A heat pipe is an extremely efficient thermal conductor. It can transfer large quantities of heat over a long distance essentially at a constant temperature. It is typically a sealed copper or aluminum tube containing a wick structure on its inner surface and a small amount of working fluid at its saturation state. The fluid absorbs heat and vaporizes at hot spots and condenses and releases heat at cool spots. As the process goes on, heat is transferred from the hot spots to the cool spots.

Because a heat pipe has no moving parts, it is a highly reliable device with demonstrated lifespan of over 20 years. The reliability depends on the manufacturing process and the purity of the materials. At MyHeatSinks, all heat pipes are 100% individually tested to ensure functionalities and reliability.

Wick Structure and Working Fluid

The performance of a heat pipe is mainly determined by its wick structure, which performs 3 primary functions: First, to allow the backflow of the liquid from the condenser section to the evaporator section; Second, to allow the heat transfer between the inner wall and the fluid; Third, to provide room for the fluid to change phase. We currently provide heat pipes with 3 different types of wick structures – the sintered wick, the micro-groove wick and the compound wick. The sintered wick allows high heat flux and wide working angle and is recommended for most electronic applications. Micro-groove wick offers light weight and low cost, but its working angle is limited and often gravity dependent. Compound wick combines the features of both sintered and micro-groove wicks and is preferable in some applications.

The most common working fluids used in heat pipes include water, ammonia, acetone and methanol. In moderate temperature range, water is the ideal working fluid due to its high latent heat and proper boiling point. For low temperature applications, ammonia, acetone and methanol can be used.

Standard Dimensions

Diameter ØD	4 mm	5 mm	6 mm	8 mm	10 mm
Length L	60-600 mm	60-600 mm	60-600 mm	60-600 mm	60-600 mm
Length L1	1-3 mm	2-4 mm	3-5 mm	4-7 mm	5-8 mm
Length L2	7-9 mm	8-10 mm	9-11 mm	11-13 mm	13-15 mm

Large Diameter Heat Pipes

The largest diameter we currently make is 12.7 mm (0.5 inch). The heat pipes have micro-groove wick and are designed for high-power LED applications and solar systems.

Reliability Test

No.	Test Item	Test Conditions	Sampling Ratio	Purpose
1	High Temp. Aging Test	Ambient Temp. 210 C for 12 hr	100%	Leakage check & aging
2	Thermal Response Test	Insert 1/3 – ½ length of pipe into 50°C water. The temp of other end shall rise to standard value in 25 seconds.	100%	Vacuum & leakage check
3	Qmax Test	Heating Length = 25-35mm, Test temp = 60°C	100%	To measure the max. heat transfer rate
4	Rth Thermal Resistance Test	Fix heat transfer rate and measure temp. difference of heat pipes	>1pcs/2hr	To ensure thermal resistance of each pipe be lower than spec
5	Accelerated Life Test	140 C for 1000hr. Performance decrease by less than 7%	By case	To predict life of heat pipe at certain operating temp.
6	Continuous Life Test	Continuous testing at normal operating conditions	By case	To measure actual life of heat pipe until failure occurs
7	Thermal Cycling Test	Temp. varies from -30 C to 120 C in 10hr, 600 cycles	By case	To measure performance variation after thermal cycling

RoHS Compliance

Our heat pipes are in compliance with the European Union Directive 2002/95/EC on the Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment (RoHS Directive).

Restricted Substances	Symbol	Limit	Test Method
Lead	Pb	<1000ppm	EPA 3050B
Mercury	Hg	<1000ppm	EPA 3052
Cadmium	Cd	<1000ppm	EN 1122
Hexavalent Chromium	Cr6+	<1000ppm	EPA 3060A
Polybrominated Biphenyls	PBB	<1000ppm	EPA 3540C
Polybrominated Diphenyl Ethers	PBDE	<1000ppm	EPA 3540C

Characteristics and Features

High Thermal Conductivity – A heat pipe has much lower thermal resistance and much higher thermal conductivity than any solid conductors such as silver, copper and aluminum, enabling it to transfer heat more efficiently and evenly in several orders. For example, a 6mm diameter heat pipe with sintered wick can transfer up to 120W heat.

Excellent Isothermal Performance – Due to the small pressure drop of saturated vapor from the evaporator section to the condenser section, a heat pipe can maintain almost a constant temperature over its full length.

Reciprocity of Heat Flow Direction – The circulation inside a sintered heat pipe is driven by capillary force, instead of gravity. So either end can be the evaporator section or the condenser section.

Adaptability to Environment – Due to the various wick structures, we can supply heat pipes that are suitable and reliable to meet any environmental challenges.

Surface Treatment – Our heat pipes are treated by an anti-oxidation process. They can also be nickel plated or anodized to increase its weldability or heat radiation capability.

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