The breakup length of axisymmetric turbulent jet in the foam deflector type sprinkler for automatic extinguishing systems
Keywords:atomization, spray breakup length, automatic extinguishing system, sprinkler, foam, foam expansion rate, geometric parameters of sprinkler, frame arms length
Purpose. To analyze the theoretical approaches to the description of the structure of axisymmetric turbulent jets, as well as to the calculation of their breakup length in the atomization regime. To theoretically calculate the frame arms length of the foam deflector type sprinkler (i.e., the distance from the outlet of the sprinkler to its deflector), where the most intense foaming occurs and compare the obtained results with experimental data.
Methods. A number of theoretical research methods (analysis, synthesis, comparison) to analyze approaches to the description and calculation of axisymmetric turbulent jets, as well as to compare the theoretically calculated the optimal frame arms length of the foam deflector type sprinkler with the experimental data were used.
Findings. A hypothesis is formulated about the optimal frame arms length L of the foam deflector type sprinkler in order to ensure the most intense foaming in it: the optimal length should be equal to the breakup length Ln of the jet formed at the outlet of the sprinkler nozzle, i.e. L = Ln. The lower and upper limits of the range of values of the breakup length of the water jet formed at the outlet of the sprinkler nozzle of a certain geometry were calculated: 117 ≤ Ln ≤ 201 mm. In the result of the experimental determination of the expansion rate of the foam (characterizes the intensity of foaming) generated by the deflector type sprinkler, for which a theoretical calculation was performed, the optimal value for this foam characteristic was found to be L = 114 ± 4 mm. The obtained experimental result is consistent with the theory corrected for a lower surface tension coefficient foaming solution compared to water. In addition, an expression for calculating the breakup length of the jet for the considered foam deflector type sprinkler was proposed. In a first approximation, it can be used to estimate the value of Ln when using different brands and types of foaming agents, as well as when spraying in gas with a different density.
Application field of research. The results can be used to further studying the process of foaming in deflector type sprinklers for automatic extinguishing systems in order to increase their fire extinguishing efficiency. The proposed expression for calculating the breakup length of jet formed at the outlet of the foam deflector type sprinkler can be used to estimate the value of this parameter when using different brands and types of foaming agents, as well as when spraying in gas with a different density.
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