Heat Pipe Wick Structure: Sintered vs Grooved vs Mesh

Every heat pipe contains three essential elements: a sealed container, a working fluid, and a wick structure. Of these, the wick is the most critical — and the most misunderstood. While the working fluid carries heat through evaporation and condensation, it is the wick structure that pumps the condensed liquid back to the evaporator using capillary action, with no moving parts and no external power. The design of this wick determines almost everything about how a heat pipe performs: its maximum heat transport capacity, whether it can work against gravity, how thin it can be manufactured, and its final cost.

The three dominant wick technologies in production today are sintered powder, axial grooves, and screen mesh. Each offers a distinct balance of capillary pumping power, thermal performance, manufacturing complexity, and price. Choosing the wrong wick structure for an application leads to thermal failure — a grooved heat pipe installed against gravity will dry out, while a sintered wick used where it isn't needed adds unnecessary cost. This guide explains how each wick type works, compares their performance characteristics, and provides a practical framework for selecting the right wick for your thermal design.

How Wick Capillary Action Works

A heat pipe operates as a closed two-phase loop. At the evaporator (the hot end contacting the heat source), the working fluid absorbs heat and vaporizes. The vapor travels through the hollow core to the condenser (the cool end), where it releases heat and condenses back to liquid. The wick structure then transports this liquid back to the evaporator through capillary action — the same physical effect that draws water up a paper towel.

Capillary pressure is generated by the surface tension of the liquid within the small pores of the wick. Smaller pores generate higher capillary pressure (stronger pumping), but they also create higher flow resistance (slower liquid return). This fundamental trade-off defines wick design: a wick with very fine pores can pump liquid against gravity and over long distances, but its high flow resistance limits the total liquid flow rate, capping maximum heat transport. A wick with larger pores allows high liquid flow but generates weak capillary pressure, working well only with gravity assistance. The three wick types — sintered, grooved, and mesh — each occupy a different position on this capillary-pressure-versus-flow-resistance spectrum.

Sintered Powder Wick

A sintered wick is created by packing fine metal powder (typically copper, particle size 50-150 microns) against the inner wall of the heat pipe, then heating it in a sintering furnace to approximately 1000°C. At this temperature, the powder particles fuse together at their contact points (without fully melting), forming a porous, sponge-like layer bonded to the tube wall. The countless tiny gaps between the fused particles create extremely fine capillary pores.

Advantages of Sintered Wick

The fine pore structure generates the highest capillary pressure of any wick type, giving sintered heat pipes their defining capability: they can work against gravity. A sintered heat pipe can transport heat upward (evaporator above condenser) — the orientation where gravity opposes liquid return — making it the only choice for applications where the heat source sits above the heat sink. Sintered wicks also deliver the highest maximum heat transport capacity and the lowest thermal resistance, because the dense liquid-saturated structure provides excellent thermal contact at the evaporator. They tolerate any mounting orientation, which is why they dominate high-performance applications.

Disadvantages of Sintered Wick

The high capillary pressure comes with high flow resistance, and the sintering process adds significant manufacturing cost and complexity (requiring a high-temperature furnace, controlled atmosphere, and longer cycle times). Sintered wicks are also the heaviest option and have a practical minimum thickness, making them harder to use in ultra-thin form factors below about 0.4mm.

Best Applications for Sintered Wick

Sintered wicks are the standard choice for high-performance computing (CPU and GPU coolers), server and data center thermal solutions, and any application requiring anti-gravity operation or maximum heat transport. They are also preferred when the heat pipe must be bent or flattened during assembly, as the bonded structure maintains capillary integrity better than loose mesh.

Axial Grooved Wick

A grooved wick consists of fine longitudinal channels (grooves) extruded or machined directly into the inner wall of the heat pipe tube. These axial grooves — typically rectangular, trapezoidal, or triangular in cross-section — run the full length of the tube, and the sharp corners of each groove generate the capillary action that returns liquid to the evaporator.

Advantages of Grooved Wick

Grooves offer the lowest flow resistance of any wick type, allowing rapid liquid return and excellent performance when gravity assists (evaporator below condenser). Because the grooves are formed directly into the tube wall during extrusion, manufacturing is simple, highly repeatable, and low-cost in volume production — no separate sintering or mesh insertion step is required. Grooved heat pipes also offer very consistent, predictable performance because the groove geometry is precisely controlled by the extrusion die.

Disadvantages of Grooved Wick

The relatively large groove openings generate low capillary pressure, which is the critical limitation: grooved heat pipes perform poorly against gravity and effectively cannot transport heat upward. Their performance is strongly orientation-dependent, working best in horizontal or gravity-assisted positions. Grooves are also sensitive to bending — flattening or bending the tube can deform the grooves and degrade capillary performance.

