OHP Form Factors: Heat Spreaders, Transporters, and Radiators
Oscillating heat pipes (OHPs), also called pulsating heat pipes (PHPs), are efficient passive heat transfer devices that excel at spreading, transporting and rejecting heat across a wide variety of form factors. In this post we will explore three key OHP form factors: heat spreaders, transporters, and radiators.
OHP heat spreaders (also called base plates or doublers) [TRL 9]
OHP heat spreaders are designed to handle high flux heat from one or more heat sources, efficiently spreading it across a 2D plane or 3D structure and reject it to specific sink locations. In most instances the heat flux is lower at the sinks, reducing the temperature gradient through downstream components such a thermal interface material (TIM), cold plate, or fin array for convective cooling.
Key benefits include:
Efficient heat transport: The OHP’s internal channels can be routed directly between heat sources and sinks, minimizing the conduction distance through the solid envelope material (e.g., aluminum, copper, etc.)
Thin design: Channel paths typically require a thickness of only 1–4 mm, depending on the heat load and transport distance
Planar or conformal interfaces: This minimizes thermal resistance by maintaining close contact between the OHP heat spreader and the heat sources and sinks.
For example, a 3U VPX OHP heat frame measuring 10.2 cm x 14.7 cm x 0.2 cm with 1.8 cm out of plane jog was able to transport 130 W (1-10 W/cm2) with an overall ΔT of only a 3.0 °C or an effective thermal conductivity of 7,500 W/mK.
Figure 1. 3U VPX OHP heat frame
OHP transporters [TRL 9]
OHP transporters are designed to move heat across long, complex path, sometimes weaving around interstitial components within a system.
Key benefits include:
Slim form factor: Typically, 1-5 mm thick, with transport distances of up to over 1 meter.
Complex routing: The OHP be manufactured in complex 3D shapes by bending or machining to the desired shape
Planar or conformal interfaces: This minimizes thermal resistance by maintaining close contact between the OHP heat spreader and the heat sources and sinks.
Gravitational independence: OHP transporters can be designed to operate vertically in a top-heated, bottom-cooled configuration.
These properties enable OHP transporters to handle heat loads of 50 W to 1,000 W, achieving conductances of 10 W/K to over 50 W/K.
OHP heat sinks [TRL 9] / OHP satellite radiators [TRL 7]
OHP heat sinks and radiators are optimized for rejecting heat to a fluid or to a radiative sink. They are particularly effective in applications where a thin form-factor, lightweight construction, and low thermal resistance.
Key benefits include:
Efficient heat transport: The OHP can efficiently spread heat from a heat source across a large area or volume and the excess envelope material can be removed to minimize the mass
Thin design: Channel paths typically require a thickness of only 1–4 mm, depending on the heat load and rejection area
Structural: The OHP can be designed to integrate ribbing for structural integrity without substantially increasing the mass. In addition, mounting features can be integrated directly into the OHP envelope to minimize mass
For example, a 45.7 cm x 45.7 cm x 0.2 cm OHP radiator panel was developed to reject 150 W (Figure 4). It achieved a temperature difference of just 1.8 °C or a conductance of 83 W/K.
Figure 4. OHP radiator panel
Conclusion
Oscillating Heat Pipe (OHP) technology is a versatile solution that can be adapted to various form factors to address a wide range of thermal management needs. Each application, whether as a heat spreader, transporter, or radiator, offers distinct benefits compared to existing passive heat transport methods. Additionally, the flexibility of OHP design allows for the integration of multiple form factors within a single system, eliminating thermal interfaces and maximizing thermal performance.