Rising Energy Demand in Data Centers

Cooling and Energy Consumption in Data Centers

McKinsey and Company estimates that cooling accounts for nearly 40% of the total energy consumed by data centers, emphasizing the importance of implementing efficient cooling practices to reduce energy consumption and improve overall energy efficiency.

Data centers use a common metric known as Power Usage Effectiveness (PUE) to measure energy efficiency, a ratio that compares the total energy consumed by a data center, to the energy consumed just by the IT equipment.

A PUE of 1.0 means that the data center is perfectly efficient, while a PUE of 2.0 means that the facility infrastructure is consuming twice as much power as the IT equipment. Data center operators measure PUE to meet efficiency initiatives and identify areas for improvement. The average annual power usage effectiveness (PUE) reported in 2022 was 1.55, representing a slight improvement over the 2021 average of 1.57 but consistent with the trend of marginal PUE gains Uptime Institute observed annually since 2014.

However, the most efficient large hyperscale facilities achieved a PUE value of 1.2 compared to other facilities that have PUE values greater than 1.6, which means for every kW of power used for the IT task, another 600 W is consumed to power the cooling and other infrastructure equipment.

Improve Energy Efficiency with Innovative Cooling Technologies

Efficient cooling practices play a crucial role in achieving a lower PUE. By implementing innovative cooling technologies, such as liquid cooling, hot and cold aisle containment, or optimized airflow management, data centers reduce the energy consumed by cooling infrastructure, leading to improved energy efficiency. The adoption of liquid cooling in data centers is gaining momentum due to its ability to deliver more efficient and effective cooling than air-cooling, especially high-density IT racks.

The PUE analysis of a High-Density Air-Liquid Hybrid Cooled Data Center published by the American Society of Mechanical Engineers (ASME) studied the gradual transition from 100% air cooling to 25% air –75% liquid cooling. The study observed a decrease in PUE value with the increase in liquid cooling percentage. In the 75% liquid cooling case, 27% lower consumption in facility power and 15.5% lower usage in the whole data center site were obtained.

The PUE metric does not consider IT or networking equipment efficiency and provides a benchmark to evaluate efficiency gains over time within a data center facility, not comparing one facility against another. Regardless, it remains the de-facto standard to measure and compare data center energy efficiency. Despite its shortcomings, PUE provides a useful baseline to assess and improve a facility’s infrastructure efficiency.

The data center industry continues to work on new metrics to more accurately measure its energy efficiency. TUE is one such metric that considers the efficiency of the IT equipment, the cooling system, and other factors affecting energy consumption in data centers.

Boyd’s Innovative Data Center Cooling Solutions

Boyd has decades of experience and expertise innovating and manufacturing cooling solutions like coolant distribution units, 3D vapor chambers, liquid loops and cold plates, remote heat pipe assemblies, and chillers for data centers. Leverage our liquid cooling and material science heritage to design innovative AI-based solutions optimized for performance, reliability, and energy efficiency.

Our engineering and material science expertise allows us to design custom cooling solutions for specific data center types. To learn more about our thermal management solutions or to discuss your project needs, schedule a consultation with our experts.

The latest electrification trends drive products to contain more powerful and compact electrical components, which drives additional thermal management challenges to maintain or improve performance, reliability, and lifespan. Product designers and manufacturers need to maintain optimized heat source temperatures to ensure these devices operate efficiently and remain reliable over time. One way to optimize device temperatures is through effective thermal management.

What is Thermal Management?

Thermal management is the process of managing heat within a system to ensure efficient and safe operation. By designing and implementing techniques that leverage conduction, convection, and radiation, thermal management helps regulate device or system temperature by removing or dissipating excess heat.

Thermal management is essential for many device and system types, including electronic devices, vehicles, power plants, imaging systems, and high-performance computing systems. Without proper thermal management these devices can overheat, leading to reduced performance, shortened lifespan, and potential damage to components.

Effective thermal management techniques, like heat sinks, fans, liquid cooling systems, and thermal interface materials, enable devices and systems to operate safely, perform at their best, and have a longer lifespan.

Thermal Management Techniques

Most systems use a combination of thermal management techniques, so these solutions are categorized based on the primary cooling method used in the system. Categorization is generally based on working fluid and the type of convection in the cooling system.

