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Paraffin/Water Emulsion for Cold Storage and Distribution Applications
Li Huang, Christian DötschFraunhofer Institute of Environmental, Safety, and
Energy Technology UMSICHT, Germany
IEA/ECES Annex 18, The Fifth Workshop and Expert MeetingFreiburg/Germany, November 3 – 5, 2008
2
Phase Change Slurry (PCS)
§ binary fluid composed of a Phase Change Material (PCM) and a carrier fluid
§ high energy density, pumpable
Introduction
Hydrate slurry (TBAB)Ice slurry
Source: Fraunhofer UMSICHT Source: JFE Engineering Corporation
3
PCS based on paraffins
§ Suspension where paraffin is embedded into a support material
§ Suspension of microencapsulated paraffin in water
§ Dispersion of paraffin droplets in water with the help of surfactants
Microencapsulated paraffinsuspension
Paraffin/Water-EmulsionShape-stabilizedparaffin suspension
Introduction
Paraffin
Water
Surfactant
Source: H.Inaba, 1997
4
Paraffin/water-emulsion components
Emulsion Components and Properties
PCMalkanes CnH2n+2 withn=14-16 orblends with a meltingpoint of 0-20 °C
Surfactantprevent the phase separation and to stabilize emulsions
Nucleating agentprevent thesupercooling effect of the emulsions inducedby the small droplet size(1-10 µm)
50 um
5
§ Paraffin: Rubitherm RT10 with a
melting point of 10 °C and a heat
of fusion of 120 kJ/kg
§ Total heat capacity
- sensible heat capacity of water
- heat of fusion of the paraffin
§ In the temperature range of 5-12 °C
- Water: 29 kJ/kg
- Emulsion RT10-30 %: 58 kJ/kg
0
10
20
30
40
50
60
70
80
90
100
110
120
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30
Temperature [°C]H
eat
capa
city
[kJ
/kg]
Emulsion RT10-30%
Water
29 kJ/kg
58 kJ/kg
Emulsion Components and Properties
Paraffin and heat transfer capacity of emulsions
6
Emulsion Components and Properties
Paraffin and heat transfer capacity of emulsions
§ The heat capacity of the
emulsion increases proportionally
with the paraffin fraction.
§ Emulsion RT10-30 %: 2 times
Emulsion RT10-50 %: 2.8 times
§ Heat capacity of a PCS à
RT10 fraction >= 30 wt.%
0 10 20 30 40 50 60 70 80 90 100
1
2
3
4
5
Ratio
hea
t ca
paci
ty
RT10
em
ulsi
ons
to w
ater
RT10 concentration [wt.%]
7
Emulsion Components and Properties
Paraffin and rheological behaviors of emulsions
§ Non-Newtonian fluid,
shear-thinning behavior
§ Viscosity of the emulsion increases
sharply when the paraffin fraction
exceeds 50 %.
§ The optimal RT10 fraction is 30-50 %,
when considering both the heat
capacity and the viscosity. 0.01
0.1
1
10
100
1000
0 50 100 150 200Shear rate [1/s]
Vis
cosi
ty [P
as]
RT10-20 % RT10-30 %RT10-40 % RT10-50 %RT10-60 % RT10-70 %
8
Emulsion Components and Properties
Surfactant and stability of emulsions
§ Surfactants: amphipathic molecules
consisting of a non-polar
hydrophobic portion and a polar or
ionic portion (hydrophilic)
oil droplet
surfactant hydrophilicportion
hydrophobicportion
water
§ Requirements on the emulsion for
cold applications
- over long term storage and
- under thermal-mechanical loads in
the pump systems
§ Stability: change in the droplet size
9
Emulsion Components and Properties
Surfactant and stability of emulsions
§ Sample: RT10-30 %
§ No dramatic change in the drop
size distribution was detected
over one year of storage.
0.01 0.1 1 10 100 10000
2
4
6
8
10
12
14
16
measured on Februar 8th, 2007
measured on June 25th, 2008
Den
sity
dis
trib
utio
n [%
]
Droplet size [µm]
10
§ Sample: RT10-30 %
§ Temperature: 5-18 °C, 50 cycles
Emulsion Components and Properties
Surfactant and stability of emulsions
11
§ Sample: RT10-30 %
§ slight coalescence after a week
Emulsion Components and Properties
Surfactant and stability of emulsions
§ Sample RT20-30 % (melting point
20 °C) was tested at Fraunhofer ISE
§ The emulsion withstood about 8400
cooling/heating cycles.
0.01 0.1 1 10 100 10000
2
4
6
8
10
12
14
16
Den
sity
dis
trib
utio
n [%
]Droplet size [µm]
Sample before the test, on August 8st, 2008
Sample on August 11st, 2008
Sample on August 12nd
, 2008
Sample on August 13rd, 2008
Sample after the test, on August14th, 2008
12
Nucleating agent and supercooling effect of emulsions
§ Supercooling effect induced
by the small droplet size
-5 0 5 10 15 20 25-1.0
-0.8
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
Hea
t flo
w [m
W/m
g]
Temperature [°C]
Paraffin, freezing Paraffin, melting
Emulsion RT10-30%, freezing Emulsion RT10-30%, melting
Emulsion Components and Properties
§ The nucleating agent offers
the necessary embryo surface
to start the nucleation in the
paraffin droplets and thus is
acting as a nucleating
catalyst.
Emulsion RT10-30%+nucl., fr. Emulsion RT10-30%+nucl., mel.
13
Emulsion Components and Properties
Paraffin O/W Emulsion
high energy density
(min. 2 times water)
little supercoolingeffect
Surfactant
relatively low viscosity(max. 40 mPas)
good stability
Nucleatingagent
Paraffin(30-50 %)
14
Application Study
§ Application in cold supply networks or cold storage systems
Source: Fraunhofer UMSICHT
15
Application Study
§ Application in building cooling
capillary tube systems with the paraffin emulsion having a melting temperature of 20 °C for
cooling ceilings or walls
Source: Clina Heiz- und Kuehlelemente GmbH
L. Huang
Fraunhofer Institute for Environmental, Safety and Energy Technology UMSICHT
Osterfelder Strasse 3
46047 Oberhausen, Germany
Tel.: +49 (0) 208/85 98-1149
Fax: +49 (0) 208/85 98-12 90E-mail: [email protected]
Thank you very much for your attention!
