Microsoft Patent | Vapor Chamber That Emits a Non-Uniform Radiative Heat Flux
Publication Number: 20180372424
Publication Date: 2018-12-27
A vapor chamber that emits a non-uniform radiative heat flux. The vapor chamber may have a convection cavity that contains a working fluid and outer surfaces that have two or more emissivity regions to dissipate heat from the working fluid at non-uniform levels of radiative heat flux. The non-uniform levels of radiative heat flux may result from exposure to emissivity decreasing surface treatments and/or emissivity increasing surface treatments. The vapor chamber may be utilized in thermal management systems to protect heat-sensitive components from thermal radiation that results from heat being dissipated from a heat source. For example, the vapor chamber may be oriented with respect to a heat-sensitive component so that thermal radiation is emitted at a higher radiative heat flux away from the heat-sensitive component than towards the heat-sensitive component.
Thermal management is a key consideration in the design of compact electronic devices such as laptop computers, wearable technologies, or any other device in which spatial constraints lead to heat generating components being located in close proximity to heat-sensitive components. Such considerations challenge designers to balance the competing goals of both dissipating heat away from heat generating components while also preventing dissipated heat from adversely affecting heat-sensitive components.
Conventional vapor chambers are sometimes used to dissipate heat from heat generating components into heat dissipation regions within compact electronic devices. More specifically, a conventional vapor chamber converts a localized high heat flux absorbed from a heat generating component into a relatively lower heat flux that is uniformly dispersed throughout a heat dissipation region. In some compact electronic devices, heat-sensitive components are inadvertently irradiated by some conventional vapor chamber designs. Unfortunately, this leads to such heat-sensitive components operating outside of an optimal temperature range and/or to the added cost and weight of heat shield components to protect heat-sensitive components from conventional vapor chambers.
It is with respect to these and other considerations that the disclosure made herein is presented.
Technologies described herein provide a vapor chamber that emits a non-uniform radiative heat flux. Generally described, the techniques disclosed herein enable modulation of surface treatment(s) on outer surface(s) of a vapor chamber to control an emissivity and, ultimately, a radiative heat flux emitted from various predetermined emissivity regions. Unlike conventional vapor chambers which emit a uniform radiative heat flux from all exposed surfaces (e.g., regardless where heat-sensitive components are located), the techniques described herein enable heat to be dissipated away from heat generating components toward specific regions of a compact electronic device which are unfettered by heat-sensitive components. In particular, the techniques described herein enable individual surface regions of a vapor chamber that face towards, or away from, heat-sensitive components to be specifically configured to emit lower, or higher, levels of radiative flux, respectively. For example, an individual surface region may be configured to have a desired emissivity through exposure to mechanical surface abrasion (e.g., surface roughening or surface polishing), oxidation techniques, anodization techniques, applying emissivity affecting layers to the individual surface region (e.g., polymer coatings, paints, etc.), or any other surface treatment technique suitable for modulating surface emissivity.
In some configurations, a vapor chamber comprises one or more walls having inner surfaces defining a convection cavity that contains a working fluid. The working fluid absorbs heat that is emitted against a heat absorbing portion(s) of the vapor chamber and convectively transfers the heat uniformly throughout a heat dissipating portion(s) of the vapor chamber. For example, the working fluid may be a bi-phase fluid that evaporates from a liquid state into a gaseous state upon absorbing latent heat at the heat absorbing portion of the vapor chamber. The working fluid may then flow, in the gaseous state, through the convection cavity to the heat dissipating portion(s) of the vapor chamber before releasing the latent heat and re-condensing into the liquid state. Exemplary working fluids include, but are not limited to, water, refrigerant substances (e.g., R134), ammonia based liquids, or any other substance suitable for efficiently transferring heat through convection.
At the heat dissipating portion of the vapor chamber, the latent heat may be conductively transferred through the one or more walls and, ultimately, dissipated through various heat transfer mechanisms from outer surfaces of the vapor chamber into an ambient environment. In particular, a portion of the latent heat may be convectively dissipated into the ambient environment as a medium (e.g., air) absorbs some of the latent heat and then flows away from the outer surfaces. Another portion of the latent heat may be irradiated from the outer surfaces through the medium in the form of thermal radiation.
The outer surfaces may further include two or more predetermined emissivity regions that are configured to dissipate at least some of the latent heat through thermal radiation at non-uniform levels of radiative heat flux. For illustrative purposes, suppose that the outer surfaces include a first emissivity region that has a first emissivity and a second emissivity region that has a second emissivity. Further suppose that the first emissivity is less than the second emissivity. Under these circumstances, if the outer surfaces of the vapor chamber are substantially the same temperature at both of the first emissivity region and the second emissivity region, the radiative heat flux emitted from the first emissivity region will be less than that emitted from the second emissivity region. It can be appreciated that modulating the surface treatment(s) to control an emissivity at various regions may in some instances have an effect on an amount of the latent heat that is convectively dissipated at the various regions whereas in other instances the surface treatment(s) may have no such effect.
In some configurations, the non-uniform levels of radiative heat flux may result from one or more predetermined emissivity regions being exposed to an emissivity decreasing surface treatment that reduces an emissivity of the one or more predetermined emissivity regions. In particular, the emissivity decreasing surface treatment may reduce an ability of the vapor chamber to emit infrared energy from specific regions of the outer surfaces. Exemplary emissivity decreasing surface treatments include, but are not limited to, polishing a specific emissivity region, electroplating the specific emissivity region, and/or applying a low emissivity layer to the specific emissivity region. As used herein, a “low emissivity layer” refers generally to any layer (e.g., of a solid material, a paint, a clear coating, or any other suitable product) that decreases an emissivity of a region to which the layer is applied.
In some configurations, the non-uniform levels of radiative heat flux may result from one or more predetermined emissivity regions being exposed to an emissivity increasing surface treatment that increases the emissivity of the one or more predetermined emissivity regions. In particular, the emissivity increasing surface treatment may increase the ability of the vapor chamber to emit infrared energy from specific regions of the outer surfaces. Exemplary emissivity increasing surface treatments include, but are not limited to, oxidizing a specific emissivity region, anodizing a specific emissivity region, and/or applying a high emissivity layer to the specific emissivity region. As used herein, a “high emissivity layer” refers generally to any layer (e.g., of a solid material, a paint, a clear coating, or any other suitable product) that increases an emissivity of a region to which the layer is applied.
These and various other features will be apparent from a reading of the following Detailed Description and a review of the associated drawings. This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended that this Summary be used to limit the scope of the claimed subject matter. Furthermore, the claimed subject matter is not limited to implementations that solve any or all disadvantages noted in any part of this disclosure.