Yunyi Wang

Effects of air gap entrapped in multilayer fabrics and moisture on thermal protective performance

Thermal protection of firefighter protective clothing is greatly influenced by the air gap entrapped and moisture in clothing. In this paper, the effects of air gap size and position on thermal protective performance exposed to 84 kW/m2 heat source were investigated. Water was also added to thermal liner to understand the effect of air gap coupled with moisture on thermal protection. It was indicated that the TPP of fabrics system increased with the air gap size. The air gap position also greatly influenced the heat transfer during exposure to flash fire. Moisture added weakened the positive effect of air gap size when the air gap exists far from heat source, and almost eliminated the favorable effect of air gap position. However, when there is no air gap or small air gap between outer shell fabric and moisture barrier, moisture increased the thermal protection performance of multilayer fabrics system. The results obtained suggested that certain air gap entrapped in fabrics system and clothing microclimate could improve thermal protection, and the complicated effect of moisture should also be considered.

The relationship between air gap sizes and clothing heat transfer performance

The objective of the study is to establish a quantitative relationship between air gap sizes and clothing thermal performance. Using a three-dimensional human body scanner, the thicknesses and volumes of air gaps of 35 experimental shirts were measured. Relationships between the thermal insulations of clothing, measured on a thermal manikin, and air gap volumes were examined by regression analysis. Also, the regression model between clothing surface temperatures, measured by an infrared thermal camera, and air gap thicknesses was established. The results proved that the thermal insulation of experimental shirts increased with air gap sizes but began to decrease as a result of natural convection when the air gap thickness was higher than 1 cm or the air gap volume was greater than 6000 cm3. The 3D human body scanner can accurately measure air gaps under clothing, but it is expensive and is not available everywhere. A substitute method is to build a mathematical model for predicting air gap sizes. In this paper, regression models were established to estimate volumes and thicknesses of air gaps when the ease allowances of chest circumference and fabric properties were known. This study can be used to predict the thermal performance of clothing at the product’s design stage.

A new approach to characterize the effect of fabric deformation on thermal protective performance

It is very important to evaluate thermal protective performance (TPP) in laboratory-simulated fire scenes as accurately as possible. For this paper, to thoroughly understand the effect of fabric deformation on basic physical properties and TPP of flame-retardant fabrics exposed to flash fire, a new modified TPP testing apparatus was developed. Different extensions were employed to simulate the various extensions displayed during different body motions. The tests were also carried out with different air gaps. The results showed a significant decrease in air permeability after deformation. However, the change of thickness was slight. The fabric deformation had a complicated effect on thermal protection with different air gaps. The change of TPP depended on the balance between the surface contact area and the thermal insulation. The newly developed testing apparatus could be well employed to evaluate the effect of deformation on TPP of flame-resistant fabrics.

A New Approach to Evaluate the Effect of Moisture on Heat Transfer of Thermal Protective Clothing under Flashover

It’s urgent to investigate moisture effect on thermal protection of thermal protective clothing in simulated fire scene as accurately as possible. The current bench top tests can’t evaluate thermal protective performance (TPP) of fabrics under microclimate with high temperature and relative humidity (RH). In this paper, to well investigate effect of different RH under microclimate on thermal protective performance of flame-retardant fabrics exposed to flashover, a new modified TPP testing apparatus was developed. It consisted of a typical TPP tester and RH adjustable microclimate chamber. Three kinds of air gaps under fabrics were also employed to simulate different spaces between skin and clothing. The results showed that the temperature increment under microclimate of 35 % RH was highest, and that of 95 % RH was lowest. There was significant temperature difference found among above three adjusted environment. Time required of temperature rise to 12 oC highly prolonged as RH became higher. It could be deduced that the effect of RH on heat transfer became significant as air gap increasing; if the air gap width still increased, the moisture effect diminished. The newly developed testing apparatus could be well used to evaluate the moisture effect on thermal protective performance of flame-resistant fabrics.