Air Cooling, Liquid Cooling, and Two-Phase Cooling

Thermal management solutions are classified into air cooling, liquid cooling, and two-phase cooling based on the working fluid used. While air cooling is often the simplest and most cost-effective solution, liquid cooling and two-phase cooling solutions provide more efficient heat transfer and are better suited for high-performance applications.

However, liquid cooling can have potential complications with compatibility and maintenance, and two-phase cooling solutions may require additional design considerations for managing the vapor-liquid interface. The best thermal management solution depends on specific application needs and the trade-offs between performance, cost, and complexity.

Conduction Cooling

Systems that do not use any fluid are considered conduction cooling solutions. These thermal management solutions rely on the thermal conductivity of materials to effectively transport heat away from a source. Most air, liquid, and two-phase systems have some level of heat conduction within its components, but rely more heavily on fluid movement to move heat. Natural Convection and Forced Convection

Based on convection type, a thermal management solution is classified into natural convection (passive solution) or forced convection (active solution). Natural convection relies on the natural flow of air or liquid around a heat source to dissipate heat and occurs due to the temperature differences between the heat source and the surrounding environment. Whereas, forced convection uses a fan or blower, pump, or other mechanical device to circulate air or liquid around the heat source, enhancing heat transfer and improving cooling efficiency

Air cooling and two phase cooling leverage both active and passive configurations, but liquid cooling solutions are primarily active solutions.

Why is Thermal Management Important?

Incorporating thermal management into the design process helps avoid costly redesigns or repairs. Industries such as medical, aerospace, defense, and eMobility have strict regulatory requirements for thermal management. Failure to comply with these requirements results in legal consequences, fines, or even loss of life.

Inefficient thermal management leads to increased energy consumption, which not only impacts the device’s performance and lifespan but also has a negative impact on the environment. This is a major design focus for industries like data centers and high power compute. By designing devices with thermal management in mind, energy consumption can be minimized, leading to a more sustainable product.

Touch temperature is an important factor in the user experience of a product. If a device or a component is too hot to touch, it poses risks of burns or other injuries to the end-user. This can also lead to negative media coverage, potential damage to brand value, and other legal liabilities.

Overall, thermal management should be an integral part of the design process to ensure reliable and safe operation, compliance with regulatory requirements, cost savings, environmental sustainability, and brand reputation.

The Boyd Difference for Thermal Management Solutions

Boyd has several decades of experience and expertise designing and manufacturing at scale custom thermal management solutions for various industries, including eMobility, cloud, medical and more. Leverage our extensive supplier network, material science experience, and engineering expertise for comprehensive thermal management solutions that meet your unique needs and challenges. To learn more about our thermal management solutions or to discuss your project needs, schedule a consultation with our experts.

Heat Pipes and Heat Exchangers

What is a heat pipe?

A heat pipe is a heat transfer device with an extremely high effective thermal conductivity. Heat pipes are evacuated vessels, typically circular in cross section, which are back-filled with a small quantity of working fluid. They are totally passive systems, with no moving parts, and transfer heat from a heat source to a heat sink with minimal temperature gradients, or to isothermalize surfaces.

How does a heat pipe work?

Through the evaporation and condensation of the working fluid. As heat is input at the evaporator, fluid vaporizes, creating a pressure gradient in the pipe. This forces the vapor to flow along the pipe to the cooler section where it condenses, giving up its latent heat of vaporization.The working fluid is then returned to the evaporator by capillary forces in the porous wick structure or by gravity.

What are heat pipes used for?

Heat pipes are used for a wide variety of applications — anywhere heat must be transferred with a minimum thermal gradient, either to increase the size of the heat sink, to relocate the sink to a remote location or where isothermal surfaces are required. Typical applications include computer processor cooling, isothermal furnace liners and aerospace heat transfer.

What is the thermal conductivity of a typical heat pipe?

Heat pipes do not have a set thermal conductivity like solid materials because they have a two-phase heat transfer. Instead, their effective thermal conductivity improves with length. A 12-inch and a 4-inch heat pipe, each carrying 100 W, will have about the same thermal gradient, so the 12-inch pipe will have the higher effective thermal conductivity. Unlike solid materials, a heat pipe will have its effective thermal conductivity changed with the amount of power being transferred and with the evaporator and condenser sizes. Effective thermal conductivities can range from 10 to 10,000 times (4,000 W/meter·K to 4,000,0000 W/meter·K) the effective thermal conductivity of copper, depending on the length of the heat pipe.

