# Presentation: 547823

## Experimental Results for Thin and Thick Liquid WallsM. Yoda and S. I. Abdel-Khalik

**G. W. Woodruff School of **
**Mechanical Engineering**
**Atlanta, GA  30332-0405**

***Experimental Results for Thin and Thick Liquid Walls*****M. Yoda and S. I. Abdel-Khalik**

## Overview

- Thin liquid protection:  Experimental study of high-speed thin liquid films on downward-facing surfaces around cylindrical dams [*J. Anderson, D. Sadowski*]
- Ports for beam entry and target injection
- Effect of surface wettability
- Thick liquid protection:  Experimental studies of turbulent liquid sheets [*S. Durbin, J. Reperant, D. Sadowski*]
- Quantify surface smoothness of stationary liquid sheets using planar laser-induced fluorescence (PLIF) technique
- Impact of initial conditions:  nozzle geometry, flow straightener design, flow straightener blockage

## Thin Liquid Protection

**IFE chamber**
**(Prometheus)**

**First Wall **

**Injection Point**

**Detachment**
**Distance *****x*****d**** **

**Liquid Film/Sheet**

**X-rays **
**and Ions**

***Thin Liquid Protection***

## Objectives

- 17 GPM
- 10.7 m/s
- 10o inclination
- Re = 20000

- 2 mm nozzle
- 17 GPM
- 10.7 m/s
- 10o inclination
- Re = 20000

***Objectives***

- Determine “design windows” for high-speed liquid films proposed for thin liquid protection of IFE reactor chamber first wall
- In the absence of film dryout, films most likely to detach on downward-facing surfaces on top endcap
- Chamber curvature probably negligible:  chamber radius ~6.5 m, *vs.* film radius of curvature at detachment point *O*(1 cm)
- How does film flow around cylindrical obstructions, or dams (*e.g.* beam ports)?

## Experimental Apparatus

**A****	****Glass plate **
**	****(1.52  ******** 0.40 m) **
**B****	****Liquid film**
**C****	****Flow straightener**
**D****	****Film nozzle**

**A**

**B**

**C**

**D**

- Adjustable
- angle 

*x*

*z*

*g*cos 

*g*

***Experimental Apparatus***

## Cylindrical Obstructions

***Cylindrical Obstructions***

- Cylindrical dam/obstruction at *x* = 7.6–9 cm from nozzle exit
- Held in place by permanent rare-earth magnet above glass plate
- Vary cylindrical dam height *H* and diameter *D*
- Height (axial dimension) *H* ~ 

- How does high-speed film flow around obstructions (*e.g.* beam ports)?

## Experimental Parameters

- Nozzle exit thickness (*z*-dimension)  = 0.1, 0.15, 0.2 cm
- Average speed at nozzle exit *U*0 = 1.9–5.1 m/s
- Jet injection angle  = 0°, 30°
- Cylindrical dam outer diameter *D* = 1.58, 2.54 cm
- Cylindrical dam height *H* = 0.051, 0.12, 0.24 cm
- Reynolds number *Re* = *U*0 / = 3800–9800
- Froude number *Fr* = *U*0 /* *[(*g** *cos )* *]1⁄2 = 15–55
- Weber number *We* = *U*02 / = 100–700
- Cylindrical dam aspect ratio *AR* = *H*/*D* = 0.02–0.093
- Film nozzle aspect ratio *AR*f = (5 cm)/ = 25–50

## Results

**Detachment Type I**
-  = 0.15 cm
*Re* = 7600
*H* = 0.24 cm
*D* = 2.54 cm
*AR* = 0.093

**Dam**

**Detachment Type II**
-  = 0.15 cm
*Re* = 3800
*H* = 0.24 cm
*D* = 2.54 cm
*AR* = 0.093

**Dam**

## Detachment Type I:  H > 

*Re* = 3800
*H* = 0.12 cm
*D* = 2.54 cm

***Detachment Type I:  H***** > ******

*AR* = 0.047

****** ****= 0******

****** ****= 30******

## Detachment Type II:  H > 

-  = 0.2 cm
*Re* = 3800
*H* = 0.24 cm
*D* = 1.59 cm
*AR* = 0.15

***Detachment Type II:  H***** > ******

****** ****= 0******

****** ****= 30******

## Flow Over Dam:  H < 

-  = 0.1 cm
*Re* = 3800
*H* = 0.051 cm < 
*D* = 2.54 cm
*AR* = 0.02

***Flow Over Dam:  H***** < ******

****** ****= 0******

****** ****= 30******

**Flow Over Dam**

## Summary:  Obstructions

***H***** < ******: Flows over obstruction, blocking hole
- Occurs at lowest speeds (and *Re*)
- Cylindrical beam ports incompatible with wet wall concept
- “Streamlined” fairings?
- No beam ports on upper endcap  fewer beams?

