1. 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
Complex Fluids and
Multiphase Transport
& Multiscale
Thermofluidics Labs
Background
• Cooling of power plants account for 40% of total fresh water withdrawals in the US
• Dependency of power plants to increasingly scarce water resources is not affordable
• Novel cooling systems are to be developed for power plants
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
Motivation
Once-through cooling (Fig. a): intake structures withdraw water, which is run through
power plant for cooling.  Thermal discharges face increasing regulatory challenges
(b) Commonwealth Edison’s Byron Nuclear Plant, IL
(http://commons.wikimedia.org/wiki/File:Byron_IL_Byron_Nuclear_Generating_Station_2.jpg)
(a) Encina Power Plant, CA
(http://www.kpbs.org/news/2012/apr/19/power-plant-replace-
encina-needed-future-reliabili/)
Array of Air Cooled Condensers
(http://www.hudsonproducts.com/products/stacflo/tech.html)
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
Water-Based Cooling
Source: U.S. Energy Information Administration,
Form EIA-860, Annual Electric Generator Report
Cost effective technology needed for reducing
water usage for power plant cooling
Funding for this work was provided by the National Science Foundation (CBET-1357918) and The Electric Power Research Institute (EPRI).
Innovative Solution
Focus Areas of On-Going Research Slurry Side Thermal-Fluid Analysis
Experimental Work
Test rig: (a) Test section, (b) PCM
reservoir, (c) control box
(a)
(b)
(c)
Outer Dimension:
2 m x 1.5 m x 0.6 m
Major components of the control
system; (a) and (b) DAQ and control
hardware, (c) control software
(b)
(a)
(c)
t = 0.5 s t = 1.5 s t = 2.0 s t = 2.5 s
Parameter Real
System
Scaled-down sub
system
Power load, Ptotal 700 MW 5 kW
Heat flux, Jtotal 2,000 W/m2 2500 W/m2
Number of tubes, Ntube 345,000 36
Reynolds number, ReD 450-1,100 300-1,000
Test section dimensions (mm) - 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
Solid PCM volume fraction 0.1-0.4 0.1-0.4
PCM slurry flow rate - 0.168-0.569 L/s
A 5 kW test setup designed and manufactured
Melting of PCM particles in slurry flow through heated tube bundle
Key design parameters of the large-scale
and pilot-scale systems
dparticle = 6 mm, particle loading 
2000/sec, Re = 1000
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
0
5
10
15
20
25
0.01 0.1 1 10 100
Re
t* = t/(d/Umax)
Gan et al. (2003)
Current simulation
temperature field for 50
particles with sedimentation
(6% solid fraction)
T
Wall Nusselt number and solid volume fraction for
28 particles with sedimentation (solid Vf = 6%)
Time variations of settling velocity of a
single particle with simultaneous melting
Combustion, Flammability, and Safety
Eicosane
280 μm particles
c = 0.1262 kg/m3
Experimental apparatus to
study flammability
• Experimental and theoretical assessment of flammability risk
• Guarantee the safety and minimal environmental effects
5 mm PCM
particles
• Millions of spherical particles
required for the experiments
• A particle manufacturing unit is
built for timely production of
uniform spherical particles
PCM and Phase Change Characterization
Thermal Conductivity Measurement
Novel air-cooled power plant cooling tower/condenser based on
spray-freezing of recirculating phase change materials (PCMs)
20 30 40 50 60
0.0
0.2
0.4
0.6
0.8
1.0
Effectivethermalconductivity,keff
(W/mK)
Temperature, TPCM
(o
C)
Solid Liquid
0 1.5wt% 3.0wt%
Solid
Liquid
• Hot wire method; well established and accurate
for low k material
1μm
Graphite nanoplatelets (GNP) from XG
Science (25 μm dia., 15 nm thick)
Thermal conductivity enhancement of
eicosane with various GNP loadings
Hot wire test rig
About 80% enhancement in keff is
obtained with 3 wt% GNP loading
Wax Reservoir
Nozzle
Blower System
Micro pump
Vibration Damper
• Design and construction of
spray-freezing PCM sub-
system
• Spray characteristics of
liquefied PCM
• Freezing characteristics of
PCM spheres in air
• Design and construction of
5kW PCM slurry heat
exchanger
• CFD analysis
Material Characterization Air Side
Slurry Side
• Thermal conductivity
• Melting/solidification
Safety
• Combustion and
flammability Solid-liquid PCM bath Steam/water tubes
Freezing PCM
droplets
Settling solid PCM particles
Air inlet
Air outlet
Small-Scale Cylindrical Melting and
Freezing
Validation
Solidification of eicosane in cylinders with
inner diameters of 14 mm and 6 mm
• Millimeter-scale melting
and solidification
• Constant wall temperature
• Center temperature
monitored
• Pressure transducer to
track phase change
fraction during process
Experimental Setup
Air Side Spray Freezing
PCM Spray Characteristics
• Fluid delivery system
for PCM spray nozzle
• Controlled PCM flow
rate and temperature
• Controlled air flow rate
Experimental apparatus to study
PCM spray characteristics
Freezing of PCM spheres in air
dsphere = 38 mm, freezing in wind tunnel,
Thermocouples at the center and inner wall
About 25% reduction in solidification
time for 1.5 wt% GNP
Tair = 23 °C
likelihood of ignition as a function
of particle concentration
minimum concentration vs.
particle size causing ignition
• Significant reduction in steam condensation temperature using environmentally benign PCM for > 8%
production gain
• Improved air-side heat transfer coefficient by up to 4 times due to the use of sprayed droplets
• Reduced primary steam tubing and pressure drop
• Reduced system cost by 50% and size by  20%
Potential Advantages
(http://www.rubitherm.de/english/)
0
0.02
0.04
0.06
0.08
0
4
8
12
16
20
24
28
0 10 20 30 40
Solidvolumefraction
Nuwall
t (s)
Slurry flow
Single phase
Solid VfVf
Modeling Approach:
• Arbitrary Eulerian-Lagrangian method with deforming mesh
• Simultaneous melting/settling of PCM particles