Preliminary Spray Cooling Simulations Using a Full-Cone Water Spray

Transcription

1 39th Dayton-Cincinnati Aerospace Sciences Symposium Preliminary Spray Cooling Simulations Using a Full-Cone Water Spray Murat Dinc Prof. Donald D. Gray (advisor), Prof. John M. Kuhlman, Nicholas L. Hillen, Krishna Teja Medam, J. Stephen Taylor March, 2014

2 Outline Computational Model for Spray-Wall Film Interactions and Spray Cooling The Discrete Phase Model (DPM) The Eulerian Wall Film (EWF) Model Preliminary 3D Spray Cooling Simulations Improved 3D Spray Cooling Simulations Ongoing/Future Work 2

3 Computational Model For Spray-Wall Film Interactions and Spray Cooling The Discrete Phase Model (DPM) (ANSYS FLUENT v 14.5) The Eulerian Wall Film (EWF) Model (ANSYS FLUENT v 14.5) 3/19/2014 3

4 The Discrete Phase Model (DPM) The Discrete Phase Model (DPM) is a Lagrangian-Eulerian based modeling method and it has been used by many authors for spray simulations. The DPM includes two different phases: the continuum and the discrete phases. The continuum phase is the gas phase (e.g. air) and it has a high volume fraction compared to the discrete phase. The discrete phase contains a number of particles (e.g. spray drops). The continuum phase Navier-Stokes and continuity equations are solved in 3D rectangular coordinates using the Finite Volume Method for unsteady, incompressible, turbulent flow (the k-ε model). 4

5 The Eulerian Wall Film (EWF) Model The EWF model is based on the Eulerian approach. One single 2D equation is solved for the film (film flow in the vertical direction to the surface is neglected). The EWF model assumes that film always flows parallel to the surface. Film mass, momentum and heat transfer are solved. Impinging particle (DPM drops) mass and momentum is added as a source term in the film equation. The film is assumed to have: 1) A parabolic velocity profile, 2) A bilinear temperature profile across its depth Film Surface T s Liquid Film V T f h Wall Surface T w Film Velocity and Temperature 5

6 Preliminary 3D Spray Cooling Simulations 3/19/2014 6

7 3D 30 DPM-EWF Model: Domain and Boundary Conditions Boundary Conditions and Computational Domain: 30⁰ Sector Domain 7

8 3D 30 DPM-EWF Model: Mesh and Spray Mesh (Computational Cells) Mesh Size: 0.5 mm (Triangular Prism) Number of Cells: 119,400 Number of Faces: 304,870 Surface Mesh Spray Nozzle: Full Cone Cone Half Angle: 28 Spray: Water (T boiling = 373 K) T drop = 300 K T air = 300K Constant Surface Temperature B.C.: T wall = 393 K Initial Film Thickness = 1 micron, Initial Film Temperature = 372 K 8

9 Drops Velocity Magnitude Time (ms) Constant Surface Temperature = 393 K ms Spray Injection Red: m/s Blue: m/s Drops Re#: Drops We#: ~ ms Drops Velocity Magnitude (Side view) Spray Injection Drops Velocity Magnitude (Top view) 9

10 Results at ms Time (ms) Constant Surface Temperature = 393 K Liquid Film Velocity Magnitude Time (ms) Constant Surface Temperature = 393 K Liquid Film Temperature Red: m/s Blue: m/s Red: K Blue: K ms Contours of Liquid Film Velocity Magnitude (Top view) Liquid Film Thickness ms Contours of Liquid Film Temperature (Top view) Surface Heat Flux Red: μm Blue: μm Red: MW/m 2 Blue: MW/m 2 Contours of Liquid Film Height (Top view) Contours of Surface Heat Flux (Top view) 10

11 Results at ms Time (ms) Constant Surface Temperature = 393 K Time (ms) Constant Surface Temperature = 393 K Liquid Film Velocity Magnitude Liquid Film Temperature Red: m/s Blue: m/s Red: K Blue: K ms Contours of Liquid Film Velocity Magnitude (Top view) Liquid Film Thickness ms Contours of Liquid Film Temperature (Top view) Surface Heat Flux Red: μm Blue: μm Red: MW/m 2 Blue: MW/m 2 Contours of Liquid Film Height (Top view) Contours of Surface Heat Flux (Top view) 11

