Abstract
A comparative experimental study was conducted in order to investigate the convective heat transfer characteristics of water-based suspensions of microencapsulated phase change material (MEPCM) flowing through rectangular copper minichannels. The hydraulic diameter of the channels was 2.71 mm. MEPCM particles with an average size of 4.97 μm were used to form suspensions with mass concentrations ranging from 0 to 20%. The comparative experiments were performed for varying mass flow rates in the laminar region and varying thermal conditions. The cooling performance of the MEPCM suspensions strongly depended on the mass flow rate and the MEPCM mass concentration. The 5% suspension always showed a better cooling performance than water resulting in lower wall temperatures and enhanced heat transfer coefficients within the whole range of mass flow rates. The suspensions with higher mass concentrations, however, were more effective only at low mass flow rates. At higher mass flow rates they showed a less effective cooling performance than water.
Abbreviations
- A :
-
Total area of channel bottom and side walls (m2)
- c :
-
Mass concentration of MEPCM in the fluid
- c * :
-
Volume concentration of MEPCM in the fluid
- C :
-
Specific heat (J/kg K)
- d :
-
Diameter (m)
- D h :
-
Hydraulic diameter (m)
- h :
-
Heat transfer coefficient (W/m2 K)
- H ch :
-
Height of a minichannel (m)
- H w2 :
-
Distance between thermocouple position and channel bottom wall (m)
- I :
-
Total electrical current supplied to heaters (A)
- k :
-
Thermal conductivity (W/m K)
- M :
-
Mass flow rate of the fluid (kg/s)
- N :
-
Total number of minichannels
- Nu :
-
Nusselt number
- q 0 :
-
Heat flux at thermocouple position from below (W/m2)
- Q :
-
Total electrical heating power (W)
- T in :
-
Inlet temperature (°C)
- T out :
-
Outlet temperature (°C)
- T tci :
-
Thermocouple reading (i = 1–6) (°C)
- T wi :
-
Channel bottom wall temperature (i = 1–6) (°C)
- ΔT m :
-
Mean temperature difference between fluid and channel bottom wall (°C)
- U :
-
Electrical voltage at heaters (V)
- W ch :
-
Width of a minichannel (m)
- ρ:
-
Density (kg/m3)
- μ:
-
Viscosity (kg/m s)
- b :
-
Bulk
- cb :
-
Copper block
- p :
-
MEPCM particle
- mc :
-
MEPCM core
- ms :
-
MEPCM shell
- w :
-
Water
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Acknowledgments
The author Yu Rao is grateful for the financial support from Deutscher Akademischer Austausch Dienst (DAAD), Chinese Scholarship Council (CSC) and Chinese Natural Science Foundation for his doctoral study. The authors would like to thank Dr. Ekkehard Jahns (BASF AG) for the supply of the MEPCM and helpful discussions, Dr. S. Hardt for the numerical simulation of the flow distribution in the multichannels and Prof. Dr. M. Wilhelm for his help with the rheological investigations.
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Rao, Y., Dammel, F., Stephan, P. et al. Convective heat transfer characteristics of microencapsulated phase change material suspensions in minichannels. Heat Mass Transfer 44, 175–186 (2007). https://doi.org/10.1007/s00231-007-0232-0
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DOI: https://doi.org/10.1007/s00231-007-0232-0