Influence of variability in hygrothermal properties on analytical results of simultaneous heat and moisture transfer in porous materials

Depending on the data source used, the material hygrothermal properties that are used in the numerical analysis of simultaneous heat and moisture transfer will not be consistent. Differences in measurement methods and the individuality of specimens account for this. It is necessary to choose values from these different physical property sets to conduct a numerical calculation, which can cause the calculated results to differ. The subsequent range of variation in the calculated results should be quantitatively evaluated. In this study, the physical properties of several types of porous building materials were first gathered from four databases. The data were then categorized based on the kind of material and compared in terms of each physical property (density, porosity, specific heat, moisture capacity, thermal conductivity, and vapor permeability). The density, porosity, and specific heat varied by 10% on average, and the moisture capacity, thermal conductivity, and vapor permeability varied by 20% or more for all types of materials. In particular, the vapor permeability of plywood and moisture capacity of gypsum board differed by 50%. The influence that these physical property value variations had on hygrothermal calculation results was then quantitatively demonstrated for moisture and heat flow rate under a step change in the relative humidity or temperature of indoor air for a single layer wall. The moisture and heat flow rate into a single layer wall fluctuated by approximately 10%–40% due to differences in the vapor permeability and moisture capacity of the materials. For all types of materials, moisture was transferred more slowly than heat. Therefore, differences in moisture property values, such as vapor permeability and moisture capacity, influenced the results more significantly. Moreover, the moisture flow was accompanied by a phase change. The differences in moisture property values thus affected the heat flow.

Evaluation method for the hygroscopic and cooling function of knitted fabrics

The evaluation of thermal-wet properties contributes to the research and development of fabrics, but there is no effective method to address and achieve evaluation of the hygroscopic and cooling properties of knitted fabrics to date. Therefore, an evaluation method aiming at this issue was proposed, and based on experimental investigation the hygroscopic and cooling property of fabrics was estimated by the combined evaluation of moisture management and the thermal property in a dynamic state. The moisture management property shows the liquid water absorption and diffusion performance of fabrics. Beside this, the thermal properties of fabrics were tested respectively in the dry and wet states. The thermal property of dry fabric showed the heat transfer and radiation of fabric itself, whereas the thermal property of wet fabric demonstrated the combined effect of the coupled heat–moisture property of wet fabric and the cooling function of moisture evaporation and diffusion. Furthermore, the thermal properties of fabrics were tested using a YG606 II thermal resistance tester, which was refitted by a program to control heating power. Eight knitted fabric samples having different cooling comfortability rates or values were selected to verify the feasibility and effectivity of this method. The consistency of this method was also verified by the obtained experimental results. Based on the obtained results, it can be observed that this method was well consistent with verified experimental results. Therefore, an effective method for the evaluation of hygroscopic and cooling knitted fabrics was obtained that satisfies the measurement of performance, and desirable fabric properties can be achieved for various applications.

The Dependence of Moisture Induced Die Stresses Upon Moisture Properties of Polymer Materials in Electronic Packages

Polymer materials have been widely used in electronic packaging with many advantages such as: lower cost, light weight and good performance. They however suffer a major drawback that results in a number of challenges for reliability engineers and researchers, in which polymer materials are quite sensitive to moisture absorption when exposed to humid environment, causing many failure modes in electronic packages such as: popcorn cracking, delamination or corrosion. It is well-known that finite element simulation is a powerful tool to evaluate the effects of moisture on electronic package reliability. In this study, three moisture properties (diffusivity, saturated concentration, and coefficient of moisture expansion) were experimentally characterized. The obtained results were then used to perform moisture diffusion simulations on various types of electronic package. Finally, a numerical study was conducted on the dependence of the moisture effects (weight gains, die stresses) upon each moisture property of polymeric components of three kinds of electronic packages (Quad Flat Package, Plastic Ball Grid Array, and Flip Chip on Laminate). The results of the study provided valuable insights into how moisture induced die stresses vary with each moisture property of polymeric components in the packages.

Relationship between Structure and Properties of High Tenacity Polyamide 6 upon Different Draw Ratios and Heat Styling Temperatures

This paper has studied the structure and property of high tenacity polyamide 6 upon different draw ratios and heat styling temperature process conditions, characterized with wide-angle X-ray diffraction (WAXD), sound velocity method, Fourier transform infrared (FTIR) spectroscopy, amino-terminated content determination and essential property texts such as the absorption of moisture and dyeing. It was demonstrated that increasing the draw ratio (DR) and heat styling temperature were conducive to crystal-to-crystal transformation and stabilizing the internal structure of fibers. The temperature played a significant role in orientation of high tenacity polyamide 6, particularly subjected to a higher heat styling temperature, owing to its thermo plasticity. And increasing the draw ratio and heat styling temperature were both conducive to the tensile property, but little beneficial impact on moisture property. The high tenacity polyamide 6 exert a good effect on absorption of moisture and acid dye, and for dyeing the effects of hydrogen-bond as well as the van der Waals’ force play a significant role in dye pickup, especially in the high tenacity polyamide 6 upon different draw ratios.