Heat Pipes Research

Research Links:

https://blog.fluidflowinfo.com/heat-transfer-in-pipes

Heat Pipe Technology

The Basics of Heat Transfer

Important Details/Facts Considering Our Application:

• Heat pipes lose heat transfer the longer they are in length (shorter heat pipes provide better overall thermal conductivity)

  • good for solar car application considering space constraints and need to minimize weight

• The thicker the inner insulation is, the less the operating cost is. However, the initial cost of insulation increases with its relative thickness

  • Need to find a balance within insulation thickness that provides enough value and stays within budget

• Heat Pipes conventionally use an evaporation and condensation end to convert liquid to vapor

  • the liquid (typically water) has to be maintained above freezing point and below vapor condensation point (important detail when considering application)

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Working Fluid Types

• Heat pipes can be designed in various shapes

  • provides valuable flexibility when designing. However, the design of heat pipe will definitely impact its maximum efficiency/maximum power transport capacity (big need for ANSYS)

• Heat pipes are typically made with these materials (most used to least used):

  • Copper ---> Aluminum ----> Stainless Steel === Titanium (need to consider weight vs energy benefits for solar car)

• Heat Wick Structures are structures that are within the heat pipe that transport fluid from condensed areas. Essentially, it separates fluid traveling back to heat source and the vaporized fluid. Most popular three:

  • Sintered Wicks: linked walls of (typically) copper within the heat pipe that are baked at high temperatures. Deal with high heat flux and gravity forces very well, giving them versatility when designing the heat pipe

  • Screen/Braided Wicks: designed like a screen door and are used to make thin heat pipes (will reduce weight). Less expensive than sintered wicks but not as efficient with heat flux

  • Grooved Wicks: cheapest option as they are part of the heat pipe. Less flexibility as can only operate in gravity neutral situations (condenser on same level as evaporator)

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Different types of Wicks

• Evaporation portion has to be at or above condenser area to work

• Heat pipes have incredibly long lifespans (up to 20 years) when operating between limitation ranges

• Types of Heat Pipes:

  • Constant Conductance heat pipes (CCHP): fixed thermal conductance between evaporator and condenser, most popular for cooling electronics

  • Variable conductance heat pipes (VCHP): minimize temperature swings and include a non-condensable gas

    • probably not ideal for our application

  • Thermosiphons: gravity aided heat pipes without a wick structure (except possibly near evaporator)

  • Loop Heat Pipes: used for long distances and are quite expensive

    • not applicable for us

  • Rotating Heat Pipes: used to remove heat from motors and have a groove wick similar to rifles

  • Oscillating Heat Pipes: function very well against gravity, strong for larger/longer areas

• Heat Pipes in general are strong suited for situations with weight restrictions, limited airflow, and space constraints