Global scarcity of energy sources, the ever-increasing use of energy and the excessive consumption of energy by various communities in addition to environmental pollution and wasting of national funds, has endangered the future of human life. Although Iran gracefully has one of the richest sources of energy on global scale; however, misuse of the God given gift can lead to irreparable and fundamental damages to national interests. Therefore, the rational use of energy resources and constant endeavor in optimization of efficient energy use must be a national priority. The use of thermal insulators is one of the most important means of energy consumption management. Nonwoven fabrics due to their unique properties including short production process, low weight to volume ratio, high flexibility, high porosity, low heat transfer, fairly low cost, ease of installation and the suitability of use in wide spectrum of applications have been considered as the most desirable thermal insulators. In this research, the effect of the factors affecting the heat transfer properties of nonwoven fabrics is studied. Experimental needled specimens of different mass per unit area and thickness were produced on a laboratory needling production line equipped with carding machine and horizontal cross-lapper. Effect of factors such as in- and through-plane fiber orientation on thermal conductivity and resistance coefficient was investigated. In the absence of the much needed measuring apparatus, a togometer was designed and fabricated to conduct the heat transfer experiments. Realistic 3D images of specimens were obtained using X-ray Micro-computed tomography and spacial fiber orientation was calculated using image processing method. Results showed that increase in needle density leads to increase in through-plane fiber orientation and decrease in in-plane fiber orientation of the specimens. It was found that increase in through-plane fiber orientation leads to increase in thermal conductivity coefficient of the specimens. Change in in-plane fiber orientation was found to have no effect on the thermal conductivity of the specimens. Results showed that thermal conductivity coefficient of specimens increases with increase in mass per unit area of specimens. Finally it was concluded that volume fraction of the fibers is the most effective factor that determines thermal conductivity coefficient of needled nonwoven fabrics.
