Tag Archives: flow visualization

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 www.qats.com.

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Flow Visualization in PCB Testing: Part 3

Part 3: Best Wind Tunnels for Flow Visualization

In our final post of the 3 part blog series, we discuss lab equipment that easily allow for optimal flow visualization when testing PCBs.

Our first two posts show the benefits of air and liquid flow visualization in PCB testing. In order to successfully evaluate the thermal performance of a component and PCB, the proper test environment must exist:

A test system that:

  • Accommodates both single components and multiple PCBs
  • Reflects the actual system
  • Can simulate elevated temperature conditions with a controlled flow, if required


ATS offers a family of wind tunnels that offer an automated facility for thermal characterization, testing, and optimization of PCBs, components, and heat sinks.

ATS Wind Tunnels


All ATS wind tunnels have a large Plexiglas test section for optimal flow visualization. Wind tunnel controllers, such as the WTC-100 and CLWTC-1000 automate testing while accessories such as the HP-97 simulate heat dissipation. Most wind tunnels are easily portable and can be operated vertically or horizontally, maximizing compact lab space.

Rework of PCB layout using flow visualization techniques

Flow visualization is an easy and effective way to understand the flow condition of a component. It allows the PCB layout to be changed at the design stage, reducing the development costs of reworking the board layout after the design has be solidified. It minimizes thermal component costs, increases system reliability, and speeds up a product’s time to market.

To learn more about the wide range of ATS Wind Tunnels, please visit http://www.qats.com/Products/Wind-Tunnels or email ats-hq@qats.com.

Click here for part 1 of this three part series
Click here for part 2 of this three part series

Flow Visualization in PCB Testing: Part 2

In part 2 of our blog series on flow visualization, we discuss the benefits of liquid flow visualization, along with several primary methods for creating successful flow visualization.

Part 2: Liquid Flow Visualization

Liquid Flow Visualization

Flow visualization is usually easier to perform in water than air and yields results of better quality. As with smoke visualization, dye entrainment is successful mostly in laminar flow. The enhanced mixing in turbulent flow causes the smoke streaks to diffuse too rapidly to be of value as tracers. Compared to smoke visualization in air, dye entrainment in liquids is helped by the fact that the mixing between most dyes and water is less intense than between smoke and air. As a result, water-flow tunnels are frequently used to study air flows by testing scaled models at lower velocity. This often provides a better description of the flow.
A liquid flow model is scaled with a different working fluid than air using dimensional analysis. For a treatment of the principals of dimensional analysis and similitude that should be used in applying flow visualization in model experiments, reference can be made to any standard textbook on fluid mechanics. For the flow conditions around a model to be completely similar to those of the prototype, all relevant dimensionless parameters must have the same corresponding values: the model and prototype are then said to possess geometric, kinematic, dynamic and thermal similarity.
To visualize the flow, water-soluble dyes such as food coloring, potassium permanganate, methylene blue, ink and fluorescent ink may be injected using hypodermic needles or entrained from holes or slots in the walls of a test section. It is important that the velocity and density of the injected dye equal those of the surrounding fluid to maintain a stable dye filament and reduce disturbance of the surrounding flow.

In summary, fluid flow visualization is a powerful and unique technique for quickly identifying the flow distribution and approach air velocity to thermally challenging components in a complex PCB structure. By using this technique, one can attain the following:
-Examine the PCB layout at the design stage for expected thermal performance, e.g., determine flow stagnation areas.
-Make component layout recommendations that provide a thermally optimum board.
-Identify approach air velocities necessary for component thermal management and the choice of cooling system.

Click here for part 1 of this three part series
Click here for part 3 of this three part series

Flow Visualization in PCB Testing: Part 1

In our first post about flow visualization, we discuss the benefits of flow visualization, along with several primary methods for creating successful flow visualization.

Part 1: Best Techniques for Air Flow Visualization

PCBs support a multitude of components with varied geometries, electrical functions, power dissipation and ther­mal performance needs. For a PCB to work properly, a component’s thermal requirements must be met locally or at the system level. Regardless of the type of housing that surrounds a PCB, its cooling system must be designed so that diverse components are electrically functional and run at temperatures that help them reach their expected life spans.

Much effort is needed to meet a component’s thermal re­quirements, whether by enhanced fluid flow (liquid or air) or by adding a cooling solution, e.g., heat sink, onto the component. Except for a conduction cooled PCB, where a cold plate extracts heat from the board, electronics are typically in contact with some sort of cooling fluid. In many cases, the PCB is in direct contact with the coolant. This creates a very complex problem along with a unique opportunity.

The problem stems from the intricate topology of the PCB. Highly complex flows are observed on PCBs due to their three dimensional protrusions, i.e., components. A typi­cal PCB sees every imaginable flow structure. These include laminar, turbulent, separated flow, reversed flow, pulsating, locally transient and others. Flow visualization has the potential to yield more insight into a fluid flow or convection cooling problem than any other single method. Many misconceptions can usually be cleared up by flow visualization. However, it is important to use the technique most suited to a given problem.

Air Flow Visualization

Smoke entrainment is the most common visualization technique for laminar air flows. But it has somewhat limited use in turbulent flows due to its rapid diffusion by turbulent mixing. Smoke can be produced from many sources, but essentially it is made by either smoke-tube or smoke-wire.

In the smoke-tube method, vaporized oil is used to form a visible whitish cloud of small particles as the hot oil vapor condenses. Consideration must be given to the vortices shed by the smoke probe itself, since the most visible small-scale features often arise from the probes own wake. This effect is important for probe diameter-based Reynolds numbers exceeding about 15. Because it is impractical to reduce the probe diameter beyond a point and still get a reasonable amount of smoke flow, the smoke can be injected upstream of a convergence section to eliminate wake effects. A key disadvantage to the smoke-tube method is that the smoke is produced hot and rises due to its own buoyancy, thus it doesn’t follow the local flow faithfully. To reduce buoyance effects, the smoke can be cooled in a long length of tubing from the point of generation before its introduction into the flow.

In the smoke-wire method, smoke is generated as a sheet by coating a thin wire with oil, stretching it across the flow, and heating it with a pulse of current. Almost any wire and power supply can be used in this technique. The oil should be chosen carefully to have a broad boiling plateau, rather than a single temperature, in order to generate good smoke. Model train oil is suitable for this method.

The end result of board level flow visualization is PCBs that are thermally optimized and require no re-spin because of thermal constraints. If the board is thermally laid out, heat sinks and other cooling solutions are often not required.

Click  here for part 2 of this three part series
Click here for part 3 of this three part series