Yaspan Tech, Computers, Gadgets, Reviews, News and Analysis
Samsung’s Galaxy S7 packs a variety of new features and capabilities, as well as some returning favorites, like a microSD slot. One of the more interesting aspects of the announcement, however, was Samsung’s declaration that the S7 would use liquid cooling. Typically, liquid cooling conjures images of an external radiator block and liquid reservoir, or at least an integrated close-loop liquid cooler (CLLC).
What Samsung is actually using is known as a heat pipe — and while it does involve a tiny bit of liquid, it’s not “liquid cooling” as we commonly use the term. Since smartphones don’t include fans, the SoC’s cooling performance is limited to how much heat its passive cooler can dissipate. Tablets often have ventilation holes, even if they lack fans, but phones typically lack them. Apple uses layers of graphite applied to its processors and modem, as shown in the image below.
There comes a point, however, when a material layer alone isn’t sufficient. Microsoft also used a liquid cooler for the Lumia 950 and 950XL when it launched those devices, and we aren’t surprised to see Samsung following suit.
How a heat pipe works
Heat pipes use evaporative cooling and a tiny amount of fluid — typically water — to offer superior cooling performance compared with using an equivalent amount of solid copper. A tiny amount of fluid is sealed within a pipe, with part of the pipe positioned over the components to be cooled.
As the temperature within the pipe rises, the water inside the pipe vaporizes. Since the vapor can’t escape the system, it travels into the “cool” side of the heat pipe, transitions back into a liquid, and flows down to the “warm” side again. The GIF below, courtesy of Wikipedia, shows how water is heated at the bottom of a heat pipe, rises to the top, cools back to a liquid, and returns to the bottom of the heatsink.
Heat pipes don’t just outperform a solid block of copper; they also weigh less, since the pipe itself is hollow. Websites that refer to this as “liquid” cooling are playing a bit with the truth — it’s a technology we’ve used in CPU coolers for over a decade — but it does rely on a tiny drop of fluid inside the copper core.
No such thing as a free lunch
Smartphone companies are moving to adopt heat pipes because the technology should allow for more sustained boost clocking and steadier overall performance. Smartphone workloads are typically modeled as short cycles with long intervals of rest between them (“short and “long” are both relative to machine cycles, not human perceptions of time). The VR applications and advanced functionality that companies like Samsung and Microsoft are targeting for next-generation devices make this approach a smart one, and I suspect the heat pipe exists partly because Samsung has more aggressive plans for VR content than it did a year ago. That’s also why pre-orders in the US and UK will receive a free Gear VR.
The other advantage of a heat pipe is that Samsung can position it to cool particular hot spots on the SoC die. While the entire system would still benefit from integrating a heat sink, even a heat pipe alone can improve performance compared to the graphite method Apple uses, whereas a copper plate would be too heavy. There are similarities to this approach and Intel’s use of Turbo Boost — the smartphone cooler can deliver increased performance until the heat pipe becomes too hot to allow it. Turbo Boost is designed to give x86 CPUs a similar advantage by allowing the CPU to hit higher-than-normal clocks for short periods until it exceeds a pre-programmed TDP or thermal trip point.
Expect to see more techniques like this used on SoCs as high-performance demand continues to grow. Large phones bought the industry a temporary breather, since bigger devices have more thermal dissipation space and allow for larger batteries, but the three-way fight between device thickness, performance, and battery life can’t have three winners.
Oculus has announced that anyone who pre-orders a Galaxy S7 and receives their free Gear VR will also be eligible to download six VR games with an estimated value of $50. Bundles will vary by carrier; specific information is not available at this time.