12 Film Thickness (micron) Liquid Film Thickness and Temperature Film Temperature (K) Symmetry surface R Symmetry surface ms ms 4.75 ms ms ms ms ms ms ms ms ms ms ms ms Radius (mm) Radius (mm) 12

13 Liquid Film Thickness: Exp. vs CFD Film Thickness (µm) Film Thickness (micron) CFD ms 4.75 ms ms ms ms ms ms 50 Experiment Radius (mm) Radius (inches) 13

14 Improved 3D Spray Cooling Simulations 3/19/

15 To Obtain Improved 3D Spray Cooling Simulations 1) Computational Cell Shape and Size Different domain angle (30, 45, 90 ) for 3D model were compared. Different computational cell shape (non-uniform quad, non-uniform tri, uniform quad elements) were also analyzed. 2) Computational Domain Height (H = 30 mm, 19 mm, 16 mm, 14 mm, 10 mm, 4.2 mm, 2 mm) 3) Computational Cell Size at Spray-Wall Impact Region (DPM-EWF model interactions) 4) The Species Transport Model to include Vapor Phase (bubble formation) in the liquid film 3/19/

16 Computational Cell Shape and Size Mesh (Triangular Prism) Larger mesh elements Surface Mesh Non-uniform Triangular Prism Elements Mesh: 0.5 mm (Triangular Prism) Number of Cells: 97,740 Number of Faces: 249,909 3/19/ Smaller mesh elements compared to other elements

17 Surface Mesh Full Quad Mesh: 45 and 90 Domain 45 Domain 90 Domain : Spray Center Pressure Outlet BC Symmetry BC Wall BC Pressure Outlet BC Symmetry BC Wall BC Pressure Outlet BC Symmetry BC Symmetry BC Mesh: 0.5 mm (uniform quad except the upper edge symmetry BC) R = 26 mm Number of Cells: 82,684 Mesh: 0.5 mm (uniform quad) R = 26 mm Number of Cells: 162,240 Number of Faces: 252,520 Number of Faces: 495,664 17

18 51.75 ms Time (ms) Full Quad Mesh: 45 and 90 Domain Constant Surface Temperature = 393 K 45 Domain 90 Domain Liquid Film Temperature Time (ms) Constant Surface Temperature = 393 K Liquid Film Temperature Red: K Blue: K Red: K Blue: K ms Contours of Liquid Film Temperature (Top view) Surface Heat Flux ms Contours of Liquid Film Temperature (Top view) Surface Heat Flux Max: 1.67 MW/m 2 Red: MW/m 2 Blue: MW/m 2 Contours of Surface Heat Flux (Top view) Red: MW/m 2 Blue: MW/m 2 Contours of Surface Heat Flux (Top view) 18

19 Computational Domain Height 90 domain with full quad cells was chosen based on the comparisons of different domain angle and computational cell types. However, it is computationally expensive. Need to decrease the domain height. The most effective domain height was obtained based on parametric analysis (H = 30 mm, 19 mm, 16 mm, 14 mm, 10 mm, 4.2 mm, 2 mm). The most effective domain height was found to be 14 mm (more than 50% decrease on the total number of computational cells (the base model had 30 mm height). 3/19/

20 Ongoing/Future Work Computational Cell Size at Spray-Wall Impact Region (DPM-EWF model interactions): the most effective mesh size for the EWF liquid film calculations (improvement of the near wall mesh) and validation of the results with the experiments. The Species Transport Model: to include Vapor Phase (bubble formation) in the liquid film and wall-boiling correlations. Analyze some of the basic parameters computationally: to derive correlations for the Monte-Carlo Spray Cooling Model.

