Tag Archives: liquid cooling

Tubed and Submerged-Fin Cold Plates in Electronics Thermal Management

Posted on February 26, 2019 by | 1 comment

By Norman Quesnel
Senior Member of Marketing Staff
Advanced Thermal Solutions, Inc. (ATS)

Many of today’s electronic devices need the performance of liquid cooling to meet the thermal demands of certain hot components. Liquid cold plates are common cooling systems in high power lasers, fuel cells, battery coolers, motor drives, medical equipment, avionics and other high-power, high-heat flux applications.

Cold Plates
Figure 1. A Custom liquid cold plate design by D6 Industries. [1]

Cold plates provide localized cooling by transferring heat from a device to a liquid that flows to a remote heat exchanger and dissipates into either the ambient or to another liquid in a secondary cooling system. Component heat flows by conduction through a thermal interface material and the metal plate to the metal tubing. Then it flows by convection from the internal surface of the fluid path material into the flowing coolant.

A cold plate in electronics cooling is often an aluminum block with an embedded, coolant-filled metal tube. Another common cold plate type is made with metal shells that are brazed or friction-welded together and filled with a liquid coolant.  On the inside, the metal shells have integral cooling fins that are submerged in the coolant.

Tubed Cold Plates

Embedded tube designs are the simplest version of cold plate cooling devices. They feature a continuous tube set into grooves in a metal plate, and are often bonded in place with thermal epoxy. The flowing coolant moves heat from the component away from the cold plate to a heat exchanger, where it is cooled before being pumped back into the plate. 

A common example of a tubed cold plate features an aluminum plate with an exposed copper tube. The tubes can be routed in different pathways to optimize the thermal performance.

The tubing can be continuous or constructed from straight tubes connected by soldered joints, though joints may increase the potential for leakage.

Figure 2. A Tubed cold plate consists of copper or stainless-steel tubing pressed into a metal plate. [2]

This design can provide a cost-effective thermal solution for component cooling where the heat load is low-to-moderate. Tubed cold plates ensure minimum thermal resistance between the power device and the cold plate by placing the coolant tube in direct contact with the power device’s base. Direct contact reduces the number of thermal interfaces between device and fluid, thus increasing performance for the application.

A variant of this design features a thermal epoxy completely applied over the pressed in tubing and flush with the metal plate surface. These are sometimes called buried tube liquid cold plates. This provides a gap-free thermal interface between the tube and the plate. The epoxy layer protects from any leakage from the metal tube. Another key feature is that that fully buried tube is not exposed to the outside environment.

Figure 3. A buried tube cold plate’s metal tube is covered with a conductive epoxy layer. [3]

The choice of liquid coolant affects thermal performance as well. Choosing the right coolant depends to a great extent on the tube material. Copper tubes are compatible with water and most other common coolants, while stainless steel tubes can be used with deionized water or corrosive fluids.

One cold plate OEM offers a proprietary technology with a tube locking system and pressing techniques that ensure the tube is flush with the plate surface, providing good thermal contact with the component being cooled. This manufacturing method eliminates the need for thermal epoxy between the tube and plate which improves thermal performance. [4]

Submerged Fin Cold Plates

Another type of cold plate is an all-metal construction with brazed or friction welded internal fin field.

Figure 4. Standard, liquid coolant-containing metal cold plate [5]

The integral, internal fins increase the surface area that contacts the fluid and enhances heat transfer. Fin shape and fin density affect the performance of heat exchangers and cold plates. By their geometry, the fins also create turbulence, which minimizes the fluid boundary layer and further reduces thermal resistance.

One high-performance version features tightly packed aluminum pin fins that create turbulence with low flow rate values, resulting in high thermal performance with low pressure drop. In this design, the high density of the internal fins increases the heat transfer area without adding bulk to the cold plate assembly. [6]

Figure 5. Close-spaced pin fins with complex geometry create turbulence with low flow rate values inside submerged fin cold plates. [6]

In most high-performance applications, fins are made of copper or aluminum. Aluminum fins are preferred in aircraft electronic liquid cooling applications due to their lighter weight. Copper fins are mostly used in applications where weight is not an important factor, but compatibility with other cooling loop materials is.

