Using Pulsating Heat Pipes vs. HiK™ Plates for Thermal Management
Pulsating heat pipes (PHPs) have emerged in the last two decades as a high-performance thermal management alternative to traditional heat pipes. Operating in two-phase mode, PHPs have successfully demonstrated superior performance compared to conventional conduction-based thermal management options.
Along with its existing technology offerings, ACT is committed to offering PHP-based thermal solutions to meet customer needs. Two thermal management solutions that provide better performance over simple conduction are PHPs and copper-water heat pipe embedded cards (also known as HiK™ plates).
Below, we’ll outline the benefits of using pulsating heat pipes vs. HiK™ plates to control the thermal load of your electronics.
Pulsating Heat Pipes vs HIK™ Plates: How They Work & How They’re Different
PHPs were first introduced as a concept by Akachi1 in 1990. They consist of capillary-sized meandering tubes, usually connected end-to-end, containing a two-phase fluid that pulsates or circulates within the loop. The fluid, typically charged into the vacuum-filled PHP at a 20-80% volume fill ratio, naturally forms into liquid slugs and vapor plugs within the tubes.
When heat is applied to the PHP’s evaporator zone, the liquid slug next to the heated area partially vaporizes, increasing the vapor pressure. At the condenser zone where heat is rejected, the vapor shrinks or collapses, reducing the vapor pressure. The simultaneous pressure changes at both ends cause the working fluid to pulsate or circulate between the heat input and rejection points.
In contrast, HiK™ plates utilize copper-water heat pipe technology embedded into an aluminum base plate. They work by transferring heat away from the source and evenly distributing it across the heat spreader plate.
₁ Akachi, H., Structure of a Heat Pipe, US4921041, 1990
Pulsating Heat Pipe (PHP) Performance Criteria
The performance of a PHP is influenced by both its geometry and the choice of working fluid. Engineers must carefully balance tube diameter with the number of turns in the tube when designing the PHP. The tubes can only make a limited number of turns within the given size of the PHP, smaller tubes promote fluid oscillation but limit heat transfer, and larger tubes remove heat better but may inhibit oscillation.
The liquid inside a PHP also needs to be selected properly. Engineers choose from various refrigerants, alcohols, water, and other fluids. The best fluid depends on the 1 Akachi, H., Structure of a Heat Pipe, US4921041, 1990 desired operating temperature range and how much heat needs to be transferred. Ideal fluids have certain properties that make them oscillate well within the tubes across the expected temperatures. Engineers test different fluids to find the one that works best for each PHP design and application.
When should I use Pulsating Heat Pipes (PHP) vs. Hik™ Plates?
PHPs, similar to HiK™ plates, operate passively. Depending on the application either PHP or HiK™ might be the preferred solution. A unique aspect of PHP is they don’t explicitly require a wick structure for the working fluid to return as seen in conventional heat pipes. The capillary-sized tubes in PHPs help keep the working fluid slug’s integrity for the fluid pulsation to work. Also, like HiK™ plates, PHPs are known to withstand high heat fluxes up to 50 W/cm².
Knowing when to use pulsating heat pipes vs. HiK™ plates will depend on certain criteria. Pulsating heat pipes tend to be preferred over HiK™ plates when:
- Operating temperatures are at or below the water freezing point. HiK™ plates are an excellent choice at or above room temperature.
- If the profile of the thermal management solution required is very thin or must conform to complex geometries. For instance, if a thin electronics heat spreader with a sharp 90° corner is required, a PHP heat spreader can incorporate fluid channels in these locations. HiK™ plate heat pipes require a certain bend radius that may not be compatible.
- Non-metallic envelopes are required. HiK™ plates are typically built on metallic envelopes.
Technology Readiness Level of Pulsating Heat Pipes (PHPs)
PHPs are an emerging thermal management technology, rapidly gaining attention for their high performance and adaptability. First patented in the 1990s, PHPs have since been proven to manage high heat loads with their two-phase oscillating flow and simple, versatile design.
ACT’s decades of heritage delivering mission-critical HiK™ plates (TRL ranking of 9) in many defense, aerospace, and commercial applications is helping to engage with customers where PHP would be a relevant thermal management solution.
Pulsating heat pipes’ simple design and flexibility make them an ideal comparable alternative to HiK™ plates in certain situations. As PHP technology continues to mature, we can expect wider adoption across electronics, manufacturing, and other industries.
ACT has taken note of the growing interest in PHP-based thermal management solutions. As a pioneer in delivering innovative, high-performance thermal management technologies, ACT is dedicated to providing its customers with outstanding customer care through innovative systems and solutions.
Let’s work together to solve your thermal management problems. Reach out to our team of engineers to discuss your thermal challenge.
Article credit: Sai Kiran Hota and Kuan-Lin Lee, Engineers championing PHP research at ACT. For more information, refer recent paper comparing PHP and HiK™ performance for space electronics – https://www.sciencedirect.com/science/article/pii/S2214157X23005622
