Category Archives: Thermal Analysis

The Importance of Thermal Management

Excess heat has affected electronic devices since their earliest days, becoming more critical with the advent of integrated circuits. Today, excess heat impacts the reliability, performance, and lifespan of devices and circuits across all applications. Common impacts of excess heat in electronics are:

Overheating: This can cause sudden shutdowns or failures. Elevated temperatures damage internal components, leading to permanent failure and potential safety risks—especially in high-power systems such as batteries and automotive electronics.

Lower performance: Overheating devices often throttle to reduce heat, and signal integrity may degrade, resulting in reduced performance. Maintaining operation within the designated temperature range lowers electrical resistance and power consumption while improving energy efficiency.

Shorter lifespans: High temperatures cause differential material expansion and deformation, damaging component structures and internal connections.

Thermal issues can also lead to field recalls and warranty claims. Dense PCB layouts may introduce thermal coupling between components, compounding heat-related risks.

Best practice is to engage thermal management specialists early. Effective thermal management controls and dissipates heat to maintain safe operating temperatures. Cooling solutions vary widely, but viable approaches exist for nearly every application.

Applying Professional Thermal Design

Effective cooling solutions require rigorous analysis at the concept stage, development, and testing. The thermal design process includes analytical modeling, experimental validation, and computational simulation across the full packaging domain—components, PCBs, shelves, chassis, and system enclosures.

Figure 1. CFD Simulation of Forced Airflow Across Areas of a Populated PCB.

Robust thermal design leverages both experimental and computational methods, using lab instrumentation and CFD tools such as FloTHERM, CFdesign, and Icepak, among other commercially available tools.

Empirical methods may include airflow or liquid testing, with measurements of velocity, temperature, and pressure, along with thermography using IR or liquid crystal techniques.

A disciplined, methodical approach consistently delivers strong results across diverse cooling challenges. OEMs can often avoid costly redesigns or recalls through expert thermal review, whether on-demand or via ongoing engineering partnerships. Subscription-based thermal services further accelerate validation and integrate thermal considerations earlier in development. More on these below.

Following are examples of carefully applied cooling design methodology.

Dual-Environment Thermal Analysis of a Sealed Offshore Electronics Enclosure

After detailed analytical modeling to envelop the solutions, CFD analysis was performed on a sealed offshore aquaculture enclosure operating in two passive environments: submerged seawater at 30°C and outdoor air at 40°C. The objective was to determine whether passive cooling could maintain component temperatures below 60°C.

Figure 2. (left) Outer Enclosure Temperature Contours. (center) An Internal Aluminum Sled to Transfer Component Heat to the Outer Enclosure. (right) Velocity Vectors Indicate the Slow Motion of the Internal Air.

The analysis showed the passive design was insufficient for the outdoor air case. Key limitations included weak natural convection and poor internal conduction to the enclosure walls. Hot spot spreading resistance significantly contributed to overall temperature rise.

Addressing the air case would also resolve the submerged case. Recommended improvements:

  1. Increase external surface area with fins or a bonded heat sink
  2. Improve internal conduction and reduce interface resistance
  3. Integrate heat pipes or vapor chambers to reduce spreading resistance

Multi-Cold-Plate Liquid Cooling System Design and Optimization

An EV battery manufacturer developed a 4 kW liquid cooling system with four cold plates integrated into a loop including a heat exchanger, DC-DC converter, and onboard charger. The design required balancing thermal performance, manufacturability, and flow distribution.

Figure 3. Four Cold Plates Receive Chilled Coolant from a Heat Exchanger as Part of a Liquid Loop that Included a DC-DC Converter and On-board Charger.

ATS combined analytical modeling with CFD to optimize cold plate geometry and system flow. Key parameters included tube routing, thermal resistance, and pressure drop.

Figure 4. CFD Simulation of a Revised Cold Plate with 10 Tube Passes and 9 Tube Bends.

A 10-pass serpentine tube design maximized heat transfer while maintaining acceptable pressure drop and manufacturability. Additional improvements included optimized tube diameters and balanced manifold routing.