What materials can be used to construct a heat pipe?

The heat pipe wall or shell material selection is driven by compatibility of the working fluid. The heat pipe working fluid is selected based on the operating temperature range of the application. After a working fluid is selected, the heat pipe wall or shell material is selected based on its chemical compatibility with the working fluid to prevent corrosion or chemical reaction between the fluid and the heat pipe wall or shell material. A chemical compatibility problem between the working fluid and wall material within a heat pipe can create a chemical reaction that produces a non-condensable gas. Non-condensable gases within a heat pipe can cause operational failure.

What are the primary heat transport limitations of a heat pipe?

The four basic heat pipe heat transport limitations are:

Capillary limit: This is the maximum capillary pumping pressure of the wick structure to transport the working fluid from the heat pipe condenser to evaporator. The capillary pumping pressure must overcome three basic pressure drops within the heat pipe, namely, vapor pressure drop, liquid pressure drop and gravitational/body force pressure drops.

Boiling limit: The boiling limit occurs when the maximum radial heat flux (W/cm2) is exceeded resulting the rate of working fluid vaporization to exceed the rate at which the liquid condensate is returning from the condenser section of the heat pipe. When the boiling limit is reached, liquid working fluid is not available to absorb heat and the heat pipe goes into a dry-out condition and will not operate.

Sonic limit: The maximum flow rate of the working fluid vapor flow rate traveling from the heat pipe evaporator to condenser. When the vapor flow rate exceeds the sonic velocity, chocked flow is achieved and the heat pipe will not operate isothermal.

Entrainment limit: This occurs when the sheer force of the vapor flowing from the evaporator to the condenser section of the heat pipes at the vapor-wick interface causes liquid droplets to be entrained and carried to the condenser section. Exceeding the entrainment limit may prevent the working fluid from returning from the condenser section to the evaporator section, as a result the heat pipe will not operate.

Are heat pipes reliable?

Yes, mainly because they have no moving parts. They are ideal for applications such as aerospace where maintenance is not feasible. The main cause of heat pipe failures is gas generation in the heat pipe, but this can be completely avoided by proper cleaning and assembly procedures. Boyd is the only heat pipe manufacturer in the world that can claim over 40 years of heat pipe reliability and life test data.

Are heat pipes expensive?

Compared with traditional (and less effective) heat transfer methods such as aluminum extrusions and cast heat sinks, heat pipes can have a higher initial cost. That is why heat pipes are not recommended for applications where cooling can be performed by simple conductive heat sinks. In more demanding applications, however, the overall cost of heat pipes is competitive with other alternatives. The initial cost is also partially offset by improvements in system reliability and increased life of cooler running electronics. In large quantities, the cost of heat pipes drops significantly and often makes them the most economical solution to a cooling application.

Can heat pipes work against gravity?

Yes, this occurs whenever the evaporator is located above the condenser. In these applications the working fluid must be pumped against gravity back to the evaporator. This occurs through wick structures that pump working fluid through capillary pressure developed in the porous wick. The finer the pore radius of a wick structure, the higher against gravity the heat pipe can operate. (Nanoscale wicks are available.)

Not all types of passive heat transfer can operate against gravity. A thermosiphon is similar to a heat pipe but has no wick structure and will only operate gravity-aided.

What fluids are used in heat pipes?

Heat pipe working fluids range from helium and nitrogen for cryogenic heat pipe applications, to liquid metals like sodium and potassium for high-temperature heat dissipation. Some of the more common heat pipe fluids used for electronics cooling operations are ammonia, water, acetone and methanol. Boyd has experience making heat pipes using all of these fluids for cryogenic applications to high temperature (>1,000 °C) applications.

How does a water heat pipe work below 100° C?

Water at atmospheric pressure boils at <100° C, but inside a heat pipe, water is not at atmospheric pressure. The internal pressure of the heat pipe is the saturation pressure of the fluid at the corresponding fluid temperature. The fluid in a heat pipe will boil at any temperature above its freezing point. Therefore, at room temperature (20° C) a water heat pipe is under partial vacuum, and the heat pipe will boil as soon as heat is input.

Can heat pipes freeze?

