We had a huge response from so many of our followers regarding a recent free white paper offer for vapor chambers. We actually had 2x the number of engineers and others open it relative to the number we emailed.
So, we thought we’d ask followers and customers of qats.com some questions in a simple poll on vapor chambers. We don’t collect any data, but, we’d really welcome your input, so here is our survey:
Posted in Heat Sinks, Vapor Chamber
Our team has literally seen thousands of applications for heat sinks. Check out the articles here on our blog or in our Thermal eJournal, Qpedia, and you’ll see even more evidence of this.
So what does this mean to you and your new thermal management project?
It means that our library of usable designs is at your disposal. It’s highly likely we’ve seen your particular thermal challenge before and that we already have a solution we can apply to your design point.
Reusing a design or modifying an existing design means your solution is less expensive than doing it on your own and quicker to deploy. Which means you’ll meet your project schedule and ship revenue producing units faster than you would otherwise.
Give us a call at 781-769-2800 or email us at [email protected] or use our heat sink request tool to submit your heat sink design on-line and let us help you ship your production faster and in budget.
Posted in heat sink design, Heat Sinks, thermal management
Today we are kicking off a series of articles on how to select a heat sink for an OEM project. The principles are the same for overclockers building their own systems with one difference. In OEM projects, mechanical engineers usually (but not always) have a chance to simulate the design before hand and suggest changes to chassis and layout to help with airflow.
So, let’s get started with some basics. First, why is thermal management a challenge? There’s a few reasons and many of these are only getting worse if you consider them from the world of thermal engineering.
First on our list is higher frequency circuits. The International Technology Roadmap for Semiconductors notes that, “projected power density and junction-to-ambient thermal resistance for high-performance chips at the 14 nm generation are >100 W/cm2 and <0.2°C/W, respectively.” In other words, semiconductors are simply getting hotter as their clock speeds are increased.
Second, generally, semiconductors are being assembled into smaller packages. The packages are smaller, the circuits are denser and this combination means that they are warmer.
Third on our list of why thermal management is a (growing) challenge is low acoustic noise requirements. End users don’t want to be deaf just for using electronics. The result is many specifications that set a reasonable acoustic range for their equipment, often in the 100LFM to 400LFM range. This relatively low airflow is great for end users but creates a real challenge for mechanical engineers and systems integrators trying to create a solid system that meets end users needs and still operates at its optimal levels.
Fourth, circuit designers determine component placement. On the surface of this, this is how it should be. Electrical engineers have alot of pressure on them to reduce board latency and design for performance. While they often consider the thermal needs of the systems and circuits, it’s not their primary design point. For mechanical engineers that is what we do and so our challenge is the balancing act of working with EE’s to insure great placement, but also great airflow.
Fifth and finally, thermal management is a challenge because EMI shielding. Higher frequency components require better shielding and that shielding can restrict airflow.
When we pick this topic up next, we’ll cover why temperature is so important to manage. If you have any questions in the mean time about heat sinks or thermal management, contact us and lets see how can make your next project a success! Email us at ATS thermal [email protected] , call us at 781-769-2800 or visit our heat sink catalog at qats.com
As electronics become faster and more powerful, thermal management solutions must evolve to deal with the increasing heat loads. Simply increasing the size of a heat sink, or adding a fan, was once enough to provide the required increased performance. But, while air cooling remains the dominant method of thermal management in the electronics industry, there are applications where traditional air cooling is not sufficient. These are bound to increase in frequency in the near future. This week we have a two part series on Hybrid Liquid/Air Cooling Systems and how you can use them to cool some of your toughest thermal challenges.
Today, liquid cooling is being used in a steadily increasing number of thermal applications. Desktops, servers, and even laptops are all potential products for such cooling methods. The attractiveness of liquid is its density and specific heat over air (Table 1). However, these material properties can be misleading if compared side by side.
Table 1: Physical Properties of Air and Water[1]
In electronics, there is no basis for comparison between air and liquid for cooling. The term liquid cooling is itself misleading, as air is the final coolant in nearly all applications. The role of the liquid is not as a coolant, but as an active thermal transport vehicle. The main benefit from using liquid is the reduced thermal resistance from the heat source to the air cooled system peripheries. This is due to forced convection replacing pure conduction as the heat transport method, where the heat is delivered to the convective surfaces.
In general, all electronics cooling systems can be divided into three important components as shown in Figure 1:
Figure 1: Typical Electronics Cooling System used in Thermal Management
The Interface refers to the junction between the component and heat sink or cold-plate. This resistance is typically minimized with a high performance grease or phase-change material, and is the same in both liquid and air cooling systems.
The spreading resistance in a thermal solution can be described as the transport of heat from the component to the cooling surfaces that are in contact with the ambient air. This is the only part of a cooling system that greatly differs from air to liquid cooling. With a typical air cooled heat sink, the thermal spreading is done at the base of the heat sink through pure conduction. When using liquid, the spreading is done by the movement of the liquid in a loop from the cold-plate to heat exchanger by mass transport, i.e. coolant.
The final part of an electronics cooling system is the ambient heat exchanger. For air cooling, this part is the heat sink fins, and for liquid cooling is the radiator fins. Both systems work in the same way, by using extended surfaces (fins) to transfer heat into the ambient air through convection.
In part 2 we’ll cover the liquid part of our article and more about integrating for a best in class solution!
