DIMENSIONING OF A FRESH-AIR-IMPULSE-DAMPER

Transcription

1 DIMENSIONING OF A FRESH-AIR-IMPULSE-DAMPER Pruckmayer G. 1, Steinrück H. 2, Brandl A. 2 Alletto M. 2 1 SIROCCO Luft- & Umwelttechnik, Austria 2 Vienna University of Technology; Institut für Strömungslehre und Wärmeübertragung, A ABSTRACT The usage of big multileave dampers in tunnel ventilation systems for punktual extraction of smoke is in the meanwhile relatively popular respectively a requirement of the new safety regulations and standards. And furthermore the system has already shown his functionality and reliability in a couple of simulations, tests and also real fires. One of the most important premesis for this system is to reduce the air-speed inside the traffic room as quick as possible to a minimum to ensure a complete and compact de-smoking of the traffic room. To influence (slow down) the length speed of the air inside the tunnel is often realised with jet.fans at the portals. Other possibilities could be regulation via exhausting in neighbouring ventilation sections, air curtains in the traffic room or fixed nozzles in the fresh air channels to inject air (Saccardo ejectors). In some cases it is an advantage to use an adjustable multileave damper instead of the saccardo ejectors to get more flexibility and options for the system. The system of the Frischluftimpulsklappe (Fresh-air-impulse-damper) is already investigated and tested amongst others by the Technical University of Graz. Keywords: Frischluftimpulsklappe (Fresh-air-impulse-damper) Abbr. FLIK Figure 1: Working surface of the selection software

2 INTRODUCTION Within the scope of a research assignment of the Technical University of Vienna the stream conditions influenced by a Fresh-air-impulse-damper FLIK were investigated. Furthermore it was a target to develop a basis to assist dimensioning and the layout of a FLIK for different applications and projects. To receive a very variable description for different applications the calculation results were summarized in a small choice- and exposition software within that a multitude of variables are selectable. 2. CALCULATIONS AND SIMULATION The calculation of the stream conditions are done in a combination of an 3D-Fluent simulation, showing a 100m long part of a Tunnel and some additional 1 dimensional calculations showing an additional left and right tunnel part beside the 3D simulation field. Basis of the calculations is a real tunnel cross section including a fresh air and an exhaust channel. The FLIK model is of a realistic design, the frame is built into the tunnel ceiling, the blades are of a fish-tailed design to minimise pressure losses, also the needed frame splittings and stiffeners are considered. The damper dimensions are selected in 4 sizes between 2x4m and 3x7m. The blade angle varies from 15 to 140 in steps of 15. The simulation considers a ventilation system with an axialfan with variable blades, the related characteristic diagram is included in the calculations. The result of the calculations are the pressures, resistance coefficient trough the damper and between the limits of the 3D part, division of the volume flows and mass flows of the system. Figure 1 shows the calculation model and the description of the results of the calculations. In addition to the 3D Simulation a 1D calculation is combined to the 100m field of the 3D model. This 1D calculation allows to various also the length of the complete tunnel (or ventilation part) and the position of the FLIK in the tunnel. Also the pressures at the portals and the coefficient of friction are selectable for the calculation and will be considered. Figure 2: Description of the results It is the prior intention of the simulations to get comparisons in the calculations related to different damper sizes and to find the optimal blade angle for an impulse effect.

3 Damper size 3x7m Damper size 3x4m Figure 3: Shows the comparison of damper sizes of the FLIK. The blades of the FLIK are designed to allows blade angles up to 140 for an inversion of the flow direction through the damper. This gives possibilities to act on the air velocity in the traffic room in two directions. The Simulation gives good results of this inversion of the flow and shows the possibility to create an impulse effect also in this case of inverse. See results in Figure 4 (showing a sample calculation) Blade angle 30 Blade angle 140 Figure 4: Inversion of Flowdirection

4 INFLUENCE OF TRUCKS Up to this point the investigations have shown the influence of the air flow inside an empty tunnel without any disturbance. Therefore it was decided to continue the calculations with investigations on the influence of trucks in the area of the FLIK. Different situations have been simulated. (Truck below the damper, beside the damper; with 5 m and also with 30 m distance to the damper in airflow direction). In addition these simulations are done with one truck in the line below the damper and with one truck on each line of the traffic room. Figure 5: Comparison of results with and without a truck in the traffic room. Figure 6: Comparison of results with and without a truck in the traffic room.

5 CONCLUSION The first part of the investigation has proven, that the longitudinal air flow within the traffic section of the tunnel can be influenced by the means of fresh air fans in combination with the FLIK in the required extend and manner. The second part of the investigation has been shown, that the negative influence of hindrances as trucks is by far not that big as expected. The designated effect of the FLIK to the air flow in the traffic room is reached also in the case of hindrances. Finally it can be pointed out, that a FLIK could give positive properties for tunnel ventilation systems. In the design phase it could be worth to compare the effect of Saccardo ejectors with the effects of a FLIK. Furthermore in some cases of tunnel refurbishment, the FLIK could even give an alternative to jet fans.