Yes, heat pipe working fluids, including water, maintain their normal freezing point. Heat pipes will not operate until the temperature rises above the freezing temperature of the fluid. Properly designed heat pipes, however, will not be damaged by freezing or thawing of the working fluid. Boyd has successfully designed, developed and manufactured freeze tolerant heat pipes that have over 20 years of demonstrated and proven field application experience.

What heat exchanger alarm features can you provide? How?

Temperature control, speed control and fan-failure alarms can be integrated into each heat exchanger. These features can be provided by installing a solid-state control board and/or integrating the feature into the fan itself.

How do you seal the core element in the Boyd HXi^® Heat Exchanger series?

Boyd uses an RTV sealant to provide a cohesive gasket around both the inner core cassette and the core flange assembly. Each inner core cassette and core flange assembly is subjected to a vacuum test design to simulate NEMA 4 conditions.

Can the fins in an HX^® be coated for environmental protection?

Yes, the typical coating is either a hexavalent chromate or a RoHS compliant clear chromate. Coatings such as Herresite or E-Coat can be added to heat exchangers to provide environmental protection to the unit (minimum volumes apply).

What is the difference between the HX^®, HXi^® and HXc^® technologies?

Each technology offers its own merits in regard to size, efficiency, adaptability for customization and power capability. Allow Boyd to review the application in order to recommend a great solution.

Do you build custom designs?

Boyd utilizes a broad scope of technologies to deliver fully optimized, custom solutions as well as our standard offerings.

Can you provide a computer-generated model of how your heat exchanger will operate in my application?

Yes, Boyd can utilize CFD (computational fluid dynamics) programs such as SmartCFD to model the performance of a heat exchanger.

Why should we buy a heat exchanger from Boyd?

Understanding of the total thermal circuit is crucial to a product’s success. Boyd has the capability to design and manufacture thermal management solutions at the component, board, and system levels.

An economical option for increasing surface area, folded fins increase heat transfer and performance in heat sinks, heat exchangers, and liquid cold plates.

The World of Folding

Most of the time when we hear folding, and not folded fin heat sinks. We first think of folding typical daily things like laundry or paper. Most of us don’t think or know about the awesome applications that folding has in technology. Science, technology, and engineering have embraced folding as a resource for innovations in a variety of fields. Material innovations that improve strength or flexibility of individual material sheets stem from the study of folding. Folding has improved storage for air bags for vehicles or solar arrays for space applications. Origami has helped develop heart stents to self-expand into place making heart surgery a tad less complication. Folded batteries, circuits, and foldable robotic forms are pushing the applications of electronics and robotics.

While not so flashy as paper origami, robotics, or medical applications, we can apply folding techniques in thermal management. In the thermal management world, folding metal sheets enables us to increase the amount of surface area within a given volume. Surface area is crucial for effective heat transfer.

We’ve Taken Paper Origami and Gone Metal!

What Are Folded Fins?

Folded fins come in a variety of materials and types. Most material that can be formed into thin sheets and easily folded can be used as a folded fin material. In thermal management, the most popular materials are copper and aluminum, since those have the highest thermal conductivities of commercially available materials. Copper and aluminum folded fins are the default materials used in Genie. Stainless steel, cupro nickel, titanium, Inconel or other nickel alloys are other common folded fin materials. Their use is heat transfer assemblies is highly dependent on the final application. You can use these materials in Genie by selecting the Custom option in the Heat Sink Design page of your project.

Folded Fins and Their Many Styles

Flat crest is the most common type of folded fin, since the crests or tops are where the fin stack is usually joined with a heat sink base. The flat crest fins maximize the amount of surface contact with the base, so the most heat can transfer from the base to the fins. These are the types of fins used in Genie. Other types of fins are available, but their use is application specific, just like materials other than aluminum and copper. These include round crest, louvered, lanced and offset, wavy, and ruffled.

How We Actually Use These Fin Stacks

Folded fins are rarely used on their own. Folded fin stacks are typically joined with a base that serves as an interface between the heat source and the fins. Genie defaults to either copper or aluminum bases, in which both have the option of embedded heat pipes. But like the fins, you can define other materials you would like to use for the base.

Mix and Match Materials of Your Folded Fin Heat Sink

The material selection determines the joining method between the fins and the base. Aluminum resists soldering, so aluminum/aluminum joints are epoxy bonded. Epoxy doesn’t adhere well to copper, so copper/copper joints tend to be soldered. If mixed between the two, typically the aluminum component is nickel plated, then the assembly is soldered together.

