pool and convective boiling heat transfer control/design laboratory department of mechanical...
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Pool and Convective BoilingPool and Convective Boiling
Heat Transfer Control/Design Laboratory
Department of Mechanical Engineering
Yonsei University
Introduction
h (W/m2K) 5~25
Naturalconvection
Forcedconvection
10~15,000
Pool boiling(liquid)
2,500~35,000
h (W/m2K) 5,000~100,000
Impinging jetboiling
Heat transferenhancement
Impinging jet
Convective boiling (liquid)Convective boiling (liquid)
Introduction – Applications
Slab/Billet Casting Hot rolling of Steel
…X-ray medical equipment, laser weapons and textile dryers
Medical Instruments
Gas Turbines
Hydrodynamics of jet impingement
Circular, submerged jet
Wall jet region
x or r
V
dNozzle
Stagnation region
Hv=VPotential
core length
y
Impingement surface (target surface)
Boundary layer Free jet region
Liquid
Liquid
Heat transfer regimes
Wall Superheat, log ΔTsat
Wal
l Hea
t F
lux,
log
q
Single-phase
convection
Nucleate boiling
Transition boiling
Film boiling
Critical heat flux
Minimum heat flux
Fully developed nucleate boiling
Partial boiling
Boilingincipience
(G)
(C)(B
) (A’)(A)
(E)
(D)
(F)
Pool boiling(1)
Microporous Coating – pool boiling enhancement
bare coated bare coated
Nucleate boiling Near CHF
S. M. You (U. of Texas, Arlington)
Pool boiling(2)
Microporous Coating – pool boiling enhancement
S. M. You (U. of Texas, Arlington)
SEM Image of Surface
Micro-Structure of DOM Coating
(side view )
Experimental Setup
Main Reservoir
Line drain & Vacuum port
Secondary Reservoir
Test
Section
Relief valve
Filter or Filter/dryer
Data Acquisition system
Flow meters
Constant temp. bath
Power supply & controller
Cooling water
Cooling water
Cooling water
Immersion Heater
Immersion Heater
Flow control valve
Heat exchanger
Drain
Vacuum port
Magnetic pump
Pressure gage
Pressure gageThermo-
couples
Pressure transducers
Temp. control relays
Filling line
TC1
TC3 TC2
Filling line
Test Section (Thin-Plate Heater Module)
Heated Surface
- Inconel alloy 600
- 0.467 mm thick
Heated Surface
- Inconel alloy 600
- 0.467 mm thick
Hydraulic Characteristics
Unconfined single circular jets for H/d=9
V=1.7 m/s
V=5.0 m/s
V=10.0 m/s
V=15.6 m/s
Unconfined array circular jets for H/d=9
V=1.8 m/s
V=2.5 m/s
V=3.3 m/s
Confined Free-Surface Planar jet
Convection coefficient distributions at H/w=4, V=1.7 m/s and z/w=0.0.
Convection coefficient distributions at H/w=4, V=1.7 m/s and z/w=0.0.
Velocity effects on normalized single-phase Convection coefficient distributions
at H/w=4, and z/w=0.0.
Velocity effects on normalized single-phase Convection coefficient distributions
at H/w=4, and z/w=0.0.
Free-Surface Planar jets: Confined vs. Unconfined
Confinement effects on temperature distributions at H/w=4 and V=1.7 m/s
Confinement effects on temperature distributions at H/w=4 and V=1.7 m/s
Confinement effects on convection coefficient distributions at H/w=4 and V=1.7 m/s.
Confinement effects on convection coefficient distributions at H/w=4 and V=1.7 m/s.
Confined Free-Surface Planar jets: Boiling Curves
h vs. Tf h vs.q
Convection coefficient increase at H/w=4, V=1.7 m/s and z/w=0.0.
q vs. Tsat (=Tw-Tsat) q vs. Tf (=Tw-Tf)
Boiling curves at H/w=4, V=1.7 m/s and z/w=0.0.
Confined Free-Surface Planar jets: Subcooling effects
Effects of subcooling on boiling curves at
H/w=4, V=1.7 m/s and z/w=0.0.
Effects of subcooling on boiling curves at
H/w=4, V=1.7 m/s and z/w=0.0.Effects of subcooling on boiling curves
at H/w=4, V=1.7 m/s and z/w=0.0.
Effects of subcooling on boiling curves
at H/w=4, V=1.7 m/s and z/w=0.0.
q vs. Tf (=Tw-Tf)q vs. Tsat (=Tw-Tsat)
Nozzle Geometry Effects on Confined Jets
Identical Flowrate (Q=3.0 l/m)
Non-normalized Normalized (single-phase convection)
Heat Transfer Control/Design Lab.Yonsei University
Nozzle geometry effects on convection coefficient distributions at H/d or H/w=1 and z=0.0.
V=16.2, 5.3, and 3.3 m/s for single-circ., array-circ., and planar jet, respectively.
Nozzle geometry effects on convection coefficient distributions at H/d or H/w=1 and z=0.0.
V=16.2, 5.3, and 3.3 m/s for single-circ., array-circ., and planar jet, respectively.
Summary of Jet impingement Boiling
Under a thin supercritical wall jet condition, the boundary layer transition to turbulence precipitated by the bubble-induced disturbance caused considerable decrease in wall temperature of further downstream only in the highest velocity case in this study.
The confinement letting the free surface exist had only slightest effect.
The highly-confined jet which allowed no free-surface produced a sooner and salient transition to turbulence, increasing overall heat transfer.
With the developed boiling, the heat transfer characteristics became similar for all the tested cases.
Circular jets provided remarkable heat transfer enhancement with a high confinement in either single or array form.
Heat Transfer Control/Design Lab.Yonsei University