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HIGH FLUX HEAT TRANSFER IN MICROCHANNELSPRESENTED BY, GUIDED BY,
NEETHIN NANDAKUMAR DR.BINOY BABY
S7,ME-B HOD
ROLL NO-14 DEPT. OF MECH ENGG.
2CONTENTS
1. HEAT EXCHANGERS2. MICROCHANNEL COOLING3. NEED FOR SMALLER CHANNELS4. APPLICATIONS5. CHANNEL DIMENSIONS6. SINGLE PASS VS SPLIT FLOW7. MANUFACTURING8. COOLANTS USED9. NANOFLUIDS10. LIMITATIONS11. CONCLUSIONS12. REFERENCES
3HEAT 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
4MICROCHANNEL 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
5NEED FOR SMALLER CHANNELS
Channels serves two purposes:1. Path for coolant flow2. Provides intimate contact
D/LDDL
VA 4
42
As D h
Dkh 657.3
6APPLICATIONS
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
7CHANNEL DIMENSIONS
Channel dimensions are chosen after taking into consider the following factors:
1. Maximum allowable temperature of channel surface2. Maximum coolant temp3. Cost considerations4. Maximum pressure drop
8SINGLE PASS VS SPLIT FLOW Disadvantages of single pass:1. Pressure drop higher for longer lengths2. As length increases coolant temp rises3. Large variation of channel surface temperature
Split flow nullifies these effects
9MANUFACTURING
Traditional machining operations used initially. The last two decades have seen significant improvement in
microscale manufacturing technologies. Major technologies used are1. Water jet cutting2. Electrical discharge machining3. Ultrasonic cutting4. Steriolithography
10GENERAL LAYOUT
Mounted on part that need cooling. Coolant passed over the surface Coolant cooled in secondary heat exchanger
11
12COOLANTS USED
Conventionally used refrigerants in a microchannel are:1. Air2. Water3. Refrigerant But none of these coolants are considered ideal to reach present
requirements
13NANOFLUIDS
Suspended metallic nanoparticles in traditional coolants High thermal conductivity increase heat transfer Other factors are:1. Brownian motion2. Nature of heat transfer in nanoparticles
14
15LIMITATIONS
Machining processes Pressure drop Deviation from continuum Boundary effects
16CONCLUSIONS
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
17REFERENCES
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