Effects of inner and outer clothing combinations on firefighter ensembles’ thermal- and moisture-related comfort levels

The special clothing ensembles firefighters wear should provide not only thermal protective performance but also thermal- and moisture-related comfort. The comfort property of protective clothing has great influence on work efficiency. In this study, inner clothing was designed to combine with firefighters’ protective clothing in order to create different clothing ensembles. Two separate wear trials were carried out under the temperatures of 28°C (warm) and 15°C (cool), respectively; cardiopulmonary indexes, temperature and relative humidity under clothing microclimate and subjective sensations were evaluated. These objective and subjective experimental data were analysed to differentiate clothing ensembles’ thermal- and moisture-related comfort properties. The effect of different inner clothing items, combined with the firefighters’ protective clothing, on the overall comfort level of the clothing ensembles was also investigated. The results showed that there were significant differences in the thermal, moisture and clingy sensations of various clothing ensembles under the temperature of 28°C (warm), but the differences were not significant under the temperature of 15°C (cool), except for clingy sensation. Combined with the same firefighter clothing, there was no significant difference in the thermal- and moisture-related comfort properties, but the differences in clingy sensation were significant. The clothing ensembles with polyester inner clothing were not very good for providing thermal and moisture comfort. The clingy comfort of clothing ensembles with linen inner clothing was better than those with cotton or polyester inner clothing.

Heat transfer properties of the numerical human body simulated from the thermal manikin

This paper seeks to predict the heat transfer properties of the numerical manikin. It also aims to establish a simplified clothing model based on computational fluid dynamics (CFD) to predict the temperature in air layers between thermal manikin and clothing under different environments. The field experiments of naked or clothed thermal manikin were conducted in a climatic chamber. The CFD method was employed to build a naked or clothed numerical manikin to simulate the field experiment. The distribution of temperature and the velocity field around the naked human body and heat transfer coefficients was simulated in the optimized numerical climate chamber with a temperature of 20°C and velocity of 0.05 m/s. The temperature in air layers entrapped in clothing on the torso of manikin was also predicted under the same environmental condition. The CFD results showed good agreement with that of the naked or the dressed thermal manikin experiment. It demonstrated that CFD could properly predict the heat transfer properties of indoor human and temperature distribution in the air layer between human body and clothing.

Correlation between clothing air gap space and fabric mechanical properties

To investigate the distribution of clothing air gap layers, clothes with the same pattern but different fabrics were put on a standard scan model. The [TC]2 NX-16 three-dimensional (3D) body scanning technique was used to collect point cloud data and the overall 3D visualization model of clothing air gaps was represented in a novel way through computer graphics processing. The volumes of air gap space were calculated. The main fabric mechanical properties were investigated and the relationship among them was analyzed by stepwise regression. The results demonstrated a close relationship between clothing air gap space and fabric mechanical properties. The volumes of air gap space were significantly positively correlated with stiffness-bending length and warp density and significantly negatively correlated with drape-crest angle uniformity. The conclusion could play a role in predicting and controlling the clothing design process, especially the material design process of clothing.

Effect of air gap thickness on thermal protection of firefighter’s protective clothing against hot steam and thermal radiation

Hot steam from a hose spray and dew or rains directly threatens firefighter’s health and lives. The thickness of air gap between the protective clothing and the skin has an important and complicated influence on thermal protection. The purpose of this study was to examine the effect of air gap thickness on thermal protection in dry heat exposure (thermal radiation) and wet heat exposure (hot steam and thermal radiation). The results showed that the air gap between the clothing and the skin, while providing better thermal protection for dry heat exposure, also slowed down the steam transfer rate to provide heat protection. There was no critical air gap in dry and wet heat exposures. It was also found that hot steam increased sharply the heat flux absorbed by the skin, leading to the occurrence of steam burns. The increase of air gap thickness could reduce the heat flux during the exposure while no significant correlation between the air gap thickness and the final heat flux was observed during the cooling of wet heat exposure (P>0.05).