Three-dimensional simulation of flash evaporation of non-uniform spray in saturated vapor environment
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ORIGINAL
Three-dimensional simulation of flash evaporation of non-uniform spray in saturated vapor environment Can Ji 1 & Naihua Wang 2
&
Zhigang Liu 1
Received: 10 October 2019 / Accepted: 31 July 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract A 3D numerical study of water spray flash evaporation occurring in a positive-pressure saturated vapor environment is conducted. The spray is non-uniform with a Rosin-Rammler droplet size distribution. The characteristics of the flashing spray and vapor flow field are obtained by calculating within the Eulerian-Lagrangian framework. The spray undergoes violent evaporation and significant temperature reduction in the beginning within the vicinity of the nozzle exit. As the spray develops downstream, evaporation becomes moderate. Smaller droplets are found to distribute in the spray central region with a comparatively higher evaporation rate and larger velocity variation. Meanwhile, larger droplets evaporate at a lower speed but cover a wider range. The vapor flow field near the nozzle exit is featured by high velocity and high turbulence intensity. Two sets of vortices with different scales and directions are observed in the upper and lower parts of the chamber. Keywords Spray flash evaporation . Numerical simulation . Spray characteristics . Multiphase flow . Waste heat recovery
Nomenclature Roman symbols Ad Droplet surface area, m2 Ap Droplet cross-sectional area, m2 CD Drag coefficient cp Specific heat, kJ·kg−1·K−1 DAB Diffusion coefficient, m2·s−1 Dd Droplet diameter, m E Total energy, kJ ! F Force, N G Generation of turbulent kinetic energy, kg·m−1·s−3 g Gravity acceleration, N·kg−1 hfg Latent heat of vaporization, kJ·kg−1 ! Diffusion flux of species, kg·m−2·s−1 Jj k Turbulent kinetic energy, m2·s−2 m Mass, kg ˙ m Evaporation rate, kg·s−1 ˙md;0 Initial mass flow rate of the droplet injection, kg·s−1 * Naihua Wang [email protected] 1
Energy Research Institute, Qilu University of Technology (Shandong Academy of Sciences), Jinan 250014, Shandong, China
2
Institute of Thermal Science and Technology, Shandong University, Jinan 250061, Shandong, China
p pev rd Re S T t Tb Td td u Vd Y
Pressure, Pa Evaporation pressure, Pa Droplet radius, m Reynolds number Source terms Temperature, K Time, s Boiling temperature, K Droplet temperature, K Droplet temperature, °C Velocity, m·s−1 Droplet volume, m3 Mass fraction, %
Greek symbols αs Overall heat transfer coefficient, kJ·s−1·m−2·K−1 ΔT Degree of superheat, K ε Turbulent dissipation rate, m2·s−3 μ Dynamic viscosity, Pa·s μt Eddy viscosity, Pa·s ρ Density, kg·m−3 Subscripts d Droplet f Vapor 0 Initial
Heat Mass Transfer
1 Introduction Flash evaporation of liquid spray is frequently encountered in many industrial scenarios, such as cooling, desalination, ice production, energy-saving systems and fuel atomization [1–5]. It is a complex process involving multiphase flows and phase change. In the past few decades, many experimental studies have been conducted on various types of spray flash evaporat
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