For submerged-fin cold plates, many different fin geometries can be tested to find the best improvement in performance. Some of the most commonly used are louvered, lanced offset, straight, and wavy fins.

Figure 6. Fin designs for submerged-fin cold plates. Clockwise from top: louvered, lanced offset, wavy, and straight fins. [7]

With cooling requirements increasing in many areas of electronics, engineers are turning to liquid cooling to replace air cooling. Lower cost, safer liquid cooling systems have also spurred the trend to liquid cooling.

The prime example is the cold plate – relatively simple in design, affordable, available in alternative versions, and extremely customizable. Cold plates should be considered wherever thermal performance above air cooling is needed.

References:

  1. https://d6industries.com/portfolio/custom-designs-liquid-cold-plate-hydroblock/
  2. https://www.lytron.com/Cold-Plates
  3. http://www.wakefield-vette.com/products/liquid-cooling/liquid-cold-plates/standard-liquid-cold-plates.aspx
  4. https://www.lytron.com/Tools-and-Technical-Reference/Application-Notes/Assessing-the-Quality-of-a-Tubed-Cold-Plate
  5. https://www.qats.com/Products/Liquid-Cooling/Cold-Plates
  6. http://www.cooltech.it/products/liquid-cold-plates/
  7. https://www.lytron.com/Tools-and-Technical-Reference/Application-Notes/Fins-for-Cooling-Success

For more information about Advanced Thermal Solutions, Inc. (ATS) thermal management consulting and design services, visit https://www.qats.com/consulting or contact ATS at 781.769.2800 or [email protected]. To register for Qpedia and to get access to its archives, visit https://www.qats.com/Qpedia-Thermal-eMagazine.


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Recent Research Into Next-Generation Heat Exchangers for Electronics Thermal Management

Posted on January 24, 2019 by | 1 comment

Since it was published around one year ago, the “What is a Heat Exchanger” video (watch it below) has been one of the most watched on the ATS YouTube page. With the obvious interest in heat exchangers in particular (and liquid cooling in general), we are curating recent research into the technology and its applications in the thermal management of electronics.

Heat Exchangers
Heat Exchangers are a common component in liquid cooling solutions for electronics. Below is recent research into this growing technology. (Advanced Thermal Solutions, Inc.)

The following are three examples of papers written about heat exchangers including applications in the automotive space to developing microchannels to enhance thermal performance to optimizing heat exchangers for use with high-powered electronics.

We have posted several pieces of content on this blog about heat exchangers in the past. Examples include:

Since heat exchangers remain a popular topic for engineers, we will continue to add new pieces about the technology in the coming months.

Novel Power Electronics Three-Dimensional Heat Exchanger

Read the full paper at https://www.nrel.gov/docs/fy14osti/61041.pdf.

Abstract: Electric-drive systems, which include electric machines and power electronics, are a key enabling technology to meet increasing automotive fuel economy standards, improve energy security, address environmental concerns, and support economic development. Enabling cost-effective electric-drive systems requires reductions in inverter power semiconductor area, which increases challenges associated with heat removal. In this paper, we demonstrate an integrated approach to the design of thermal management systems for power semiconductors that matches the passive thermal resistance of the packaging with the active convective cooling performance of the heat exchanger. The heat exchanger concept builds on existing semiconductor thermal management improvements described in literature and patents, which include improved bonded interface materials, direct cooling of the semiconductor packages, and double-sided cooling. The key difference in the described concept is the achievement of high heat transfer performance with less aggressive cooling techniques by optimizing the passive and active heat transfer paths. An extruded aluminum design was selected because of its lower tooling cost, higher performance, and scalability in comparison to cast aluminum. Results demonstrated a 102% heat flux improvement and a package heat density improvement over 30%, which achieved the thermal performance targets.

Microchannel Heat Exchanger for Electronics Cooling Applications

Read the full paper at http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=1636343.

