Numerical study of flow boiling flow patterns and pressure drop of R134a in small tubes under high flight acceleration
- PDF / 3,702,457 Bytes
- 10 Pages / 595.276 x 790.866 pts Page_size
- 47 Downloads / 200 Views
(2020) 42:482
TECHNICAL PAPER
Numerical study of flow boiling flow patterns and pressure drop of R134a in small tubes under high flight acceleration Yu Xu1 · Zihang Zhu1 · Xinyue Xiong1 Received: 27 November 2018 / Accepted: 7 August 2020 © The Brazilian Society of Mechanical Sciences and Engineering 2020
Abstract A series of numerical simulations of R134a flow boiling in two small tubes with inner diameters of 1 and 2.17 mm under high flight acceleration were conducted based on the VOF model. Six acceleration levels from 1 to 15 g and three directions from 0° to 180° were investigated. At first, the simulated frictional pressure drops under low flight acceleration are compared with previous experimental findings, and the comparison results show a consistent trend. Then, the simulated flow patterns and pressure drops under high flight acceleration with different levels and directions are intercompared, and the influences of high flight acceleration are obtained. The intercomparison results reveal that the flow patterns and pressure drops are influenced by high flight acceleration dramatically. The total and frictional pressure drops decrease with the increasing flight acceleration at θ = 0°, decrease slightly at θ = 90°, and increase at θ = 180°, monotonically, because of the variation of flow patterns. The vapor phases gradually turn into quasi-ellipsoids/spheres, quasi-stratified state, and elongated slugs at θ = 0°, 90°, and 180°, respectively, as the flight acceleration increases. Keywords Flight acceleration · Flow boiling · Flow patterns · Pressure drop · VOF List of symbols A Area (m2) ah Flight acceleration (m/s2) D Inner diameter (m) E Energy (J/kg) Fvol Body force (N/m3) G Mass flux (kg/m2 s) g Gravitational acceleration (m/s2) hlv Latent heat of vaporization (J/kg) L Channel length (m) n̂ Unit normal n Surface normal p Pressure (Pa) Q Heat source term (W/m3) q Heat flux (W/m2) r Frequency (1/s) S Mass source term (kg/m3 s) T Temperature (K)
t Time (s) v Velocity vector (m/s) x Vapor quality Greek symbols α Volume fraction θ Angle between flow and acceleration directions (°) κ Surface curvature λ Thermal conductivity (W/m K) μ Viscosity (Pa s) ρ Density (kg/m3) σ Surface tension coefficient Subscripts in Inlet l Liquid out Outlet sat Saturation sub Subcooling v Vapor
Technical Editor: Jose A. R. Parise. * Yu Xu [email protected] 1
Key Laboratory of Aircraft Environment Control and Life Support, MIIT, Nanjing University of Aeronautics and Astronautics, 29 Yudao Street, Nanjing 210016, China
1 Introduction Since the thermal loads of avionics on advanced aircrafts increase rapidly, the onboard vapor cycle system (VCS) having higher coefficient of performance is urgently needed.
13
Vol.:(0123456789)
482
Page 2 of 10
Journal of the Brazilian Society of Mechanical Sciences and Engineering
Given that the volume and weight of onboard devices should be small and light, the evaporators composed of small tubes attract wide attention. Furthermore, some aircra
Data Loading...
