07 convestav heat transfer during air-mist spray...
TRANSCRIPT
-
CCC ANNUAL REPORTUIUC, August 18, 2011
Heat Transfer During Air Mist Spray Cooling
*Alberto HernandezHumberto Castillejos
Air-Mist Spray Cooling
Humberto CastillejosAndres AcostaXiaoxu Zhou
* Brian G ThomasBrian G. Thomas
* University of Illinois at Urbana ChampaignUniversity of Illinois at Urbana-ChampaignCINVESTAV, Unidad Saltillo, Mexico
Project Objectives
Q tif h t t f t d i i i t• Quantify heat transfer rate during air-mist spray cooling:
• measure: size, velocity, flow rate, and impact densitymeasure: size, velocity, flow rate, and impact density distributions of water droplets from commercial nozzles spraying air-water mists
• interpret steady-state heat-transfer measurements with• interpret steady-state heat-transfer measurements with computational models
• develop empirical heat flux relation based on f d t l t d l t tfundamental water droplet parameters
_____________________________________________________________________________________________________________________________________________University of Illinois at Urbana-Champaign • Metals Processing Simulation Lab • BG Thomas 2
-
Steady Heat Transfer Measurement
• Induction heating is used to heat up platinum sample
• Power controller is used to maintain• Power controller is used to maintain sample temperature at a specific value
_____________________________________________________________________________________________________________________________________________University of Illinois at Urbana-Champaign • Metals Processing Simulation Lab • BG Thomas 3
Experiment Details
Side Vie TC Wire
Cylinder Plastic CoverSpray Nozzle
Side View
Ceramic BodyX
Top ViewY
Z Platinum Sample
Top ViewBox and SampleY
C
Copper Coil
Quartz Glass
TC Wires
• Plastic cover and quartz glass are used to keep spray water from ceramic body, only exposing front surface of platinum
_____________________________________________________________________________________________________________________________________________University of Illinois at Urbana-Champaign • Metals Processing Simulation Lab • BG Thomas 4
sample to the water
-
Typical Ts and Itot Measurements Water Flow Rate=4.6lpm, Air Flow Rate=104lpm,Nozzle Centered (June 26, 09)
Total current measurement approaches steady state at the end of the 8 min for each stage
25 s20 s
Sample temperature Ts=300 C
_____________________________________________________________________________________________________________________________________________University of Illinois at Urbana-Champaign • Metals Processing Simulation Lab • BG Thomas 5
Heat Source Distribution and Temperature Distributionand Temperature Distribution
Temperature distributionHeat Source distribution
670680690
, oC D
620630640650660670
Tem
pera
ture
C
Heat Generated, W Heat Out, W
Sample 264.49Spray 229.14
Coil 206.22
Window 14 96
_____________________________________________________________________________________________________________________________________________University of Illinois at Urbana-Champaign • Metals Processing Simulation Lab • BG Thomas 6
6200 0.5 1 1.5 2 2.5 3 3.5 4
T
Platinum Sample Radius, mm
Coil 186.19Window 14.96
Natural convection 0.44
Total 450.68 Total 450.76
-
Nozzle CenterSpray Heat Transfer Coefficientsp y
Y=0mm(Nozzle Centered)
24
26
K
WaterFlowRate=4.6lpm, Heating
WaterFlowRate=4.6lpm, Cooling
16
18
20
22
24
cien
t, kW
/m^2
K WaterFlowRate 4.6lpm, CoolingWaterFlowRate=3.5lpm, Heating
WaterFlowRate=3.5lpm, Cooling
WaterFlowRate=2.5lpm, Heating
