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    207 lokesh 207 lokesh Presentation Transcript

    • Numerical Analysis of Micro Channel Heat Sink Cooling System for Solar Concentrating Photovoltaic Module by 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
    • 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 – – Serpentine Flow Channel – • Parallel 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 Reduce use of semiconductor material Higher efficiency can reduce area costs • Reduced area allows to afford the high cost for cells. R. King, “MultijunctionCells: Record Breakers,” Nature Photonics, Vol2, 284-286 (2008).
    • Types of CPV System  Based on Concentrator SPIE 2009 David Miller, et al  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 Images courtesy of Airlightr Energy courtesy of Solar Systems, Australia
    • Dense Array CPV System Components of CPV System Parabolic Concentrator Secondary Concentrator Optical Homogenizer CPV Module Active Cooling System Images courtesy of IBM CPV Cells Substrate Images courtesy of Airlightr Energy
    • Need for an effective cooling system • Increased light intensity will –Increases photocurrent (additional photons) –Reduces open-circuit voltage (increased heat) I sc Voc • • • • CI sc0 Voc0 nVt h ln(C ) n - diode factor and Vth -thermal dependency of the cell efficiency 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.
    • Parallel Serpentine and Straight Flow Module Parallel Serpentine Module Parallel 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 Complete micro-channel module 6 inlets -single flow 6 inlets - alternate flow
    • 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 Properties of plate (Copper) Parameter values 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 Viscosity µS 0.6 W/m K 0.000653 Pa s  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 Boundary conditions used in micro channel heat sink simulations.
    • Results for Straight Flow channel Effect of Reynolds number on pressure drop Effect of width of micro channel on T ,Tavg and UT(K) Effect of aspect ratio on T ,Tavg and UT. Effect of Reynolds number on T , Tavg and UT.
    • Results for Serpentine Flow channel • • • 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
    • Analysis of profile region Figure : Velocity contours of micro-channel and profile region in transition flow conditions Figure : Pressure contours of micro-channel and profile region in transition flow conditions
    • Results for Combined Flow Channel Cumulative pressure drop along flow direction Variation of Vout2-Vin2and pressure drop for different profile regions Complete velocity profile in single channel Variation of flow velocity pressure drop for different microchannel arrays
    • Results for Combined Flow Channel Temperature profile of surface of water along fin height with the flow direction Temperature contour of bottom surface of heat sink along the flow direction
    • 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), 10991103. 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.