Experimental Study on the Influence of HRR Evolution on the Pressure Variation in an Air-Tight Compartment
Résumé
Air-tight buildings are increasingly used in modern constructions, e.g. energy-efficient buildings, nuclear installations, tropical region buildings, et al. From a fire safety perspective, the air-tightness introduces a potential risk of high pressure build-up, which could hinder evacuation and even damage the structure [1]. In order to validate field and zone fire models, this experimental study investigated the influence of heat release rate (HRR) on the pressure variation, in a reduced scale air-tight facility, developed and qualified by IRSN [2]. The internal dimensions of the facility are 1.5 m in length, 1.25 m in width and 1 m in height, resulting in an internal volume of 1.875 m3. The walls, ceiling and floor consist of two layers from outside to inside: one 2 mm thick steel layer and one 25 mm thick calcium silicate layer. The pressure, gas temperatures, gas concentrations and ventilation flow rates are measured during the experiments. For the present cases, the facility is ventilated through an admission line and an extraction line. An exhaust fan worked in the extraction line, leading to a ventilation flow rate of about 24 m3/h. The fire source is a square sand propane burner located at the center of the room (180 mm width and 60 mm height). A regulating valve allows applying prescribed propane flow rates following a defined model: (growth phase), (steady phase) and (decay phase), where ṁf is the fuel mass flow rate (g/s), α is the fire growth rate (g/sn+1), t is the time (s), n is the fire growth exponent (-), ṁf,max is the maximum fuel mass flow rate (g/s), td is the time to start the decay (s). Tests with various fire growth rates, maximum fuel mass flow rates and fire growth exponents are conducted to illustrate the effect of HRR evolution on the pressure build-up. The results are shown in Fig. 1. It can be seen that with a higher fire growth rate, the over-pressure and under-pressure are higher. When the fire growth rate is high enough, the pressure peak approaches a maximum value. Besides, a higher maximum fuel flow rate results in higher over-pressure and under-pressure. For different settings of the fire growth exponent, the fire growth rate was chosen accordingly to get the same fire growth time. It can be seen that the exponent has little influence on the over-pressure peak, but has an effect on the evolution of the pressure and the under-pressure peak.
Domaines
Sciences de l'ingénieur [physics]
Origine : Fichiers produits par l'(les) auteur(s)
