Heat transfer in microchannels
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This document discusses heat transfer in microchannels. It begins by defining microchannels as channels less than 1mm wide used for heat exchange. Microchannels allow for higher heat flux transfer due to their small size. They have various applications, especially in cooling electronics. The document outlines different channel designs, manufacturing methods, coolants used like nanofluids, and limitations of microchannels. It concludes that microchannels enable high heat flux transfer and have significant potential for further development.
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- 1. HIGH FLUX HEAT TRANSFER IN MICROCHANNELS PRESENTED BY, GUIDED BY, NEETHIN NANDAKUMAR DR.BINOY BABY S7,ME-B HOD ROLL NO-14 DEPT. OF MECH ENGG.
- 2. CONTENTS 1. HEAT EXCHANGERS 2. MICROCHANNEL COOLING 3. NEED FOR SMALLER CHANNELS 4. APPLICATIONS 5. CHANNEL DIMENSIONS 6. SINGLE PASS VS SPLIT FLOW 7. MANUFACTURING 8. COOLANTS USED 9. NANOFLUIDS 10. LIMITATIONS 11. CONCLUSIONS 12. REFERENCES 2
- 3. HEAT EXCHANGERS Used to transfer heat between one or more fluids Three primary classifications 1. Parallel flow 2. Counter flow 3. Cross flow Most common type: Shell and tube heat exchanger 3
- 4. MICROCHANNEL COOLING At least one fluid flows in channels of width less than 1mm Share the same principles as conventional heat exchangers First developed by Tuckerman and Pease (1981) Cannot reduce width indefinitely Coolant viscosity sets limits 4
- 5. NEED FOR SMALLER CHANNELS Channels serves two purposes: 1. Path for coolant flow 2. Provides intimate contact 5 D/LD DL V A 4 42 As D h D k h 657.3
- 6. APPLICATIONS Major application is in cooling electronic equipments where area is of essence Cryogenic industry is a major user due to high heat transfer Refrigeration industry High performance aircraft gas turbine engines Chemical reactors 6
- 7. CHANNEL DIMENSIONS Channel dimensions are chosen after taking into consider the following factors: 1. Maximum allowable temperature of channel surface 2. Maximum coolant temp 3. Cost considerations 4. Maximum pressure drop 7
- 8. SINGLE PASS VS SPLIT FLOW Disadvantages of single pass: 1. Pressure drop higher for longer lengths 2. As length increases coolant temp rises 3. Large variation of channel surface temperature Split flow nullifies these effects 8
- 9. MANUFACTURING Traditional machining operations used initially. The last two decades have seen significant improvement in microscale manufacturing technologies. Major technologies used are 1. Water jet cutting 2. Electrical discharge machining 3. Ultrasonic cutting 4. Steriolithography 9
- 10. GENERAL LAYOUT Mounted on part that need cooling. Coolant passed over the surface Coolant cooled in secondary heat exchanger 10
- 11. 11
- 12. COOLANTS USED Conventionally used refrigerants in a microchannel are: 1. Air 2. Water 3. Refrigerant But none of these coolants are considered ideal to reach present requirements 12
- 13. NANOFLUIDS Suspended metallic nanoparticles in traditional coolants High thermal conductivity increase heat transfer Other factors are: 1. Brownian motion 2. Nature of heat transfer in nanoparticles 13
- 14. 14
- 15. LIMITATIONS Machining processes Pressure drop Deviation from continuum Boundary effects 15
- 16. CONCLUSIONS In microchannels the use of reduced sized channels lead to high heat flux The last two decades saw considerable increase in microchannel technology Wide variety of processes available today for manufacture Different coolants used in microchannels were also analysed Microchannels have huge potential for further devolopment 16
- 17. REFERENCES Mohammed,H.A;Bhaskaran,G;Shuaib,N.H;and Saidur,R; Heat transfer and fluid flow characteristics in microchannels heat exchanger using nanofluids: A review; Renewable and Sustainable Energy Reviews;2010;P1502-1512 Przemysław Smakulski;and Sławomir Pietrowicz; A review of the capabilities of high heat flux removal by porous materials, microchannels and spray cooling techniques; Applied Thermal Engineering,2016 Muhammad-Umar Saeed;Bin-Bin Li;and Zhao-Feng Chen; Mechanical effects of microchannels on fiber-reinforced composite structure;Journals on Composite Structures;2016;P129-141 17