Tag Archives: Norman Quesnel

Industry Developments in Thermal Management of Electric Vehicle Batteries

Posted on October 12, 2018 by | 11 comments

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

Electric vehicles (EV) fall into two main categories: vehicles where an electric motor replaces a combustion engine and vehicles that feature a combustion engine assisted by an electric motor. All EV contain large, complex, rechargeable batteries, sometimes called traction batteries, to provide all or a portion of the vehicle’s propelling power.

Electric Vehicle Batteries

(Wikimedia Commons)

In EV batteries, current flow, both charge and discharge, generates heat inside the cells and in their interconnection systems. This heat is proportional to the square of the flowing current multiplied by the internal resistance of the cells and the interconnect systems. The higher the current flow the more the heating will be produced. [1]

Battery manufacturers and researchers routinely investigate how the rate of heat generation in cells varies over the course of charging and discharging. Heat can be generated from multiple sources including internal losses of joule heating and local electrode overpotentials, the entropy of the cell reaction, heat of mixing, and side reactions. [2]

Figure 1. Structure of a basic lithium-ion battery. [3]

Proper thermal management of EV batteries (lithium-ion is the most common) is essential to maintain adequate and consistent performance of the battery and the vehicle. Excessive temperature will negatively affect an EV’s battery and its performance. Features that can be impacted include its electrochemical system, charge acceptance, power output, safety and life cycle/replacement cost and the vehicle’s driving distance.

From a thermal point of view, there are three main aspects to consider when using lithium-ion batteries in an EV:

  1. At temperatures below 0°C (32°F), batteries lose charge due to slower chemical reactions taking place in the battery cells. The result is a significant loss in power, acceleration and driving range, and higher potential for battery damage during charging.
  2. At temperatures above 30°C (86°F) the battery performance degrades, posing a real issue if a vehicle’s air conditioner is needed for passengers. The result is an impact on power density and reduced acceleration response.
  3. Temperatures above 40°C (104°F) can lead to serious and irreversible damage in the battery. At even higher temperatures, e.g. 70-100°C, thermal runaway can occur. This is triggered when the runaway temperature is reached. The result is a self-heating chain reaction in a battery cell that causes its destruction while propagating to adjacent cells.

The ideal temperature range for an EV’s lithium-ion battery is akin to that preferred by human beings. To keep it in this range, the battery temperature must be monitored and adjusted. A battery thermal management system (BTMS) is necessary to prevent temperature extremes, ensure proper battery performance, and achieve the expected life cycle. An effective BTMS keeps cell temperatures within their allowed operating range. [1]

As defined by engineers at the U.S. Department of Energy’s NREL (National Renewable Energy Laboratory), EV battery pack thermal management is needed for three basic reasons: [5]

  1. To ensure the pack operates in the desired temperature range for optimum performance and working life. A typical temperature range is 15-35°C.
  2. To reduce uneven temperature distribution in the cells. Temperature differences should be less than 3-4C°.
  3. To eliminate potential hazards related to uncontrolled temperature, e.g. thermal runaway.

Figure 2. Chevy Bolt EV battery pack is liquid cooled via a base plate below the cells. [6,7]

Various cooling agents and methods are in use today as part of the thermal management of EV batteries. Among these are air cooling, the use of flowing liquid coolants, or direct immersion.

Air Cooling

The lowest cost method for EV battery cooling is with air. A passive air-cooling system uses outside air and the movement of the vehicle to cool the battery. Active air-cooling systems enhance this natural air with fans and blowers. Air cooling eliminates the need for cooling loops and any concerns about liquids leaking into the electronics. The added weight from using liquids, pumps and tubing is also avoided.

Figure 3. The Nissan Leaf’s battery pack is cooled by air. [8]

The trade-off is that air cooling, even with high-powered blowers, does not transport the same level of heat as a liquid system can. This has led to problems for EV in hot climates, including more temperature variation in battery pack cells. Blower noise can also be an issue.

