Textile auxiliary wall

Developing thermophysical sensors with textile auxiliary wall... 

Thus, this chapter describes an innovative smart textile a heat fluxmeter with a textile auxiliary wall, also called a textile heat fluxmeter (THF), which can detect, analyze, and monitor the heat and mass transfers with minimum dismrbance due to their porosity. It is a yam-based sensor that can be defined as the yarn itself as a sensing element and thus it is easier to be used by conventional knitting and weaving processes [15]. Moreover, it is desirable to use flexible electronics and this is especially tme when they need to be in contact with the human body, in which case the flexibility and nonirritability requirements are of utmost importance (Fig. 19.2) [16]. 

This textile heat fluxmeter consists of a network of thermocouples (assembly of two dissimilar conductor or semiconductor), also called a thermopile, assembled into a textile auxiliary wall. Thus, heat and mass transfer properties of textile substrate used as auxiliary wall will be smdied in the first part of this work. Afterward, the principle and the production technology of the conventional heat fluxmeters and the textile heat fluxmeter will be defined. 

In order to eliminate inconveniences of conventional heat fluxmeters such as impermeability, rigidity, a heat fluxmeter with a textile auxiliary wall, also called a textile heat fluxmeter (THF) has been developed. 

The insertion of the electroconductor wire as a sensing element (yam-based sensor) into a textile auxiliary wall was carried out during the weaving process. A number of thermocouples (type k constantan (Cn)/copper (Cu)) formed a thermopile, created with a posttreatment (Fig. 19.7(a)). This thermopile is judiciously disposed on both sides of the textile auxiliary wall to measure the temperature gradient (Fig. 19.7(b)). 

In the following section, textile auxiliary wall conception with weaving process and thermopile design with two different methods will be described. 

Figure 19.7 (a) Conductor 1 (constantan) is taken as core and is covered with another conductor 2 (copper) to create a thermocouple, and (h) electroconductor wire insertion during the weaving process and creation of thermocouple junctions on both sides of the textile auxiliary wall. 

The materials used for both warp and weft yams of the textile auxiliary walls were 100% polyester (PES) and 70/30 polyester/cotton (PES/CO) with a yam count of 30/2 Nm. The choice of material can be explained by the hygroscopic properties of the fibers. 

Although there are several weaves, three basic ones were chosen plain, twill, and satin. Research has shown that the plain weave and twill weave have, respectively, better thermal conductivity and thermal resistance than satin weave. Satin weave is suitable for complex surfaces due to its flexibility. Thus, PES,- and PES/CO, ie, [1,3], respectively, yams of polyester and polyester/cotton, were used for the textile auxiliary wall with the stracture of plain (PESi, PES/COi), twill 4/lZ (PES2, PES/CO2), and satin 5 (PES3, PES/CO3). Although the warp density is 21 yams/cm for all woven stmctures, the weft density changes depending on the woven stmcture plain, 10 yams/cm twill, 15 yams/cm and satin, 18 yams/cm. 

The insertion of the electroconductor wire, either monoconductor or biconductor, into the textile auxiliary wall was realized during the weaving process. The weaving process was followed by a posttreatment to transform the textile substrate to a heat flux-meter by obtaining the Cn/Cu thermocouple junctions (thermopile) on both sides of the textile auxiliary wall. 

This biconductor wire of Cn/Cu was inserted into the textile auxiliary wall during the weaving process. Insertion was undertaken between two PES/CO and PES weft yams in a form of weft floats with the length equal to covering of the five warp yams (0.2 cm) (Fig. 19.12). 

In order to shorten the production process, the monoconductor wire of constantan with a diameter of 76 pm (Omega Engineering, USA) was inserted into the textile auxiliary wall during the weaving process with the same characteristics as discussed previously. 

The weight (ISO 3801 1977), thickness (ISO 5084 1996), porosity and air permeability (ISO 9237 1995) of textile auxiliary walls were studied. Thermal resistance (Skin Model, ISO 11092 1993) and water vapor transmission rate (Dish Method Test, BS 7209 1990) tests were performed for heat and mass transfer properties [55—59]. 

Porosity values of textile auxiliary walls were calculated using Eq. [19.5]. 

The sweating guarded hot plate apparatus was used to measure the thermal resistance f th of textile auxiliary walls, under steady state conditions according to ISO 11092 1993 [58]. 

Water vapor transfer properties of the textile auxiliary walls were analyzed by the evaporative dish method, using an experimental setup defined by the standard BS 7209 1990 [59]. 

Textile auxiliary wall characteristics such as thermal resistance and water vapor permeability are presented in Table 19.3. Additionally, reference heat fluxmeter characteristics, ie, weight, thickness, and thermal resistance, are compared with the textile auxiliary walls. However, the impermeability and rigidity of the reference heat fluxmeter limit measuring the porosity, air permeability, and water vapor permeability index. 

Table 19.3 Characteristics of the textile auxiliary walls and the reference heat fluxmeter (Captec Entreprise, France)...

According to Eq. [19.4], the observed output voltage AV depends on the thermal resistance of the heat fluxmeter under steady state. It is observed that fabrics with twill stmctures provide better thermal insulation properties since they have higher thermal resistance than plain or satin stmctures. Moreover, the porosity and water vapor permeability values are slightly higher for PES/CO fabrics than pure PES fabrics. Therefore, PES/CO fabric with a twill stmcmre (PES/CO2) was selected as a textile auxiliary wall. 

The second choice for the textile auxiliary wall was satin-stractured samples with both PES (PES3) and PES/CO (PES/CO3) yams. Satin stmcture has the highest weft density, so theoretically it is possible to insert more electroconductor wire per centimeter than other stmctures. Additionally, its smooth surface provides better contact with the human body. 

Six textile heat fluxmeters with three different textile auxiliary walls, ie, PES/CO2, PES3, and PES/CO3, and two different sizes, ie, small size (2x2 cm) and large size (5x5 cm), were produced with subtractive method. Their sensitivities were compared to a commercial reference heat fluxmeter (Captec Entreprise, France) (Table 19.4). 

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