Standard Heat Pipes

Part Number	Diameter (mm) +/- 0.1	Length (mm) +/- 1.0	Weight (g)	Qmax (W)	Availability	Request Quote
S704-100-000	4	100	5	28	In stock	Quote
S704-150-000	4	150	8	22	In stock	Quote
S704-200-000	4	200	10	16	In stock	Quote
S704-250-000	4	250	13	12	In stock	Quote
S704-300-000	4	300	15	10	In stock	Quote
S704-350-000	4	350	18	9	In stock	Quote
S704-400-000	4	400	20	8	In stock	Quote
S704-LLL-000	4	LLL	–	–	Ship in ~2 weeks	Quote
S705-100-000	5	100	6	52	In stock	Quote
S705-150-000	5	150	9	45	In stock	Quote
S705-200-000	5	200	11	40	In stock	Quote
S705-250-000	5	250	14	35	In stock	Quote
S705-300-000	5	300	17	30	In stock	Quote
S705-350-000	5	350	20	25	In stock	Quote
S705-400-000	5	400	24	22	In stock	Quote
S705-LLL-000	5	LLL	–	–	Ship in ~2 weeks	Quote
S706-100-000	6	100	8	60	In stock	Quote
S706-150-000	6	150	12	53	In stock	Quote
S706-200-000	6	200	16	45	In stock	Quote
S706-250-000	6	250	20	38	In stock	Quote
S706-300-000	6	300	24	33	In stock	Quote
S706-350-000	6	350	28	29	In stock	Quote
S706-400-000	6	400	32	26	In stock	Quote
S706-LLL-000	6	LLL	–	–	Ship in ~2 weeks	Quote
S708-100-000	8	100	15	72	In stock	Quote
S708-150-000	8	150	22	67	In stock	Quote
S708-200-000	8	200	29	61	In stock	Quote
S708-250-000	8	250	35	55	In stock	Quote
S708-300-000	8	300	42	50	In stock	Quote
S708-350-000	8	350	50	45	In stock	Quote
S708-400-000	8	400	58	41	In stock	Quote
S708-LLL-000	8	LLL	–	–	Ship in ~2 weeks	Quote
S710-100-000	10	100	22	90	In stock	Quote
S710-150-000	10	150	33	84	In stock	Quote
S710-200-000	10	200	45	78	In stock	Quote
S710-250-000	10	250	56	72	In stock	Quote
S710-300-000	10	300	67	65	In stock	Quote
S710-350-000	10	350	78	57	In stock	Quote
S710-400-000	10	400	90	47	In stock	Quote
S710-LLL-000	10	LLL	–	–	Custom order	Quote
S712-100-000	12	100	33	110	Ship in ~2 weeks	Quote
S712-150-000	12	150	47	98	Ship in ~2 weeks	Quote
S712-200-000	12	200	64	89	Ship in ~2 weeks	Quote
S712-250-000	12	250	80	79	Ship in ~2 weeks	Quote
S712-300-000	12	300	98	68	Ship in ~2 weeks	Quote
S712-350-000	12	350	114	60	Ship in ~2 weeks	Quote
S712-400-000	12	400	130	53	Ship in ~2 weeks	Quote
S712-LLL-000	12	LLL	–	–	Custom order	Quote

Notes: Q_max values are measured using our standard setup in a horizontal orientation. In a vertical orientation with the heat source at the bottom (gravity-aided), Q_max can double. Actual performance may vary based on the heat pipe’s orientation and the specific locations of heat input and condensation.