***Summary:  Obstructions***

- For all cases studied, film flow on downward-facing surfaces either:

## Surface Wettability

- Water on glass:  contact angle  30°
- Water on glass coated with Rain-X®:  contact angle  85°

***Surface Wettability***

**Water on glass w/Rain-X**
**(drop dia. ~4 mm;**
**vol. 0.4 mL)**

**Water on glass**
**(drop diameter ~5 mm; **
**volume 0.4 mL)**

## Wettability Effects

***x*** **/** ****** **

***W*** **/*****W*****o**

- At *Re* = 3800, xd /   **100** for Rain-X surface; **180** for glass
- At *Re* = 14700, xd /   **550** for Rain-X surface; **700** for glass

- 	**Glass, *****Re***** = 3800**
-  	**Rain-X, *****Re *****= 3800**
- 	**Glass, *****Re***** = 14700**
- 	 **Rain-X, *****Re *****= 14700**

-  = 0.2 cm
-  = 0

***Preliminary data***

**Non-wetting surface ******** Earlier detachment**

## Future Work

- Examine effect of surface wettability/contact angle
- Non-wetting surfaces (a la Prometheus) **worse**:  earlier detachment, smaller lateral spread
- Measure film thickness with ultrasonic probes
- Measure lateral (*y*) velocity profile across film using laser-Doppler velocimetry (LDV)

***Future Work***

***Sketch courtesy L. Waganer***

## Thick Liquid Protection

- Protect IFE reactor chamber first walls by using molten salt or liquid metal “curtain” to absorb neutrons, X-rays, ions and target debris from fusion events

- HYLIFE-II conceptual design based on turbulent liquid sheets as “building block”
- Oscillating slab jets, or liquid sheets, create protective pocket to shield chamber sides
- Lattice of stationary liquid sheets shield front and back of chamber while allowing beam propagation, target injection

***Sketches courtesy P.F. Peterson***

***Thick Liquid Protection***

## Design Issues

- Irradiation of final focus magnets
- Interferes with target injection, beam propagation
- How do various jet (nozzle, flow straightener) designs impact the free-surface geometry and its fluctuations?
***Robust***** protection**  thick liquid protection system must withstand occasional disturbances
- How does partial blockage of the flow straightener (due, for example, to debris) affect the free-surface geometry and hence surface ripple?

***Design Issues***

## Objectives

- Liquid probability distribution (LPD): probability of finding liquid at any given spatial location
- Mean surface ripple *z*:  Average standard deviation of the *z*-position of the free surface
- Study turbulent vertical sheets of water issuing downwards into atmospheric pressure air at Reynolds numbers *Re* = *U*o/ = 53,000–130,000  (prototypical *Re* = 200,000)
- 	*U*o average speed at nozzle exit;  nozzle thickness (short dimension);  fluid kinematic viscosity

- Quantify impact of nozzle designs and blockage on surface ripple in liquid sheets typical of HYLIFE-II

## Experimental Apparatus

- C		Flow meter	D	Pitot tube
**E****	****	****Flow straightener**
**F****	****	****Nozzle**	G	Oscillator
**H****	****Sheet**		I	400 gal tank
- J Butterfly valve	K	350 gal tank

- Pump-driven recirculating flow loop
- Test section height ~1 m
- Overall height ~5.5 m

***Experimental Apparatus***

## Nozzle Geometries

**A**

**B**

**C**

***x***

*** ******y***

***z***

- Fabricated with stereolithography rapid prototyping
- Nozzle exit dimensions 1 cm ()  10 cm
- 2D contractions:  nozzle *z*-dimension contracts from 3 cm to 1 cm at exit
- Three different nozzles
**A** Matched circular-arc contraction

**B**** **5th order polynomial contraction
**C** B with rounded corners

***Nozzle Geometries***

## PLIF Technique

- Water dyed with fluorescein
-  Jet illuminated by Ar+ laser light sheet at 514 nm
-  Free surface imaged obliquely from below by CCD camera
- 100 (1008  1008 pixel) consecutive images acquired at 30 Hz over 3.3 s for *x*  25 cm
- Image exposure 5 = 4.3–11.2 ms, where  = /*U*o

