Convective Heat Transfer of Phase Change Slurries

Convective Heat Transfer of Phase Change Slurries

Convective Heat Transfer of Phase Change
Slurries
Tobias Kappels – Fraunhofer UMSICHT
IRES Berlin
12. November 2012
Slide 1
© Fraunhofer UMSICHT
© Fraunhofer UMSICHT
AGENDA
 Introduction
 Phase Change Slurry
 Natural Convection Measurements
 Forced Convection Measurements
 Comparison of results
Slide 2
© Fraunhofer UMSICHT
Introduction
 Raising amounts of
fluctuating energy
 High grid balancing
demand
 High energy demands
for cooling and domestic
heating
 Electric energy storages
are expensive and with
low efficiency
 Need for small, local,
cost-efficient heat
storages for load
management
Scenarios of power plants development
Slide 3
© Fraunhofer UMSICHT
Comparison of storage media – heat capacity
300
250
[kJ/kg]
200
20 K
150
6K
100
50
0
Water
Slide 4
© Fraunhofer UMSICHT
Paraffin
Comparison of storage media – heat capacity
300
250
[kJ/kg]
200
20 K
150
6K
100
50
0
Water
Slide 5
© Fraunhofer UMSICHT
PCS (30%)
PCS (50%)
Paraffin
Comparison of storage media – heat exchange
Conduction
Convection
1.4
500
natural convection (max)
10000
natural convection (min)
450
1.2
400
0.6
0.4
8000
300
6000
250
200
4000
150
100
0.2
0
2000
50
0
0
n.c.
f.c.
Water (literature)
Slide 6
© Fraunhofer UMSICHT
[W/(m²*K)]
0.8
forced convection (min)
350
[W/(m²*K)]
[W/(m*K)]
1
forced convection (max)
CryoSolplus as Phase-Change-Slurry
 High energy density (50 to 120 kJ/kgK)
 High power in- and output due to high thermal conductivity
 Ecologically harmless
 Pumpable (viscosity between 20 to 30 mPas)
 Various fields of application
Slide 7
© Fraunhofer UMSICHT
Formation of the dispersion
Water
Emulsifier
Water
Oil
droplets
Melting
Homogenizer
Paraffin
T = 50 – 80 °C
Emulsifiers
Paraffin/Water-Dispersion
Slide 8
© Fraunhofer UMSICHT
Method – Natural convection
Water
T
heat exchanger temperature
TC_1
TC_4
TC_2
PCS
TC_6
TC_3
TC_7
Temperature
measuring point
Slide 9
© Fraunhofer UMSICHT
starting vessel temperature
t
Analysis – Natural convection
𝑇0 = 𝑇𝑙𝑚,𝑤
Water
𝑄 = 𝑚𝑤 ∙ 𝑐𝑝,𝑤 ∙ ∆𝑇𝑤 = 𝑘 ∙ 𝐴 ∙ 𝑇0 − 𝑇∞
𝑘=
𝑚𝑤 ∙ 𝑐𝑝,𝑤 ∙ ∆𝑇𝑤
𝐴 ∙ 𝑇0 − 𝑇∞
TC_1
TC_4
TC_2
𝑇∞ = 𝑇𝑙𝑚,𝑃𝐶𝑆
PCS
TC_6
TC_3
TC_7
Temperature
measuring point
Slide 10
© Fraunhofer UMSICHT
Results – Natural convection
Overall heat exchange coefficient - k [Wm-2K-1]
200
k (water)
k (PCS, 25..35 °C)
175
k (PCS, 0..18 °C)
150
k (PCS, 18..25°C)
125
100
75
50
25
0
0
Slide 11
© Fraunhofer UMSICHT
50
100
150
200
250
Heat flux per heat transfer area q [W m-2]
300
350
Method – Forced convection
Source: Christoph Taetz, Ruhr-Universität Bochum