Part Number	Original Diameter (mm)	Thickness (mm) +/- 0.1	Width (mm) +/- 0.2	Length (mm) +/- 1.0	Weight (g)	Qmax (W)	Availability	Request Quote
S704-100-020	4	2.0	5.3	100	5	18	In stock	Quote
S704-150-020	4	2.0	5.3	150	8	16	In stock	Quote
S704-200-020	4	2.0	5.3	200	10	14	In stock	Quote
S704-250-020	4	2.0	5.3	250	13	12	In stock	Quote
S704-300-020	4	2.0	5.3	300	15	10	In stock	Quote
S704-350-020	4	2.0	5.3	350	18	8	In stock	Quote
S704-400-020	4	2.0	5.3	400	20	6	In stock	Quote
S704-LLL-TTT	4	TTT/10	–	LLL	–	–	Ship in ~2 weeks	Quote
S705-100-025	5	2.5	6.6	100	6	50	In stock	Quote
S705-150-025	5	2.5	6.6	150	9	45	In stock	Quote
S705-200-025	5	2.5	6.6	200	11	39	In stock	Quote
S705-250-025	5	2.5	6.6	250	14	34	In stock	Quote
S705-300-025	5	2.5	6.6	300	17	29	In stock	Quote
S705-350-025	5	2.5	6.6	350	20	24	In stock	Quote
S705-400-025	5	2.5	6.6	400	24	19	In stock	Quote
S705-LLL-TTT	5	TTT/10	–	LLL	–	–	Ship in ~2 weeks	Quote
S706-100-030	6	3.0	8.0	100	8	56	In stock	Quote
S706-150-030	6	3.0	8.0	150	12	50	In stock	Quote
S706-200-030	6	3.0	8.0	200	16	44	In stock	Quote
S706-250-030	6	3.0	8.0	250	20	38	In stock	Quote
S706-300-030	6	3.0	8.0	300	24	32	In stock	Quote
S706-350-030	6	3.0	8.0	350	28	27	In stock	Quote
S706-400-030	6	3.0	8.0	400	32	24	In stock	Quote
S706-LLL-TTT	6	TTT/10	–	LLL	–	–	Ship in ~2 weeks	Quote
S708-100-040	8	4.0	10.6	100	15	70	In stock	Quote
S708-150-040	8	4.0	10.6	150	22	65	In stock	Quote
S708-200-040	8	4.0	10.6	200	29	60	In stock	Quote
S708-250-040	8	4.0	10.6	250	35	55	In stock	Quote
S708-300-040	8	4.0	10.6	300	42	50	In stock	Quote
S708-350-040	8	4.0	10.6	350	50	45	In stock	Quote
S708-400-040	8	4.0	10.6	400	58	40	In stock	Quote
S708-LLL-TTT	8	TTT/10	–	LLL	–	–	Ship in ~2 weeks	Quote
S710-100-040	10	4.0	14.0	100	22	85	In stock	Quote
S710-150-040	10	4.0	14.0	150	33	80	In stock	Quote
S710-200-040	10	4.0	14.0	200	45	74	In stock	Quote
S710-250-040	10	4.0	14.0	250	56	68	In stock	Quote
S710-300-040	10	4.0	14.0	300	67	62	In stock	Quote
S710-350-040	10	4.0	14.0	350	78	55	In stock	Quote
S710-400-040	10	4.0	14.0	400	90	45	In stock	Quote
S710-LLL-TTT	10	TTT/10	–	LLL	–	–	Custom order	Quote
S712-100-040	12	4.0	17.3	100	33	100	In stock	Quote
S712-150-040	12	4.0	17.3	150	47	94	In stock	Quote
S712-200-040	12	4.0	17.3	200	64	85	In stock	Quote
S712-250-040	12	4.0	17.3	250	80	78	In stock	Quote
S712-300-040	12	4.0	17.3	300	98	65	In stock	Quote
S712-350-040	12	4.0	17.3	350	114	58	In stock	Quote
S712-400-040	12	4.0	17.3	400	130	50	In stock	Quote
S712-LLL-TTT	12	TTT/10	–	LLL	–	–	Custom order	Quote

Notes: (1) Flat heat pipes are produced by flattening round heat pipes to achieve the desired thickness. (2) Q_max values are measured using our standard setup in a horizontal orientation. In a vertical orientation with the heat source at the bottom (gravity-aided), Q_max can double. Actual performance may vary based on the heat pipe’s orientation and the specific locations of heat input and condensation.

Heat pipes are sealed copper or aluminum tubes lined with a wick structure and contain a small amount of working fluid in a saturated state. When heat is applied at hot spots, the working fluid absorbs it and vaporizes. The vapor moves to cooler areas of the heat pipe, where it condenses and releases the heat. This continuous cycle efficiently transfers heat from hotter regions to cooler ones.

Heat pipes were extensively studied at Los Alamos National Laboratory in the 1960s. In 1963, Los Alamos physicist George Grover demonstrated the first heat pipe and coined the term. The technology attracted interest due to its lightweight and ability to handle high heat flux. NASA was among the first to adopt heat pipes, using them to regulate satellite temperatures. Since then, heat pipes have been applied to a wide range of fields, including air conditioning, engine cooling, and electronics cooling.

The wick structure of a heat pipe is essential to its thermal performance and reliability. It serves three main functions. First, it returns condensed liquid from the condenser section to the evaporator section. Second, it facilitates heat transfer between the heat pipe’s inner wall and the working fluid. Third, it creates the space needed for phase change, allowing continuous evaporation and condensation during operation.

Heat pipes commonly use three types of wick structures: sintered wick, micro-groove wick, and compound wick. Sintered wick provides the highest performance, supporting greater heat flux and allowing operation in any orientation, including against gravity. This makes it well-suited for demanding applications. Micro-groove wick is lightweight and cost-effective but performs best when aligned with gravity. Compound wick blends features of both sintered and micro-groove designs, offering improved performance for specialized uses. At MyHeatSinks, we use sintered wick heat pipes due to their reliable thermal performance and ability to operate in all orientations.