Folded fins are also common components in liquid cold plates and heat exchangers since they easily increase surface area and improve system and device performance. Please reach out to our team if you need help with your folded fin application!

What are Zipper Fins?

Zipper fins are sheets of metal that are progressively punched out of stock material. First the geometry of the fin is created with the punches. The length, height, and fin pitch are determined in this first set of punches. The fin thickness is defined by the thickness of the fin stock used. Secondary punching processes then fold the fin and lock them into place with the previous fin. When the fin stack has enough fins for the application this stack was designed for, it’s removed from the punching area, ready to become a full zipper fin heat sink.

Each zipper fin heat sink has it’s own design for the progressive punches for the fins. This makes zipper fin assemblies more application specific since any new zipper fin heat sink configuration typically needs a new set of punches. Zipper fin heat sinks are ideal for high volume applications as opposed to low quantity production runs since the cost of the punches will be spread out across fewer heat sinks.

How Genie Uses Zipper Fin Heat Sinks

Let’s Mix and Match Materials in Our Zipper Fin Heat Sink

What’s neat about having separate components is that you can mix and match materials. You can have a copper base and aluminum fins or vice versa. Depending on your application needs, you may need an all aluminum or all copper heat sink. The material selection determines the joining method between the fins and the base. Aluminum resists soldering, so aluminum/aluminum joints are epoxy bonded. Epoxy doesn’t adhere well to copper, so copper/copper joints tend to be soldered. If mixed between the two, typically the aluminum component is nickel plated, then the assembly is soldered together.

Zipper fins heat sinks are a great heat transfer solution. While Genie uses them in the simplest form, zipper fins have a wide range of application and design flexibility. Contact Boyd Design Engineers for assistance with your zipper fin heat sink design.

Brazing generates solid thermal and mechanical joints for fabricating heat sinks, liquid cold plates, heat exchangers, and chassis.

What is Brazing?

Brazing is the process of melting a metal between two other pieces of metal in order to join them. Common metals for this process in the thermal management world include copper and copper based alloys, aluminum-silicon based alloys, and nickel alloys. This process allows us to create brazed fin heat sinks and expands our thermal management technology toolbox.

Brazing is not to be confused with braising, which is a cooking process where your first sear the meat at a high temperature then cook it low and slow with some amount of liquid in a closed container like a pot. Brazing metals is more like high temperature baking anyways.

Brazing, if applied well, can generate tight joints since the process relies on capillary action wicking the braze material between the parts. Braze material is an alloy that melts at a temperature lower than the parts you’re joining together. Stronger and more consistent joints are made with materials that closely match the mating parts. In all brazing processes, mating parts are fixtured together to ensure they retain their geometric relationship to each other during the brazing process. Once parts cool, they’re either ready to go or need some finishing like residual flux removal or final straightening or machining.

What’s the difference between brazing and soldering?

For those of you wondering, brazing sounds awfully like soldering. Brazing essentially is soldering, just at a much higher temperature (above 450°C, or 840°F). The higher temperature opens the door to a bigger material selection, which includes one of our favorites, aluminum. Both processes use a filler material, like a solder, to join the metal pieces together. If the metals and atmosphere require it, flux is also added to the mix to prevent oxidation of the joint.

In Genie, Brazed Fin Heat Sinks refer both to brazed and soldered assemblies. Sometimes we only solder copper heat sinks, but we wanted to include those heat sinks as part of the options available to Genie users.

Brazed Fin Heat Sinks: Bonded Fin’s Older, Stronger Sibling

Pick your Process: The Different Types of Brazing

While they’re many types of brazing, we’ll go over the common ones used in thermal management.

Controlled Atmosphere Brazing

Controlled Atmosphere Brazing (CAB) is conducted in an oven with a specific mixture of air surrounding the parts. This mixture is primarily inert gasses and not oxygen that can oxidize the joints. Since the parts are placed in an oven, the braze material flows horizontally outwards where it’s not pulled by capillary action. This process is great for making a brazed fin heat sink since the base grooves are ideal in wicking the braze material.