Got a question on part 2 already or maybe part 1 from today? Contact us and lets see how ATS thermal engineers can make your next project a success! Email us at [email protected] , call us at 781-769-2800 or visit our Design Services
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References:
1. Soul, C., The Benefits of Liquid Cooling over Air Cooling for Power Electronics, www.icepak.com/prod/icepak/solutions/articles/iceart19.htm
2. Sauciu, I., Chrysler, G., Mahajan, R., Spreading in the Heat Sink Base: Phase Change Systems or Solid Metals?, IEEE Transactionson Components and Packaging Technologies, Vol 23, No.4., 2002.
3. Jeung, S., Quantitative Thermal Performance Evaluation of a Cost-effective Vapor Chamber Heat Sink Containing a Metaletched Microwick Structure for Advanced Microprocessor Cooling, Sensors and Actuators, A: Physical Volume 121, Issue 2, 2005.
4. Wei, J., Cha, A., Copeland, D., Measurement of Vapor Chamber Performance, IEEE SEMI-THERM Symposium, 2003.
5. Xiong, D., Azar, K., Tavossoli, B., Experimental Study on a Hybrid Liquid/Air Cooling System, IEEE, Semiconductor Thermal Measurement
and Management Symposium 2006.
Posted in Heat Sinks, Heat Spreaders, Liquid Cooling, thermal management
Tagged engineering, heat sink, liquid cooling, thermal management
We’re concluding a two part series today on what a heat pipe is and how it works in thermal management. In part one we talked about what a heat pipe is and the anatomy of a heat pipe. Here in part 2 we’ll conclude with factors that can limit a heat pipes effectiveness, differences in the thermal performance of various heat pipe types, and the spreading resistance of different materials.
Table 1 shows experimental data for the operating temperature and heat transfer for three different types of heat pipes [1].
Table 1: Heat Pipes with Different Structures and Operating Conditions [1]
Certain factors can limit the maximum heat transfer rate from a heat pipe. These are classified as follows:
A heat pipe has an effective thermal conductivity much larger than that of a very good metal conductor, such as copper. Figure 4 shows a copper-water heat pipe and a copper pipe dipped into an 80oC water bath. Both pipes were initially at 20oC temperature. The heat pipe temperature reaches the water temperature in about 25 seconds, while the copper rod reaches just 30oC after 200 seconds. However, in an actual application when a heat pipe is soldered or epoxied to the base of a heat sink, the effective thermal conductivity of the heat pipe may be drastically reduced due to the extra thermal resistances added by the bonding. A rule of thumb for the effective thermal conductivity of a heat pipe is 4000 W/mK.
Figure 4. Experiment Comparing Speed of Heat Transfer Between a Heat Pipe and a Copper Pipe [1].
Heat pipe manufacturers generally provide data sheets showing the relationship between the temperature difference and the heat input. Figure 5 shows the temperature difference between the two ends of a heat pipe as a function of power [2].
Figure 5. Temperature Difference Between the Evaporator and the Condenser in a Heat Pipe [2]
There are many heat pipe shapes in the market, but the most common are either round or flat. Round heat pipes can be used for transferring heat from one point to another. They can be applied in tightly spaced electronic components, such as in a laptop. Heat is transferred to a different location that provides enough space to use a proper heat sink or other cooling solution. Figure 6 shows some of the common round heat pipes available in the market.
Figure 6. Typical Round Heat Pipes in the Market.
Flat heat pipes (vapor chambers) work conceptually the same as round heat pipes. Figure 7 shows a flat pipe design, they can be used as heat spreaders. When the heat source is much smaller than the heat sink base, a flat heat pipe can be embedded in the base of the heat sink, or it can be attached to the base to spread the heat more uniformly on the base of the heat sink. Figure 8 shows some common flat heat pipes.
Figure 7. Conceptual Design Schematic of a Flat Heat Pipe
Figure 8. Commonly-used Flat Heat Pipes
Although a vapor chamber might be helpful in minimizing spreading resistance, it may not perform as well as a plate made from a very high conductor, such as diamond. A determining factor is the thickness of the base plate. Figure 9 shows the spreading resistance for 80 x 80 x 5 mm base plate of different materials with a 10 x 10 mm heat source. The vapor chamber has a spreading resistance that is better than copper, but worse than diamond. However the price of the diamond might not justify its application. Figure 9 also includes the spreading resistance from the ATS Forced Thermal Spreader (FTS), which is equal to that of diamond at a much lower cost. The FTS uses a combination of mini and micro channels to minimize the spreading resistance by circulating the liquid inside the spreader.
Figure 9. Thermal Spreading Resistances for
Different Materials.
Heat pipes have a very important role in the thermal management arena. With projected lifespans of 129,000-260,000 hours (as claimed by their manufacturers), they will continue to be an integral part of some new thermal systems. However, with such problems as dry out, acceleration, leakage, vapor lock and reliable performance in ETSI or NEBS types of environments, heat pipes should be tested prior to use and after unsatisfactory examination of other cooling methods have been explored.
That ends our two part series on heat pipes. Have you got a question on heat pipes or their application? How about an interest in bringing ATS’s team of experienced thermal engineers into one of your projects? You can reach us by visiting http://www.qats.com Purchase heat sinks through our Heat Sink eShop or email us at [email protected] or give us a call at 781-769-2800
References:
1. Faghri, A. Heat Pipe Science and Technology Taylor & Francis, 1995.
2. Thermacore Internation, Inc., www.thermacore.com.
3. Xiong, D., Azar, K., Tavossoli, B., Experimental Study on a Hybrid
Posted in heat pipe, Heat Sinks, Liquid Cooling
Tagged heat pipe, heat sink, thermal design, thermal management