# Thermal Effusivity Tester (TET)--A New Device to Determine Thermal Effusivity of Textiles
## 2 Experimental  
Fabric thickness was measured at the pressure of 1 kPa according to ISO 5084 [12]. For Alambeta test device, the thickness was measured automatically with a photoelectric sensor in the device at its working pressure of 200 Pa [13], where the resulting thickness is not necessarily identical with manual measurement. The fabrics were measured with TET as described below, and the results compared with existing data from previous measurements of the same fabrics using TCi, Alambeta and KES-f-Thermo Labo. Alambeta measurements were performed by placing the fabric between the upper plate, which has a temperature of 32 \({}^{\circ}\)C, and the lower plate, which is at room temperature (20 \({}^{\circ}\)C). The upper plate is lowered until a pressure of 200 Pa on the surface is reached. The heat streams onto the fabric are measured and the measurement ends when a heat flux equilibrium is reached. Textile thickness, thermal conductivity and thermal effusivity are measured. The process is repeated at 18 different positions on the fabric and the average value is calculated. TCi measurements were performed at C-Therm Technologies using the TGi Thermal Conductivity Analyzer in the MTPS configuration along with a compression test accessory (CTA). The test procedure is described at the C-Therm website [11]. A 500 g weight was applied on the fabric surface. Considering the measurement head diameter of 18 mm, a pressure of 19 kpa is calculated. Pre-testing of heat penetration showed that multilayer sample positioning was required. KES-f Thermo Labo measurements were performed by IFTH, France [14]. In this measurement, a square-shaped copper block is used as a skin probe. Its temperature is raised to 10 \({}^{\circ}\)C above the sample surface temperature and the peak heat dissipation Qmax is measured. Thermal Effusivity Tester (TET)The TET measurement unit comprises two plates, with the upper plate maintained at a temperature of 35 \({}^{\circ}\)C and the lower plate at 23 \({}^{\circ}\)C. The fabric sample is positioned on the stationary lower plate, while the upper plate is automatically lowered to establish contact with the fabric, applying a predefined compression rate based on the fabric thickness measurement. In this study, a fabric compression rate of 10% was used. The key measurement parameters include thermal conductivity, specific heat capacity and fabric density (previously determined by weight and thickness measurements). Figures 1 and 2 show the TET device in more detail. When the fabric is placed on the lower sensor plate, a heat flux takes place through the fabric due to the temperature difference. Once thermal equilibrium between the fabric and the lower sensor plate is reached (i.e., the fabric has reached the same temperature as the lower plate), the warmer upper plate is gradually lowered at a defined speed, pressing the specimen between the two plates. During the movement of the upper plate, the heat flow through both sensors is recorded for a specified duration (Figure 3). The temporal behavior of both heat flows is utilized to determine the thermal conductivity and the heat capacity of the test specimen. Figure 1: (a) Thermal effusivity tester (TET); (b) detail view of measurement unit. When the upper plate makes contact with the specimen, the longitudinal surface area of the fabric is much larger as compared to the transverse area; hence, the difference in heat  
Figure 3: (**a**) Measurement principle of TET device; (**b**) heat flow at the upper (red line) and the lower (white line) plate. Figure 2: Sample placed on the measurement unit; (**a**) photo, (**b**) schematic drawing. flux between the sensors can be used to quantify the heat absorbed by the material. Once the heat flows have reached an equilibrium (curve flattening in Figure 3), it can be assumed that there exists a uniform temperature gradient across the fabric, from which the average temperature rise in the fabric can be calculated.