Figure 4. Air cooler battery thermal management system used in Toyota’s Prius. [9]

Still, air-cooling solutions have their roles and value. An example is the custom-built Volkswagen EV race car that finished first in the Pikes Peak International Hill Climb in Colorado Springs, Colo. To optimize performance, the car was designed to combine minimum weight, as much downforce as possible, and maximum power. Volkswagen used air-cooling systems to reduce weight. It used thermal software in virtual driving tests along the entire race to ensure the air-cooling system would perform sufficiently. [10]

Figure 5. Volkswagen’s EV won a grueling race while powered by air-cooled batteries. [10]

Liquid Cooling

Piped liquid cooling systems provide better battery thermal management because they are better at conducting heat away from batteries than air-cooling systems. One downside is the limited supply of liquid in the system compared with the essentially limitless amount of air that can flow through a battery.

Tesla’s thermal management system (as well as GM’s) uses liquid glycol as a coolant. Both the GM and Tesla systems transfer heat via a refrigeration cycle. Glycol coolant is distributed throughout the battery pack to cool the cells. Considering that Tesla has 7,000 cells to cool, this is a challenge. [11]

Figure 6. Tesla uses a metallic cooling tube that snakes through the EV battery pack. [11]

The Tesla Model S battery cooling system consists of a patented serpentine cooling pipe that winds through the battery pack and carries a flow of water-glycol coolant; thermal contact with the cells is through their sides by thermal transfer material.

Figure 7. GM’s Chevrolet Volt uses cold plates interwoven with battery cells as liquid cooling system. [12]

General Motor’s Chevrolet Volt features a liquid cooling system to manage battery heat. Each rectangular battery cell is about the size of a children’s book. Sandwiched between the cells is an aluminum cooling plate. There are five individual coolant paths passing thru the plate in parallel, not in series as the Tesla system does. Each battery pouch (cell) is housed in a plastic frame. The frames with coolant plates are then stacked longitudinally to make the entire pack. [12]

Thermodynamic engineers at Porsche develop and optimize each vehicle’s entire cooling system. This includes the battery, of course, and one example is the liquid-filled cooling plate from the traction battery in the Boxster E. [13]

Figure 8. Thermal model of a battery cooling plate in the Porsche Boxster. [13]

Based on the results of the analysis in the thermal model described above, the cooling plate was designed geometrically and optimized using computational fluid dynamics (CFD). The result is a highly efficient and lightweight heat exchanger, optimally tailored and adapted to the battery pack, with low pressure losses, high cooling performance and a very even distribution of temperature.

Liquid Immersion

Instead of snaking coolant through lines and chambers within a battery pack’s case, XING Mobility takes a different approach by immersing its cells in a non-conductive fluid with a high boiling point. The coolant is 3M Novec 7200 Engineered Fluid, a non-conductive fluid designed for heat transfer applications, fire suppression and supercomputer cooling.

Figure 9. The XING Battery has 4,200 individual lithium-ion cells encased in liquid-cooled module packs. [14]

XING’s batteries take the form of 42 lithium-ion-cell modules that can be put together to build larger battery solutions. The complete XING battery houses 4,200 individual 18,650 lithium-ion cells encased in liquid-cooled module packs. [14]

Simulation Technologies

Design of thermal management solutions requires extensive knowledge of cooling systems and the amount of heat generated by cells throughout the battery pack. Engineers must also weigh various tradeoffs and factors such as cost, packaging, manufacturability, efficiency, reliability of heat dissipation components, and battery pack as an integrated, modular system.

Figure 10. Simulation tools speed the development of EV batteries and their thermal management systems. [2]

Batteries require a unique range of issues be taken into consideration. First, detailed models and sub-models are needed to simulate the chemical and physical phenomena inside battery cells. Then, these models need to be tied into a system-level model of a battery pack, which can comprise hundreds of cells and cooling circuits. Finally, the battery pack model needs to be integrated with the system model of the entire powertrain and vehicle.

