Temperature of gases in a trace of water droplets during their motion in a flame

Abstract

The paper experimentally investigates the integral characteristics of the process¬es 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 second), a multi-channel 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 re¬cording 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 characteris¬tics of temperature traces of water droplets: size (0.04-0.4 mm) and concentra¬tions (3·10-5-11·10-5 m3 of droplet per m3 of gas) of droplets in a pulse, the ini¬tial temperature of water (280-340 K), the duration of a pulse (1-5 seconds), 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 seconds). Finally, we forecast the parameters of temperature traces under the conditions of actual fires with combustion product temperatures over 1000 K.