Heat Pipes

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HEAT PIPES :

HEAT PIPES

CONTENTS:

CONTENTS Introduction Need for Heat Pipe History Components of a Heat Pipe Working Applications Conclusion

Modern Day Microchips:

Modern Day Microchips Microchips already contain millions of transistors In three decades, circuit elements will be the size of a single atom 40 – 60 °C

Dealing with the Heat:

Dealing with the Heat Traditional stacked heat sink and fan set up not feasible in a laptop Need to separate the two where you have more space

Requirements for Cooling:

Requirements for Cooling Solid metal rods lose too much heat to the environment Cannot use a powered cooling system, too much power consumption caused the problem

What is a Heat Pipe?:

What is a Heat Pipe? A heat pipe is a simple device that can quickly transfer heat from one point to another. They are often referred to as the "superconductors" of heat as they possess an extra ordinary heat transfer capacity & rate with almost no heat loss.

Heat Pipe Background:

Heat Pipe Background 1800s – A. M. Perkins and J. Perkins developed Perkins tube 1944 – R. S. Gaugler introduced the use of a wicking structure 1964 – G. M. Grover published research and coined the “Heat Pipe” name

Components of a Heat Pipe:

Components of a Heat Pipe Container Working fluid Wick or Capillary structure

Container:

Container Metal Tubing, usually copper or aluminum. Provides a medium with high thermal conductivity. Shape of tubing can be bent or flattened.

Working Fluid:

Working Fluid Pure liquids such as helium, water and liquid silver Impure solutions cause deposits on the interior of the heat pipe reducing its overall performance. The type of liquid depends on the temperature range of the application.

The prime requirements :

The prime requirements Good thermal stability Wettability of wick and wall materials Vapor pressure not too high or low over the operating temperature range High latent heat High thermal conductivity Low liquid and vapor viscosities High surface tension Acceptable freezing point

Examples of Working Fluid:

MEDIUM MELTING PT. (° C ) BOILING PT. AT ATM. PRESSURE (° C) USEFUL RANGE (° C) Helium Ammonia Water Silver - 271 - 78 0 960 - 261 - 33 100 2212 -271 to -269 -60 to 100 30 to 200 1800 to 2300 Examples of Working Fluid

The Wicking Structure:

The Wicking Structure The prime purpose of the wick is to generate capillary pressure to transport the working fluid from the condenser to the evaporator. Carbon fiber filaments have many fine longitudinal grooves on their surface, have high capillary pressures and are chemically stable.

COMMON TYPES OF WICKS Axial Groove Wick:

COMMON TYPES OF WICKS Axial Groove Wick Created by carving out grooves on the interior core of the Heat Pipe.

Screen Mesh Wick:

Screen Mesh Wick Utilizes multiple wire layers to create a porous wick. Sintering can be used.

Sintered Powder Wick:

Sintered Powder Wick This process will provide high power handling, low temperature gradients and high capillary forces for anti-gravity applications.

Purpose of the Wick:

Purpose of the Wick Transports working fluid from the Condenser to the Evaporator. Provides liquid flow even against gravity.

How the Wick Works:

How the Wick Works Liquid flows in a wick due to capillary action. Intermolecular forces between the wick and the fluid are stronger than the forces within the fluid. A resultant increase in surface tension occurs.

Capillary Limitation:

Capillary Limitation Wick must have minimum pressure difference between the condenser and the evaporator for liquid to flow. Dry-out occurs when there is insufficient pressure difference.

WORKING Evaporator:

WORKING Evaporator The working fluid is heated to its boiling point and converted into a vapor. Pressure and temperature differences forces the vapor to flow to the cooler regions of the heat pipe.

Condenser`s operations:

Condenser`s operations Condensation Vapor gives up its latent heat of vaporization Vapor cools down and returns to its liquid state Working fluid then flows back to the evaporator through the wick.

Heat Exchanger:

Heat Exchanger Dissipates heat into environment High Thermal Conductivity Improve heat exchanger's performance Increase surface area with more fins Include a fan

Heat Pipe:

Heat Pipe

Applications of Heat Pipes:

Applications of Heat Pipes

SPACE TECHNOLOGY :

SPACE TECHNOLOGY Spacecraft temperature equalization Component cooling, temperature control and radiator design in satellites.

LAPTOP HEAT PIPE SOLUTION :

LAPTOP HEAT PIPE SOLUTION

HEAT PIPE IN CPU:

HEAT PIPE IN CPU

OTHER APPLICATIONS:

OTHER APPLICATIONS Heat Exchangers Modern Cameras Refrigerators Transistors Capacitors Field of Cryogenics

CONCLUSION :

CONCLUSION The cost of heat pipes designed for laptop use is very competitive compared to other alternatives. Cost is partially offset and justified by improved system reliability and the increased life of cooler running electronics. Heat pipe manufacture has been a difficult area to compete in. Simple in concept, but difficult to apply commercially, the heat pipe is a very elusive technology & holds the key to the future of heat transfer & its allied applications.

  REFERENCES :

REFERENCES Andrews, J; Akbarzadeh, A; Sauciue, I.: Heat Pipe Technology, Pergammon, 1997. Dunn, P.D.; Reay, D.A.: Heat Pipes, Pergammon, 1994. www.heatpipe.com. www.cheresources.com. www.indek.com www.wikipedia.org

Slide 31:

THANK YOU