Enhanced Heat Transfer

• General Information for Heat Sink-Thermalloy concerns heat sink testing, comparison, and calculation

Technology

• Heat Sink Guide-discusses cooling of electronic components
• Basic Electronic cooling-compares different types of enhanced heat transfer for electronic cooling
• Pentium Design Guides and Others

Measurement Technology

• Liquid Crystal Thermography-the use of Liquid Crystals to measure temperature
• Microthermal Imaging in the Infrared-temperature measurement based on the infrared technology
• Temperature Measurement Using Optical Fibers-the use of fiber optic technology for thermal measurements

Relevant Subjects

• Heat Pipe Technology- Thermacore provides information on the heat pipe technology  

• PC Fan Selection-An article covering the basics of fan selection for personal computer, from positioning to sizing

• Thermoelectric Cooler-Explains the use of thermoelectric coolers, operating based on the Peltier effect

Cooling of Electronic Packages

Electronic equipment has become increasingly important to our daily life.  Improvement of these systems requires continued miniaturization of electronic components.  However, one of the most significant restrictions to achieve this goal is the inability to dissipate enough heat from these very closely-spaced devices.   Accordingly, poorly designed thermal management system will result in high operating temperatures for electronic equipment, leading to many potential problems or even premature failures.  For example, in order to keep a Pentium CPU running smoothly, it is recommended by Intel that the maximum device junction (CPU die) temperature must not exceed 90 deg. C.  Therefore, additional thermal enhancement to dissipate the heat is necessary.  The most popular way of achieving that is to use a heat sink module as shown below. 

Heat Sink Module for a Pentium II CPU Processor, from AAVID Thermal Products, Inc.

It is nothing more than just a set of extended fin structures.  By protruding out from the CPU chip using highly conductive materials, the heat sink module effectively increases the contact surface between the CPU unit and ambient air.  According to Newton's cooling law, the amount of heat transfer through convection increases.  When combining with a fan unit, the heat sink can significantly reduce the CPU temperature which allows the Pentium CPU to run smoother or even faster by overclocking at higher clock rates.

Heat Pipe Technology

Unfortunately, the heat sinks usually are bulky and can not be used in systems where the space is limited, such as a laptop computer.  Therefore, other heat transfer enhancing devices are necessary to reduce the temperature of a laptop CPU.   One candidate to achieve this goal is the heat pipe technology.  A heat pipe is a condenser-evaporator system in a simple form as a hollow tube with layers of wire screens along the wall to serve as a wick, as shown in the following figure.

Schematic of a Heat Pipe

Heat is transferred into the evaporator section to vaporize liquid.   Vapor is returned to the condenser section and releases the heat to a heat sink by condensation at the other end.  The liquid is returned to start the process over through a wick structure on the inside of the heat pipe.  Heat pipe has an advantage that it has very low thermal resistance and its performance is relatively insensitive to its length.  Consequently, it can be arranged in many shapes to accommodate different configurations.  It has been successfully implemented in laptop computers.  Shown below is a heat pipe connected to a laptop computer chip.

Heat Pipe Technology Used in a Laptop Computer