WaterFlowRate=2.5lpm, Cooling
10
12
14
16
Tran
sfer
Coe
ffi
WaterFlowRate 2.5lpm, Cooling
2
4
6
8
Spra
y H
eat T
•Increasing water flow rate increases heat transfer coefficient.During heating HTC peaks around 150 200 C then decreases as sample surface increases
00 100 200 300 400 500 600 700 800 900 1000 1100 1200
Sample Surface Temperature, C
_____________________________________________________________________________________________________________________________________________University of Illinois at Urbana-Champaign • Metals Processing Simulation Lab • BG Thomas 7
•During heating, HTC peaks around 150~200 C, then decreases as sample surface increases•During cooling, HTC keeps increasing gradually.•Hysteresis is shown in heat transfer coefficient curves. HTC is independent of temp at temp >850 C
Nozzle Centered - Spray Heat Flux
( )
4.5
5.0Nucleate boiling
Transition boiling
Stable Film boiling
3.5
4.0
W/m
^2
g
2.0
2.5
3.0
y H
eat F
lux,
MW
WaterFlowRate=4.6lpm,HeatingWaterFlowRate=4.6lpm,CoolingWaterFlowRate=3.5lpm,HeatingWaterFlowRate=3.5lpm,CoolingWaterFlowRate=2.5lpm,HeatingWaterFlowRate=2.5lpm,CoolingTransient 2 02lpm
0 5
1.0
1.5Spra
y Transient_2.02lpmTransient_1.761lpmTransient_3.321lpmTransient_3.34lpm
•Increasing water flow rate increases spray heat flux
0.0
0.5
0 100 200 300 400 500 600 700 800 900 1000 1100 1200Sample SurfaceTemperature, C
_____________________________________________________________________________________________________________________________________________University of Illinois at Urbana-Champaign • Metals Processing Simulation Lab • BG Thomas 8
•Increasing water flow rate increases spray heat flux.•Heat transfer almost independent of temperature above ~850 oC•Hysteresis is observed below Leidenfrost temperature ~850 oC•Steady measurement gives higher heat flux than transient measurement
--Transient results by Sami Vapalahti, etc, Spray Heat Transfer Research at CINVESTAC,P26, CCC report, 2007
-
Mechanism of Hysteresis
sample
Steam LayersampleWater Layer
Spray DropletWater Layer
•Heating process: Fig. 1 Fig. 2
•spray droplet impinges on water layer, touches surface, boils, and takes heat away. (Fig. 1)•High heat removal keeps surface cold.
•Cooling process:•At high sample surface temperature (>~860oC), a stable steam layer forms on the sample surface. (Fig. 2)•This steam layer acts as a barrier to heat transfer and decreases heat removal
_____________________________________________________________________________________________________________________________________________University of Illinois at Urbana-Champaign • Metals Processing Simulation Lab • BG Thomas 9
•This steam layer acts as a barrier to heat transfer and decreases heat removal.•Low rate of heat removal sustains the air gap to low temperatures before droplets finally can penetrate through
•Result: difference in heat transfer at intermediate temperatures according to history (heating or cooling)
Nozzle Water Flow Rate=4.6lpm--Spray Heat Transfer Coefficientsp y
2426
W/m
2 K
WaterFlowRate=4.6lpm
Y=0mm,HeatingY=0mm Cooling
25
30000
35000100 C300 C500 C700 C
1416182022
Coe
ffici
ent,
kW
Y=0mm,CoolingY=9mm,HeatingY=9mm,CoolingY=18mm,HeatingY=18mm,Cooling
15
20
20000
25000
30000, l/m2 s
700 C900 C1100 CWater Flux Rate
468
101214
Hea
t Tra
nsfe
r C
10
10000
15000
20000
r Flux Rate
HTC,W/m2 K
024
0 100 200 300 400 500 600 700 800 900 1000 1100 1200
Spr
ay
Sample Surface Temperature, C0
5
0
5000
10000
Wate
•Hysteresis exists for different location from spray centerline.•Moving further away from spray centerline decreases HTC.
