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Analysis of Influencing Factors in the Testing of Cool Feeling Fabrics
When the human body is in contact with the fabric at a temperature higher than the ambient temperature, the human body heat is lost through the fabric, which makes the human body feel cool [1]. In the previous research, the transient and steady state heat transfer process of the human body in contact with the fabric, the theoretical calculation formula of heat transfer, the heat flux-time curve, the heat absorption of the fabric, the influencing factors of the fabric's coolness, and the thermal flow-type fabric's coolness test instrument The development and principle of the system have been systematically studied, and it is proposed to use the maximum value of the heat flux at the moment of contact qmax (W/m2), the heat absorption of the fabric at the moment of contact Qs (J/m2), and the steady-state heat flux qbal (W/m2) as The evaluation index of fabric coolness. From the fabric sample itself, the surface state of the fabric, the content and fineness of the high thermal conductivity yarn, the organizational structure [2-3], and the thermal contact resistance are the fundamental factors that determine the coolness [4]. In terms of test conditions, the same sample, the environmental temperature and humidity, wind speed, test sample area, probe temperature, the determination conditions of steady-state heat transfer equilibrium time, the type of insulation board, etc., will also lead to differences in the cooling sensation test results. . Therefore, in order to form a universal test method standard for fabric coolness, it is necessary to further clarify the impact of test conditions and parameters on the test results. 1 Test section 1.1 Test principle 1.1.1 The principle is shown in Figure 1. Place the sample on the thermal insulation board. After heating the test probe with built-in constant temperature heat source and heat flow sensor and having 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 that simulates the human body temperature will be transferred to the sample through the heat flow sensor with a certain heat flux density, and will be absorbed by the sample and transferred out [5-6]. Record the curve of the heat flow density q passing through the heat flow sensor over time t, 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 lost 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. The fabric continuously conducts heat Q3 to the outside, that is, Qu003dQ1+Q2+Q3. In the formula: A is the contact area between the human body and the fabric (cm2), ρ is the volumetric 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 (cm) where the human body is in contact with the fabric sample, kf is the thermal conductivity of the high thermal conductivity filament [W/(m·K)], and df is the high thermal conductivity filament The diameter (cm), ρf is the volumetric mass of the yarn (g/cm3), T0 is the initial temperature of the fabric (℃), Ts is the skin temperature (℃), lx is the heat transfer distance (cm), t1 is the heat transfer Time to reach equilibrium (s). 1.2 Evaluation index The maximum value of instantaneous heat flux qmax is the peak value of heat flux obtained at the moment of contact, that is, the peak value of heat flux on the curve in Figure 2, which represents the instantaneous coolness of contact. The total heat transfer at the moment of contact is the initial heat transfer Qs per unit area obtained through integral calculation, namely Q1+Q2. The steady-state heat flow density qbal is the heat flow density when the heat transfer reaches equilibrium, that is, the heat flow density value corresponding to the time t1 on the curve in Fig. 2, which represents the steady-state heat transfer capacity of the fabric. 2 Influencing factors of fabric cooling sensation test 2.1 The test sample test instrument is FFZ415 heat flow cooling sensation tester [7]. Before the test, all samples are pre-equilibrated for 24 h under the conditions of temperature (20±2)℃ and relative humidity (65±5)%. The samples and their parameters are shown in Table 1. Turn on the instrument to warm up. When the temperature of the test probe stabilizes at 35 ℃, place the sample on the thermal insulation board, place the test probe in the center of the sample, and start the test. On-line software can set test parameters, probe temperature, termination conditions, test time, and equilibrium change rate, collect heat flux density change data over time, and display the heat flux density-time curve. 2.2 Test plan 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 through a large number of experiments. Therefore, when selecting the parameter of the steady-state equilibrium time, different thicknesses of woven fabrics and For knitted fabrics, the organizational structure and mass per unit area of u200bu200beach sample should be different. For other influencing factors, the test found that the results reflected by different sample tests are similar. Therefore, in order to reduce the influence of variables and facilitate the discussion, choose one of the samples for analysis and discussion. The following uniformly select sample 1. 2.2.1 Test environment temperature and humidity Put sample 1 at a temperature of 27 ℃ and a relative humidity of 43%. The test is performed under two temperature and humidity conditions of 21 ℃ and 63% relative humidity. Through comparison to determine the appropriate environmental temperature and humidity. 2.2.2 Sample area The sample area should be determined by the probe size and the conduction distance (lx) required to achieve sufficient heat exchange between the sample and the environment [8-9]. The probe area of u200bu200bthe tester is 100 mm×50 mm.
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