Vacuum Brazing

As the name suggests, vacuum brazing is conducted in a vacuum chamber. This is to remove any sort of oxygen that can oxidize the braze joints or other gasses that could get caught in tiny pockets in the joints. In practice, vacuum brazing has an advantage over other types of brazing since it doesn’t require flux to prevent oxidation. That makes vacuum brazing popular for complicated assemblies like heat exchangers and liquid cold plates, since they’re tough to clean any residual flux out.

Dip Brazing with a Salt Bath Flux

Torch Brazing

In a few occasions, we’ll use torch brazing to make tricky prototypes, proofs of concept, or complex, small production runs. Torch brazing utilizes a gas flame to melt the filler material between the two metal parts being joined. Since this typically is a manual process, it’s reserved for small quantities. Since we’re not using a tightly controlled atmosphere that aluminum brazing requires, this process is normally reserved for copper and nickel alloy brazing.

All in All

Brazing gives us a whole bunch of options when it comes to constructing high quality or high complexity thermal management products. Genie offers both copper and aluminum brazed fin heat sinks in the technology selection page.

Are you looking help designing or manufacturing a Brazed Assembly? We can help with either your brazed heat sinks, heat exchangers, or liquid cold plates. Contact Us today for assistance!

Bonded Fin Heat Sink: What is it and how does it compare to other heat sinks?

Genie has a bonded fin heat sink as one of the options available to you in the Technology Matrix. For those unfamiliar to them, a bonded fin heat sink consists of 3 main parts: a base with grooves, fins, and an adhesive to “bond” the fins to the base. Hence the name “Bonded Fin Heat Sink.”

Bonded Fin Bases:

Extruded Bases from a Multi-Ton Extrusion Press

The base can be made in a variety of ways. In the thermal management and production world, extruded bases are the preferred method. The extruded aluminum alloy has great thermal conductivity and extrusion is pretty easy to manage when it comes to production and labor.

Hog Heat Sink Bases Out of a Metal Block

Another option for making bases is to take large slabs o’ metal and machine out a bunch of grooves for the fins. This can be a little less accurate (when using the saw) or time and labor intensive (if milling). Generally, these methods are solely used for prototype or small quantity runs.

I Cast…An Aluminum Base!

Casting is also an option for large quantities. But casting requires a large upfront investment in a die and you sacrifice a great deal of thermal performance by using a die cast aluminum. These alloys have much less thermal conductivity than it’s extruded or machined cousins. While these are useful alternatives, machined bases are good for small quantities and customized bonded fin heat sink bases and extruded bases are great for production.

Fun with Fins:

For the most part, all fins are cut from coil stock. A progressive punch cuts off short pieces of a huge coil of thin metal to make the fins. Another machine straightens the fins so they fit into the grooves of the heat sink base. The coil stock can come in a variety of standard thicknesses and standard heights, so these can be mixed and matched with all sorts of bases.

Quality Bonding Time:

When you have your base and your fins, you’re ready to put them together to make your bonded fin heat sink assembly. Typically, a thermally conductive epoxy is used to bond the fins into the grooves of the base. These grooves are specially designed to balance the need for adhesion while minimizing the amount of epoxy between the fins and base. While the epoxies used for bonding are created to transfer as much heat as possible, they still aren’t as conductive at aluminum. The effectiveness of this design relies on keeping this layer as thin as possible. Once you put everything together and let the epoxy cure, you’ve got yourself a bonded fin heat sink.

The Big Picture for a Bonded Fin Heat Sink:

A bonded fin heat sink has a few advantages over other heat sink technologies. For one, the aspect ratio between the fin gap and fin height exceeds anything you can produce with extrusion. You can get a 60:1 ratio with a bonded fin assembly, where extrusions can only get up to a 20:1 ratio. Besides the aspect ratio, you have the sheer height compared to other technologies. Applications that have more vertical height available can take advantage of fins up to 6″ tall to generate more surface area for heat transfer. Where tooling costs are similar to extruded heat sinks, you pay more for the added design flexibility with labor and assembly time. Compared to other assembled fin types, bonded fins are economical.

There You Have It: A Bonded Fin Heat Sink

Try out a bonded fin heat sink in Genie or discuss how you can use one in your application with Boyd Design Engineers.

Ducted Versus Bypass Flow

Heat sink performance is impacted directly by how air flows through or around the fins of the heat sink. Ducting helps focus air flow through the fins, maximizing how much of the fluid is in direct contact with the fin surface area. This directly impacts flow resistance, which is limited by the “strength” of the fan or blower generating the flow. If we let air flow around the heat sink, that is considered bypass flow. Let’s define the differences between ducted, bypass, and free flow.

