| 研究実績の概要 |
The experiment seeks to measure the reduction in cooling from a mist fan when a worker wears clothing, especially PPE in hot summer conditions.
A prototype low-cost thermal mannequin setup was built and performed fairly well. Mist and fan cooling rates were measured with heat flux sensors for the unclothed, clothed, and clothed with PPE on 6 days in hot weather. PPE was found to reduce natural convection, fan convection, and mist fan convection/evaporation cooling by 20-45%, depending on body location. The heat transfer coefficients of the 3 types of cooling are being found, but more data (from Year 2) will be required to assess precision.
A 3D CFD simulation of the thermal mannequin and experiment setup is being created to evaluate a wider range of air conditions. The detailed 3D velocity profile of the misting fan is being measured by ultrasound anemometer in an improvised wind-tunnel set up outdoors. The components of the fan velocity field can be used to make the CFD simulation more accurate.
Thus, although PPE reduces cooling equivalent by about 0.5-1.0 met, a significant portion remains, thus mist fan cooling may be effective to conveniently cool workers wearing PPE. Preliminary results are to be presented at SHASEJ 2022.
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
2: おおむね順調に進展している
理由
The prototype low-cost thermal mannequin is being refitted. There was a problem with the prototype wherein pressurizing the small water tanks with circulating warm water resulted in some water leakage from two locations’ water tanks, 1 so severe (the back side) that the data was not useful. The same issue made temperature control unstable at those locations. Both issues are solved by making and installing small copper-pipe heat exchangers to circulate water inside still water in the small tanks, instead of pressurizing the small water tanks. However, the wetting problem was useful in planning the Year 2 experiment for wetted skin/clothing surfaces as simulated sweat. The improvised wind tunnel worked well, but on windy days, the wind velocity profile was slightly diverted perpendicular to the blown air axis by 0.2-0.5m/s. A different location will be used in summer 2022 experiments.
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| 今後の研究の推進方策 |
As the data from experiments on cooling effect under 3 regimes (natural convection, fan convection, mist and fan convection) for 5 cases (nude, work clothing, work clothing with PPE, wet work clothing, wet work clothing with PPE) is compiled to yield expected cooling effects at 8 body locations (heat flux and heat transfer coefficient), the agreement with a standard model adjusted with those results will be evaluated, as well as a simple model of a mannequin in CFD software.
In future, it will be desired to progress the CFD model to a transient model, which will require more computing power and more recent software.
These results will hopefully be compared to actual human subjects wearing work clothes and PPE under mist fan cooling on hot days as a future research project, likely requiring collaboration with researchers in physiology and worker safety.
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