Numerical Investigation of Water Droplets Shape Influence on Mathematical Modeling Results of Its Evaporation in Motion through a High-Temperature Gas

The numerical investigation of influence of a single water droplet shape on the mathematical modeling results of its evaporation in motion through high-temperature gases (combustion products of a typical condensed substance) has been executed. Values of evaporation time, motion velocity, and distance passed by various droplet shapes (cylinder, sphere, hemisphere, cone, and ellipsoid) in a high-temperature gases medium were analyzed. Conditions have been defined when a droplet surface configuration affects the integrated characteristics of its evaporation, besides temperature and combustion products concentration in a droplet trace, insignificantly. Experimental investigations for the verification of theoretical results have been carried out with using of optical diagnostic methods for two-phase gas-vapor-liquid flows

Water Droplet With Carbon Particles Moving Through High-Temperature Gases

An experimental investigation was carried out on the influence of solid inclusions (nonmetallic particles with sizes from a few tens to hundreds of micrometers) on water droplet evaporation during motion through high-temperature gases (more than 1000 K). Optical methods for diagnostics of two-phase (gas and vapor-liquid) flows (particle image velocimetry (PIV) and interferometric particle imaging (IPI)) were used. It was established that introducing foreign solid particles into the water droplets intensifies evaporation rate in high-temperature gas severalfold. Dependence of liquid evaporation on sizes and concentration of solid inclusion were obtained

Numerical Analysis of Integral Characteristics for the Condenser Setups of Independent Power-Supply Sources with the Closed-Looped Thermodynamic Cycle

The mathematical model of heat and mass transfer processes with phase transition is developed. It allows analysis of integral characteristics for the condenser setup of independent power-supply plant with the organic Rankine cycle. Different kinds of organic liquids can be used as a coolant and working substance. The temperatures of the working liquid at the condenser outlet under different values of outside air temperature are determined. The comparative analysis of the utilization efficiency of different cooling systems and organic coolants is carried out

Numerical and Experimental Research of Heat and Mass Transfer at the Heterogeneous System Ignition by Local Energy Source with Limited Heat Content

Numerical and experimental investigations were executed for determination of macroscopic regularities of heat and mass transfer processes under the conditions of the phase transformations and chemical reaction at the ignition of vapors coming from fabrics impregnated by combustible liquid into oxidant area at the local power supply. It was established that initial temperature Θp>1 of local energy source and volume fraction φ>30% of combustible liquid vapors in fabric are necessary for realization of ignition conditions in a system “fabric—combustible liquid—oxidant.”. Thus three ignition modes are possible for such system. The most widespread mode is an arrangement of ignition zone near the lateral side of local energy source. Also we obtained approximating expressions of ignition delay time on initial temperature and characteristic size of a local energy source for fabrics impregnated by some kinds of combustible liquids (gasoline, kerosene, and diesel fuel). Its dependences may be useful at engineering calculations of fire danger for processes of single hot particles interaction with liquid combustible substances

Research of Macroscopic Regularities of Heat and Mass Transfer at the Ignition Condition of a Liquid High-Energy Material by an Immersed Source with a Limited Energy Capacity

We carried out a numerical and experimental investigation of heat and mass transfer at the ignition condition of a liquid high-energy material by a typical immersed source with a limited energy capacity, being a small, intensely heated metallic particle. The numerical research is made on the basis of a model taking into account a group of interrelated physicochemical processes (thermal conductivity, diffusion, convection, mixing, and radiative heat transfer) with phase transitions (evaporation of the liquid and crystallization of the particle's material). We established such terminal conditions for the immersion energy source that prevent inflammation of the high-energy material

Influence of radiative heat and mass transfer mechanism in system “water droplet-high-temperature gases” on integral characteristics of liquid evaporation

Physical and mathematical (system of differential equations in private derivatives) models of heat and mass transfer were developed to investigate the evaporation processes of water droplets and emulsions on its base moving in high-temperature (more than 1000 K) gas flow. The model takes into account a conductive and radiative heat transfer in water droplet and also a convective, conductive and radiative heat exchange with high-temperature gas area. Water vapors characteristic temperature and concentration in small wall-adjacent area and trace of the droplet, numerical values of evaporation velocities at different surface temperature, the characteristic time of complete droplet evaporation were determined. Experiments for confidence estimation of calculated integral characteristics of processes under investigation - mass liquid evaporation velocities were conducted with use of cross-correlation recording video equipment. Their satisfactory fit (deviations of experimental and theoretical velocities were less than 15%) was obtained. The influence of radiative heat and mass transfer mechanism on characteristics of endothermal phase transformations in a wide temperature variation range was established by comparison of obtained results of numerical simulation with known theoretical data for “diffusion” mechanisms of water droplets and other liquids evaporation in gas

Numerical research of heat and mass transfer at the ignition of system “fabric – combustible liquid – oxidant” by the local energy source

A numerical research was executed for macroscopic regularities determination of heat and mass transfer processes under the conditions of phase transformation and chemical reaction at the ignition of vapour coming from fabrics impregnated by typical combustible liquid into oxidant area at the local power supply. Limit conditions of heterogeneous system “fabric – combustible liquid – oxidant” ignition at the heating of single metal particle was established. Dependences of ignition delay time on temperature and rates of local power source were obtained

Experimental determination of water droplet “strain cycles” characteristic in the gas area

Experimental investigation of deformation regularities of widely used in industry liquid (water, kerosene, ethanol) droplets during the motion through the gas area under the action of gravitational forces has been conducted. Droplet characteristic sizes were varied in the range from 3 mm to 6 mm. Droplet motion velocities were come up to 5 m/s. Cross-correlation video recording system with optical methods of droplet size and velocity measurement was used. More than 10 characteristic droplets “strain cycles” have been established during they pass the distances up to 1 m through the gas area. The characteristic droplet forms, times, extents and amplitudes have been determined for each “strain cycle”. The expression has been formulated which describes the characteristic “strain cycles” time dependencies on droplet velocities and sizes, also on the fundamental properties (viscosity, density, surface tension) of liquid and gas area in a first approximation. The conditions of droplet deformation intensification and this process in industry gas-vapor-droplet setups stabilization have been determined

Experimental determination of water droplet “strain cycles” characteristic in the gas area

Experimental investigation of deformation regularities of widely used in industry liquid (water, kerosene, ethanol) droplets during the motion through the gas area under the action of gravitational forces has been conducted. Droplet characteristic sizes were varied in the range from 3 mm to 6 mm. Droplet motion velocities were come up to 5 m/s. Cross-correlation video recording system with optical methods of droplet size and velocity measurement was used. More than 10 characteristic droplets “strain cycles” have been established during they pass the distances up to 1 m through the gas area. The characteristic droplet forms, times, extents and amplitudes have been determined for each “strain cycle”. The expression has been formulated which describes the characteristic “strain cycles” time dependencies on droplet velocities and sizes, also on the fundamental properties (viscosity, density, surface tension) of liquid and gas area in a first approximation. The conditions of droplet deformation intensification and this process in industry gas-vapor-droplet setups stabilization have been determined