Best Applications for Grooved Wick

Grooved wicks excel in gravity-assisted or horizontal applications such as LED lighting heat sinks, solar thermal collectors, and aerospace systems operating in microgravity (where the absence of gravity removes the grooved wick's main weakness). They are also widely used where cost is the dominant factor and the mounting orientation can be controlled to favor gravity-assisted operation.

Screen Mesh Wick

A mesh wick is made from one or more layers of woven metal screen (typically copper or stainless steel) wrapped against the inner wall of the heat pipe. The mesh is held in place by a spring or by the natural springback of the wrapped screen. The capillary pores are formed by the openings in the woven wire mesh, and capillary pressure is tuned by selecting the mesh count (wires per inch) and the number of layers.

Advantages of Mesh Wick

Mesh wicks offer a tunable middle ground — by selecting mesh count and layer count, designers can adjust the balance between capillary pressure and flow resistance to suit the application. Fine mesh (high wire count) provides moderate anti-gravity capability, while coarse mesh favors flow rate. Mesh is relatively low-cost (no high-temperature sintering required), flexible enough to conform to bends, and well-suited to non-cylindrical or custom geometries where sintering or grooving is difficult.

Disadvantages of Mesh Wick

Mesh capillary performance falls between sintered and grooved — it cannot match the anti-gravity capability or maximum heat transport of a sintered wick. The contact between the mesh and the tube wall is less intimate than a bonded sintered layer, which increases thermal resistance at the evaporator. Mesh wicks can also suffer from inconsistent performance if the screen is not wrapped uniformly, and the mesh-to-wall contact can loosen over time or under thermal cycling.

Best Applications for Mesh Wick

Mesh wicks suit moderate-performance applications with mild anti-gravity requirements, custom or non-standard heat pipe geometries, and situations where designers need to tune capillary performance without the cost of sintering. They are common in consumer electronics, telecommunications equipment, and general-purpose thermal management where the application is not severe enough to require a sintered wick but needs more capability than a simple groove.

Side-by-Side Comparison: Sintered vs Grooved vs Mesh

How to Select the Right Wick Structure

Wick selection comes down to matching the wick's strengths to your application's most critical constraint. Work through these questions in order:

1. Does the heat pipe need to work against gravity?

If the heat source will sit above the heat sink (evaporator above condenser) in any operating orientation, you need a sintered wick. No other wick type reliably transports heat upward. If the mounting is always horizontal or gravity-assisted, grooved or mesh becomes viable. This single question eliminates the most options fastest.

2. What is the required heat transport capacity?

For high heat flux applications (high-performance CPUs, GPUs, server processors with 200W+ loads), the high transport capacity and low thermal resistance of sintered wicks justify their cost. For moderate loads (LED lighting, consumer electronics under 100W), grooved or mesh wicks often provide sufficient performance at lower cost.

3. Will the heat pipe be bent or flattened?

If assembly requires significant bending or flattening (common in laptop and smartphone thermal modules), sintered or mesh wicks tolerate deformation better than grooves, which can be damaged by bending. Ultra-thin flattened heat pipes typically use sintered or fine mesh structures.

4. What is the cost target?

In high-volume, cost-sensitive applications where orientation can be controlled to favor gravity, grooved wicks offer the lowest cost. Where some anti-gravity capability is needed but budget is tight, mesh provides a middle option. Sintered wicks command a premium but deliver performance the others cannot match.

5. Is the geometry standard or custom?

Standard cylindrical heat pipes work with all three wick types. Custom or non-cylindrical geometries often favor mesh (flexible and conformable) or sintered (bonded to any inner surface), while grooves are limited to shapes that can be extruded or machined.

Conclusion

There is no single best wick structure — only the right wick for a specific application. Sintered powder wicks deliver maximum performance and anti-gravity capability at the highest cost, making them the choice for high-performance computing and demanding orientations. Grooved wicks offer the lowest cost and excellent gravity-assisted performance, ideal for LED lighting and horizontal applications. Mesh wicks provide a tunable middle ground for moderate-performance and custom-geometry needs. By matching the wick's characteristics to your application's most critical constraint — gravity orientation, heat load, bending requirements, cost, and geometry — you can select the wick structure that delivers the performance you need without paying for capability you don't.

CoolingThermal manufactures complete heat pipe production equipment for all three wick types, including sintering furnaces for sintered wicks, groove-forming equipment, and mesh insertion systems. Whether you are setting up a new production line or optimizing an existing process, our engineering team can advise on the optimal wick technology and equipment for your specific heat pipe designs and production volumes.

• Written by

  CoolingThermal Engineering Team

  CoolingThermal is an automation equipment manufacturer based in Kunshan, China, specializing in heat pipe and vapor chamber production equipment since 2017. Our engineering team designs, builds, and commissions complete production lines covering forming, degassing, welding, testing, and assembly processes. The technical content on this blog is written by the same team that develops the equipment — based on real production experience, not secondary research.