Abstract: The power consumption of electronic devices, such as semiconductor diode laser bars, has continually increased in recent years while the heat transfer area for rejecting the associated thermal energy has decreased. As a result, the generated heat fluxes have become more intense making the thermal management of these systems more complicated. Air cooling methods are not adequate for many applications, while liquid cooled heat rejection methods can be sufficient. Significantly higher convection heat transfer coefficients and heat capacities associated with liquids, compared to gases, are largely accountable for higher heat rejection capabilities through the micro-scale systems. Forced convection in micro-scale systems, where heat transfer surface area to fluid volume ratio is much higher than similar macro-scale systems, is also a major contributor to the enhanced cooling capabilities of microchannels. There is a balance, however, in that more power is required by microchannels due to the large amount of pressure drop that are developed through such small channels. The objective of this study is to improve and enhance heat transfer through a microchannel heat exchanger using the computational fluid dynamics (CFD) method. A commercial software package was used to simulate fluid flow and heat transfer through the existing microchannels, as well as to improve its designs. Three alternate microchannel designs were explored, all with hydraulic diameters on the order of 300 microns. The resulting temperature profiles were analyzed for the three designs, and both the heat transfer and pressure drop performances were compared. The optimal microchannel cooler was found to have a thermal resistance of about 0.07 °C-cm2 /W and a pressure drop of less than half of a bar.

Thermal Analysis of the Heat Exchanger for Power Electronic Device with Higher Power Density

Read the full paper at http://pe.org.pl/articles/2012/12a/70.pdf. Abstract: Liquid cooling system has been used in high power electronic device systems to cool down the temperature of power electronic device. Heat exchanger is an important part of liquid cooling system to transfer the heat generated by power electronic device into air. In this paper, a Streamline-upwind/Petrov-Galerkin (SUPG) stabilized finite element analysis method was proposed to solve the water and air governing formulas including the mass conservation equation, the momentum conservation and the energy conservation equation. Furthermore, the thermal characteristic of a heat exchanger is simulated, and the result was compared with an experiment. The comparison shows that this method is effective.

For more information about Advanced Thermal Solutions, Inc. (ATS) thermal management consulting and design services, visit https://www.qats.com/consulting or contact ATS at 781.769.2800 or [email protected].

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Technology Review: Liquid Cooling Solutions

Posted on September 14, 2018 by | Leave a comment

(This article was featured in an issue of Qpedia Thermal e-Magazine, an online publication dedicated to the thermal management of electronics. To get the current issue or to look through the archives, visit http://www.qats.com/Qpedia-Thermal-eMagazine.)

Qpedia continues its review of technologies developed for electronics cooling applications. We are presenting selected patents that were awarded to developers around the world to address cooling challenges. After reading the series, you will be more aware of both the historic developments and the latest breakthroughs in both product design and applications.

Liquid Cooling Solutions

The focus of this article is to highlight recent patents for liquid cooling devices. (Advanced Thermal Solutions, Inc.)

We are specifically focusing on patented technologies to show the breadth of development in thermal management product sectors. Please note that there are many patents within these areas. Limited by article space, we are presenting a small number to offer a representation of the entire field. You are encouraged to do your own patent investigation.

Further, if you have been awarded a patent and would like to have it included in these reviews, please send us your patent number or patent application.

In this issue our spotlight is on liquid-based cooling solutions.

There are many U.S. patents in this area of technology, and those presented here are among the more recent. These patents show some of the salient features that are the focus of different inventors.

Liquid Cooling Devices

Embedded Microchannel Cooling Package for a Central Processing Unit

US 7515415 B2, Monfarad, A. and Yang, J.

An indirect cooling liquid embedded package design for use with a computer central processor unit is suitable for thermal management of high heat dissipation electronic components such as server processors. The indirect contact cooling liquid embedded packaged CPU has mechanical coupling and embedded plumbing that attaches to the board pumped liquid supply and indirect cooling of the heat-generating portion of the CPU with an embedded microchannel heat exchanger. The coolant package system for the CPU removes higher levels of heat indirectly from the core of the processors by convective cooling.