Selecting the right working fluid is another important aspect of heat pipe design. Ammonia, acetone, and methanol are commonly used for low-temperature applications, while water is preferred for moderate-temperature environments. Water’s high latent heat and suitable boiling point make it an efficient choice for electronic cooling.

The standard wall thickness for most heat pipes is 0.3 mm. For heat pipes that require milling, the wall thickness is typically between 0.4 and 0.5 mm to maintain flatness after flattening. Ultra-thin heat pipes, with a wall thickness of approximately 0.2 mm, are often used in smartphones and wearable devices.

Below are the 27 typical steps involved in the manufacturing of heat pipes:

1. Receiving Materials – Copper tubes (containers), wick material (copper powder), and working fluid (distilled water).
2. Cutting – Tubes are cut to rough lengths.
3. Cleaning – Degreasing and deoxidation of the tubes.
4. Bottom-End Shrinking and Sealing – The bottom end is shrunk to 3 mm and sealed by welding.
5. Filling Wick Material – Copper powder is filled into the tubes.
6. Sintering – The filled tubes undergo sintering to structure the wick.
7. Core Rod Removal – The core rod is removed from the tubes.
8. Top-End Shrinking and Sealing – The top (filling) end is shrunk and welded to seal.
9. Rounding (If needed) – The tubes are rounded as required.
10. Annealing – Relieves stress and improves material properties.
11. Filling Working Fluid – Distilled water is added as the working fluid.
12. First-Stage Vacuuming – Air is removed at room temperature.
13. Heating and Second-Stage Vacuuming – After deep vacuuming, tubes are cut to the exact length and crimp sealed.
14. Arc Welding – Completes the sealing process.
15. Leak/Thermal Response Test – Tests for leaks and verifies thermal performance.
16. Q_max and Thermal Resistance Test – Measures heat transport capacity and thermal resistance.
17. Rounding (If needed) – Performed again if necessary.
18. Bending (If required) – Pipes are bent to the required angle.
19. Flattening (If required) – Pipes are flattened to the required thickness.
20. Progressive Shaping (If required) – Pipes are shaped further to achieve the final form.
21. Accelerated Life Test – Simulates extended operation to ensure longevity.
22. Leak/Thermal Response Test (Second Time) – Conducted to detect leaks and confirm performance.
23. Qmax and Thermal Resistance Test (Second Time) – Repeated to verify performance consistency.
24. Cleaning – Pipes undergo a final cleaning process.
25. Surface Finishing – Antioxidation treatment or nickel plating is applied.
26. Quality Inspection – Comprehensive inspection to ensure product quality.
27. Packing and Delivery – Pipes are packed and delivered to stock.

Heat pipes are partially filled with distilled water or another working fluid and then heated until the fluid boils and expels air. The pipe is sealed while still hot to preserve the vacuum. The fluid amount typically slightly exceeds the pore volume of the wick, ranging from 0.1 to 20 ml (or 0.1 to 20 g).

The internal vacuum pressure of heat pipes usually falls between 0.1 and 1.0 Torr (13 to 133 Pa). Lower vacuum pressure can increase the maximum heat transfer capacity (Q_max), following an exponential relationship between Q_max and vacuum pressure.

The sealed ends of heat pipes create thermally ineffective zones at both ends. The ineffective length at the first end (where the hollow tube is initially sealed to prevent leakage during wick powder and fluid filling) is referred to as L1. The ineffective length at the second end (where the tube is crimp-sealed after fluid filling and vacuuming) is referred to as L2. To optimize performance, the heat source and heat sink should be placed outside these ineffective areas unless constrained by other factors.

Diameter ØD	4 mm	5 mm	6 mm	8 mm	10 mm	12 mm
Length L	80-600 mm	80-600 mm	80-600 mm	80-600 mm	80-600 mm	80-600 mm
Length L1	1-3 mm	2-4 mm	3-5 mm	4-7 mm	5-8 mm	6-10 mm
Length L2	7-9 mm	8-10 mm	9-11 mm	11-13 mm	13-15 mm	15-18 mm

No.	Test Item	Typical Test Conditions	Sampling Ratio	Purpose
1	High Temperature Aging Test	Ambient temperature of 210°C for 12 hours	100%	Check for leakage and aging
2	Thermal Response Test	Insert 1/3 to 1/2 length of pipe into 65°C water. The opposite end should reach the standard temperature in 25 seconds	100%	Verify vacuum integrity and check for leakage
3	Qmax Test	Heating length: 25-35 mm, Test temperture: 60°C	100%	Measure maximum heat transfer rate
4	Thermal Resistance Test	Fix heat transfer rate and measure temperature difference along the heat pipe	1 sample per 2 hours	Ensure thermal resistance is within specifications
5	Accelerated Life Test	140°C for 1000 hours, with performance degradation of less than 7%	Case-by-case	Predict heat pipe lifespan under specific operating conditions
6	Continuous Life Test	Continuous testing under normal operating conditions	Case-by-case	Measure actual lifespan until failure
7	Thermal Cycling Test	Temperature cycles from -30°C to 120°C (or -55°C to 125°C) over 10 hours	Case-by-case	Evaluate performance degradation or structural deformation

