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首页> 外文期刊>International Journal of Heat and Mass Transfer >Transient characteristic of the flow of heat and mass in a fire as the basis for optimized solution for smoke exhaust
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Transient characteristic of the flow of heat and mass in a fire as the basis for optimized solution for smoke exhaust

机译：火中热量和物质流的瞬态特性，作为烟气排放优化解决方案的基础

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摘要

Smoke and Heat Exhaust Ventilation Systems (SHEVS) are technical solutions used to limit the consequences of a fire in a building, related to the spread of the smoke. Currently, the design methodologies follow an assumption, that if a system constantly exhausts amount of the smoke estimated with a calculation method based on an onerous steady-state fire scenario, the building should be safe. This paper introduces a different approach to optimal system design, based on the transient characteristic of the fire. The main idea is that a system can adapt to the momentary density of the removed smoke, to benefit from the thermal expansion of gases in the fire. As the fire grows, the temperature does rise, and the pressure within installation falls down, and so do the forces acting on ducts, dampers and other elements. This behaviour is observed in high-temperature furnace tests of exhaust fans, during which the change of pressure and power-supply requirement in changing temperature can be measured. The author presents results of 9 high-temperature tests that are a proof of the concept. The practical implementation of the idea presented in this paper could mean, that a system designed with an existing methodology for ambient conditions, could work with a higher capacity in high-temperature, without additional strain on the elements of the system. This shift in thinking allows using higher capacity systems, in place of currently used, by artificially limiting the capacity of an oversized fan in ambient conditions and increasing it, following the measurements of the temperature of the exhausted air or pressure in the shafts. Beside the theoretical introduction to a new concept, the paper presents results of 8 numerical analysis (CFD) of airflow in an enclosed car park during a fire, performed in ANSYS® Fluent® solver. The author created an User Defined Function (UDF) to automate the transient change of the fan boundary condition, dependant on the exhausted smoke temperature - following the assumptions of the adaptive solution presented in the paper. Four CFD analysis were performed for each traditional and new solution, and their results were compared in with qualitative and quantitative approach. Results of the CFD analysis show a possible gain of 25-41% of system capacity, using the same ductwork and reaching the same design goal, as contemporary SHEVS. The pressure within the ductwork and at fans is almost constant in the adaptive analysis. The paper is closed with a discussion of legal aspects, possible limitations in the design and the further research necessary to establish the new method of the design.
机译：排烟和排热通风系统（SHEVS）是用于限制建筑物火灾与烟雾传播有关的后果的技术解决方案。当前，设计方法遵循一个假设，即如果系统不断排放用基于严重稳态火灾场景的计算方法估算的烟雾量，则建筑物应该是安全的。本文基于火灾的暂态特性，介绍了一种用于优化系统设计的方法。主要思想是，系统可以适应排出的烟雾的瞬时密度，从而受益于火灾中气体的热膨胀。随着火势的增长，温度的确会升高，安装中的压力会下降，作用在管道，风门和其他元件上的力也会下降。在排气扇的高温炉测试中观察到了这种行为，在此期间可以测量温度变化时压力的变化和电源需求。作者介绍了9个高温测试的结果，以此证明了这一概念。本文提出的想法的实际实施可能意味着，使用现有环境方法设计的系统可以在高温下以更高的容量工作，而不会给系统的元件造成额外的负担。这种思想上的改变允许通过在环境条件下人为地限制超大型风扇的容量并在测量排出的空气温度或轴中的压力之后人为地限制超大型风扇的容量并使用它来使用更高容量的系统。除了对新概念的理论介绍之外，本文还介绍了在ANSYS®Fluent®求解器中对火灾期间封闭式停车场中的气流进行8个数值分析（CFD）的结果。作者创建了一个用户定义函数（UDF），以根据排气烟气温度自动控制风扇边界条件的瞬态变化-遵循本文提出的自适应解决方案的假设。对每个传统解决方案和新解决方案进行了四次CFD分析，并将其结果与定性和定量方法进行了比较。 CFD分析结果表明，使用与现代SHEVS相同的管道系统和达到相同的设计目标，可能会增加系统容量的25-41％。在自适应分析中，风管内部和风机处的压力几乎恒定。本文以法律方面的讨论，设计中的可能限制以及建立新设计方法所必需的进一步研究作为结尾。

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