Liquefied extinguishing agent discharge to an overpressure-sensitive enclosed volume Lukáš Hurda 1,* , and Richard Matas 1 1 University of West Bohemia in Pilsen, New Technologies – Research Centre, Univerzitní 8, Pilsen, Czech Republic Abstract. The throttling of liquefied substances from high pressure vessels to an enclosed volume starting at atmospheric pressure is described in order to determine thermodynamic state of the extinguished room gaseous contents. Time dependent, 0D mathematical model is implemented describing the state inside the agent container, the isenthalpic throttling in the distribution system, agent vaporization and mixing with air. The agent is modelled as real gas. Other influences on the process including the heat transfer from selected solid parts inside the room and the gas mixture leakage out of the room are taken into account. Main outcome is an MS Excel tool for integrated fire extinguishers design optimization. The optimization balances the two contradictory requirements: Agent volumetric concentration to sustain the fire extinguishing capabilities and tolerable room overpressure. Agent fill weight and discharge time are being adjusted. The discharge time is controlled by the distribution piping and spray nozzles design. System operation is checked concerning various initial and boundary conditions. 1 Introduction The design apparatus for integrated fire extinguishing system is described. Many aspects of the process are covered by standards, but the need to be worried about the emerging overpressure in the extinguished volume asks for careful analysis and proposal of new techniques. The thermodynamic system of interest consists of two main parts: an enclosed volume (a room) and extinguishing agent container (a pressure vessel). The room is initially filled with clean, dry air at atmospheric or near-atmospheric pressure and arbitrary temperature. The heat transfer between walls and its surroundings is omitted completely as the real-life object being modelled is well insulated and relatively low temperature gradients are expected. The model is not completely closed speaking of mass conservation, a simple model of gas mixture leakage based on the pressure rise or fall during extinguishing agent discharge is implemented. The vessel may have different initial temperature than the room. The heat transfer through the vessel wall is also neglected as the conditions for its evaluations are unclear. The vessel is mounted inside the room, but it is covered in a way that prevents immediate * Corresponding author: hurda@ntc.zcu.cz © The Authors, published by EDP Sciences. This is an open access article distributed under the terms of the Creative Commons Attribution License 4.0 (http://creativecommons.org/licenses/by/4.0/). MATEC Web of Conferences 168, 07010 (2018) https://doi.org/10.1051/matecconf/201816807010 XXI. AEaNMiFMaE-2018