Engineers must consider the physical placement of the battery pack within the EV, not only to minimize the effects of ambient temperatures and maximize heat dissipation but also to avoid excessive mechanical stresses, structural fatigue from road vibrations, and potential impact from road debris. The team also must consider crash scenarios in which passengers must be protected from toxic acids released from the battery pack.

References:
1. https://avidtp.com/what-is-the-best-cooling-system-for-electric-vehicle-battery-packs/
2. Hu, X., Battery Thermal Management in Electric Vehicles. Ansys, Inc., 2011.
3. https://www.mpoweruk.com/chemistries.htm
4. Wang, Q., Jiang, B., Xue, Q., Sun, H., Li, B., Zou, H. and Yan, Y., Experimental Investigation on EV Battery Cooling and Heating by Heat Pipes, Applied Thermal Engineering, 2015.
5. Rugh, J., Pesaran, A. and Smith, K., Electric Vehicle Battery Thermal Issues and Thermal Management Techniques, NREL, SAE Alternative Refrigerant and System Efficiency Symposium, 2011.
6. https://www.hybridcars.com/chevy-bolt-evs-battery-is-as-big-as-a-teslas/
7. https://cleantechnica.com/2018/07/08/tesla-model-3-chevy-bolt-battery-packs-examined/
8. https://www.greencarreports.com/news/1064332_nissan-leafs-battery-pack-should-last-as-long-as-the-car
9. http://synergyfiles.com/2016/07/battery-thermal-management-system-review/
10. https://www.theverge.com/2018/6/24/17078544/volkswagen-ev-race-car-pikes-peak-hill-climb-record https://media.vw.com/en-us/releases/1008
11. https://insideevs.com/tesla-or-gm-who-has-the-best-battery-thermal-management-bower/
12. https://www.youtube.com/watch?time_continue=113&v=h4nM7rXpsJg
13. Thermal Management in Vehicles with Electric Drive System, Porsche Engineering Magazine, January 2011.
14. https://www.greencarreports.com/news/1114188_new-approach-to-electric-car-battery-cooling-immerse-cells-in-coolant

Advanced Thermal Solutions, Inc. (ATS) is hosting a series of monthly, online webinars covering different aspects of the thermal management of electronics. This month’s webinar will be held on Thursday, Oct. 25 from 2-3 p.m. ET and will cover the cooling of automotive batteries. Learn more and register at https://qats.com/Training/Webinars.

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

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Posted in Automotive, Battery Cooling

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Industry Developments: Advances in Thermal Interface Materials for Electronics Cooling

Posted on January 24, 2018 by | 2 comments

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

For decades, thermal interface materials (TIMs) have been used as pathways allowing heat to flow from one location to another. TIMs are often part of cooling systems that remove heat from component dies by dissipating it into heat spreaders, such as heat sinks, and ultimately out of the dies’ surrounding enclosures.

As a product line, TIMs have continuously evolved, driven by market needs for higher thermal conductivity, lower thermal impedance, new applications and lower costs.

Thermal Interface Materials

Figure 1. Thermal Interface Materials are Used Both Inside and Outside Chip Packages. (Indium) [1]

From a broad view, most TIMs fall into three material categories. Some are made from elastomers or other polymers with a thermally-conductive filler added. Other TIMs are solder-based. Like elastomers, these solder-based TIMs are soft and conformable to mating surfaces, filling air gaps that compromise thermal transfer. Finally, newer carbon-based TIMs have emerged that demonstrate superior performance, though many of these are not yet commercialized.

Here is a brief look at recent developments within the major TIM categories:

A New TIM Filler

A new generation of polymer-based TIMs uses boron nitride nanosheet (BNNS) fillers to enhance thermal conductivity. BNNS is a two-dimensional crystalline form of hexagonal boron nitride (h-BN), also known as white graphene. BNNS ranges in thickness from just one to a few atomic layers. It has a similar geometry to its all-carbon analog graphene, but some very different properties. For example, graphene is highly electrically conductive while BN nanosheets are electrical insulators.

