Complex Fluids and
Multiphase Transport
& Multiscale
Thermofluidics Labs
Indirect Dry Cooling of Power Plants using Spray-Freezing of Phase Change Materials
Hamidreza Shabgard, Han Hu, Md Mahamudur Rahman, Philipp Boettcher, Matthew McCarthy, Young Cho and Ying Sun
Department of Mechanical Engineering and Mechanics, Drexel University
Motivation
Focus Areas of On-Going Research
• Cooling of electric power plants account for 40% of total fresh water withdrawals in the
US
• Fresh water resources are limited and increasingly scarce worldwide
• Dependency of power plants to water resources is not affordable anymore
• Novel cooling systems are to be developed for power plants
Material Characterization
• Thermal conductivity
• Melting/solidification
Air Side
• Design and construction of
spray-freezing PCM subsystem
• Spray characteristics of
liquefied PCM
• Freezing characteristics of
PCM spheres in air
Air outlet
Freezing PCM
droplets
Background
(b) Commonwealth Edison’s Byron Nuclear Plant, IL
Slurry Side Thermal-Fluid Analysis
Experimental Work
A 5 kW test setup designed and manufactured
Melting of PCM particles in slurry flow through heated tube bundle
(a)
Outer Dimension:
2 m x 1.5 m x 0.6 m
5 mm PCM
particles
Air inlet
Safety
• Combustion and
flammability
Solid-liquid PCM bath
Steam/water tubes
PCM and Phase Change Characterization
(a) Encina Power Plant, CA
(a)
(b)
(c)
Major components of the control
Test rig: (a) Test section, (b) PCM system; (a) and (b) DAQ and control
hardware, (c) control software
reservoir, (c) control box
Effective thermal conductivity, keff (W/mK)
Thermal Conductivity Measurement
• Hot wire method; well established and accurate
for low k material
Dry-air cooling
• Uses essentially no water
• Steam runs through large number of finned-tubes
• Large fans are used to circulate air
 Up to 10% power production penalty
 Costly
1.5wt%
3.0wt%
0.8
Liquid
0.6
Hot wire test rig
0.4
0.2
Solid
0.0
20
Liquid
30
40
1μm
50
Graphite nanoplatelets from XG
Science (25 μm dia., 15 nm thick)
60
Thermal conductivity enhancement of
eicosane with various nanoparticle loadings
About 80% enhancement in keff is
obtained with 3 wt% GNP loading
Small-Scale Cylindrical Melting and
Freezing
• Novel air-cooled power plant cooling tower/condenser
• Based on spray-freezing of phase-change materials (PCMs)
• Potentially eliminates water usage for power plant cooling
Power load, Ptotal
700 MW
5 kW
2,000 W/m2
2500 W/m2
Number of tubes, Ntube
345,000
36
Reynolds number, ReD
450-1,100
300-1,000
-
199.31191244
Heat transfer coefficient, h
200 W/m2K
250 W/m2K
Total heat transfer area, At
350,000 m2
0.7 m2
0.1-0.4
0.1-0.4
-
0.168-0.569 L/s
Test section dimensions (mm)
Solid PCM volume fraction
t = 0.5 s
25
28
Gan et al. (2003)
20
Slurry flow
Single phase
Solid Vf
24
Current simulation
15
10
Experimental Setup
PCM Spray Characteristics
t = 2.5 s
12
0
0.1
1
10
0.02
0
100
Time variations of settling velocity of a
single particle with simultaneous melting
T
0
0
10
20
30
40
t (s)
Wall Nusselt number and solid volume fraction for
28 particles with sedimentation (solid Vf = 6%)
temperature field for 50
particles with sedimentation
(6% solid fraction)
Combustion, Flammability, and Safety
• Experimental and theoretical assessment of flammability risk
Nozzle
Blower System
0.04
4
Validation
t* = t/(d/Umax)
Freezing of PCM spheres in air
16
0.06
8
5
0.01
Air Side Spray Freezing
t = 2.0 s
0.08
20
Solidification of eicosane in cylinders with
inner diameters of 14 mm and 6 mm
t = 1.5 s
Theoretical Analysis
• Obtain insight on heat transfer between solid and liquid phases
• Complementary tool for designs of slurry-side
• Establish Nu correlations for PCM slurry flow with melting and settling
Modeling Approach:
• Arbitrary Eulerian-Lagrangian method with deforming mesh
• Simultaneous melting/settling of PCM particles
Re
• Millimeter-scale melting
and solidification
• Constant wall temperature
• Center temperature
monitored
• Pressure transducer to
track phase change
fraction during process
Innovative Solution
Spray Freezing of Recirculating PCM
Scaled-down sub
system
PCM slurry flow rate
Temperature, TPCM ( C)
Cost effective technology needed for reducing
water usage for power plant cooling
Real
System
Heat flux, Jtotal
•
Millions of spherical particles
required for the experiments
A particle manufacturing unit is
built for timely production of
uniform spherical particles
dparticle = 6 mm, particle loading 
2000/sec, Re = 1000
Parameter
Solid
o
Array of Air Cooled Condensers
Key design parameters of the large-scale
and pilot-scale systems
1.0
0
•
(c)
(b)
Nuwall
Water-Based Cooling
Once-through cooling (Fig. a): intake structures withdraw water, which is run through
power plant for cooling.  Thermal discharges face increasing regulatory challenges
Closed-cycle cooling (Fig. b): Partial evaporation of recirculating water removes heat
from the power plant.
 Water usage may not be sustainable at some locations
Source: U.S. Energy Information Administration,
Form EIA-860, Annual Electric Generator Report
Slurry Side
• Design and construction of
5kW PCM slurry heat
exchanger
• CFD analysis
Solid volume fraction
Settling solid PCM particles
dsphere = 38 mm, freezing in wind tunnel,
Thermocouples at the center and inner wall
• Guarantee the safety and minimal environmental effects
Vibration Damper
•
•
•
Fluid delivery system
for PCM spray nozzle
Micro pump
Wax Reservoir
Controlled PCM flow
rate and temperature Experimental apparatus to study
Controlled air flow rate PCM spray characteristics
Tair = 23 °C
About 25% reduction in solidification
time for 1.5 wt% GNP
likelihood of ignition as a function
of particle concentration
minimum concentration vs.
particle size causing ignition
Eicosane
280 μm particles
c = 0.1262 kg/m3
Experimental apparatus to
study flammability
Funding for this work was provided by the National Science Foundation (CBET-1357918) and The Electric Power Research Institute (EPRI).