Category Archives: Wind Tunnel

ATS Wind Tunnels Designed for SSD and PCIe Thermal Characterization

As was outlined in an earlier article on this blog, it is critical for manufacturers to characterize solid-state drives (SSD) to establish performance parameters in real-world conditions. The previous article explained that SSD experience higher failure rates and reduced lifespan when temperatures increase beyond the standard operating range of 30-40°C.

Wind Tunnels
ATS designed wind tunnels for companies looking to characterize solid-state drives in the PCIe form factor, as show above. (Wikimedia Commons)

Testing processes for SSD are similar to those used for characterizing typical semiconductors. A wind tunnel provides a consistent, controlled, and repeatable environment for data collection and sensors, thermocouples, and an analog-to-digital capture system allows engineers to measure performance when the SSD is impacted by external factors.

ATS designs and fabricates research-quality wind tunnels that can be used for characterizing SSD. The wind tunnels give engineers control over air temperature and velocity. Closed-loop wind tunnels can create environments with temperatures as high as 80°C to provide stressed conditions well above standard operating temperatures. The manufacturer can use this data to set reference points for different environments, such as in 1-U telecommunications chassis or large server boxes.

Recently, ATS has worked with two of the industry’s largest producers of SSD to design wind tunnels that could be used for characterizing drives in PCIe applications. PCIe (peripheral component interconnect express) cards are high-speed serial computer extension cards that connect peripheral devices to the motherboard. In addition to SSD, these cards can be used for graphics processors, Wi-Fi, or other hard drives.

ATS wind tunnels can be used to test airflow and thermal performance for components and boards, as shown in this smoke flow visualization test over a maxiFLOW™ heat sink. (Advanced Thermal Solutions, Inc.)

One of the wind tunnels was a standard, open loop CWT-107™. It can produce uniform and homogeneous flow, up to 5.5 m/s (1100 ft/min) within the wind tunnel’s test section due to its polynomial shape and internal flow management system, which features honeycombs and screens to break up turbulence. The wind tunnel can be operated either vertically or horizontally and the customer chose to use it lying down.

In fact, the customer was very creative in its use of the wind tunnel. A customized cart was built for the wind tunnel to be bolted to and then the cart was wheeled into a large environmental chamber where temperatures could be raised to test levels. The SSD being characterized was a PCIe card with memory installed. There was no fan for the memory and the memory had no shielding or housing.

The customer placed its PCIe-based SSD flat in the test chamber. Power was pulled through the test ports included in the test chamber of the CLWT-107™ (as shown below).

While the wind tunnel was bought for testing SSD, it could be used by the customer to test any electronic component or board.

The second customer purchased a CLWT-115™ closed-loop wind tunnel. In this case, the application required the SSD to be powered through the PCIe back plane, so ATS custom-designed slots in the test section to fit the PCIe form factor. The slots allowed the SSD to remain inside the test section and be connected to a motherboard residing outside the wind tunnel (see below).

Again, the wind tunnel could be used to test any PCIe cards, not just SSD, if the customer desired, as there were also fillers created for the slots to allow the wind tunnel to be used when testing other devices.

The second customer did all of its air velocity and temperature testing in the CLWT-115™, rather than using an environmental chamber like the first customer, because the wind tunnel has a self-contained heating unit that heats air while it circulates during testing.

Wind tunnel controllers and ATVS systems were also purchased by both customers to ensure accurate data collection. The first customer bought an ATVS-NxT™, which is a fully portable scanner that operates with an embedded PC and touch screen control, while the second customer bought the ATVS-2020™, which allows single- or multi-point measurement of both temperature and velocity, and a CLWTC-1000™, which automatically controlled the airflow and temperature through the test chamber.

Both come with Candlestick sensors to control the air velocity in the wind tunnel and thermocouples to control the temperature.

One of the customers also requested a custom, rugged sensor to avoid damage through multiple uses. ATS was able to adapt one of its handheld surface probes, a stainless-steel probe with a pointed tip for exact positioning of the sensor on the desired spot, by reducing the length and designing a custom port that would hold the sensor in place.

SSD are gaining traction in the market, with major hard drive manufacturers and the companies that utilize them both making the switch to solid-state technology. This means that thermal characterization of SSD and thermal management systems deployed to dissipate the heat of these drives are going to be of increasing importance in the coming years.

