Heat Pipe Assemblies

Heat pipes offer extremely high thermal conductivity in their longitudinal directions. Depending on the lengths and manufacturing factors, the effective thermal conductivity of heat pipes can be 10 to 1000 times of the thermal conductivity of pure copper. When coupled with highly conductive fins or spreaders, heat pipes become a powerful tool that can quickly dissipate large quantities of heat to the environment or a location where additional cooling systems can be installed.

Design and Modeling

Thermal Analysis of Heat Pipe Assembly

Three-dimensional simulation is extremely valuable in the design of heat pipe assemblies. Because of the complex thermodynamic process (evaporation and condensation) within a heat pipe, direct simulation of physical process is difficult and time-consuming. For most engineering designs, a simple workaround is to model the heat pipe as a super conductor with a high effective thermal conductivity. The longer the heat pipe is, the higher the effective thermal conductivity should be. The assumed effective thermal conductivity shall be corrected after prototypes are made and thermal measurements are performed.



MyHeatSinks brings expertise and innovation to solving complex thermal management problems in areas as diverse as electronics cooling, LEDs, aerospace, medical devices and so much more. Our team is dedicated to the optimization of designing and manufacturing custom high-performance thermal solutions with innovative and advanced technologies. To begin designing heat pipe assemblies, follow the steps below.

Step 1: Start with the Basics

Heat pipe assemblies are great thermal energy transporters. They are used to move heat from a high powered component in a constrained area, to an area placed with a larger and more conductive fin array. With the use of an evaporator and condenser with capillary actions, heat can be transferred with the use of heat pipe assemblies. Heat pipe assemblies have 3 major components: heat collector, heat pipes, and fins.

COLLECTOR

To begin with, the collector is the part of the assembly that interfaces with the hot component and heat pipes. The collector works as the evaporator section of the assembly as the heat from the hot component vaporizes the working fluid inside the heat pipes. Collectors can be manufactured with different materials and machining options.

Machining Options

  • Extrusion
  • CNC Machining
  • Cold Forging
  • Die-Casting

Materials

  • Copper
  • Aluminum


HEAT PIPES

Heat pipes are thermal devices that transfers heat with minimal temperature difference and spreads heat across an area. When being used in a heat pipe assembly, heat pipes are used to transfer heat from the collector to a heat sink. Heat pipes have a very high effective thermal conductivity and uses liquid-vapor phase transitions to transfer and spread heat. A heat pipe itself is a vacuum-tight containment unit composed with a capillary wick structure and a working fluid. MyHeatSinks can provide solutions with custom heat pipes and different types of working fluids to create a heat pipe assembly. We can flatten and bend heat pipes into different shapes that meets our customer’s design requirements.


Wick Structures

Sintered Wick

A capillary wick made of sintered powder that adheres to the inner walls of a heat pipe.

Benefits

  • Allows High Heat Flux
  • Wide Working Angle

Micro-Groove Wick

A copper tube with a series of shallow grooves on the inside of the heat pipe.

Benefits

  • Light Weight
  • Low Costs

Compound Wick

Includes the features of both sintered and micro-groove wicks.

Benefits

  • Allows High Heat Flux
  • Operates on Planetary Surfaces

For more information about heat pipes, please check our pages for Standard Heat Pipes, Custom Heat Pipes and Heat Pipe Assemblies. **(link to each)**


Working Fluids

Thermal energy is transferred from one point to another by evaporation and condensation of a working fluid or coolant. The heat inputted to a heat pipe vaporizes the working fluid in liquid form at the wick surface. Vapor then flows toward the colder condenser section where it condenses and releases heat to be dispersed by the fins. Capillary action then moves the condensed liquid back to the evaporator section through the wick structure.

H2O Distilled Water Working Fluid

Best for applications with working temperature at room temperature (20°C) or above.

CH3OH Methanol Working Fluid

Best for applications with low working temperature.


FINS

The fins are at the condenser section of the assembly. Fins are designed to increase the surface area for heat dissipation. The number and size of fins depends on the requirements of the projects and airflow (if any).

Skived Fins

Made by using a sharp and controlled tool to peel fins from a solid bar of aluminum or copper. The tool shaves a small thickness of the material, lifts it up, and bends it vertically to form the fin. This allows heat sinks to have very thin fins, high aspect ratio and high fin density.