The study demonstrated that effective kilowatt-scale liquid cooling requires coordinated optimization of geometry, pressure drop, and flow distribution. General findings:

  1. Balanced conduction and convection are critical
  2. Targeted passive changes can yield significant gains
  3. System-level optimization outperforms isolated fixes

CFD-Driven Thermal De-Risking of a Ruggedized Rack System

A baseline-to-optimization CFD study was conducted on a sealed 241 W ruggedized rack system with a 55°C ambient limit. The goal was to identify thermal violations and develop a reliable cooling strategy.

Figure 5. CFD Baseline Model and Surface Temperature Contours of a Ruggedized Rack System.

Through iterative CFD-driven design changes, ATS improved airflow efficiency, heat sink performance, and heat routing. Final modifications included revised heat pipe routing, heat sink replacement, fan reconfiguration, and removal of airflow obstructions. All components achieved thermal compliance.

Figure 6. Surface Temperature Contours of the System’s (left) Original Pin-Fin Heat Sink, and Its Replacement (right) maxiFLOW Heat Sink.

The study showed that sealed systems require holistic optimization across airflow, heat flow routing, fan placement, and heat sink design. General findings:

  1. Analytical modeling identified areas requiring attention and possible solutions
  2. Baseline CFD validated the findings in ‘1’ and identified thermal risks before failure
  3. Heat sink upgrades alone are insufficient without airflow optimization
  4. Iterative CFD enables targeted, low-risk refinement
  5. Final designs improve both compliance and thermal margin

Thermal Optimization of a Passive Aluminum Enclosure

ATS evaluated a sealed passive aluminum enclosure dissipating 75.8 W at 25°C ambient. CFD and parametric analysis identified key thermal constraints and guided optimization.

Figure 7. (left) Distribution of Enclosure Components, (right) Enclosure Baseline Thermal Distribution CFD.

Using 3D CFD with conjugate heat transfer, ATS modeled conduction and natural convection. Results showed that achieving target performance required coordinated improvements across both mechanisms.

Enhancements included improved thermal interface materials, better heat spreading, optimized fin geometry, reduced obstructions, and added vent gaps to enhance natural convection pathways.

Figure 8. The Enclosure Thermal Optimization Included Adding Cross-Cut Venting Gaps to Optimize Natural Convection.

Passive cooling performance is governed by the interaction of internal conduction and external convection. Key limitations included interface resistance and restricted airflow, with diminishing returns from geometry-only changes. Findings:

  1. Balanced conduction and convection are essential
  2. Targeted passive improvements deliver measurable gains
  3. System-level optimization is more effective than isolated changes

Conclusion

Modern electronics—including AI hardware—generate substantial heat loads, making thermal management a first-order design constraint. Large-scale systems such as data centers incorporate cooling from the outset, but thermal design is equally critical at smaller scales.

Figure 9. ATS Thermal Engineers Use Thermochromic Liquid Crystals to Reveal Hot Spots in Electronic Devices. See a Demonstration Video: https://www.youtube.com/watch?v=peewxRlNVqg

Every application presents unique challenges, and thousands of new devices each year require tailored cooling solutions.

When clients have excess heat issues, ATS engineers work closely with them to deliver cost-optimized, practical thermal and mechanical solutions that align with real-world schedules. The objective is consistent: deliver the right solution the first time.

For OEMs and others with continuing needs for thermal engineering, ATS now provides a subscription service. This comes with tiered support levels, ranging from periodic consultation to embedded engineering support within development teams. Contact ATS for more information on the thermal engineering subscription service.

Figure 10. ATS Thermal Engineering Consulting Tiers Match a Manufacturer’s Ongoing Needs.

To see more details on the above cooling applications, and others, see the Advanced Thermal Solutions, Inc. website, https://www.qats.com/Consulting

Where Can Thermal Solutions for Electronics Equipment be Tested and Characterized? at ATS!

One of ATS’ core principles is basing our solutions on data: from analytical modeling, to CFD to manufacturing the thermal solution then actually testing it in our labs. Our vertical integration allows for excellent quality control and reliable solutions. With our investment in 6 characterization labs, we take this seriously for ourselves and for our customers.

ATS runs six Thermal Characterization Labs. Featuring a unique selection of air velocity, air temperature and air pressure measurement instruments and wind tunnels for thermal management research, testing and analysis. Virtually any electronic system can be characterized.