- Visualize free surface as interface between fluorescing (white) water and (black) air

***x***

***y***

**10 cm**

***z***

***PLIF Technique***

## Liquid Prob. Distribution

- Grayscale > threshold  liquid; < threshold  air
- Average over 100 images  LPD; assemble composite LPD over half the flow by overlapping side, edge sections
- Probability of finding liquid inside 50% contour  50%
- Distance between contours measure of surface ripple

**LPD ****(part of side **
**view)**

**LPD ****(edge view)**

***Liquid Prob. Distribution***

## Nozzle Geometry Effects

**5****	****25****	****50****	****75****	****95****% LPD Contours**

**A**

**B**

- LPDs for nozzles A, B, C:  *Re* = 130,000; *x* = 25 cm

**C**

- Surface ripple similar for all 3 nozzles
- Surface ripple greatest at edge
- C has largest surface ripple
- B “best” nozzle

**1 cm**

***Nozzle Geometry Effects***

## Reynolds Number Effects

- Re = 22,000

- Side and edge fluctuations increase with *Re*

- LPDs for Nozzle B:  *x* = 25 cm

**5****  ****25****  ****50****	****  ****75****	****  ****95****% LPD Contours**

***Re***** = 53,000**

***Re***** = 97,000**

***Re***** = 130,000**

**1 cm**

***Reynolds Number Effects***

## Mean Standard Deviation

**D**

- Edge, side fluctuations increase with *x*
- *z* = 0.10 mm at *x* = 10 cm from nozzle exit
- *z* = 0.19 mm at *x* = 25 cm [scaled HYLIFE-II pocket:  *x*  30 cm]
******* ******Max. surface ripple for HYLIFE-II 1.4 mm***

- LPDs for Nozzle B:
*Re* = 130,000

***Mean Standard Deviation***

**5****	****25****	****50****	****75****	****95****% LPD Contours**

## Flow Straightener

**Perforated Plate (PP)**
- Open area ratio 50% with staggered 4.8 mm dia. holes
**Honeycomb (HC)**
- 3.2 mm dia. hexagonal cells
**Fine Screen (FS)**
- Open area ratio 37.1%
- 0.33 mm dia. wires woven with open cell width of 0.51 mm
- 195 mm from FS to nozzle exit
- All elements stainless steel

***x***

***y***

***z***

**PP**

**HC**

**FS**

***Flow Straightener***

## Flow Straightener Blockage

- Flow straightener blocked just upstream of fine mesh screen (element most likely to trap debris)
- “Blockage” = 1.5 cm  0.5 cm rectangle (blockage area = 2.5% of total screen area)

- Studied blockage at two different locations
- Centered along *y*, *z *[“center blockage”]
- On right edge centered along *z *[“edge blockage”]

***Flow Straightener Blockage***

## Blockage Effects

**G**

- 2.5% area blockage 19.5 cm upstream of  nozzle

***y***

***z***

**No Blockage**

**Edge Blockage**

**No blockage**

**Center blockage**

**5**
**25**
**50**
**75**
**95****%**

- LPDs for Nozzle B:  *Re* = 97,000; *x *= 25 cm

***Blockage Effects***

## Summary:  Thick Liq. Prot.

- Results at 2/3 the prototypical *Re* imply:
- Standard deviation of side free-surface geometry ~1.4 mm at bottom of lattice typical of HYLIFE-II
- At higher *Re* and *x*, free surface ripple on sheet side AND edge can “clip” driver beams
- Surface ripple appears relatively insensitive to small changes in nozzle geometry (circular-arc, *vs.* 5th order polynomial, contraction)
- Rounding nozzle corners ( elliptical nozzle) does _not_ reduce surface ripple
- Blockage of flow straightener (due to debris, for example) will drastically increase surface ripple  filtration required

***Summary:  Thick Liq. Prot.***

## What remains to be done?

**All concepts:**
***Chamber clearing***
***Droplet formation/ejection***
**High-speed film/Wet wall:**
***Beam port designs compatible with film flow*** [GT]
***Surface wettability*** [GT]
- Surface curvature [GT]
**Porous wall/Wetted wall:**
***How does heat transfer affect film stability?***
**Thick liquid protection:**
***Vacuum effects (We) on sheet breakup***
- Oscillating sheets at high *Re*

***What remains to be done?***