Ducted Flow

When fluid is fed through a sealed channel or duct that forces all the fluid through the fins of the heat sink, that flow is considered ducted. The top of the air duct is in contact with the fin tips.

Bypass Flow

Bypass flow is a modification of ducted flow, where the walls of the sealed channel are not right up against the edges of the heat sink. This extra space between the heat sink and the channel walls allows the flow to bypass the fins, hence the name.

Typically we refer to vertical bypass as additional clearance added between the tip of the fins and the top of the duct. Fluid flow will be able to move more freely in the space above the fins.

If we add clearance to the sides of the heat sink, that is considered horizontal clearance. If the width of the horizontal bypass is greater than the fin gap, fluid can travel more freely in the bypass than it can in between the fins.

Ducted Versus Free Flow

The flow is considered “free flow” if the heat sink doesn’t have a well defined duct or the duct is fairly far away from the edges of the heat sink. Free flow is common in natural convection applications, but there may be forced convection that may have a free flow situation. An example would be an enclosure that has a fan blowing air into the system, with grilles or perforation that allow air.

In most simulation software, there needs to be some sort of boundary in order to limit the amount of computation the program undergoes. Otherwise, you’ll be asking you’re computer to calculate more than you need it to.

Ducting in Genie

Genie has a few different options when it comes to defining flow for your thermal simulation. Genie defaults to having ducted flow for all three flow types in the Flow Definition portion of a project. One flow type, standard fixed flow, has the option of adding bypass flow around your heat sink.

Mimicking Free Flow in Genie

You can mimic free flow in Genie by increasing both the vertical and horizontal bypass. By adding all this extra space, you reduce the influence of any boundary layers generated by the duct walls and let the flow acting on the heat sink be unhindered. Just make sure you use a flow velocity instead of a flow rate. Flow rate is volumetric, and by increasing your flow area, you’re drastically cutting down on the actual velocity.

There you have it, ducted versus bypass flow. Try it out in Genie in the Flow Definition page of your project! Test out what works best for your custom heat sink design. If you need some assistance in determining the constraints of your flow, Contact Us to talk with experienced Boyd Design Engineers.

We’re a Big Fan of Forced Convection

In the thermal management industry, we are highly concerned with the convection type. Is it natural or is it forced convection? The answer to that question makes a big difference when it comes to designing a cooling solution. With natural convection, we use buoyancy to do the lifting. Forced convection solutions get outside help to move fluid through a system. Many applications need to make the switch from a natural convection solution to a forced convection one when more heat transfer is required and adding surface area isn’t an option. Adding more surface area can add more weight to a cooling solution or the extra surface area might choke flow produced from natural convection.

Forced Convection for Air: Fans and Blowers

What’s the Difference Between a Fan and a Blower?

Both a fan and a blower have a motor with engineered blades that produce a pressure differential when spun. The pressure differential is what drives the air flow through the device. The difference between the fan or blower is the direction the air is expelled from the blade.
Axial fans pull air from one end of its axis of rotation, then force the air out along the other direction along that same axis.

Things to Consider When Using a Fan or Blower

Performance

PQ curves, also known as pressure flow curves, characterize the performance of a fan or blower. The motor that drives the fan has a certain amount of speed and torque it can handle. A motor has only so much oomph to push air through the impeller blades. This relationship on how much air it can move at particular speed is depicted in the PQ curve for a fan or blower. If you try to exceed this curve, the motor will stall out and then you won’t have any flow for your application. That leads to overheating and potential product failure.

Not only do you need to consider the mechanical flow performance of your fans and blowers, you also need to check how to power your fan. Unfortunately, fans and blowers don’t magically power themselves, so we need to design a board or power supply to give the voltage and current a fan needs to push air. While the voltage a fan utilizes can be consistent, the current it draws can vary greatly from manufacturer to manufacturer. Make sure you supply your fan with the right voltage and current while you still maintain a significant safety factor on the current draw. You don’t want any burnt out boards and unhappy customers since you weren’t good to your fans.

