New Aerogel Products for Construction Use: Product Specifications, Application Examples, Practical Aspects

Two new high-performance insulation materials (HPIM) for the usage in buildings are presented. We show how to use and apply the upcoming aerogel products and give examples for structural details. While both materials achieve very low lambda values due to Knudsen-Effect of aerogels, they differ clearly in other key characteristics. SLENTEX® is a slim, mechanically flexible, non-combustible aerogel mat. It is open for water vapor diffusion but water-repellent. It is suitable for applications with strict fire regulations since it is a purely mineral-based product. SLENTITE® is a homogeneous polyurethane-based aerogel insulation board without lamination or encapsulation layers and also vapor open. Its surface adheres to almost any organic or inorganic binder. It can be processed very much like conventional insulation boards. While their handling and application are very similar to other insulation materials, aerogels are however no general-purpose insulation products: due to their sophisticated production process, and thus higher price compared to conventional insulation products, HPIM are best applied as problem solvers. In well-motivated situations, e.g. where space is limited or particular aesthetic requirements apply, they offer cost effective alternatives to standard solutions.

The Imaging Resolution and Knudsen Effect on the Mass Transport of Shale Gas Assisted by Multi-length Scale X-Ray Computed Tomography

The spatial resolution of 3D imaging techniques is often balanced by the achievable field of view. Since pore size in shales spans more than two orders of magnitude, a compromise between representativeness and accuracy of the 3D reconstructed shale microstructure is needed. In this study, we characterise the effect of imaging resolution on the microstructural and mass transport characteristics of shales using micro and nano-computed tomography. 3D mass transport simulation using continuum and numerical physics respectively is also compared to highlight the significance of the Knudsen effect on the reconstructed solid surface. The result shows that porosity measured by micro-CT is 25% lower than nano-CT, resulting in an overestimated pore size distribution and underestimated pore connectivity. This leads to a higher simulated intrinsic permeability. An overestimated diffusive flux and underestimated permeability are obtained from the continuum mass transport simulation compared to the numerical ones when the molecular-wall collision is accounted, evidenced by the large deviation of the measured Knudsen tortuosity factor and permeability correction factor. This study is believed to provide new knowledge in understanding the importance of imaging resolution and gas flow physics on mass transport in porous media.

Cellulose Aerogels for Thermal Insulation in Buildings: Trends and Challenges

Cellulose-based aerogels hold the potential to become a cost-effective bio-based solution for thermal insulation in buildings. Low thermal conductivities (<0.025 W·m−1·K−1) are achieved through a decrease in gaseous phase contribution, exploiting the Knudsen effect. However, several challenges need to be overcome: production energy demand and cost, moisture sensitivity, flammability, and thermal stability. Herein, a description and discussion of current trends and challenges in cellulose aerogel research for thermal insulation are presented, gathered from studies reported within the last five years. The text is divided into three main sections: (i) an overview of thermal performance of cellulose aerogels, (ii) an identification of challenges and possible solutions for cellulose aerogel thermal insulation, and (iii) a brief description of cellulose/silica aerogels.