Using research-quality wind tunnels gives manufacturers a leg up in determining how their drives will perform in different real-world environments and makes the process of SSD characterization easier for users. By working with ATS, companies can tailor their wind tunnels to their specific applications and can be assured of the accuracy of the data that they collect.

Learn more about ATS wind tunnels, sensors, and the entire line of next-generation thermal test instruments at
Instruments. If you have questions about any products or ATS thermal testing services, email

For more information about Advanced Thermal Solutions, Inc. (ATS) thermal management consulting and design services, visit or contact ATS at 781.769.2800 or

ATS Expands in the COTS Market with its Wind Tunnel Sale to the US Navy

ATS has continued to expand in the COTS industry because of its expertise in resolving thermal challenges through its consulting services, cooling solutions, and thermal test instruments. Most recently, the CWT-107 open loop wind tunnel was sold to the United States Navy for use in their Research Development Labs.



CWT-107 Open Loop Wind Tunnel

The CWT-107 is a research quality wind tunnel designed for multiple PCB and component level testing. It is used in air flow characterization and flow visualization, thermal resistance measurements and generation of P-Q curves. The large test section (24″ x 2″ x 7″) is designed to accommodate multiple PCBs, as seen in a typical ATCA chassis. The wind tunnel can also be used to characterize different heat sink sizes for natural and forced convection cooling. Additionally, multiple heat sinks can be tested side by side to determine their thermal performance in the same environment.

The following video is a brief demonstration and walk through of the CWT-107 Open Loop Wind Tunnel:

To learn more about the CWT-107 and how ATS products can be utilized in COTS applications, please visit

Want to keep up to date on ATS products, services, free engineering webinars and our monthly Qpeda Thermal eMagazine? Subscribe to ATS

Benchtop Wind Tunnel Can Produce High Flows of Warm Air for Thermal Testing

The CLWT-115 research quality, closed loop wind tunnel from ATS can generate air flows from ambient to 85°C and a rate of up to 50 m/s (10,000 ft/min) for thermally characterizing PCBs and individual components.

The new CLWT-115 wind tunnel from Advanced Thermal Solutions facilitates thermal management studies of electronic components by providing controllable air flows at controllable air temperatures. These features allow faster evaluation of elevated temperatures on component and PCB response and reliability. The CLWT-115 wind tunnel offers a convenient, accurate system for thermally characterizing PCBs and individual components at controlled temperatures from ambient to 85°C.

The new wind tunnel creates consistent, low turbulence air flows of up to 5 m/s (1000 ft/min). It can be customized to generate flows up to 50 m/s (10,000 ft/min) using optionally available orifice plates. The instrument has a clear Lexan test section lets the user view the test specimen and allows for flow visualization.

Because of its closed loop design, the CLWT-115 recirculates internal air. The system heater can quickly warm the air to a specific temperature. This feature is ideal for testing boards and components in hot air, which is a requirement in some NEBS standards. The CLWT-115 wind tunnel can also be used for testing heat sink performance and for calibrating air and temperature sensors.

The CLWT-115 features a test section that can be open from the top door or sides for mounting and repositioning of boards, components and sensors. Rail guides provide an easy mechanism to install test specimens of different sizes (e.g., PCB, heat sink).
Instrument ports (6) are provided in the side walls of the test section for placing temperature and velocity sensors including thermocouples and hotwire

To learn more about the CLWT-115 benchtop wind tunnel, visit Qats.CLWT-115

Some Basic Principles of Wind Tunnel Design

Wind tunnels generate uniform air flows, with low turbulence intensity, for thermal and hydraulic testing. These devices have been around for more than a century, and are used in many industries, including aerospace, automotive, and defense. They also play a key role in electronics thermal management. Wind tunnels are made in different shapes and sizes, from just 30 cm long to large enough to contain a passenger airplane. But the basic idea behind all wind tunnels is universal.

