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