Wall and Corner Effects on Fire Plumes as a Function of Offset Distance
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Wall and Corner Effects on Fire Plumes as a Function of Offset Distance Kevin McGrattan*, National Institute of Standards and Technology, Gaithersburg, MD, USA David Stroup , U.S. Nuclear Regulatory Commission, Washington, DC, USA Received: 5 August 2020/Accepted: 16 October 2020
Abstract. A series of compartment fire experiments is described in which a square natural gas burner was positioned in a corner or against a wall and gradually moved towards the room center to assess the relative effects on the plume and compartment temperatures. The experiments were conducted to validate computational fluid dynamics simulations that were performed to provide guidance for probabilistic risk assessments in nuclear power plants. The measurements consist of one dimensional vertical thermocouple arrays to measure the hot gas layer temperature and height, and a three dimensional thermocouple array to measure the temperature of the fire plume as the burner is moved away from the corner or wall. As a result of the modeling and experiments, recommendations have been made that quantify wall and corner effects as a function of offset distance. Keywords: Fire plumes, Wall effects, Corner effects
1. Introduction In performing probabilistic risk assessments (PRA) of nuclear power facilities, plant engineers and consultants make use of various empirical correlations to estimate potential damage to critical safety equipment in the event of a fire. One of these, Heskestad’s plume correlation [1], has been supplemented by a so-called ‘‘location factor,’’ kF , that accounts for the change in plume behavior if the fire is against a wall or in a corner. The idea behind this modification, first proposed by Zukoski et al. [2], is that a wall or corner fire plume is assumed to behave as if it were ‘‘mirrored’’ in the wall or corner with kF ¼ 2 or kF ¼ 4 times its base area and heat release rate, respectively. Based on this assumption, the Heskestad correlation for centerline plume temperature rise, DT0 ðzÞ, is modified as follows: T1 DT0 ðzÞ ¼ 9:1 g c2p q21
!1=3
kF Q_ c
2=3
ðz z0 Þ5=3
ð1Þ
* Correspondence should be addressed to: Kevin McGrattan, E-mail: [email protected]
1
Fire Technology 2020 Here T1 is the ambient temperature, g is the acceleration of gravity, cp is the specific heat of air, q1 is the ambient air density, Q_ c is the convective heat release rate, z is the height above the fire, and z0 is the ‘‘virtual’’ origin, given by z0 2=5 ¼ 1:02 þ 1:4 Q_ ; DF
Q_ ¼
kF Q_ pffiffiffiffiffiffiffiffiffi q1 cp T1 g DF D2F
ð2Þ
pffiffiffiffiffi Here, DF is the diameter of the ‘‘mirrored’’ fire base, DF ¼ kF D, where D is the diameter of the actual fire, and Q_ is the total heat release rate of the actual fire. Heskestad [1] and Lattimer and Sorathia [3] provide a number of references to studies that seek to develop correlations for flame heights and plume temperatures of wall and corner fires. A number of these studies suggest that the location factors given above may be overly ‘‘conservative;’’ that is, may over-estimate the impact of a wall or corner on plume
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