Analysis of Influencing Factors of Cooling Fabric Testing

When a human body with a temperature higher than the ambient temperature is in contact with the fabric, the heat of the human body is dissipated through the fabric, which makes the human body feel cool [1]. In the previous research, the transient and steady-state heat transfer process of human body contacting the fabric, the theoretical calculation formula of heat transfer, the heat flux density-time curve, the heat absorption of the fabric, the influencing factors of the fabric coolness, the thermal flow fabric coolness test instrument The development and principle of the fabric have been systematically studied, and it is proposed to use the maximum heat flux density qmax (W/m2) at the moment of contact, the heat absorption Qs (J/m2) of the fabric at the moment of contact, and the steady-state heat flux density qbal (W/m2) as the The evaluation index of fabric cooling feeling. As far as the fabric samples themselves are concerned, the surface state of the fabric, the content and fineness of the high thermal conductivity filaments, the organizational structure [2-3], and the contact thermal resistance are the fundamental factors that determine the cooling sensation [4]. In terms of test conditions, for the same sample, differences in ambient temperature and humidity, wind speed, test sample area, probe temperature, conditions for determining the steady state heat transfer equilibrium time, and types of thermal insulation boards will also lead to differences in the results of the cooling sensation test. . Therefore, in order to form a general fabric cooling feeling test method standard, it is necessary to further clarify the influence of test conditions and parameters on the test results. 1 Test part 1.1 Test principle 1.1.1 Principle As shown in Figure 1, the sample is placed on the thermal insulation board. After heating the test probe with built-in constant temperature heat source and heat flow sensor and with a certain pressure to the specified temperature, it is quickly placed on the surface of the sample. Due to the existence of the temperature difference, the heat of the constant temperature heat source in the test probe simulating the human body temperature will be conducted to the sample through the heat flow sensor with a certain heat flux density, absorbed by the sample and transferred out [5-6]. The heat flux density q through the heat flux sensor as a function of time t is recorded, as shown in Figure 2. 1.1.2 Theoretical calculation According to the previous research, the area under the curve in Figure 2 is the total heat Q dissipated by the constant temperature heat source through the fabric, including the heat Q1 absorbed by the fabric as a heat capacity, the heat Q2 conducted by the fabric at the moment of contact, and the equilibrium state by The fabric continues to conduct heat Q3 to the outside world, that is, Q=Q1+Q2+Q3. In the formula: A is the contact area between the human body and the fabric (cm2),ρis the volume mass of the fabric (g/m2), d is the thickness of the fabric (cm), and c is the specific heat capacity of the yarn [J/(g·℃)], m is the mass of the fabric (g), a is the long side of the rectangle in contact with the human body and the fabric sample (cm), kf is the thermal conductivity of the high thermal conductivity filament [W/(m·K)], df is the diameter of the high thermal conductivity filament (cm),ρf is the volume mass of the yarn (g/cm3), T0 is the initial temperature of the fabric (°C), Ts is the skin temperature (°C), lx is the heat transfer distance (cm), and t1 is the time for heat transfer to reach equilibrium (s ). 1.2 Evaluation Index The maximum value of instantaneous heat flux density qmax is the peak heat flux density obtained at the moment of contact, that is, the peak value of heat flux density on the curve in Figure 2, which represents the cool feeling at the moment of contact. The total heat transfer at the moment of contact is the initial heat transfer per unit area Qs obtained by integral calculation, that is, Q1+Q2. The steady-state heat flux density qbal is the heat flux density when the heat transfer reaches equilibrium, that is, the heat flux density value corresponding to the time t1 on the curve in Figure 2, which characterizes the steady-state heat transfer capability of the fabric. 2 Influencing factors of fabric cooling sensation test 2.1 Test sample The testing instrument is FFZ415 thermal flow cooling sensation tester [7]. Before testing, all samples were kept at temperature (20±2) ℃, relative humidity (65±5) Pre-equilibrate for 24 h under the condition of %. The samples and their parameters are shown in Table 1. Turn on the instrument to warm up. When the temperature of the test probe is stable at 35 °C, place the sample on the thermal insulation board, place the test probe in the center of the sample, and start the test. The online software can set test parameters, probe temperature, termination conditions, test time and equilibrium rate of change, collect data on the change of heat flux density with time, and display the heat flux density-time curve. 2.2 Test scheme When discussing the influence of the following test parameters on the test results, the determination of the steady-state heat transfer equilibrium time needs to be determined by a large number of tests. For knitted fabrics, the organizational structure and mass per unit area of ​​each sample should be different. For other influencing factors, the test found that the results reflected by different sample tests were similar. Therefore, in order to reduce the influence of variables and facilitate the discussion, one of the samples is selected for analysis and discussion. The following sample 1 is selected uniformly. 2.2.1 Temperature and humidity of the test environment Put the sample 1 at a temperature of 27 °C and a relative humidity of 43%. The test was carried out under two temperature and humidity conditions of 21 °C and 63% relative humidity. Determine the appropriate ambient temperature and humidity by comparison.
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