21 Acknowledgments The financial support of this work under NASA Cooperative agreement NNX10ANY0YA Helpful discussions with Dr. Eric Silk, NASA GSFC, Greenbelt, MD Helpful discussions with Dr. Kirk Yerkes, AFRL, Wright- Patterson AFB, OH 3/19/

22 Thank You QUESTIONS OR SUGGESTIONS 3/19/

23 The Discrete Phase Model (DPM) The dispersed phase can exchange momentum, mass, and energy with the fluid phase. The droplet trajectories are computed individually at specified intervals during the fluid phase calculation The trajectory of discrete phase particles (droplet) are predicted by integrating the force balance equation on the particle in a Lagrangian reference frame. This force balance equates the particle inertia with the forces acting on the particle. Particle Motion: m p du p dt = 1 2 C dρ a (u a u p ) 2 A + mg 23

24 The Eulerian Wall Film (EWF) Model Conservation of Mass: Conservation of Momentum: Conservation of Energy: 24

25 Preliminary 3D Spray Cooling Simulations Constant Surface Heat Flux Boundary Condition q wall = 10,000 W/m 2 3/19/

26 11.75 ms Time (ms) Constant Surface Flux: 10,000 W/m 2 Constant Surface Heat Flux=10000 W/m 2 Liquid Film Velocity Magnitude Time (ms) Constant Surface Heat Flux=10000 W/m 2 Liquid Film Temperature Red: m/s Blue: m/s Red: K Blue: K ms Contours of Liquid Film Velocity Magnitude (Top view) Liquid Film Thickness ms Contours of Liquid Film Temperature (Top view) Surface Temperature Red: μm Blue: μm Red: K Blue: K Contours of Liquid Film Height (Top view) Contours of Surface Temperature (Top view) 26

27 51.75 ms Time (ms) Constant Surface Flux: 10,000 W/m 2 Constant Surface Heat Flux=10000 W/m 2 Liquid Film Velocity Magnitude Time (ms) Constant Surface Heat Flux=10000 W/m 2 Liquid Film Temperature Red: m/s Blue: m/s Red: K Blue: K ms Contours of Liquid Film Velocity Magnitude (Top view) Liquid Film Thickness ms Contours of Liquid Film Temperature (Top view) Surface Temperature Red: μm Blue: 0 12 μm Red: K Blue: K Contours of Liquid Film Height (Top view) Contours of Surface Temperature (Top view) 27

28 Liquid Film Thickness (micron) Liquid Film Thickness (micron) Liquid Film Thickness (micron) Liquid Film Thickness (micron) Constant Surface Flux: 10,000 W/m 2 Liquid Film Thickness at Symmetry Surface 1.75 ms ms t=1.75 ms 60 t=20.75 ms R (mm) R (mm) ms ms t=4.75 ms 100 t=50.75 ms R (mm) R (mm) 28

29 Liquid Film Temperature (K) Liquid Film Temperature (K) Liquid Film Temperature (K) Liquid Film Temperature (K) Constant Surface Flux: 10,000 W/m 2 Average Liquid Film Temperature at Symmetry Surface ms ms t=1.75 ms t=20.75 ms R (mm) R (mm) ms ms t=4.75 ms t=50.75 ms R (mm) R (mm) 29

30 Contours of Surface Heat Flux (Top view) Contours of Surface Heat Flux (Top view) Time (ms) Liquid Film Temp. and Wall Heat Flux ms QUAD Mesh TRI Mesh Constant Surface Temperature = 393 K Liquid Film Temperature Time (ms) Constant Surface Temperature = 393 K Liquid Film Temperature Red: K Blue: K Red: K Blue: K ms Contours of Liquid Film Temperature (Top view) Surface Heat Flux ms Contours of Liquid Film Temperature (Top view) Surface Heat Flux Red: MW/m 2 Blue: MW/m 2 Red: MW/m 2 Blue: MW/m 2 30

31 51.75 ms Time (ms) Full Quad Mesh: 45 and 90 Domain Constant Surface Temperature = 393 K Liquid Film Velocity Magnitude 45 Domain Time Constant Surface Temperature = 393 K 90 Domain (ms) Liquid Film Velocity Mag. Red: m/s Blue: m/s Red: m/s Blue: m/s ms Contours of Liquid Film Velocity Magnitude (Top view) Liquid Film Thickness ms Contours of Liquid Film Velocity Magnitude (Top view) Liquid Film Thickness Red: μm Blue: μm Contours of Liquid Film Height (Top view) Red: μm Blue: μm Contours of Liquid Film Height (Top view) 31