Presentation on theme: "BRI2002 ： TWO LAYER ZONE SMOKE TRANSPORT MODEL _ TANAKA Takeyoshi DPRI, Kyoto University _ YAMADA Shigeru Fujita Corporation."— Presentation transcript:
BRI2002 ： TWO LAYER ZONE SMOKE TRANSPORT MODEL _ TANAKA Takeyoshi DPRI, Kyoto University _ YAMADA Shigeru Fujita Corporation
INTRODUCTION CONTENTS 1 OUTLINE OF THE MODEL 1. 1 CONCEPTUAL MODEL OF THE MODEL 1. 2 MATHEMATICAL DESCRIPTION OF ZONE PHYSICS 1. 3 COMPONENT PROCESS MODELING Combustion and Heat Release Species Generation Due to Combustion Burning Rate Of Gasified Fuel Opening Flow Rate Fire Plume Flow Rate Opening Jet Plume Flow Rate Penetration Of Fire And Opening Jet Plumes Into Layers Thermal Radiation Heat Transfer Convective Heat Transfer Thermal Conduction In Walls Efficiency Of Mechanical Smoke Extraction
2 OUTLINE OF THE COMPUTER PROGRAM 2. 1 STRUCTURE OF THE PROGRAM 2. 2 MAIN PROGRAM 2. 3 DATA I/O SUBPROGRAMS 2. 4 COMPONENT PHYSICS SUBPROGRAMS 2. 5 NUMERICS SUBPROGRAMS 3 USE OF THE PROGRAM 3. 1 EXECUTION OF THE PROGRAM 3. 2 OUTPUT FILES 3. 3 DATA INPUT FORMAT 3. 4 SAMPLE CALCULATIONS 4 LIMITATIONS AND FUTURE ISSUES 4.1 LIMITATION ON PHYSICS 4.2 PROBLEMS IN APPLICATIONS
_ For this purpose, two layer zone models, particularly multi-story, multi-room smoke transport model: BRI2 have been extensively used. _ In performance-based smoke control designs, some engineering tool that can predict the smoke behavior with a reasonable accuracy under a prescribed design fire condition is indispensable. _ It is no more than recent 15 years since that a variety of new smoke control methods, which are not prescribed in the building codes, has begun to be introduced into actual buildings in Japan.
_ On the other hand, more than 15 years have already passed since the first version of BRI2 was made available from Building Center of Japan. _ The understanding has significantly progressed in several aspects of fire owing to the active research during this period. _ So it is thought to be appropriate to take the opportunity of reprinting the manual to revise the model taking into account the new research results and more convenience for users.
Upper layer Lower layer Room iRoom j Mechanical air supply Mechanical smoke extraction Opening jet plume Fire plume Schematic of Two Layer zone Model
(g)radiation heat transfer between rooms is neglected. (a) any space in a building is filled with an upper and a lower layers; (b) the upper and the lower layers are distinctly divided by a horizontal boundary plane (discontinuity); (c) each of the layer is uniform with respect to physical properties by virtue of vigorous mixing; (d) mass transfer across the boundary of a layer occurs only through a fire plume, doorjets and doorjet plumes;
(e) heat transfer across a layer boundary occurs by ・ the radiation heat exchange among the layers and the boundary surfaces ・ the convective heat transfer between a layer and the wall surface contacting with the layer as well as that associated with the mass transfer referred in (d) (f) all the heat released by a fire source is transported by the fire plume, in other word, the flame radiation loss is neglected. (g) radiation heat transfer between rooms is neglected.
