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: ksreddy@iitm.ac.in, 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.