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Numerical Analysis of Micro Channel Heat Sink Cooling System for Solar Concentrating Photovoltaic Module
K. S. Reddy1*, S. Lokeswaran1, Pulkit Agarwal1,Tapas K. Mallick2
Department of Mechanical Engineering
Indian Institute of Technology Madras, Chennai - 600 036, India.
Environment and Sustainability Institute, University of Exeter, Cornwall, UK
*Corresponding Author-E-mail: [email protected], Tel: (044) 22574702, Fax: (044) 22574652
International Conference on Advances in Energy Research
IIT Bombay, Powai, 10th-12th December 2013
by
Organization of Talk
• Introduction to CPV
• Types of CPV system
• Need for an Effective Cooling system
• Dense Array CPV system
• Numerical Simulation of Micro-channel heat sink
– Parallel Flow Channel
– Serpentine Flow Channel
– Combined Flow Channel
• Summary
Introduction to CPV
• Cost of electricity by conventional photovoltaic system is high• CPV objective is to reduce system cost by
Replace expensive semiconductors with inexpensive lenses/mirrors
Incorporate small-area, high-efficiency solar cells
• The generation cost per unit energy is given by
• Reduced area allows to afford the high cost for cells.
R. King, “MultijunctionCells: Record Breakers,” Nature Photonics, Vol2, 284-286 (2008).
Reduce use of semiconductor material
Higher efficiency can reduce area costs
Types of CPV System Based on Concentrator
Based on geometry• Single cells
cell has an area roughly equal to that of the
concentrator available for heat sinking• Linear geometry
parabolic troughs or linear Fresnel lenses
Heat dissipated from two of the sides
and the back of the cell.• Densely packed modules
dishes or heliostat fields
Only way to dissipate heat is from cells’s rear side
Images courtesy of Amonix
courtesy of Solar Systems, Australia
SPIE 2009 David Miller, et al
Images courtesy of Airlightr Energy
Dense Array CPV System
Images courtesy of Airlightr Energy
Images courtesy of IBM
CPV Cells
Components of CPV System
Parabolic Concentrator
Secondary Concentrator
Optical Homogenizer
CPV Module
Active Cooling System
Substrate
Need for an effective cooling system
• Increased light intensity will
–Increases photocurrent (additional photons)
–Reduces open-circuit voltage (increased heat)
• Irradiance on cell should be homogeneous both in quantity and quality• Conversion efficiency increase with concentration factor but fill factor is degraded by
increasing resistance losses• The solar cell performance will decrease drastically by 50% when the cell’s surface
temperature increased from 46°C to 84°C [1]. • Excessive thermal energy may degrade the CPV resulting in permanent damage.
0scsc CII
)ln(0
CnVVV htococ n - diode factor and Vth -thermal dependency of the cell efficiency
Parallel Serpentine Module
Parallel straight flow Module
Parallel Serpentine and Straight Flow Module
A combinatory model
High heat removal effectiveness of Serpentine micro-channels
Low pressure drops in straight micro channels
Combined Micro-channel for CPV Module
Flow arrangements patterns
3 inlets 6 inlets -single flow 6 inlets - alternate flow
Complete micro-channel module
Numerical Simulation of Micro-channel heat sink
• The analysis was carried out Using CFD software ANSYS 13 • Steady, incompressible, laminar flow conditions Parameters used for micro channel heat sink simulations.
Parameters Values Parameter values Properties of plate (Copper) Properties of coolant (water) at 40°C
Density 8978 kg/m3 Density 998.2 kg/m3
Specific heat Cp,S 381 J/kg K Specific heat Cp,S 4182 J/kg K
Thermal conductivity Kp
387.6 W/m K
Thermal conductivity Kw
0.6 W/m K
Viscosity µS 0.000653 Pa s
Boundary conditions used in micro channel heat sink simulations.
The optimal design is determined by minimizing and comparing the following four parameters:Pressure drop the micro channel ΔP,Average temperature of the heat sink bottom Temperature uniformity index UT
Surface temperature difference ΔT = Tmax - Tmin
Results for Straight Flow channel
Effect of Reynolds number on pressure drop Effect of aspect ratio on T ,Tavg and UT.
Effect of Reynolds number on T , Tavg and UT.Effect of width of micro channel on T ,Tavg and UT(K)
• PV cell width constrain is 12 mm• Decreasing pitch results in higher volume flow rate leading to higher pressure drops across
the micro channel array• Micro channel
Width 0.5 mm
Pitch = 0.5 mm
Aspect ratio = 0.125
Results for Serpentine Flow channel
Analysis of profile region
Figure : Pressure contours of micro-channel and profile region in transition flow conditions
Figure : Velocity contours of micro-channel and profile region in transition flow conditions
Cumulative pressure drop along flow direction Complete velocity profile in single channel
Variation of Vout2-Vin
2and pressure drop for different profile regions Variation of flow velocity pressure drop for different microchannel arrays
Results for Combined Flow Channel
Temperature contour of bottom surface of heat sink along the flow direction
Temperature profile of surface of water along fin height with the flow direction
Results for Combined Flow Channel
Summary
• Investigation of micro-channel cooling technology with different flow arrangement has been carried out.
• The optimized geometry of micro channel for the CPV receiver was found to be
W=0.5 mm
Aspect ratio = 0.125
Pitch = 0.5mm
• The final results
Temperature of CPV module of dimensions 24x24 cm = 10 K rise
Pressure drop of 8.8 kPa along a single channel with six such channels
Flow rate of 6.35 L/min.
References
• Leonardo Micheli, NabinSarmah, XichunLuo, K.S.Reddy, Tapas K Mallick, (2013) Opportunities and challenges in micro-and nano-technologies for concentrating photovoltaic cooling: A review, Renewable and Sustainable Energy Reviews, 20: pp. 595–610.
• Royne, C.J. Dey and D.R. Mills, (2005) Cooling of photovoltaic cells under concentrated illumination: a critical review. Solar Energy Materials and Solar Cells, 86(4): pp. 451-483.
• Lasich, J.B. (2002) Cooling circuit for receiver of solar radiation.Patent no. WO02080286.• Vincenzi, D., Bizzi, F., Stefancich, M., Malagu, C., Morini, G.L., Antonini, A. and Martinelli,
G. (2002) Micromachined silicon heat exchanger for water cooling of concentrator solar cells. PV in Europe Conference and Exhibition - From PV technology to Energy Solutions, Rome
• Min, J.Y., Jang, S.P. and Kim, S.J. (2004) Effect of tip clearance on the cooling performance of a microchannel heat sink.International Journal of Heat and Mass Transfer 47 (5), 1099-1103.
• Lee, D.-Y.andVafai, K. (1999) Comparative analysis of jet impingement and microchannel cooling for high heat flux applications. International Journal of Heat and Mass Transfer 42 (9), 1555-1568.
• Ryu, J.H., Choi, D.H. and Kim, S.J. (2003) Three-dimensional numerical optimization of a manifold microchannel heat sink. International Journal of Heat and Mass Transfer 46 (9), 1553-1562.
• Bejan, A.(1993) Heat Transfer, John Wiley & sons, Inc.,Singapore.