==> Learn more on our web site here: https://www.qats.com/Consulting/Lab-Capabilities
==> Got questions on our labs and how we might help your next project? email us at ats-hq@qats.com

How to Achieve Localized Cooling with Cold Plates

Many applications in electronics cooling require a cold plate to remove heat from discrete components laid out on a board. In these circumstances, it is more efficient that the liquid does not completely fill the cold plate, but is only transferred to areas that need to be cooled.

With this kind of design, the required volumetric flow rate of the coolant will be significantly lower than if the entire cold plate was filled with liquid. The schematic for a typical example of this scenario is given in Figure 1. [1]

Localized Cooling With Cold Plates

Figure 1. Schematic of a Board with a Localized Area of Heat Dissipation . [1]

In Figure 1, areas A, B, C and D must be cooled for the components dissipating from 5 to 15 W/cm2. The other areas, designated as open, have components that interfere with the cold plate and must be avoided in the design. Two designs were considered for this case: a drilled hole and a press-fit tube. Figure 2 shows the drilled hole concept.

As can be seen, there are multiple small holes around the heat dissipating components under the cold plate surface. Large holes are machined to interconnect the smaller holes. A technique called gun drilling was used for machining the long holes. The entire cold plate was made from a copper block.

Cold Plates

Figure 2. Schematic of the Drilled Hole Cold Plate Design. [1]

Figure 3 shows the press-fit tube design. In this approach, a copper tube with high thermal conductivity is routed through the areas of heat transfer and either brazed or epoxied to the aluminum cold plate base. This design is considerably lighter and cheaper than the drilled hole design.

Cold Plates

Figure 3. Schematic of the Press-Fit Tube Cold Plate Design. [1]

To analyze the performance of this cold plate configuration, simple analytical tools can be used for a standard cold plate design. A brief summary of the equations is described here. To analyze the problem, we first have to calculate how much flow is going through the cold plate, and evaluate the pressure drop of the flowing fluid.

Pressure drop is calculated from:

Where
Um = bulk mean fluid velocity (m/s)
f = fanning friction factor
Awet = wetted surface area of the tube
Ac = cross section of the tube
K = loss coefficients related to turns, sudden expansion and contraction, etc.

The friction factor was obtained from the following equation which is in satisfactory agreements for the laminar, turbulent and transition regimes [2]

Where

Where ν is the kinematic viscosity of the fluid (m2/s) and P is the wetted perimeter of the tube.

For the heat transfer calculation, the Nusselt number can be calculated from standard correlations in the literature for fully developed flow. The Nusselt number is related to the heat transfer coefficient as:

Where
Kf = fluid conductivity

For thermally developing flow the following correlation can be used: [3]

Where
Num = mean Nusselt number
Nu = fully developed Nusselt number
L = duct length

Then the convective resistance can be calculated as:

Where
hm = mean heat transfer coefficient

For the tube fitted design the overall thermal resistance is made of four components: convection, tube conduction resistance, epoxy conduction resistance and the cold plate. It is stated as:

Where
Rh = convection resistance
Rtube = conduction resistance of tube walls
Repoxy = conduction resistance of the epoxy
Rcoldplate = conduction resistance of the cold plate

For the drilled design the overall thermal resistance can be written as:

If the heat transfer coefficient is based on the local fluid temperature, then a caloric resistance must be added based on the fluid mass flow rate. The effective heat transfer coefficient is then:

Where
ṁ = mass flow rate (kg/s)
Cp = fluid heat capacitance (kJ/kg·K)

Figure 3 shows the pressure drop of the two designs as a function of water flow rate. It can be seen that with a water flow rate up to 1.89 l/min (0.5 GPM) the pressure drop between the two designs is almost the same, but at higher flow rates the drilled design’s pressure drop exceeds the tube design. The sharp 90-degree turn of the drilled holes, which lead to a higher loss coefficient, is the major contributor to the higher pressure drop.

Figure 4. Total Pressure Drop of the Drilled Design and the Tube Design as a Function of the Volumetric Flow Rate. [1]

Figures 5 and 6 show the effective heat transfer coefficient of the two designs as a function of flow rate. The bend and sharp increase of the curves around 0.95 l/min (0.25 GPM) is due to the flow transitioning from laminar to turbulent. The drilled hole design shows effective convection heat transfer between 7,000 and 27,000 W/m2K for the range of flow between 0 and 7.56 l/m (2.6 GPM). The press-fit tube design on the other hand shows a lower effective heat transfer coefficient of between 6,000 and 17,000 W/m2K.