Cooling liquid flows into the microchannel piping in the CPU substrate. Cooling liquid continues to flow out of the microchannel piping into a silicon or metallic microchannel heat exchanger that is directly bonded to a silicon die for cooling of the heat-generating portion of the CPU. As a result, an embedded microchannel indirect contact cooling liquid package for a CPU can be utilized to remove substantially higher levels of heat from the core of the processors by forced convective liquid flow through the microchannel heat exchanger attached to the core of the CPU. Cooling liquid is introduced into the package of the server CPU by mechanically attaching the CPU to the board through a socket interconnect. Pins of the socket serve to provide electrical connection between the board and the CPU, while a few pins are designed for the purpose of providing an inlet and an outlet for cooling liquid into and out of the CPU package.

The cooling system of the present invention also uses the existing package-to-board practice of using sockets and therefore the entire cooling system is embedded into the processor-to-board assembly. From the end user’s point of view, there is a tremendous amount of simplification of board design as the bulky fan and heat sink assemblies are removed. The replacement, according to the present invention, is a central liquid cooling system that can be made redundant to substantially prevent any reliability issues in the field.

Planar Heat Pipe for Cooling

US 8305762 B2, Wits, W., Mannak, J. and Legtenberg, R.

The invention claimed is a circuit board for cooling of heat-dissipating components assembled thereon, including at least two panels at least one of which is populated With heat-dissipating components, both panels being metal clad on a side, at least one of the panels being formed from a printed circuit board laminate and comprising a plurality of grooves on its metal clad side, the panels being bonded together by an adhesive layer With their metal clad sides oriented face to face so as to form a circuit board containing a sealed cavity having a height defined by a thickness of the adhesive layer and the separation of the metal clad sides, the cavity being partly filled with a fluid, the fluid circulating by capillary action along the grooves towards zones exposed to heat where the fluid vaporizes.

Vapor may circulate back by pressure gradient effect through the cavity towards zones not exposed to heat where it condenses. In a mode of implementation, the heat pipe may be embedded in a circuit board formed by the panels for inherent cooling of heat-dissipating components.

Thus, key advantage provided by the present invention in any of its aspects is that it is based on most standard processes of multilayer PCB fabrication such as laminating, selective metal plating and etching. Therefore, it is a highly cost-effective solution. Furthermore, the invention provides a very flexible design solution enabling to adapt the cooling paths to the PCB layout, especially to the higher heat dissipation locations. Not requiring any supplementary materials, it is even considerably lighter than a tubular heat pipe-based solution.

Implemented as enhancement of a computer aided engineering tool, heat pipe cooling cavities could be designed concurrently with the layout of components placement and printing of circuits, ensuring optimized thermal management. This enables multilayer PCB assemblies, which are high density electronic devices, to benefit the most from the integrated heat pipe cooling function.

Cooling System for Electronic Equipment

US 7508666 B1, Henneberg, M. and Johnson, L.

A cooling solution includes a system providing thermal energy dissipation for electronic equipment located in support racks or cabinets of a facility. According to one embodiment, the system is integrated with a facility where the support cabinets are located. The system providing thermal energy dissipation includes a cooling loop, a fan unit for moving air across the cooling loop and one or more ducts forming a confined flow pathway for the moving air between the fan unit and cabinets for delivery to the electronic equipment.

More specifically, the cooling loop contains a supply of circulating heat absorbing fluid such that the heat absorbing fluid removes thermal energy from the air moved by the fan unit. Each cabinet is formed with an exhaust pathway such that the moving air enters the cabinet from the duct, flows across the electronic equipment to remove thermal energy therefrom, and exits the cabinet.

