# Electronics Cooling MPE 635 Mechanical Power Engineering Dept

• Slides: 16

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 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=I 2 R -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 4 th 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.

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 Coolant -Direct cooling system (cont. ) FC. 77 Application • Common Examples of Direct Liquid Cooling FC-104, EGW, deionized water Cray-2 supercomputer Laser target illumination for electro-optical systems C 25 R Radar transmitter and TWTs on F-15 and F-16 fighter aircraft and others FC-77, EGW Antenna and klystron tubes for E 3 -AWACS radar system C 25 R, 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,

Liquid Cooling System Consideration • Pressure drop and pump requirements

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 Where: Q (in ft 3/min) and the pressure Δp (in inches of water)

AIR COOLING SYSTEM 2. Fans and Blowers Range of specific speeds for various Fans and blowers Fan and blower impeller designs