_ Zone Conservation and State of Gas (1) Conservation of mass (2) Conservation of species (3) Conservation of heat (4) State of gas
Combustion Combustion product Gasified fuel Gasification Residual char Fuel at elevated temp Ts : Residual char 100 ℃ Temp. rise Original fuel T 0 : Initial temp. H2OH2O H 2 O(v) Tp : Gasification (Pyrolysis) H 2 O(v)
Opening Flow Rate In case that the pressure in room i is higher than j at height z the rate of flow m ij between the height (0<) Z 1
Fire Plume Flow Rate a) Initial region c) Far field region b) Turbulent flame region
Penetration of Fire and Opening Jet Plumes Into Layers
Radiation Heat Transfer
Convective Heat Transfer
Efficiency of Mechanical Smoke Extraction
Heat Conduction in Wall (a) Heat conduction equation (b) Boundary conditions q ” out =0 BRI2002 does not chase the heat transferred to an adjacent room through a wall
LIMITATIONS AND FUTURE ISSUES (1) LIMITATION ON PHYSICS (1. 1) Entrainment of Fire Plume The fire plume model integrated in this model is based on the model by Zukoski et al. The entrainment coefficient of which is basically from measurements in a calm environment, which can be attained only with careful control of experimental conditions. In more disturbed environment, which may be the case in actual situation, the plume flow rate may be significantly greater than the prediction. In fact, the increase of the plume flow rate due to HVAC or blow down effect by an inflow door jet is reported by Zukoski et al. and Quintiere et al. In BRI2002, such an effect on plume entrainment is not considered since it was not clear to what extent plumes from realistic burning items, a chair for example, behave like the plume from burner or pool fire sources.
(1. 2) Plume Penetration The penetration of a plume, originated from fire source or a door jet, through a layer discontinuity is simplistically dealt with the critical temperature difference in this model. But it is suspected that not only temperature difference but also plume momentum is involved in this phenomenon. Further investigations will be desired in this respect.
(1. 3) Air-tightness of Spaces The algebraic equation for pressure condition in this model is based on the premise that the pressure build up in fire is relatively small so that it does not affect the gas density. In addition, the room pressures are taken relative to the pressure in an outdoor space. So a completely air-tight space is not allowed but any system of spaces to which this model apply must have some leak that connect the system to outdoor space as the sink of mass flow. It is not necessary, however, that every room in the system has a leak to outdoor but is sufficient that every room is connected with outdoor whether directly of indirectly via other rooms.
(2. 1) On Fire Source Conditions In this model, scheduled burning rate or heat release rate of fire source is specified as a given condition, the manner of which is considered to be appropriate for most of practical applications. But since the fire spread itself is not predicted, input of fire source conditions is required to be realistic. Particularly, due caution must be taken not to input mass loss/heat release rate excessively large compared with the size of room opening to outdoor, or compared with the fire source area. (2) PROBLEMS IN APPLICATIONS
For fire sources in a real fire, a large gasification rate without a sizable combustion in a room is a contradiction. Furthermore, the latent heat of gasification is automatically subtracted proportionally to the mass loss rate in the heat conservation equation in this model, so the drop of the fire room temperature will be caused if large mass loss rate continues without enough heat release in the room. Both will limit the air supply for combustion so result in excessive accumulation of gasified fuel in the room to small ventilation rate in case of the former and due to small entrainment rate in case of the latter.
There is no telling what the appropriate range for fire conditions is but tentative recommendations are: (a) maximum heat release rate < 1,500A√H (kW) (A√H:opening factor) or maximum mass loss rate < 0.1 A√H (kg/s) (b) maximum heat release rate per fire source area <1,000 (kW/m 2 )
(2. 2) Calculation Time Increment An adequate calculation time increment will depend on how fast the change of fire phenomena are, however, a value about (sec) seems to take care of most of the usual conditions, though empirical.
(2. 3) On upper layer This model assumes that upper layers exist at any time from the beginning for the purpose of stability of calculation. Whether an upper layer is a real smoke layer or a pseudo layer should be judged taking into account the temperature, the species concentration etc. In addition, a non-contaminated upper layer can be developed by simple ventilation due to temperature difference between rooms or between a room and outdoor, or mechanical injection of air of which temperature is higher than room temperature.
(2. 4) Pseudo Rooms Like many other two layer zone model, uniform temperature within a layer is assumed in this model. In reality, this assumption may not be appropriate for spaces laterally very long or wide. Such a room may be divided into an adequate number of pseudo rooms for which uniformity assumption can be insisted to hold, however, this will be only possible by well knowledged user since additional consideration is needed on opening flow coefficient etc.