Influence of flow properties on a structure of a mineral wool primary layer Tom Bajcar * , Bogdan Blagojevic ´, Brane S ˇ irok, Matevz ˇ Dular Faculty of Mechanical Engineering, University of Ljubljana, As ˇkerc ˇeva 6, SI – 1000 Ljubljana, Slovenia Received 27 September 2006; received in revised form 18 May 2007; accepted 31 May 2007 Abstract Mineral wool primary layer formation is influenced by the aerodynamic characteristics of the blow-away airflow and the secondary surrounding airflow. The distribution of mineral wool fibres in the primary layer was determined experimentally using a computer-aided visualization method. The flow properties in the region where the primary layer is formed were analysed. Numerical simulations with experiment-based boundary conditions were performed. The numerically obtained profile of mineral wool thickness at the collection chamber outlet agreed with the results of the experiment. Presented numerical model confirms that the forming of the primary layer is significantly dependent on local aerodynamic characteristic of the airflow in the collection chamber. Interaction between the local anomalies on the forming layer and the corresponding aerodynamic effects in the surrounding region was also analysed. Ó 2007 Elsevier Inc. All rights reserved. Keywords: Mineral wool; Turbulence; Primary layer; Visualization; Numerical analysis; Flow properties 1. Introduction Mineral wool is a general name for various inorganic insulation materials made of fibres. Mineral wool is usually divided into different subgroups depending on the raw materials they are made of, e.g. rock wool, glass wool and slag wool. The most frequently used raw materials for mineral wool production are diabase, dolomite, granite, basalt, limestone, etc. Because of its amorphous structure, mineral wool has excellent sound and thermal insulation properties. There are several production methods for mineral wool fibres, with a wide variation of quality and quantity of the final product [1]. The most commonly used mineral wool production process is the fiberisation process of mol- ten rock on fast rotating spinning discs [2–4]. At the furnace outlet, the melt should be homogeneous, single- phased, without any solid inclusions, and can be character- ised by density, surface tension and viscosity. During the mineral wool formation process, the fibres are usually formed on a four-disc spinning machine. During fibre for- mation, the moistening process of fibres with phenol solu- tion also takes place. The formed fibres enter a blow-away airflow, which blows around the circumference of the spin- ning discs and flows in the axial direction of the discs towards the perforated mesh. This airflow transports min- eral wool fibres into a collection chamber where the fibres settle onto a moving perforated mesh. Mineral wool fibres have a diameter of about 5 lm and length of about 10 mm. Beside the basic blow-away airflow that transports fibres to the region of the moving perforated mesh, a secondary air- flow is formed in the front part of the collection chamber and consists of the surrounding air that enters the collec- tion chamber because of the suction; both the blow-away and the secondary airflows are sucked out of the chamber through a suction duct at the back of the chamber. This suction (i.e. the suction airflow) ensures negative pressure in the collection chamber, and directs the blow-away air- flow (and thus the mineral wool fibres) onto the perforated 0894-1777/$ - see front matter Ó 2007 Elsevier Inc. All rights reserved. doi:10.1016/j.expthermflusci.2007.05.007 * Corresponding author. Tel.: +386 1 4771 422; fax: +386 1 2518 567. E-mail address: tom.bajcar@fs.uni-lj.si (T. Bajcar). www.elsevier.com/locate/etfs Available online at www.sciencedirect.com Experimental Thermal and Fluid Science 32 (2007) 440–449