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.

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
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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
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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
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5. NEED FOR SMALLER CHANNELS
 Channels serves two purposes:
1. Path for coolant flow
2. Provides intimate contact
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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
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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
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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
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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
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10. GENERAL LAYOUT
 Mounted on part that need cooling.
 Coolant passed over the surface
 Coolant cooled in secondary heat exchanger
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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
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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
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14. 14

15. LIMITATIONS
 Machining processes
 Pressure drop
 Deviation from continuum
 Boundary effects
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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
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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
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