Noise Reduction of an Extinguishing Nozzle Using the Response Surface Method

Abstract

An inert gas such as nitrogen is used as an extinguishing agent to suppress unexpected fire in places such as computer rooms and server rooms. The gas released with high pressure causes noise above 130 dB. According to recent studies, loud noise above 120 dB has a strong vibrational energy that leads to a negative influence on electronic equipment with a high degree of integration. In this study, a basic fire-extinguishing nozzle with absorbent was selected as the reference model, and numerical analysis was conducted using the commercial software, ANSYS FLUENT ver. 18.1. A total of 45 experiment points was selected using the design of experiment (DOE) method. An optimum point was derived using the response surface method (RSM). Results show that the vibrational energy of the noise was reduced by minimizing the turbulence kinetic energy. Pressure and velocity distributions were calculated and graphically depicted with various absorbent configurations.

Experimental Assessment of the Acoustic Performance of Nozzles Designed for Clean Agent Fire Suppression

“…In spite of the numerous advantages exhibited by clean agents, the main form of which is characterized as being electrically non-conductive, leaving no residue after discharge and having virtually null Ozone Depletion Potential (ODP), the whole related system may be somewhat complex, since they require a storage capacity larger than that of halon-based systems as a result of poorer extinction effectiveness [2]. Most clean agent fire suppression systems include a storage tank, where the agent is superpressurized-usually by nitrogen-if in the form of a liquified gas, as is the case for most halocarbon compounds, or is simply contained at high pressure (usually in the range of 150-300 bar) in the case of an inert gas system [2,3]; valves, piping, nozzles and controllers (e.g., flow rate and pressure) are also part of the design. While the mechanical strength of pipes and nozzles to withstand the gas pressure does not currently appear a major concern for designers, the noise generated by the agent, mostly at the nozzle exit and, to a lesser extent, through valves and channels, represents a potentially relevant cause of damage to the equipment in the compartment, as well as first responders (e.g., firefighters) if present within the compartment as the discharge occurs [4].…”

“…As a technical solution to reduce the noise generated by clean agent discharge, silent nozzles-often also referred to as acoustic nozzles-have been developed. Since modifying the nozzle outlet does not appear to fully address the challenge, given that SPL was proven to be largely independent of nozzle shape [7], adding sound absorptive layers to the nozzle outer surface has become the most employed approach [3,12,13], with the insertion of horizontal plates also being recommended to make the released flow rate and pressure as balanced as possible in multiorifice nozzles [12,14]. Currently, the open literature presents relatively few studies that focus on the design of such nozzles and on assessing their acoustic performance, especially when compared with that exhibited by standard nozzles under the same discharge conditions.…”

“…The extensive use of numerical modeling generally permeates the works on silent nozzles, most of which [12,14] are focused on determining the most effective nozzle selection and configuration within an enclosure towards making SPL at the HDD locations lower than the previously mentioned threshold (110-120 dB, in those studies). On the other hand, the more recent contributions by Kim et al [3,13] present a computational approach-remarkably validated through dedicated experiments-to optimize some design parameters of silent nozzles. Guided by DOE (Design of Experiments), their research effort led to them identifying the diameter of the external sound-absorbing shell as the most impactful variable.…”

“…Guided by DOE (Design of Experiments), their research effort led to them identifying the diameter of the external sound-absorbing shell as the most impactful variable. It is worth noting that some of the reviewed works suggest a certain dependence of the emitted noise on the orientation of the nozzle and the location at which SPL is evaluated [14,15], whether the nozzle is a standard or a silent one; on the other hand, other studies appear to practically consider the nozzle as a point source [3,12]. This aspect may be mostly related to the nozzle geometry.…”

“…More specifically, an experimental methodology allowing investigators to carry out such a comparison in terms of variables of interest for fire protection system designers (e.g., type of clean agent, released flow rate, orifice diameter) is still in demand. The present research is aimed at embarking on this quest, with the experimental datasets and facilities provided and described in the studies by Kim et al [3] and Loureiro et al [12] serving as a foundation. Arguably an unprecedented effort, this work may set a standard methodology to quantitatively compare the acoustic performance of various standard and silent nozzles, also leading to discussion in reference to the relevant physical quantities.…”