# Electronics Cooling MPE 635

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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 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 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.

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. In addition, moisture absorption can lead to a chemical breakdown in some coolants, which in turn lowers the flash point, hence creating a potential safety hazard.

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 Application Coolant Cray-2 supercomputer FC.77 Laser target illumination for electro-optical systems FC-104, EGW, deionized water Radar transmitter and TWTs on F-15 and F-16 fighter aircraft and others C25R Antenna and klystron tubes for E3-AWACS radar system FC-77, EGW TWTs on F-16 and ATF radars C25R, PAO

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, the velocity head term () is replaced by (), where G is the mass flow per unit area, kg/m2.s, a more commonly used heat exchanger parameter.

Liquid Cooling System Consideration
Pressure drop and pump requirements the velocity head term () is replaced by (), where G is the mass flow per unit area, kg/m2.s, a more commonly used heat exchanger parameter.

AIR COOLING SYSTEM Induced or Draft Cooling Forced Cooling
For small heat dissipation applications, the prime mover of the air cooling system may be the draft or circulation created by density variations. 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 Where: Q (in ft3/min) and the pressure Δp (in inches of water)

AIR COOLING SYSTEM Fans and Blowers
Range of specific speeds for various Fans and blowers Fan and blower impeller designs