This is mostly due to the interfacial resistance and tube wall conduction. In the drilled design example, these two resistances do not exist. In a real application, the pumping of fluid is constrained by the pump and its characteristic curve. Even though the drilled hole shows a higher heat transfer coefficient for the same flow rate, the extra pressure drop caused by the drilled design may have a lower flow rate hence lowering the heat transfer coefficient.

Figure 5. Effective Heat Transfer Coefficient of the Tube Design as a Function of Flow Rate for Different Regions on the Plate. [1]

Figure 6. Effective Heat Transfer Coefficient of the Drilled Hole Design as a Function of Flow Rate for Different Regions on the Plate. [1]

Figure 7 shows another cold plate design, this one by Lytron. [4] In this design, the extended-surface cold plate material and micro-channel aluminum extrusion are sandwiched between aluminum sheets. The entire assembly is welded using vacuum brazing. It is all aluminum, which makes it very light weight. The flexibility of this design allows the placement of cooling channels in different positions to enable localized cooling.

Figure 7. Lytron Vacuum Brazing of a Cold Plate for Localized Cooling. [4]

The above analytics show that the performance of a cold plate for localized cooling can be calculated using a simple analytical tool. The designer then has to consider such factors as weight, manufacturing, cost and thermal performance to decide the best option for his or her design. The characteristic of the pump has a paramount effect on the design and cannot be neglected.

References:

1. Seaho, S., Moran, K. and Rearick, D. (IBM Corporation) and Lee, S. (Aavid Engineering), Thermal Performance Modeling and Measurements of Localized Water Cooled Cold Plate, http://www.aavidthermalloy.com/technical/papers/pdfs/water.pdf
2. Churchill, S., Comprehensive Correlating Equations for Heat, Mass and Momentum Transfer in Fully Developed Flow in Smooth Tubes, Ind. Eng. Chem. Fundam., Vol.16, 1977.
3. Al-Arabi, M., Turbulent Heat Transfer in the Entrance Region of a Tube, Heat Transfer Eng., Vol. 3, 1982.
4. http://www.lytron.com

For more information about Advanced Thermal Solutions, Inc. (ATS) thermal management consulting and design services, visit www.qats.com/consulting or contact ATS at 781.769.2800 or ats-hq@qats.com.

Thermal Performance of Macro and Microchannel Cold Plates in Electronics Cooling

In recent years, intense activity has been gone into improving the capabilities of cold plates. Specifically, the use of microchannels has provided great improvements in cold plate thermal performance. Regardless of a cold plate’s channel size, the following equations can be used for heat transfer coefficients when determining thermal performance. [1]

Where,

= Nussselt number

Dh = hydraulic diameter

= Reynolds number

 

ν = kinematic viscosity
Pr = Prandtle number

The pressure drop can also be calculated as:

Where,
P = density
f = friction factor

In recent years, microchannel cold plates have gained popularity due to their high performance. Webb shows that the best results can be achieved when the channel aspect ratio is about 7.4, and with a fin aspect ratio of 8. [2] Figure 1 shows a Fin-H copper microchannel with a channel hydraulic diameter of 0.49 mm. Due to the small size of the channels, the flow is generally considered to be laminar. The optimization resulted in a 25-mm wide and 20-mm long microchannel cold plate. [2]

Webb considered both single-pass and two-pass designs on the water side. The two-pass version was made to determine if there was any mal-distribution of the water from the single-pass case.

Microchannel Cold Plates

Figure 1. Copper Microchannel Fin-H Used in a Cold Plate. [2]

Figure 2 shows the thermal resistance of the Fin-H for the 1-pass and 2-pass designs as a function of flow rate.

Figure 2. Thermal Resistance of a Fin-H Cold Plate as a Function of the Water Flow Rate. [2]

This figure shows that the 1-pass version has a much better thermal resistance than the two-pass model for the same flow rate. It also shows that the flow has been distributed relatively uniformly. Figure 3 shows the pressure drop of the cold plate as a function of flow rate for the Fin-H and the Thermaltake Bigwater 735 cooler. [3] The figure shows the pressure drop of the 1-pass design is only 38% of the 2-pass design.