Stamped & Zipped Fins

Made by having metal sheets of aluminum or copper stamped into the desired configuration. The stamped fins can then be folded and zipped together by being interlinked. This offers higher mechanical stability compared to skived or folded fins.The fins are then attached to a heat sink base. This allows heat sinks to have high efficiency, high aspect ratio and to be more lightweight.


Optional

Fans or blowers can be added to be used to cool the fins by supplying airflow to the fins.

Fans

Electrical devices that have blades to help create a continuous airflow and circulate the air around in every direction. Air is pushed out axially and the direction of airflow is along the axis of the rotor.

Blowers

Mechanical devices with impellers that channel the air in a specific direction towards a particular location. Blowers use centrifugal force to blow out the air and use the kinetic energy created by the impellers to increase or decrease the volume of air.

TIM (Thermal Interface Materials)

Creates heat conductive paths at interfaces between components and reduces thermal interface resistance. TIMs are compounded to fill in thermally insulative air gaps, maximize heat transfer efficiency, improve device reliability and extend longevity.

Step 2: Know Your Design Requirements

In order to customize a heat pipe assembly with the best performance for specific projects, we will need to know the following information about the application:

  1. Heat to Dissipate (Watts)
  2. Side and Location of the Heat Source
  3. Maximum Allowed Temperature on Your Device (or Required Thermal Resistance)
  4. Airflow Speed (If Any)
  5. Ambient Temperature
  6. Orientation During Normal Use (Important)

Step 3: Choose the Right Components & Method

Based on the design requirements, we can move forward with choosing heat pipes, types of fins and assembly method.

Heat Pipe Requirements:

  • Heat Flux
  • Power
  • Wick

Types of Fins:

  • Skived
  • Stamped & Zippered (Interlocked Fins)

Assembly Method:

  • Soldering
  • Epoxy
  • Mechanical Fitting

Assembly Methods

Soldering

Direct copper to copper bonds or nickel plating over aluminum.

Advantages:

  • Provides a thermally and mechanically superior joint
  • Best for aluminum block or plate
  • Less internal vapor pressure
Four Stages:

1. Preheat Zone
  • First stage of reflow process.
  • Slow warm up allows solvent and water in the paste vapor to come out on time.
  • Big component can heat up consistently with other small components.
2. Soaking Zone
  • Typically, a 60-120 seconds exposure.
  • Flux is activated and removes the oxidized substitute on the metal surface to prepare to make a solder joint between two components.
3. Reflow Zone
  • Part of the process where the highest temperature is reached.
4. Cooling Zone
  • Temperature gradually decreases and makes solid solder joints.
  • Maximum allowable cooling down slope needs to be considered to avoid any defect from occurring.


Our Machines:

Thermo Scientific

  • Preheat

Reflow Oven

  • Soak (approaching melting T)
  • Reflow (above melting T)

Cooling Chamber

  • Cooling (4 fans)
Types of Solders:

1. Traditional non-RoHS compliant solder
2. RoHS compliant high temperature solder
3. RoHS compliant medium temperature solder
4. RoHS compliant low temperature solder

Epoxy

Thermally conductive glue typically used for electronic components and heat sinks.

Advantages:

  • Good for very large parts
  • Versatile low costs
  • Excellent bonding and physical strength properties

Mechanical Fitting (Press Fit or Friction Fit)

The fins have holes that are slightly smaller than the diameter of the heat pipe for the fins to be pressed onto the heat pipes with pressure.

Advantages:

  • Assembly becomes more secure as temperature rises
  • Cost and time efficient
  • Easily repaired

Step 4: Design, Refine, Optimize

MyHeatSinks works with you to analyze the design and specifications that provide the best level of performance, cost, quality and lead time. Send your current design to us and we will help to optimize and create prototypes. After we receive your design, we will give more information on the following:

Design for Manufacturability & Cost

  • Mass Production with Low Costs (Highly Competitive Prices)
  • High Efficiency Manufacturing
  • Competitive Lead Times

Refine & Optimize

  • Custom Design & Optimization to Achieve the Highest Performance
  • High-Quality and High-Performance Products
  • Thermal Laboratory with Wind Tunnel, TIM Tester, and Heat Pipe Tester

For design assistance, please let us know your requirements – and we will help you design the right thermal solution that best fits your needs.

Quote Your Heat Pipe Assembly Design

Please click here to request a quote for your heat pipe solutions. Upon evaluation, we will send you a quote as soon as it is ready.

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