- 7 - PRESSURE LOSSES DUE TO THE LEAKAGE IN THE AIR DUCTS - A SAFETY PROBLEM FOR TUNNEL USERS? Pucher Krl, Grz Uniersity of Technology, Austri E-Mil: pucherk.drtech@gmx.t Pucher Robert, Uniersity of Applied Sciences Wien, Austri ABSTRACT There is requirement in Austri to suck off n exhust olume of t lest 1m 3 /s t the end of n exhust duct in cse of fire (RVS 9.61). To fulfil this, the lekge olume must be known for not tight exhust duct. The pper shows how the lekge olume cn be clculted. 1. INTRODUCTION 3 yers go mny long motorwy tunnels where plned in Austri. For instnce: the 6,4 km long Tuerntunnel, the 5,4 km long Ktschbergtunnel, the 7 km long Pfändertunnel nd the 1 km long Plbutschtunnel. All these tunnels where plned for two tubes. But the trffic mount t tht time ws low nd the cr emission ws ery high. Therefore only one tube ws built nd equipped with trnserse entiltion system. The trffic mount ws growing in the lst 3 yers ery much. Also the philosophy bout the fire in rod tunnel ws chnged totlly fter the bd fire disster in the Mont Blnc nd Tuerntunnel. Smll exhust hoods with n re of,5m where instlled eery 1m in the exhust ducts of these tunnels. The ide ws to suck up the smoke in cse of fire to the flse ceiling nd extrcted it oer long prt of the exhust duct. The dntge of this solution ws thought to he smoke free bottom zone on the one hnd nd not extreme hot smoke in the exhust duct becuse of mingling with fresh ir on the other hnd. Lekge of fresh ir into the exhust duct ws therefore no big problem. But now we think it is better to suck off the smoke directly ner the fire plce into the exhust duct through lrge djustble exhust dmpers (open re ~1m ) to oid smoke propgtion in the tunnel. The djustble smoke dmpers re instlled eery 1m. In norml cse of opertion ll dmpers re little bit open, so tht the sme mount of exhust ir cn be sucked off through ech dmper. But in cse of fire only this dmper will be opened fully which is closed by the fire plce nd ll others will be closed. So concentrted smoke extrction is possible. There is requirement in the new Design Guidelines Tunnel Ventiltion tht the exhust fn must be ble to suck off 1m 3 /s t lst t the end of long exhust duct. In this cse lekge ir which is sucked into the exhust duct between the fn nd the end of the duct hs to be minimized or een preented. If it is not possible to preent the lekge ir in the exhust duct we he to know it becuse the flow rte in the exhust fn will then be enlrged. Thus the power input is higher thn in cse of tight exhust duct. Therefore we he to focus our ttention on the clcultion on the lekge ir.
- 8 -. CALCULATION OF THE LEAKAGE AIR Under the ssumption tht the ir is incompressible, the cross section of the exhust duct is constnt nd the re of the lekge strip is constnt too oer the whole length of the duct we cn drie the following differentil eqution system: The pressure in the exhust duct is gien by the eqution dp dx λ ρ ρ du =. u ² k (1) D dx ² The elocity in the exhust duct cn be clculted with du dx = f F ( p ρ F p ) + F 1+ ξ u () nd the pressure in the tunnel follows from dp λ ρ ρ du ² = u ² k z ) (3) dx D dx The connection between u nd u is gien by du F du = (4) dx F dx Here in is p (x) [N/m ] pressure in the exhust duct x [m] coordinte in the exhust duct λ [-] friction coefficient in the exhust duct λ [ ºº ] friction coefficient in the tunnel D [m] hydrulic dimeter in the exhust duct D [m] hydrulic dimeter in the tunnel ρ [kg/m 3 ] ir density u [m/s] ir elocity in the exhust duct u [m/s] ir elocity in the tunnel [m/s] ir elocity in the lekge strip α [ ] ngle under which the lekge strems into the ir duct f [m /m] re of the lekge strip F [m] cross section of the ir duct F [m] cross section of the tunnel p [N/m ] pressure in the trffic duct ξ [-] resistnce coefficient for the entrnce of lekge ir into the ir duct ξ [-] resistnce coefficient for the entrnce in the tunnel k [-] is fctor which tke into considertion the profile shpe of u k [-] is fctor which tke into considertion the profile shpe of u
- 9-3. SOME RESULTS Figure 1 shows the result from clcultion of the pressure distribution (x =,p = - 4 N/m ) in the exhust duct nd the tunnel itself when the exhust duct is tight. The clcultion ws performed under the ssumption tht olume of 1m 3 /s is sucked off t the end of the duct. The ir elocity in the exhust duct nd in the tunnel is then constnt s it cn be seen in Figure. pressure pressure in the tunnel (fst=m^/m) (N/m^) - length of the exhust duct (m) -4-6 portl exhust duct is open -8-1 pressure in the tight exhust duct (fst=m^/m) -1 Fig. 1: Pressure distribution in tight exhust duct nd in the tunnel 16 elocity (m/s) 14 1 ir elocity in the tight exhust duct (fst=m^/m) 1 8 6 4 portl exhust dmper is open length of the exhust duct (m) - -4 ir elocity in the tunnel (fst=m^/m) Fig. : Velocity distribution in tight exhust duct nd in the tunnel.
- 3 - Figure 3 shows the result when the exhust duct is not tight. (f =.1m /m). The pressure distribution strts with the pressure of 5N/m ner the open exhust dmper t the end of the exhust duct. It cn be seen tht pressure in front of the exhust fn is roughly p=- 18N/m in comprison of p=-11n/m in tight duct. length of the exhust duct (m) pressure (N/m^) pressure in the tunnel - (fst=.1m^/m) -4-6 -8-1 portl one exhust dmper is open -1-14 pressure in the not tigtht exhust duct (fst=.1m^/m) -16-18 - Fig. 3: Pressure in the not tight exhust duct (fst=.1m^/m) elocity (m/s) 5 ir elocity in the not tight exhust duct 15 1 5 portl exhust dmper is open length of the exhust duct (m) -5 ir elocity in the tunnel (fst=.1m^/m) -1 Fig. 4: Velocity in the not tight exhust duct (fst=.1m^/m) The pressure behind the portl in the tunnel is only little bit lower thn in cse of tight exhust duct. The ir elocity in the exhust duct is growing from 13.5/s ner the open exhust dmper to.47/s ner the exhust fn (Fig. 4). So the flow rte in front of the fn is 181.6m^3/s in comprison to 1m^3/s in tight exhust duct. If we tke only the pressure losses in the exhust ducts into our power input clcultion for the exhust fn we need 48.7kW (ŋ Fn ~.8) for the not tight duct nd only 165kW for the tight duct to suck off 1m^3/s (ŋ Fn ~.8) t the end of the exhust duct.
- 31-4. CONCLUSION The clcultion showed tht it is importnt to know the lekge olume tht is sucked into the exhust duct between the open smoke dmper nd the exhust fn. The lekge olume nd the dditionl pressure drop in the not tight exhust duct enlrge the power input of the exhust fn to suck off 1m 3 /s t the end of n exhust duct ery much.