Figure 2. Edges of boron nitride nanosheets are atoms of all boron, all nitrogen, or alternating elements. (Wikimedia Commons)

Hexagonal boron nitride (h-BN) has other desirable properties, including a large surface area, high-thermal transport, and chemical inertness. The thermal conductivity of bulk h-BN can reach 400 W/mK at room temperature. [3]

A recent study from Rice University, which continues to expand on its original simulations of graphene’s effect on nanoscale heat transfer, demonstrated that an h-BN thin film composed layer-by-layer of laminated h-BN nanosheets can enhance lateral heat dissipation on a substrate, in this case glass. Thermal performance improved with the BN coating due to its anisotropic thermal conductivity. It had a high in-plane thermal conductivity of 140 W/mK for spreading and a low cross-plane thermal conductivity of 4 W/mK to avoid a hot spot beneath the tested device. [4]

Researchers have also created simulations showing that 3-D structures of h-BN planes connected by boron nitride nanotubes could transfer heat (move phonons) in all directions, whether in-plane or across planes. The number and length of the nanotubes connecting the h-BN layers have an effect on heat flow: more and/or shorter pillars slow conduction, while longer pillars speed heat transfer along.

Figure 3. 3-D structure of highly thermally conductive h-BN sheets connected by BN nanotubes. (Shahsavari Group/Rice University)

Solder-Based TIMs

With ever-increasing power and heat dissipation needs across the electronics industry, solder-based TIMs may be better suited to take the heat away from dies than thermal grease where electrical insulation isn’t required.

Issues with thermal grease include:

  • Grease has a low bulk thermal conductivity of 3-12 W/mK. Some solder-TIMs provide a high bulk thermal conductivity of 87 W/mK.
  • Over time, thermal grease tends to pump-out and migrate away from the center of the power die. It gets hotter and can fail prematurely. There is no pump-out with a solder-TIM.
  • Over time, grease tends to bake-out and dry (becomes powdery), thereby increasing thermal resistance and reducing heat-dissipation effectiveness. With solder-TIMs, there is no bake-out. [5]

Figure 4. SMA-TIMs conform to surface disparities over time to increasingly reduce thermal resistance. (Indium Corp.) [6]

Recent solder-based TIMs developed by Indium Corporation include a new SMA-TIM (soft metal alloy). This is made from an indium solder base and offers uniform thermal resistance at lower applied stresses in compressed interfaces. It is provided as a compressible metal foil that can be used as a TIM between a heat source and a heat sink, heat spreader, or heat pipe.

The malleability of the indium minimizes surface resistance and increases heat flow (conductance). Over time, the malleability of the solder helps fill the interface gaps even better. Thus, thermal interface resistance decreases over time as opposed to thermal grease where the thermal interface resistance increases over time. [7]

Another newer indium-containing material has been developed for use in the TIM 1 position, between the die top and its case. The material is part of a system, developed by Indium Corporation, called mdTIM. It provides a thermal conductivity of 87 W/mK.

While pure indium metal has a superb thermal transfer rate, air or gas pockets (voids) can degrade the performance of the material. These voids are created by entrapped air or gasses produced by flux component evaporation that fail to escape during reflow.

Indium’s mdTIM uses a patented system of materials and reflow technology does not use flux so there are no outgassing issues.

Carbon-Based TIMs

The very high thermal conductivity of pure carbon has long made it attractive for use in TIMs. Today’s carbon-based TIM fillers include diamond, carbon nanotubes (CNT), graphite and graphene. Often these fillers are dispersed in a spreadable (grease-like) polymer matrix.

In some cases, different forms of carbon fillers are being combined. For example, highly thermally conductive CNT have been mixed with less expensive carbon substrates like graphite and graphene to reduce costs but still deliver very high thermal conductivity.

