Download Electronics Cooling MEP 635

Electronics Cooling
MPE 635
Mechanical Power Engineering
Dept.
Course Goals
1. To establish fundamental understanding of
heat transfer in electronic equipment.
2. To select a suitable cooling processes for
electronic components and systems.
3. To increase the capabilities of post-graduate
students in design and analysis of cooling of
electronic packages.
4. To analysis the thermal failure for electronic
components and define the solution.
• Part-A
• Main topics
• Introduction to electronics cooling and thermal packaging
• Introduction to basic modes of heat transfer
• Conduction heat transfer and extended surfaces in electronic
devices
• Transient conduction
• Natural convection heat transfer (i.e. PCB cooling)
• Forced convection heat transfer (Internal and External flow )
• Fan performance
• Radiation heat transfer and its applications in electronic devices
• Solving the electronics cooling problems with EES software
• Electronics cooling problems
• Solution of selected electronics cooling problems
1. Introduction to electronics
cooling and thermal packages
• Thermal management importance in the
electronic product development
• Heat sources in electronic products:
-Power dissipated through electric resistances
P=I2R
-Switching power dissipation in transistors
Case Study
Every personal computer contains a CPU.
The CPU clock and speed progress with time, the
clock speed was increased from 200 MHz to 2
GHz from 1998 to 2003. due to this
improvement, the CPU packages should also be
improved to accommodate the increase in heat
dissipation.
You are required to study the various heat sinks
and the required fan for thermal management
for the Pentium® Processors from the MMX
generation until the 4th generation.
Reliability and temperature
• Recent studies of electronic equipment have
shown that the field reliability of equipment is
temperature related.
• The failure rate model may be competitively
described by the Arrhenius-type model
i  Bi e
  Ai




(
T
)
j


 Ei
• Where the coefficients Ai, Bi, and Ei are independent
of temperature.
Reliability and temperature
• Typical junction temperatures for
equipment presently operating in a large
number of field applications.
acceptable
uncertain
**
marginal
*
High risk
optimum
0
25
10
50
40
100
75
60
85
125
110
Junction Temperature, ºC
150
175
200
* max military allowable range
** max commercial design point
Liquid Cooling System Consideration
• System Types
-direct cooling system
• The coolant flows over the component to remove
heat from the surface and as such must be
capable of sustaining a voltage gradient
• Efficient means of heat removal because the
coolant is closest to the heat source.
Liquid Cooling System Consideration
• System Types
-Direct cooling system (cont.)
• Restrictions
- Necessity for the maintenance of coolant
purity
- The system must be absolutely airtight in
order to prevent air or moisture from
degrading the heat transfer performance of
the coolant.
- Extreme care is thus required in selecting a
dielectric for direct cooling applications.
Liquid Cooling System Consideration
• System Types
-Direct cooling system (cont.)
• Common Examples of Direct Liquid Cooling
Coolant
Application
FC.77
Cray-2 supercomputer
FC-104, EGW, deionized water
Laser target illumination for electro-optical
systems
C25R
Radar transmitter and TWTs on F-15 and F-16
fighter aircraft and others
FC-77, EGW
Antenna and klystron tubes for E3-AWACS
radar system
C25R, PAO
TWTs on F-16 and ATF radars
Liquid Cooling System Consideration
• System Types
-Indirect cooling system (cold-plate cooling)
• No requirement on the voltage drop.
• Suitable for commercial applications
• May be used in antenna array modules having
solid-state circuitry and in high-heat flux power
supply modules in aircraft applications.
Liquid Cooling System Consideration
• Coolant Selection Parameters
-
FOM (Figure of Merit)
Toxicity
Maximum wet wall temperature
Flammability
Cost
Material compatibility
Corrosion
Pressure drop characteristics
Water absorption sensitivity
Liquid Cooling System Consideration
•
Pressure drop and pump requirements
- For the viscous pressure drop through the heat
exchanger core, neglecting the entrance and exit
losses,
L  V 2 


pcore  4 f
dH  2 
Liquid Cooling System Consideration
Pressure drop and pump requirements
System impedance
curve
Static Head, m of water
•
Pump Characteristic
Curve
Liquid flow rate, m3/s
AIR COOLING SYSTEM
1. Induced or Draft Cooling
For small heat dissipation applications, the prime mover of the
air cooling system may be the draft or circulation created by
density variations.
2.
Forced Cooling
The prime movers are fans or blowers . For The general
classification of blowers is best defined in terms of
specific speed. Specific speed, Ns, is expressed by the

equation
0.5
Q
N s  rpm 0.75
p
Where:
Q (in ft3/min) and the pressure Δp (in inches of water)
AIR COOLING SYSTEM
2. Fans and Blowers
1.E+06
Propeller fans
Tubeaxial Fans
1.E+05
Vaneaxial Fans
1.E+04
Squirrral-Cage
blow ers, forw ard
curved Loose
scroll
Squirrral-Cage
blow ers, forw ard
curved Tight scroll
centraxial blow ers
1.E+03
Range of specific speeds for various
Fans and blowers
Fan and blower impeller designs