside the cabin was 48.7%. The ratio of radiative heat and convective heat acting on the human body varied over time. The heat transfer between personnel and the vehicle deck and cabin environment mainly exhibited human body heat dissipation until 9:30, when the ratio of radiative heat flux and convective heat flux of the the testees' head/face and chest/abdomen ranged from 1∶4 to 1∶7, and the ratio of the testees' feet was about 1∶3. During 10:00 to 11:00, the human body still exhibited heat dissipation towards the environment, with convective heat dissipation dominating towards the cabin environment, while the vehicle deck gradually began to transform radiative heat towards the human body, when the ratio of radiative heat flux to convective heat flux was 1∶3 to 1∶6. After 11:00, the main heat transfer pattern was from the surrounding environment to the human body, and the ratio of radiative heat flux to convective heat flux was 1∶9 to 1∶12, when the values of radiative heat flux and convective heat flux both significantly increased, and convective heat transfer was dominant.ConclusionThe temperature of the special vehicle deck, cabin environment, and near body ambient increases with higher solar radiation intensity. The radiative heat flux and convective heat flux between the cabin environment and the human body gradually increase with the radiation intensity and radiation time, and the quantitative relationship between the two changes with time. Among them, convective heat transfer is always the main heat transfer mode, and the impact of radiative heat transfer on the human body cannot be ignored.

Keywords

• special vehicle
• solar radiation
• thermal environment
• radiative heat flux
• convective heat flux