ABSTRACT
The paper experimentally investigates the integral characteristics of the processes involved in the reduction of gas temperature by injecting the aerosol flow of water droplets into a counter flow of combustion products (period of steady low gas temperature Tg’ compared to the initial Tg, range of temperature decrease (ΔTg=Tg-Tg’), rate of temperature recovery, the geometric dimensions of the temperature traces and their lifetime). We use the following recording devices: fast-response thermocouples (heat inertia less than 0.1 s), a multichannel recorder, a high-speed video camera (up to 105 frames per second), as well as a cross-correlation hardware and software package (with optical methods for recording the front and trace of the aerosol). The temperature trace of an aerosol is defined as the area with the temperature Tg’ lower than the initial Tg by at least 10 K. We determine how the following group of factors affects the characteristics of temperature traces of water droplets: size (0.04-0.4 mm) and concentrations (3•10-5-11•10-5 m3 of droplet/m3 of gas) of droplets in a pulse, the initial temperature of water (280-340 K), the duration of a pulse (1-5 s), the temperature (350-950 K) and velocities (0.5-5 m/s) of combustion products. The temperature in a trace of water droplets during their motion in a flame can be reduced due to rapid vaporization or heat exchange between the gases and water. The conditions are identified, under which the low temperature of gases in a trace of droplet aerosol can be preserved for a long time (20-30 s). Finally, we forecast the parameters of temperature traces under the conditions of actual fires with combustion product temperatures over 1000 K.
KEYWORDS
PAPER SUBMITTED: 2016-03-02
PAPER REVISED: 2017-02-17
PAPER ACCEPTED: 2017-02-17
PUBLISHED ONLINE: 2017-03-03
THERMAL SCIENCE YEAR
2018, VOLUME
22, ISSUE
Issue 1, PAGES [335 - 346]
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