2020 Volume 71 Issue 3 Pages 146-154
The heat transfer resistance of clothes made of multilayer cloth sheets was measured after the clothes were placed on a glass bottle containing hot water. The heat transfer resistance of multiple air layers divided by an imaginary cloth having no heat transfer resistance was calculated on the basis of radiant and convective heat transfer. The heat transfer resistance of single air layer for small layer thicknesses increases with layer thickness due to a decrease in the convective heat transfer coefficient. The heat transfer resistance for large layer thicknesses varies little by layer thickness because the radiant heat transfer coefficient, which is independent of layer thickness, becomes larger than the convective heat transfer coefficient. The heat transfer resistance of multiple air layers increases with the number of air layers because the radiant heat transfer is shaded with the imaginary cloth sheets. The effect of natural convection on the heat transfer resistance of an air layer is negligible for layer thicknesses less than 10 mm. The experimental heat transfer resistance of the clothes increased with the number of cloth sheets, but the resistance was smaller than that of multiple air layers. The heat transfer resistance for the clothes having uniform air gaps increased with the number of cloth sheets in the same way for the multiple air layers. The small thickness part of an air gap due to non-uniformity of air gap thickness causes a decrease in the heat transfer resistance of clothes. The decrease was largest in the clothes made of pliable cloth. Though the heat transfer resistance of the clothes was large for the clothes made of cloth having large heat transfer resistance, the difference between the heat transfer resistances of clothes made of different cloth species was several times larger than that estimated from the heat transfer resistance of cloth.
