Earlier this month the US Patent & Trademark Office published a patent application from Google relating to a possible future VR headset that will implement an advanced phase-change cooling system so that a VR gamer's face can remain relatively cool when playing for long periods of time.
Google's invention describes techniques for implementing a phase-change cooling system within a three-dimensional structure.
Google notes in their patent application that a traditional phase-change chamber is typically fabricated separately from the structure, adding expenses in terms of materials or construction. It is also limited in terms of the type of structure to which it might be applied, typically comprised of planar, two-dimensional (2D) surfaces.
As such, a traditional phase-change chamber is not applicable to a complex and curved, three-dimensional (3D) structure housing a virtual-reality headset, a personal assistant/smart speaker, a smartphone, or a gaming controller.
Google's invention covers the use of specific techniques, phase-change mechanisms and a phase-change material (PCM) that may be integrated as part of the structure, improving thermal control over the electronic system that might otherwise rely on convection or conduction based mechanisms.
A phase-change material (PCM) may be a fluid such as water, alcohol, or a refrigerant. The fluid may be in the form of a liquid, a vapor, or a combination of both. Furthermore, although a single fluid may be easiest to implement, mixtures of fluids may enhance thermal performance by altering surface tensions and allowing boiling to initiate more smoothly without excessive surface temperatures. Depending on a desired outcome, the fluids associated with a phase-change mechanism may be miscible or immiscible.
A chamber that is sealed and has three-dimensional curvatures can be fabricated using a variety of techniques, including joining two skins formed with complementary three-dimensional curvatures, shaping a chamber after joining two skins, or folding a single skin to shape the chamber.
While partially sealed, the chamber is filled with a phase-change material in a saturated thermodynamic state (e.g., a fluid in a mixture of liquid and vapor phases). The chamber is then sealed to form a phase-change chamber.
Operating Environment
Google's patent FIG. 1 below presents an example operating environment that includes a three-dimensional structure having integrated phase-change cooling. Specifically FIG. 1 illustrates a three-dimensional (3D) structure #102 is in the example form of a virtual-reality headset. The 3D structure has at least one section, such as section #104, with three-dimensional curvatures.
The 3D structure being used by a user contains a variety of electronic components integrated into the 3D structure that may generate energy in the form of heat (Q), which needs to be controlled for comfort or safety reasons.
For instance, using the example illustrated virtual-reality headset, a display of the virtual reality headset or a lithium battery may be generate heat (Q) within one or more localized regions of virtual-reality headset, and in order to maintain a comfortable and safe temperature (T) for the user, the heat needs to be absorbed, distributed, and then dissipated to the surroundings by the virtual reality headset.
Integrated into the 3D structure is a heat transport mechanism in the form of a phase-change chamber #108 that is sealed and contains a fluid #112 in a saturated, thermodynamic state. The phase-change chamber #108 (top left in FIG. 1 above) also includes a thermo-mechanical network #114 and/or wicking mechanisms #116.
The thermo-mechanical network and the wicking mechanisms in combination serve to enhance structural rigidity of the 3D structure and improve thermal performance of the phase-change chamber.
As heat is generated by electronic components attached to the 3D structure, the phase-change chamber controls the temperature (T) of the 3D structure via thermodynamic operations within the chamber, including absorbing latent heat if portions of the fluid change from a liquid phase to a vapor phase as well as controlling movement of heat within the 3D structure.
As part of controlling movement of heat within the 3D structure, the phase-change chamber redistributes heat across a variety of thermal interfaces to the 3D structure to enable other heat transfer mechanics, such as convection and radiation of heat from surfaces of the 3D structure.
Configurations of a Phase-Change Chamber
Configuration 500 below illustrates phase-change chamber including a fluid in a saturated thermodynamic state. As part of the saturated thermodynamic state, a liquid region #502 and a vapor region #504 are present in the phase-change chamber. A hot region #506 of the phase-change chamber may be within the vapor region and adjacent to an electronic component, such as a display or lithium battery, generating energy in the form of heat. As heat is introduced into the phase-change chamber via the hot region, it may be absorbed as part of a thermodynamic phase-change process transitioning fluid from a liquid phase to a vapor phase.
Configuration 508 above includes the previously described liquid region, vapor region, and hot region within the vapor region. Further included, as part of configuration 508, is a thermo-mechanical network comprising thermal-conduction mechanisms, such as thermal-conduction mechanism #510. The thermal-conduction mechanism may be in the form of a channel or ridge or rod. The thermo-mechanical network is configured such that thermal contact between the thermo-mechanical network and the hot region is optimized, maximizing heat (Q) conducted from the thermally-conductive interface to the liquid region. As a result, a thermal behavior of the phase-change chamber is improved, transitioning fluid from a liquid phase to a vapor phase at a rate that would otherwise not be realized. Furthermore, the thermo-mechanical network of mechanisms (such as the thermal-conduction mechanism #510) may provide a structural integrity to the 3D structure and, in certain instances, be external to the 3D structure.
Configuration 512 above includes the previously described liquid region, vapor region, and hot region within the vapor region. Further included as part of this configuration are wicking mechanisms, such as the wicking mechanism #514. The wicking mechanism may be in the form of a wick. Design and fabrication permutations of the wicking mechanisms may accommodate a combination of materials, pore sizes, and patterns. The wicking mechanisms are configured such that the wicking mechanisms transport liquid (1) from the liquid region to the hot region in order for the liquid (1) to absorb latent heat and be vaporized. As a result, a thermal behavior of the phase-change chamber is improved, transitioning fluid from a liquid phase to a vapor phase (and absorbing latent heat) at a rate that would otherwise not be realized, and heat transfer is improved.
Google's patent application was filed with the U.S. Patent Office in Q4 2017 and published earlier this month.
For the record, the right side image in our cover graphic covers one of Google's images related to their patent FIG. 6 that illustrates a thermo-mechanical network comprising a plurality of dimples so as to provide condensation points and/or distribute flows of fluids within the phase-change chamber.
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