Figure 3. Pressure Drop of a Fin-H Cold Plate and a Thermaltake Cooler as a Function of the Water Flow Rate. [2]

Figure 4 shows the thermal resistance of the Fin-H cooler in the 1-pass design compared to the Thermaltake cooler [3]. At 2.28 l/min the Thermaltake’s thermal resistance is 0.106 K/W. The balance point of the Fin-H for 1-pass is with a thermal resistance of 0.07 K/W at a flow rate of 0.361 l/min. This is only 16% of the flow rate for the Thermaltake cooler.

Referring to Figure 3, the pressure drop is almost the same for both coolers. The major implication is that the microchannel cold plate requires a smaller pump compared to macrochannel cold plates, and provides a 50% increase in thermal performance.

Figure 4. Thermal Resistance of a Fin-H Cold Plate and a Thermaltake Cooler as a Function of the Water Flow Rate. [2]

Another innovative approach is the concept of forced-fed boiling (FFB). [4] Figure 5 shows a schematic of this process. It consists of a micro-grooved, thin copper surface with alternating fins and channels. The microgrooves have a hydraulic diameter of 28 microns, an aspect ratio of 15, and a fin density of 236 fins per cm.

There are feed channels on top of the micro-grooved surface. The fluid is forced through these channels into the microgrooves, which are located on top of the heated surface. The fluid vaporizes in the microgrooves and moves upward, while the liquid flows beneath the escaping vapor. This keeps the surface wet, resulting in an increase of the critical heat flux (CHF).

Figure 5. A Force-Fed Boiling Cold Plate. [4]

Figure 6 shows the heat transfer as a function of the temperature difference between the inlet fluid and the surface for various values of the flow rate for R245fa, a non-aqueous fluid for low pressure refrigeration applications. The figure shows that for heat fluxes of about 200 W/cm2 or less, heat transfer is independent of the flow rate, but this is not the case at higher heat fluxes. It also shows that the slope of the heat flux decreases with increasing temperature difference.

Figure 6. Heat Flux as a Function of the Temperature Difference for the FFB Cold Plate. [4]

Figure 7 shows an interesting trend for the heat transfer coefficient as a function of heat flux for the same fluid. At first, the heat transfer coefficient increases with the increase in heat flux. This indicates that by increasing the heat flux, a phase change process takes place which changes the single-phase flow to two-phase heat transfer. After reaching an impressive peak at 300 KW/m2K, the heat transfer coefficient starts to decrease. This is attributed to local dryouts from bubble generation, which also blocks the microchannels.

Figure 7. Heat Transfer Coefficient as a Function of Heat Flux for the FFB Cold Plate. [4]

While advances in cold plate performance have been incremental, their technology is still evolving. Improvements in microchannel manufacturing will open more opportunities in this field. Microchannel cold plates provide tremendous heat transfer coefficient capacities, but limitations prevent their broad deployment.

Fouling, dryout, and fabrication issues have been major negating factors for microchannel deployment in the broader market. Microchannel cold plates may have particular value in such applications as military, space, and high capacity computing, where service and maintenance are part of the deployment.

However, from the design and problem-solution standpoint, microchannel cold plates can be an effective part of a closed loop liquid cooling system.

References
1. Dittus, F. and Boelter, L., Publications on Engineering, University of California at Berkley, 1930.
2. Webb, R., High-Performance, Low-Cost Liquid Micro-Channel Cooler, Thermal Challenges in Next Generation Electronic Systems II, Millpress Science Publishers, Rotterdam, The Netherlands, 2007.
3. Thermaltake Company, 2006.
4. Cetegen, E., Dessiatoun, S., and Ohadi, M., Force Fed Boiling and Condensation for High Heat Flux Applications, VII Minsk International Seminar: Heat Pipes, Heat Pumps, Refrigerators, Power Sources, Minsk, Belarus, 2008.

Learn more about Advanced Thermal Solutions, Inc. (ATS) standard and customized, high-performance liquid cold plates by visiting https://www.qats.com/Products/Liquid-Cooling/Cold-Plates.

For more information about ATS thermal management consulting and design services, visit www.qats.com/consulting or contact ATS at 781.769.2800 or ats-hq@qats.com.

