Experiments on fineffects for increasing heat transfer coefficients during charging heat and heat re

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Experiments on fin-effects for increasing heat
transfer coefficients during charging heat and
heat release between PCMs and thermal medium

• Katsunori Nagano, Ph.D.
• Hokkaido University, Japan
• 8th June, 2004
• ANNEX17 Work shop in Arvika, Sweden

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Objectives

• What type of fin-shapes are effective to increase
  heat transfer for PCMs?
• Three kinds of finned heat exchangers and heat
  exchanger without fin were prepared for
  experiments
• - Fin shape rectangular, circular, circular
  (half plates number)
• Three kind of PCMs are examined
• - Water, Microcapsule PCM slurry, Salt
  hydrate

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Fig.1 Four types of used heat exchanger
Fin thickness 2 mm
90
90
27
90
f35
f35
f35
f35
28
56
1000
(a) Single tube
(c) 17 Circular fins
(b) Rectangular fins
(d) 34 Circular fins
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Table 1 Used substances for measurements
Hydrated salts Mixture of 85wt Mg(NO3)26H2O
15 wt MgCl26H2O
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Fig.2 Appearance of MCS-PCM
Viscosity 48.9 cP at 20 oC (Water ?1.0 cP at 20
oC)
Fig.3 Cross section of MCS-PCM by SEM
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Fig.4 Output signal of DSC for MCS-PCM
Sample weight 10.9 mgTemperature scanning rate
1.0 ?C/min
Solidification point 57.9 ?C
Heat of fusion (Solidification) 90.4 mJ/mg
Heat of fusion (Melting) 91.9 mJ/mg
Melting point 54.3 ?C
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Fig.5 Output signal of DSC for hydrated salts
Sample weight 7.8 mgTemperature scanning rate
1.0 ?C /min
Heat of fusion (Solidification) 155 mJ/mg
Solidification point 72.2 ?C
54.3 ?C
Heat of fusion (Melting) 166 mJ/mg
Melting point 67.0 ?C
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Fig.6 Output signal of DSC for water
Sample weight 4.8 mgTemperature scanning rate
1.0 ?C /min
Solidification point -13.4 ?C
Melting point 0.4 ?C
Heat of fusion (Melting) 372 mJ/mg
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Fig.7 System diagram of experimental apparatus
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2
3
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1.Constant temperature water circulating bath
2.Constant flow regulating valve 3.Magnetic flow
meter 4.Temperature sensor (Pt-100)
5.Thermocouple (T-type)6.Heat storage tank
1
6
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Fig.8 Details of heat exchange container
Vacuum pump
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Fig.9 Changes of water temperature and exchanged
heat flux with elapsed time
(a) Single tube
(b) Rectangular fins
(c) 17 Circular fins
(d) 34 Circular fins
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Fig.10 Change of exchanged heat with elapsed time
(Water)
Discharging process
Charging process
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Table 2 Total amount of exchanged heat for 5
hours (Water)
Discharging process
Charging process
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Fig.11 Changes of MCS-PCM temperature and
exchanged heat flux with elapsed time
(a) Single tube
(b) Rectangular fins
(c) 17 Circular fins
(d) 34 Circular fins
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Fig.12 Change of exchanged heat with elapsed time
(MCS-PCM)
Discharging process
Charging process
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Table 3 Total amount of exchanged heat for 5
hours (MCS-PCM)
Discharging process
Charging process
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Fig.13 Changes of hydrated salts temperature and
exchanged heat flux with elapsed time
(a) Single tube
(b) Rectangular fins
(c) 17 Circular fins
(d) 34 Circular fins
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Fig.14 Change of exchanged heat with elapsed time
(Hydrated salts )
Discharging process
Charging process
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Table 4 Total amount of exchanged heat for 5
hours (Hydrated salts )
Discharging process
Charging process
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Fig.15 Changes of Ice-water temperature and
exchanged heat flux with elapsed time
(a) Single tube
(b) Rectangular fins
(c) 17 Circular fins
(d) 34 Circular fins
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Fig.16 Change of exchanged heat with elapsed time
(Ice-water)
Discharging process
Charging process
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Table 5 Total amount of exchanged heat for 5
hours (Ice-water)
Discharging process
Charging process
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Conclusions

• The maximum heat transfer ratio to the liquid
  water during discharging process
• (1) Ice no fin effect was observed, around 2.1
  times
• (2) Hydrate 34 circular fins, 2.0 times
• (3) MCS-PCM Rectangular fins,1.3 times
• The maximum heat transfer ratio to the liquid
  water during charging process
• (1) Ice 34 circular fins, 1.7 times
• (2) Hydrate 34 circular fins, 1.9 times
• (3) MCS-PCM Rectangular fins,1.3 times
• Suitable fin-shape for static PCM and slurry PCM
• Static PCM horizontal circular fins
• Slurry PCM vertical rectangular fins
• Needed further work
• The optimum fin plate number and those fin
  clearance, also fin plate thickness