Abstract
Modern textile stenters are designed to reduce the inefficiency of the process and to recover the flow stream, which still contains a relatively high energetic value. In recent years, research has focused on the recovery of the energy content of the low-temperature exhaust flow; nonetheless, another important aspect that may increase the efficiency of the process is the reduction of the ambient air suction. In the present research, an innovative way to improve both machine insulation and energy savings, by using preheated air, was numerically evaluated. The proposed solution utilizes an air stream transverse to the fabric (generally called air curtain), either preheated or not, to create soft gates both at the inlet and at the outlet section of the drying machine. Several valuable advantages can be listed when using this solution: reduction of the dispersion of heat and humid polluted air to the work environment, limitation of air ingestion from outside, and effective heat recovery coupled to a uniform temperature profile around the textile fabric. To analyze the insulation capability of the air curtains in terms of mass and energy transfer, a two-dimensional CFD model of the machine was realized. A test matrix including three possible fabric speeds (20, 40 and 60 m/min), three tilt angles (−15°, 0° and 15°), four mass flow rates (0% with no air curtains and 3%, 5% and 7% of the total flow rate through the machine, where the 5% case is equivalent to the flow rate ingested from the ambient) and two temperatures (15 °C and 70 °C) of the plane jets exiting from the air curtains was considered, thus covering a wide range of possible practical applications. The obtained results demonstrate that warm air curtains at both the inlet and outlet are very effective in a fabric speed range up to 40 m/min; at higher fabric speed, entrainment of warm gases from inside the machine at the fabric outlet becomes relevant, and the adoption of a cold air curtain (capable of better insulation) can be recommended in this position.
Highlights
Over the last years, the world energy scenario has experienced a sharp increase of the energy demand, which has raised attention on several issues, from the exhaustion of resources to the pressing matter of pollutant and greenhouse emissions
The results obtained for the section β (Figure 9) are a consequence of this behavior and Mindicate that for the obtained for the section β (Figure 9) are a consequence of this behavior and indicate that for the highest highest mass flow rate, with fabric moving at 20 m/min, the air curtain flow is partially directed mass flow rate, with fabric moving at 20 m/min, the air curtain flow is partially directed outside of the outside of the stenter, while for all the other configurations it is moved towards into the machine
The evaluation of the benefits of using air curtains in stenter machines performed by means of computational fluid dynamics, applyingapplying a simplified
Summary
The world energy scenario has experienced a sharp increase of the energy demand, which has raised attention on several issues, from the exhaustion of resources to the pressing matter of pollutant and greenhouse emissions. This has resulted in the promotion of research into new technologies for energy conversion, as well as in the development of technologies to recover heat that would otherwise be wasted. One of the main sectors involved in this is industrial manufacturing, which accounts for about 38% of the primary energy consumption [1].
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