This paper presents an optical method and system for contactless measurement of the mass flow rate of melts by digital cameras. Addressed problem is highly relevant in mineral wool industry because real time melt flow rate measurement is key for efficient regulation of production lines. The proposed method is based on reconstruction of melt stream geometry and flow velocity calculation by cross correlation, and is very cost-effective due its modest hardware requirements. Using a laboratory test rig with a small inductive melting pot and reference mass flow rate measurement by weighing, the proposed method was demonstrated to have an excellent dynamic response (0.1 s order of magnitude) while producing deviations from the reference of about 5% in the steady-state flow regime. Similar results were obtained in an industrial stone wool production line for two repeated measurements. Our method was tested in a wide range of melt flow rates (0.05-1.2 kg/s) and did not require very fast cameras (120 frames per second would be sufficient for most industrial applications).
COBISS.SI-ID: 16345371
In this paper, melt film dynamics in rock wool spinning machines are investigated. Good wetting and adhesion of melt on the spinner wheel surface is crucial for attaining a good quality fiberization process. High-speed visualization of the melt film structure was performed for a model spinning wheel and two industrial spinning machines. The quality of the melt film adhesion to the wheel and related heat transfer parameters were assessed by time series analysis of the image gray level for different operating conditions. During the warmup procedure for the spinning wheels investigated in laboratory experiments, the best wetting of the wheel surface (i.e. with least voids in the melt film) was observed at the lowest rotational speed and melt viscosity. In this transitional period, melt adhesion can be improved by preheating of the wheel surface and by gradual increase of the wheel rotational speed. Once the wheel surface has reached its working temperature, melt temperature and viscosity seem to have the largest effect on the melt adhesion process. The cooling rate of the melt film was observed to increase with its initial temperature and circumferential velocity. Regardless of the operating regime, no significant melt slippage against the wheel surface was observed, with melt film structure preserved over multiple spinner wheel rotations.
COBISS.SI-ID: 16472347
This paper presents an experimental study of the liquid disintegration process on an atomizer with two counter-rotating wheels by high-speed imaging. Studied phenomena (cascading liquid flow between atomizer wheels, liquid splashing on jet rebound from spinning wheel surface…) are hydrodynamically similar to the melt flow on multi-wheel stone wool spinning machines. The atomization process was investigated for a wide range of wheel rotational speeds, liquid flow rates and impingement positions. Compared to flat disc and cup atomizers operating at similar Weber numbers, proposed atomizer design is capable of producing much finer droplets in the ligament formation mode (mean diameter under 0.15 mm when Weber number is equal to 10^6) and at a significantly larger liquid throughput. Despite the atomizer gap flow complexity, approximation of mean liquid trajectories with tangent lines proved to be fairly accurate. We were able to identify two main challenges in atomizer operation, namely the occurrence of hydraulic jump upon liquid impingement causing the formation of large droplets, and escaping of the liquid spray through the wheel gap. Nevertheless, both issues can be largely mitigated by optimization of atomizer geometry and operating parameters.
COBISS.SI-ID: 14089731
In this paper, the process of mineral fiber formation and blow-off was investigated experimentally on a two-wheel spinner by means of high-speed imaging. Analogue isomalt melt was fiberized at different rotational speeds of spinner wheels, melt flow rates and impingement positions so that the fiberization process was dynamically similar to an industrial mineral wool production process. Images of fiber formation and transport reveal highly complex dynamics of these processes, as fibers mostly occur in form of 3D mutually intertwined structures such as clusters, strands and veils periodically shedding from the melt film. Despite the complexity of flow structures, there is a clear trend of increasing mean fiber length and expansion angle of the coaxial fiber-laden flow as the Weber number and the ratio of melt film velocity to blowing air velocity are increased. The fiberization efficiency (ratio of fiber mass deposited on the collecting mesh to the mass of melt poured) is affected by the impingement position and flow rate of melt as well as the Weber number of melt film. The optimum efficiency was attained at 30° (1 o’clock) impingement position and the ratio of melt film to blowing air flow velocity close to unity.
In this conference presentation (conference: Society of Glass Technology, Meeting of minds 2018 - written abstract available), the principle of high-speed camera imaging for experimental investigation of the mineral wool fiberization process was discussed. Our research work on melt- and cold experiments was presented to the glass- and stone fiber research community, with many attendees from academia and industry present at the event.
COBISS.SI-ID: 16299291