00
0 3 6 9 12 15 18Y Direction,mm
_____________________________________________________________________________________________________________________________________________University of Illinois at Urbana-Champaign • Metals Processing Simulation Lab • BG Thomas 10
•Difficult to correlate water flow rate footprint measurements with HTC. •More details of spray dynamics needed (droplet distribution, size, velocity, etc, --collaboration work at CINVESTAV, Mexico)
-
Heat Transfer in Film-Boiling Regime
Stable
No hysteresis
Almost independent of surface temperature
_____________________________________________________________________________________________________________________________________________University of Illinois at Urbana-Champaign • Metals Processing Simulation Lab • BG Thomas 11
Flow-rate and Pressure of air and water are related in a nozzle
Operating Diagram(Delavan W19822 nozzle)
Water Flow Rate (L/s)
_____________________________________________________________________________________________________________________________________________University of Illinois at Urbana-Champaign • Metals Processing Simulation Lab • BG Thomas 12
(Delavan W19822 nozzle)
-
Droplet Parameter Measurements
For a given nozzle, water flow rate and air pressureflow rate, and air pressure,Measure distributions of droplet:droplet:• Size• VelocityVelocity• Weber number
_____________________________________________________________________________________________________________________________________________University of Illinois at Urbana-Champaign • Metals Processing Simulation Lab • BG Thomas 13
Measure water flux and impact density mapsp y p
For a given: - nozzle, - water flow rate, and- air pressure
_____________________________________________________________________________________________________________________________________________University of Illinois at Urbana-Champaign • Metals Processing Simulation Lab • BG Thomas 14
-
Title
_____________________________________________________________________________________________________________________________________________University of Illinois at Urbana-Champaign • Metals Processing Simulation Lab • BG Thomas 15
New Correlations
Heat Flux (W/m2)0.319 0.317 0.144 0.036
300.307 z wq w u T d−− =
0 318 0 330 0 895 0 024
Heat Transfer Coefficient (W/m2K)0.318 0.330 0.895 0.024
30379.93 z wh w u T d− −=
2w = local water flux density (L/m2s)uz = volume-weighted mean droplet velocity (m/s)Tw = surface temperature (K)
_____________________________________________________________________________________________________________________________________________University of Illinois at Urbana-Champaign • Metals Processing Simulation Lab • BG Thomas 16
w p ( )d30 = volume-mean droplet diameter (mm)
-
Agreement of fit: 96% of h measurements fall within +/-25% of predictionp
_____________________________________________________________________________________________________________________________________________University of Illinois at Urbana-Champaign • Metals Processing Simulation Lab • BG Thomas 17
Conclusions
• Spray heat transfer coefficient and heat flux show hysteresis likely related to formation of vapor layer on sample surface.
• Heat transfer in stable film boiling regime above ~650 oC experiences no hysteresis, (above Leidenfrost temperature)
• New correlation to predict air-water spray mist heat transfer has been developed based on fundamental droplet parameters: flux density, size, velocity, & surface temperatureparameters: flux density, size, velocity, & surface temperature
• New correlation fits measurements for 3 different nozzle types and many different water-flow and air-pressure
diticonditions
• New correlation shows heat transfer depends mainly on water flux density with velocity also important but is
_____________________________________________________________________________________________________________________________________________University of Illinois at Urbana-Champaign • Metals Processing Simulation Lab • BG Thomas 18
water flux density, with velocity also important, but is almost independent of surface temperature & droplet size.
-
References (for further details)
• C.A. Hernández, J.I. Minchaca, A.H. Castillejos, F.A. Acosta, X. Zhou, and B.G. Thomas, “Measurement of Heat Flux in Dense Air-Mist Cooling: Part gI. A Novel Steady-State Technique”, CCC Report 201101, Aug. 18, 2011.
• C.A. Hernández, J.I. Minchaca, A.H. Castillejos, F.A. Acosta, X. Zhou, and B.G. Thomas, “Measurement of Heat Flux in Dense Air-Mist Cooling: Part II. The Influence of Mist Characteristics on Heat Transfer”, CCC Report 201102, Aug. 18, 2011.
• X. Zhou, Heat Transfer During Spray Water Cooling Using Steady Experiments, MS Thesis, University of Illinois, 2009.
_____________________________________________________________________________________________________________________________________________University of Illinois at Urbana-Champaign • Metals Processing Simulation Lab • BG Thomas 19
Acknowledgementsg• Continuous Casting Consortium Members
(ABB A l Mitt l B t l T t St l(ABB, Arcelor-Mittal, Baosteel, Tata Steel, Magnesita Refractories, Nucor Steel, Nippon Steel, Postech Posco SSAB ANSYS-Fluent)Postech, Posco, SSAB, ANSYS Fluent)
• National Science FoundationNational Science Foundation– GOALI DMI 05-00453
_____________________________________________________________________________________________________________________________________________University of Illinois at Urbana-Champaign • Metals Processing Simulation Lab • BG Thomas 20