There are two basic kinds of wind tunnels. One is the open type, which draws its air from the ambient and exits it back to the ambient. This kind of wind tunnel provides no temperature controls. The air follows the ambient temperature. The second type of wind tunnel is the closed loop wind tunnel, whose internal air circulates in a loop, separating it from outside ambient air. The temperature in a closed loop wind tunnel can be controlled using a combination of heaters and heat exchangers. Air temperatures can be varied from sub-ambient to over 100oC. Figure 1 shows a schematic of a closed loop wind tunnel.

In general, closed loop wind tunnels are made with the following sections:

1-Test section

2-Settling chamber

3-Contraction area


5-ÂBlower assembly

6-Heater/heat exchanger assembly

Figure 1. Schematic of an ATS Closed Loop Wind Tunnel.

A good quality wind tunnel will have a flow uniformity of 0.5-2% and turbulence intensity of 0.5-2%. It should provide temperature uniformity within 0.1-0.5oC at the inlet of the test section [1].

108K different push pin heat sink assembly configurations featuring 3 different pitch heat sink types, 3 different fin geometries, brass and plastic push pins


To achieve uniform, high quality flow in the test section, the settling chamber and the contraction area are used to smooth the flow. The role of the settling chamber, which is upstream of the contraction area, is to eliminate swirl and unsteadiness from the flow. The settling chamber includes a special honeycomb and a series of screens. As long as a flows yaw angles are not greater than about 10o, a honeycomb is the most efficient device for removing swirl and lateral velocity variations and to make the flow more parallel to the axial axis [2]. Large yaw angles will cause honeycomb cells to stall, which increases the pressure drop and causes non-uniformity in the flow. For large swirl angles, screen meshes should be placed before the honeycomb. For swirl angles of 40o, a screen with a loss factor of 1.45 will reduce yaw and swirl angles by a factor of 0.7. Several screens are needed upstream of the honeycomb to bring the swirl down to 10o.

Using a honeycomb will also suppress the lateral components of turbulence. Complete turbulence annihilation can be achieved in a length of 5-10 cell diameters [2]. Honeycombs are also known to remove the small scale turbulence caused by the instability of the shear layer in front of them. This instability is proportional to the shear layer thickness, which implies a short honeycomb has a better ratio of suppressed turbulence to that generated.

Screens break up large eddies into smaller ones which decay faster. They lower turbulence drastically when several screens are placed in a row. Screens also make flow more uniform by imposing a static pressure drop which is proportional to velocity squared. A screen with a pressure drop coefficient of 2 removes nearly all variations of longitudinal mean velocity. Low open area screens usually create instabilities. In general, screens should have openings larger than 57%, with wire diameters about 0.14 to 0.19 mm. Sufficient distance is needed between multiple screens to stabilize static pressure from perturbation. This distance is typically a percentage of the settling chamber diameter.

The contraction area is perhaps the most important part of a wind tunnel’s design. Its main purpose is to make the flow more uniform. It also increases the flow at the test section, which allows flow conditioning devices to be at lower flow section with less pressure drop. Batchelor used the rapid distortion theory and estimated the variation in mean velocity and turbulence intensity [3]

A considerable number of shapes have been investigated for contraction, including 2-D, 3-D and axisymmetric shapes with various side profiles.

The shape of the contraction can be found using potential flow analysis. Consider the axisymmetric contraction shown in Figure 2 [4]

Figure 2. Schematic of an Axisymmetric Contraction [4].

The design of a wind tunnel is a lengthy process and, as shown above, it requires extensive knowledge and experience in both theory and construction. A novice might attempt to construct a tunnel, but considering the time spent, it might not be justified economically. Wind tunnel design also depends on economic and space constraints. Larger wind tunnels allow more space to have all the conditioning elements in place. A space-constrained wind tunnel must compromise some features at the cost of reduced flow quality, but can still be acceptable for practical engineering purposes.


  1. Azar, K., Thermal Measurements in Electronics Cooling, Electronics Cooling Magazine, May 2003.
  2. Bell, J. and Mehta, R., Design and Calibration of the Mixing Layer and Wind Tunnel, Stanford University, Department of Aeronautics and Astronautics, May 1989.
  3. Batchelor, G., The Theory of Homogeneous Turbulence, Cambridge University Press, 1953.
  4. Edson, D. and Joao, B., Design and Construction of Small Axisymmetric Contractions, Faculdade de Engenharia de Ilha Solteira, Brazil, 1999.