Slide 12
© Fraunhofer UMSICHT
Analysis – Forced convection
𝑄 = 𝑚𝑤 ∙ 𝑐𝑝,𝑤 ∙ ∆𝑇𝑤 = 𝑘 ∙ 𝐴𝑙𝑚 ∙ ∆𝑇𝑙𝑚
𝑙𝑛
𝑑𝑜
1
1
1
𝑑𝑖
=
+
+
𝑘 ∙ 𝐴𝑙𝑚 𝛼𝑃𝐶𝑆 ∙ 𝐴𝑖 2 ∙ 𝜋 ∙ 𝜆𝑐 ∙ 𝑠 𝛼𝑤 ∙ 𝐴𝑜
𝛼𝑤 ∙ 𝐷ℎ
𝑁𝑢 =
= 0.023 ∙ 𝑅𝑒 0.8 ∙ 𝑃𝑟 0.3
𝜆𝑤
Slide 13
© Fraunhofer UMSICHT
Dittus-Boelter equation
Heat transfer coefficient - αPCS [W m-2 K-1]
Results – Forced convection
6000
5000
4000
3000
2000
Chilled Water 100 L/h
1000
Chilled Water 200 L/h
Chilled Water 300 L/h
0
0
20
40
60
80
Heat flux per heat transfer area - q [kW m-2]
Slide 14
© Fraunhofer UMSICHT
100
120
Heat transfer coefficient - αPCS [W m-2 K-1]
Results – Forced convection
6000
5000
4000
3000
2000
Chilled Water 100 L/h
1000
Chilled Water 200 L/h
Chilled Water 300 L/h
0
0
20
40
60
80
Heat flux per heat transfer area - q [kW m-2]
Slide 15
© Fraunhofer UMSICHT
100
120
Comparison with literature data
Conduction
Convection
1.4
500
natural convection (max)
natural convection (min)
450
1.2
forced convection (max)
400
0.6
0.4
8000
300
6000
250
200
4000
150
100
2000
0.2
50
0
0
0
n.c.
f.c.
n.c.
f.c.
Water
Water
(literature) (measured)
Slide 16
© Fraunhofer UMSICHT
n.c.
f.c.
PCS
[W/(m²*K)]
0.8
forced convection (min)
350
[W/(m²*K)]
[W/(m*K)]
1
10000
Conclusion
 Heat capacity of PCS between water and PCM
 Heat exchange of PCS similar to water at same heat flux
 Further investigations at the phase transition temperature will follow
 Investigations on rheological behavior will be conducted
Slide 17
© Fraunhofer UMSICHT
FRAUNHOFER UMSICHT
Thank you for your
interest!
Contact:
Fraunhofer UMSICHT
Osterfelder Strasse 3
46047 Oberhausen
Germany
E-Mail:
[email protected]
Internet: http://www.umsicht.fraunhofer.de
Slide 18
© Fraunhofer UMSICHT
Tobias Kappels
Phone:
+49 (0) 208/8598-1347
E-Mail:
[email protected]
CryoSolplus as Phase Change Slurry
150
 Depends on paraffin fraction
 2.5 – 3.5 as high as heat capacity
of water at ΔT of 10 K
125
Heat Capacity [kJ/kg]
 Latent heat of paraffin raises the
heat capacity of the fluid
Water
30 wt-% Paraffin
40 wt-% Paraffin
50 wt-% Paraffin
latent heat
Heat capacity
100
75
50
25
0
0
5
Temperature difference [K]
Comparison of heat capacities of water and PCS
Slide 19
© Fraunhofer UMSICHT
10
PCS properties
DSC-Measurement of a dispersion with 30 % paraffin (C-20) [2 K/min]
Slide 20
© Fraunhofer UMSICHT
PCS properties
Particle size distribution of a dispersion with 30 % paraffin (C-20)
Slide 21
© Fraunhofer UMSICHT
PCS properties
1
Viscosity [Pas]
30 wt.-% paraffin - 22 °C
0.1
0.01
0
50
100
150
200
Shear rate [1/s]
250
Viscosity of a of a dispersion with 30 % paraffin (C-20)
Slide 22
© Fraunhofer UMSICHT
300
350