The volume of the air layer between the clothing and the human body has an important influence on the thermal and moisture resistance of the clothing. McCullough EA and others have used the standing Comfortable Thermal Manikin
to measure the thermal resistance of loose trousers and tight trousers. Through comparison, they found that the thermal resistance of loose trousers is greater than that of tight trousers under the same conditions, and considered the air layer inside the clothing. Thickness is an important factor that determines the thermal resistance of clothing. Y. S. Chen et al. used a sweating thermal manikin to study the influence of the amount of jacket relaxation on the thermal and moisture resistance, and found that in a smaller air layer, the thermal and moisture resistance of the jacket gradually increased. In the research on the influence of clothing looseness on its thermal comfort, most of them are limited to the measurement of clothing thermal resistance, while the measurement of clothing moisture resistance is relatively limited. This study takes men’s double-layer thermal knitted underwear as the research object, uses Comfortable Thermal Manikin to measure its thermal resistance and moisture resistance, and uses a three-dimensional body scanner to measure the volume of the air layer on the surface of the underwear and the dummy. In this way, the influence of the thickness of the air layer between the thermal underwear and the human body on its thermal comfort is explored.
1 Experimental program
1.1 Measuring clothing
In this study, 4 men's double-layer thermal knitted underwear with sizes M, L, XL, and XXL were selected for measurement. Among them, the M, L, XL and XXL sizes correspond to tight-fitting, fit-fitting, looser, and loose-fitting, respectively. The 4 pieces of underwear are round neck and long sleeves, and with the increase of size, the indexes of bust, waist, and shoulder width increase evenly, but the indexes of clothing length, sleeve length and neck circumference remain the same. The dimensions of each part of the underwear are shown in Table 1.
In this study, the standing Comfortable Thermal Manikin Walter was used to measure the thermal resistance and moisture resistance of thermal underwear. During the measurement, the dummy wore different sizes of thermal underwear on the upper body, and the same tight-fitting knitted trousers on the lower body.
1.3 Three-dimensional human body scanner
The three-dimensional body scanner VITUS was used for this body measurement. According to the standard ISO20685:2005, it is calibrated before measurement. The human body measurement is carried out in a temperature environment of (25 ± 2) ℃. When scanning the human body, the head of the dummy is fixed and the feet are off the ground. During scanning, the naked dummy is measured first to obtain the volume of the dummy when it is naked, and then the dummy wearing different sizes of underwear is measured to obtain the volume of the dummy wearing the underwear. In order to ensure the reliability of the measurement data, the measurement of each state is performed 3 scans from 3 different angles of the dummy.
2 Results and discussion
2.1 Thermal resistance and moisture resistance measurement results
Table 3 shows the measured values of the overall thermal resistance and moisture resistance of different sizes of thermal underwear under different air layer volumes.
2.2 Moisture permeability index of heating underwear
From the measured values of thermal resistance and moisture resistance of thermal underwear in Table 3 and formula (3), the moisture permeability index can be calculated. Figure 1 shows that the moisture permeability index of thermal underwear gradually decreases as the size of the underwear increases, and the moisture permeability index is almost the same in L size and XL size. It shows that in the range of the measured size of the thermal underwear, the M size has the best thermal comfort, at this time the corresponding air layer volume is 3 283 cm3; the XXL size is the worst, the corresponding air layer volume is 11 068 cm3. It shows that the volume of the air layer is an important factor affecting the thermal comfort performance of underwear.
On the one hand, within the measured range, the thermal resistance of the thermal underwear first increases and then decreases with the increase of the air layer volume, while the moisture resistance gradually increases within the measured range. From the established regression model, the thermal resistance and moisture resistance both increase to their respective maximum values with the increase of the air layer volume, and then gradually decrease. On the other hand, the moisture permeability index of thermal underwear gradually decreases with the increase of underwear size within the range of the measured underwear size, indicating that its thermal comfort performance is gradually weakening. Based on this, this subject will further measure and evaluate the thermal comfort and aesthetics of thermal underwear to determine a suitable relaxation design that takes into account both thermal comfort and aesthetics of thermal underwear.