Ingress Protection (IP) Rating of Fans and Blowers

Users are going to put your product through all sorts of torture. Unless your product will live out its days in a clean room, your device and your fan or blower will experience dust. Consumer electronics experience all sorts of dust sources, from humans and pets shedding to stray fibers from clothing and furniture. Plus those same consumers are prone to spilling their beverages, both hot and cold, on your devices. Products on manufacturing floors will not only see those particles, but they might also see grease and grime from machines. The point is that your devices, and therefore your fans and blowers, must be designed and fabricated to handle whatever your users will throw at it. Take some time to consider how abusive your users will be to your product before you start picking out a fan or blower.

Fan and Blower Reliability

How long is your product’s life span? If your product requires active cooling, it’s going to require robust fans or blowers over the entire course of the product’s life. Specifying a fan that will wear out before the expected lifetime of your product will cut the product’s usability window short and you might get some short responses from unhappy customers in return. Otherwise you may need to plan for mid-life maintenance where you need to replace the fans to extend the lifetime of your product. In some cases, that is difficult and impractical for your end users.

Fan and blower reliability and lifetime is heavily dependent on what type of bearings the fan or blower uses. Less expensive fans typically use sleeve bearings to support the fan impeller within the fan frame. Fans using ball bearings will wear more slowly over time, giving those fans a longer lifetime. Other fans have been known to use rifle bearings, fluid bearings, or even maglev bearings, all of which have the aim to increase the overall lifespan of the fan. Be careful in selecting what sort of bearing your fan or blower uses and how that affects your overall product lifespan.

Fans and Blowers in Your Application

We’re a bunch of fanboys and fangirls of forced convection, so we would love to help you upgrade your natural convection solution. Contact us or try comparing a natural convection and forced convection heat sink in Genie.

What is Buoyancy?

You’re already well aware and experienced in the effects of buoyancy. Buoyancy is what allows boats to float and hot air balloons to fly. It is the reason that the water in the ocean is separated from the air in the sky. This is due to the variation in the densities of these different fluids.

We Like to Move it, Move it

Buoyancy is pressure generated by the kinetic energy of all the fluid molecules moving around and colliding with each other and any other object within the vicinity. While this kinetic energy pushes in all directions, its largest opposing force is gravity.

The Heavy Science behind the Force of Buoyancy

Why Does Buoyancy Matter in Thermal Management?

 Natural Convection

Buoyancy is what drives natural convection, where the pressure differential between air heated by heat sources and surrounding ambient air drives the hot air upwards and away from the heat source. The air rises up with the energy it absorbed and thus removes that energy from the area around the heat sources. Cooler ambient air then moves in and replaces the heated air that moved up. This rising and replacement of hot and cool air generates a consistent flow without the need of any active mechanisms to drive it.

Benefits of Natural Convection

One of the key points of natural convection is enabling heat transfer without the extra cost and assembly time associated with adding a fan into the product. Fans or blowers can decrease the overall reliability of the device as they are driven by motors that wear down and can break over extended use of the product.

One of the key points of natural convection is enabling heat transfer without the extra cost and assembly time associated with adding a fan into the product. Fans or blowers can decrease the overall reliability of the device as they are driven by motors that wear down and can break over extended use of the product.

How to Make Buoyancy and Natural Convection Work for You

Since buoyancy enables fluids to rise against gravity, surfaces that dissipate heat should be oriented in the same direction as the gravity vector. Typically this surface is your heat sink. The longest dimension of the heat sink surfaces should be vertical, so as the cool air contacts the bottom of the heat sink it travels upwards and continues to be heated up and increases the pressure differential.

Natural Convection and the Chimney Effect

By optimizing the amount of air that can be pulled into the fin gaps and the length of the heat sink, you can easily use natural convection to cool devices connected to your heat sink surface. You’ll typically see good natural convection heat sinks have a fin gap of around 0.25″ or 6.35mm. This allows enough space between the fins to accommodate boundary layers that form on each of the fin surfaces and still allow upward flow of heated air.

Natural Convection in Genie

Otherwise, you should at least point the fin tips upwards. Other orientations of your heat sink, such as your fin tips and flow length pointing sideways or even downwards, inhibit the natural convection flow that’s generated by buoyancy. Heated air between these fins tends to stagnate since it has a difficulty rising up and away since the fins or base of the heat sink are in the way.

To recap, the best practices for natural convection heat sinks are to point the flow length of the fins vertically and give your fins enough space to effectively pull in air. Try out your own natural convection heat sink in Genie!

Happy Designing