Claims include a cooling system for a facility housing electronic equipment, the facility having a support surface on which a cabinet holding the electronic equipment is located, the system comprising: a cooling loop located beneath the support surface and containing a supply of circulating heat absorbing fluid; a fan unit located beneath the support surface and configured to move air across the cooling loop such that the heat adsorbing fluid removes thermal energy from the moving air; at least one duct forming a confined flow pathway for the moving air between the fan unit and the cabinet, wherein the cabinet is formed with a substantially lateral exhaust pathway such that the moving air enters via a back region of the cabinet, flows across the electronic equipment, housed by the cabinets, to remove thermal energy therefrom, and exits a front region of the cabinet; and a chilling plate positioned downstream of the flow of moving air exiting the cabinet such that the chilling plate is located outside of the front region of the cabinet, the chilling plate is coupled to a secondary cooling loop containing a supply of heat absorbing fluid.

Claims also include a method for providing thermal energy dissipation for network-based electronic equipment housed within a plurality of cabinets located on a support surface of a facility, each of the plurality of cabinets having an interior formed with a through passageway extending from an entrance at a first side of each of the plurality of cabinets to an exit at a second side of each of the plurality of cabinets, the method comprising: providing a cooling loop containing a supply of circulating heat adsorbing fluid; providing a fan unit configured to move air across the cooling loop such that the heat adsorbing fluid removes thermal energy from the moving air; directing the moving air from the fan unit to the through passageway of each of the plurality of cabinets such that the moving air flows across the electronic equipment to remove thermal energy therefrom, and exits the plurality of cabinets; and providing a plurality of chilling plates positioned downstream of the flow of moving air exiting the plurality of cabinets such that one of the plurality of chilling plates is located outside of each of the plurality of cabinets, respectively, each of the plurality of chilling plates is coupled to a secondary cooling loop containing a supply of heat absorbing fluid.

For more information about Advanced Thermal Solutions, Inc. (ATS) thermal management consulting and design services, visit https://www.qats.com/consulting or contact ATS at 781.769.2800 or [email protected].

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ATS Releases New Liquid Cooling eBook

Posted on June 8, 2018 by | Leave a comment

Advanced Thermal Solutions, Inc. (ATS) has created an new Engineering eBook on Liquid Cooling and its applications in the thermal management of electronics. Click here to download this free, 16-page eBook loaded with technical content.

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ATS Unveils Heat Exchanger Selection Tool

Posted on March 7, 2018 by | 1 comment

In 2017, Advanced Thermal Solutions, Inc. (ATS) added to its liquid cooling products with a new line of tube-to-fin, liquid-to-air heat exchangers with the industry’s highest density fins, which maximize heat transfer and provide greater cooling than other heat exchangers on the market.

Heat Exchanger Selection Tool

ATS released a line of tube-to-fin, liquid-to-air heat exchangers with the industry’s highest density fins to optimize heat transfer. (Advanced Thermal Solutions, Inc.)

ATS heat exchangers are available in seven different sizes and can be ordered with or without fans depending on your specific design requirements. Altogether, ATS offers 49 different heat exchanger options (not including the customized options to meet customer needs).

To make the selection process easier for engineers, ATS has recently unveiled a new Heat Exchanger Selection Tool that will point engineers to the exact option that will meet the inputted criteria.

Heat Exchanger Selection Tool

The tool asks five questions (measurement type in parentheses):

  • Air temperature from inlet to heat exchanger (Tai°C)
  • Heat need to be extracted by heat exchanger (QtotalW)
  • Water exit temperature from heat exchanger (Tfo°C)
  • Water flow rate (GPM)
  • Fan voltage (V)

Plug answers in to these questions and hit the “Optimum Heat Exchanger” button to see which of the ATS heat exchangers fits your specific liquid cooling system needs. Once you have the right part number, you can now purchase the right heat exchanger from Digi-Key Electronics.

In addition to heat exchangers, ATS has an array of liquid cooling products, including cold plates that provide 30 percent better thermal performance than comparable products on the market.

To learn more about the full line of liquid cooling options from ATS, visit https://www.qats.com/Products/Liquid-Cooling.

For more information about Advanced Thermal Solutions, Inc. (ATS) thermal management consulting and design services, visit https://www.qats.com/consulting or contact ATS at 781.769.2800 or [email protected].

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