We use the Longwin LW-9354B to measure the thermal resistance and effective thermal conductivity of heat pipes. The system includes a water-cooling circulation unit, heating control unit, attitude adjustment device, measurement tools, data acquisition system, and advanced software, ensuring precise and repeatable testing. It supports multiple test modes, such as steady-state, cyclic, and thermal response measurements. Adjustable fixtures and programmable power supplies accommodate various heat pipe sizes and shapes. The attitude adjustment device allows for testing at different angles and orientations to simulate real-world conditions. For more information, please visit our Heat Pipe Test page.

The heat pipe testing process involves heating one end of the heat pipe with a heater while cooling the opposite end using a water-cooled cooler, simulating a heat sink. The system measures the temperature difference (∆T) between the heated and cooled ends to calculate the heat pipe’s thermal resistance (R) and effective thermal conductivity (K_eff). By gradually increasing the applied power, the system monitors the heat pipe’s performance and detects any changes. During steady-state tests, a sharp rise in thermal resistance at higher power levels signals the onset of drying inside the heat pipe. This testing method helps determine the maximum heat transfer capacity and assess the reliability of heat pipes under various thermal loads.

The maximum heat transfer capacity (Q_max) is determined by drawing two straight lines. One line follows the relatively flat curve before the sharp rise in thermal resistance, while the other follows the curve after the rise. The intersection of these two lines represents Q_max.

Heat pipes with larger diameters can transfer more heat than those with smaller diameters. Shorter heat pipes can transfer more heat than longer pipes.

Using the attitude adjustment device, we can assess how heat pipe orientation affects its heat transfer capacity. The chart below illustrates the relationship between Q_max and orientation angles. A 0-degree angle indicates a horizontal heat pipe, while 90 degrees represents a vertical orientation with the heat source at the bottom. Conversely, -90 degrees signifies a vertical orientation with the heat source at the top.

The chart shows that when the heat pipe is vertical with the heat source at the bottom, Q_max is approximately double that of the horizontal position. In contrast, when the heat pipe is vertical with the heat source at the top, Q_max is reduced by approximately half.

Thermal response tests evaluate heat pipe performance by measuring how quickly its temperature changes under a thermal load. In this test, the heat pipe is exposed to a thermostatic water tank, and its temperature is monitored. A properly functioning heat pipe transfers heat rapidly and stabilizes at the expected temperature. In contrast, leaks or internal defects result in slower or inconsistent temperature rises. By analyzing the heat pipe’s response, engineers can verify its quality and confirm that it meets performance standards.

The figure on the right shows a thermal response test on a heat pipe with a 6 mm diameter and 200 mm length. The thermostatic water tank is set to 65°C, while the initial temperature of the heat pipe is approximately 20°C. After about 7 seconds, the hot end temperature rises rapidly, reaching around 55°C within 15 seconds.

Thermal cycling tests evaluate the resilience and performance of heat pipes under extreme and varying environmental conditions. These tests simulate rapid temperature changes (thermal shock) or repetitive freeze-thaw cycles, ensuring consistent performance without structural deformation or loss of thermal efficiency. Typical cycles range from -30°C to 120°C or from -55°C to 125°C, depending on the application, and may span anywhere from 10 cycles to 1000 cycles. After testing, heat pipes are assessed for performance degradation, including structural deformations, changes in maximum heat transfer capacity (Q_max), or alterations in diameter. If a heat pipe fails the thermal cycling test, several design modifications can be implemented to improve the heat sink and ensure compliance. Please contact MyHeatSinks to discuss potential design improvements and solutions for thermal cycling issues in your heat pipes.

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
Lead	Pb	<1000ppm
Mercury	Hg	<1000ppm
Cadmium	Cd	<100ppm
Hexavalent Chromium	Cr6+	<1000ppm
Polybrominated Biphenyls	PBB	<1000ppm
Polybrominated Diphenyl Ethers	PBDE	<1000ppm
Bis (2-ethylhexyl) Phthalate	DEHP	<1000ppm
Butyl Benzyl Phthalate	BBP	<1000ppm
Dibutyl Phthalate	DBP	<1000ppm
Diisobutyl Phthalate	DIBP	<1000ppm