Electronics Protection - Summer 2016 - (Page 14)

Feature Heat Pipes and Vapor Chambers - What's the Difference? George Meyer, CEO Celsia, Inc. At some point in a thermal system design project it may become apparent that the tried and true methods of increasing thermal efficiency - solid base, fin & fan - just aren't sufficient. Reasons are: * * * * Keep out zones prohibit a larger heat sink (thicker base, added fin area, etc.) Enclosure size and/or airflow can't be increased. Transitioning to a solid copper heat sink, in whole or in part, adds too much weight and in some cases too much cost. Component power/density necessitates heat be moved to a location more than 40 to 50 mm away from the heat source. Regardless of the reason, most thermal engineers are going to need a two-phase cooling solution using either heat pipes or vapor chambers on numerous projects with which they are involved. But, which one is likely the best choice? Here's a topline overview of structural differences and thermal design considerations between these very similar yet somewhat unique two-phase devices. It probably goes without saying, but the operating principles of all two-phase devices are identical. A wick structure of sintered powder, mesh screens, and/or grooves is created on the inner walls of an enclosure. Liquid, usually water, is added to the device and vacuum sealed at which point the wick distributes the liquid throughout the device. As heat is applied to one area, the Figure 1. Inner Workings of Two-Phase Devices liquid turns to vapor and moves to an area of lower pressure where it cools and returns to liquid form whereupon it moves back to the heat source by virtue of capillary action. In this sense, heat pipes and vapor chambers are the same thing. For simplicity's sake, let's focus on the most common type of two-phase device: an all copper vessel using a sintered copper wick structure with water as the working fluid. Structural Design & Cost Table 1 highlights some of the manufacturing and cost differences between heat pipes and vapor chambers. In a nutshell, each has thermal conductivity of anywhere between three to 10 times that of solid copper and work under the same operating principles. The first two begin life as a hollow copper tube while the last starts with two stamped copper plates. As a general rule cost increases as you move from heat pipes to two-piece vapor chambers. Heat Pipes For decades, heat pipes have been the default two-phase device of choice for thermal engineers due largely to the cost difference relative to vapor chambers. They were used both for heat transport, for which they still have an advantage, and for heat spreading, typically using mul- Figure 2. Heat Pipes, Notebook Applications Source - Wikipedia tiple pipes in close proximity to one another. For lower power applications, perhaps requiring only a single, small heat pipe, or those where heat must be effectively transported, heat pipes still maintain dominance due to their low cost and design flexibility. Figure 2 shows two flattened heat pipes being used to cool three heat sources in a notebook application. To save 14 Summer 2016 * www.ElectronicsProtectionMagazine.com http://www.ElectronicsProtectionMagazine.com

Table of Contents for the Digital Edition of Electronics Protection - Summer 2016

Electronics Protection - Summer 2016
Contents
Editor's Choice
Common Coolant Types and Their Uses in Liquid Cooling Systems
The Benefits of Vertical Integration for Customized EMI Shielding Products and Services
Cool It Your Way: Versatile Cooling for Electronics Enclosure
Heat Pipes and Vapor Chambers – What’s the Difference?
Securing Electronics in Modern Railway Systems
Enclosures
Thermal
Power
Hardware
Industry News
Calendar of Events

Electronics Protection - Summer 2016

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