Journal of Textile Research ›› 2020, Vol. 41 ›› Issue (01): 139-144.doi: 10.13475/j.fzxb.20181105406

• Apparel Engineering • Previous Articles     Next Articles

Free convection calculation method for performance prediction of thermal protective clothing in an unsteady thermal state

DING Ning1, LIN Jie2()   

  1. 1. College of Aeronautical Engineering, Civil Aviation University of China, Tianjin 300300, China
    2. Sino-European Institute of Aviation Engineering, Civil Aviation University of China, Tianjin 300300, China
  • Received:2018-11-20 Revised:2019-09-25 Online:2020-01-15 Published:2020-01-14
  • Contact: LIN Jie E-mail:linj022@126.com

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Abstract:

A method for the surface heat transfer coefficient calculation of free convection is proposed, which plays an important part in the numerical heat insulation prediction of thermal protective clothing under unsteady thermal state in high temperature environments, where heat transferred by free convection cannot be ignored or even is the main part. A typical heat transfer model was presented under an unsteady thermal state, using finite difference method. Two sets of numerical results were obtained under two boundary conditions at the outer surface of clothing, these conditions being constant temperature boundary condition and Howard model's free convection boundary condition. However, the comparison between experimental and the two numerical analysis results showed obvious differences. For improvement, a method using Fourier's law, Newton cooling law and free convection condition of Howard model was proposed under linear assumption to calculate free convection heat transfer coefficient. Improving the heat transfer model with this method, three sets of numerical results were obtained using finite difference method with different time steps, and the comparison between experimental and these three numerical results showed fast convergence to experimental results with time step getting smaller. The difference between the calculated and experimental results was less than 0.1 ℃ when time step was set to 0.001 s.

Key words: thermal protective clothing, thermal insulation, heat transfer, free convection, numerical simulation

CLC Number: 

  • O242.1

Fig.1

Schematic of heat transmission"

Tab.1

Thermophysical/geometrical properties of different material"

材料
编号		 密度/
(kg·m-3)		 比热/
(J·(kg·℃)-1)		 热传导率/
(W·(m·℃)-1)		 厚度/
mm
材料1 300 1 377 0.082 0.6
材料2 862 2 100 0.370 6.0
材料3 74.2 1 726 0.045 3.6
材料4 1.18 1 005 0.028 5.0

Fig.2

Numerical results with different boundary conditios (a) and time step (b)"

Fig.3

Difference between results calculated and experiment with Δt=0.001 s"

Fig.4

Heat flux density at different time with Δt=0.001 s"

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