In the ATS Labs – Where Thermal Solutions Advance to Meet Industry Demands

Thermal management innovations need to match the rapid pace at which the electronics industry is advancing. As consumers demand new and more powerful devices or greater amounts of information at faster speeds, cooling solutions of the past will not be enough. Today’s cooling solutions must be smaller, lighter, and offer higher performance, but also need to be cost-effective, meet demanding project specifications, and be reliable for many years.

Advanced Thermal Solutions, Inc. (ATS) understands the importance of creating cutting-edge thermal solutions for its customers and has geared its thermal design capability and its research and development to match the innovations taking place in electronics design.

ATS Labs

An ATS engineer assembles a rig for testing cold plates in one of ATS’ six state-of-the-art labs. (Advanced Thermal Solutions, Inc.)

To meet the need for innovative solutions, ATS engineers are hard at work in the company’s six state-of-the-art laboratories at the ATS headquarters, located in Norwood, Mass. (south of Boston). Thermal issues of all kinds are recognized, broken down, and resolved and cooling solutions are designed, simulated, prototyped, and rigorously tested in these research-grade facilities.

When someone thinks of a research lab, the initial picture is scientists in white coats working for major corporations, such as IBM, Microsoft, or Google, but the development of new ideas is an essential tool for any company in the technology field. Working with empirical tests in a lab environment pushes concepts from the white board or the computer screen to reality. There comes a time when engineers need to produce tangible data to ensure that a design works as planned.

ATS thermal engineers are no different. They use state-of-the-art instruments and software in each of the six labs to conduct a long list of characterization, quality-assurance, and validation tests. In addition to finding custom cooling solutions for customers, ATS engineers produce thermal management products for commercial uses, including a variety of next generation heat sink, heat pipe, vapor chamber, and liquid cooling designs.

Engineers test ATS instruments using a wind tunnel and sensors in the Characterization Lab. (Advanced Thermal Solutions, Inc.)

Among the most common tests performed in the ATS labs are:

• Measurements of air velocity, direction, pressure and temperature;
• Characterization of heat sink designs, fans and cold plates
• Flow visualization of liquid and air flow
• Image visualization characterization using infrared and liquid crystal thermography.

Many of the instruments that these tests are performed on were designed and fabricated by ATS. That includes open-loop, closed-loop, and bench-top wind tunnels; the award-winning iQ-200™, which measures air temperature, velocity, and pressure with one instrument; and the thermVIEW™ liquid crystal thermography system. Engineers also use specially-designed sensors, such as the ATS Candlestick Sensor, to get the most accurate analysis possible.

Smoke flow visualization tests run in ATS wind tunnels demonstrate how air flows through a system. (Advanced Thermal Solutions, Inc.)

Heat pipes and vapor chambers are increasingly common cooling solutions, particularly for mobile devices and other consumer electronics, and ATS engineers are working to expand the company’s offerings for these solutions and to develop next generation technology that optimizes the thermal performance of these products. This research involves advanced materials, new fabrication methods, performance testing, and innovative designs that are ready for mass production.

ATS engineer Vineet Barot sets up a thermal imaging camera for temperature mapping studies in the lab. (Advanced Thermal Solutions. Inc.)

ATS has also developed products to meet the growing demand across the electronics industry for liquid cooling systems. From new designs for recirculating and immersion chillers to multi-channel cold plates to tube-to-fin heat exchangers, ATS is continuing to expand its line of liquid cooling solutions to maximize the transfer of heat from liquid to air and researching new manufacturing methods, advanced materials, and other methods of enhancing the technology.

As liquid cooling technology has grown, ATS has met this demand with new instruments and lab capabilities, such as the iFLOW-200™, which measures a cold plate’s thermal and hydraulic characteristics, and full liquid loops to test ATS products under real-world conditions.

ATS Labs

ATS engineer Reza Azizian (right) works with intern Vladislav Blyakhman on a liquid cooling loop in the lab. (Advanced Thermal Solutions, Inc.)

The labs at ATS are up to even the toughest electronics cooling challenges that the company’s global customers present. Thanks to its extensive lab facilities, ATS has provided thousands of satisfied customers with the state-of-the-art thermal solutions that they demand.

For more information about Advanced Thermal Solutions, Inc. (ATS) thermal management consulting and design services, visit www.qats.com/consulting or contact ATS at 781.769.2800 or ats-hq@qats.com.