Recent research has been made with graphite nanoplatelets (GNP) in thin thermal interface layers. These studies concerned the through-plane and in-plane alignment of GNP in a spreadable matrix. When dispersed, the GNP fillers take a naturally in-plane alignment, meaning the great majority of heat flow is in parallel to an interface. However, at the same time, the desired through-plane heat transfer from one surface to the other is much less. [8]

Figure 5. The top SEM images are graphite nanoplatelets with in-plane alignment. Bottom images show hybrid mix of GNP with a 45% volume of Al2O3 spheres. [8]

A solution was found by adding spherical microparticles. Spherical Al2O3 and Al filler particles were tested. The hybrid filler formulations resulted in enhanced through-plane thermal conductivity by disrupting the natural in-plane alignment of the GNP. This led to the disruption of the GNP in-plane alignment and the improvement of the through-plane thermal conductivity of the tested thermal greases.

Costs and other factors pose development challenges to TIMs with carbon-based heat transfer schemes. But given the high thermal conductivity and various configurations available from carbon-based materials, these will likely be at the heart of many upcoming performance advancements in TIMs.

References
1. Indium Corporation, http://www.indium.com/thermal-management/tim/
2. http://news.rice.edu/2015/07/15/white-graphene-structures-can-take-the-heat/
3. http://pubs.acs.org/doi/10.1021/acsami.5b03967
4. Nanoscale, http://pubs.rsc.org/en/content/articlelanding/2017/nr/c7nr07058f#!divAbstract
5. IEEE Xplore, http://ieeexplore.ieee.org/document/6142407/%5D
6. Engineering 360, http://www.globalspec.com/FeaturedProducts/Detail/Indium/Thermal_Interface_MaterialHeatSpring/256323/1
7. Indium Corporation, http://www.indium.com/thermal-interface-materials/heat-spring/
8. Nature, https://www.nature.com/articles/srep13108.pdf

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.

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What Fluids Can Be Used With Liquid Cold Plates in Electronics Cooling Systems

Posted on November 13, 2017 by | 15 comments

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

Liquid cooling systems transfer heat up to four times better than an equal mass of air. This allows higher performance cooling to be provided with a smaller system. A liquid cooled cold plate can replace space-consuming heat sinks and fans and, while a liquid cold plate requires a pump, heat exchanger, tubing and plates, there are more placement choices for cold plates because they can be outside the airflow. [1]

One-time concerns over costs and leaking cold plates have greatly subsided with improved manufacturing capabilities. Today’s question isn’t “Should we use liquid cooling?” The question is “What kind of liquid should we use to help optimize performance?”

Liquid Cold Plates

Figure 1. A Liquid Cooling System for a Desktop PC with Two Cold Plates. [2]

For liquid cold plates, the choice of working fluid is as important as choosing the hardware pieces. The wrong liquid can lead to poor heat transfer, clogging, and even system failure. A proper heat transfer fluid should provide compatibility with system’s metals, high thermal conductivity and specific heat, low viscosity, low freezing point, high flash point, low corrosivity, low toxicity, and thermal stability. [3]

Today, despite many refinements in liquid cold plate designs, coolant options have stayed relatively limited. In many cases, regular water will do, but water-with-additives and other types of fluids are available and more appropriate for certain applications. Here is a look at these coolant choices and where they are best suited.

Basic Cooling Choices

While water provides superior cooling performance in a cold plate, it is not always practical to use because of its low freezing temperature. Additives such as glycol are often needed to change a coolant’s characteristics to better suit a cold plate’s operating environment.

In fact, temperature range requirements are the main consideration for a cold plate fluid. Some fluids freeze at lower temperatures than water, but have lower heat transfer capability. The selected fluid also must be compatible with the cold plate’s internal metals to limit any potential for corrosion.

Table 1 below shows how the most common cold plate fluids match up to the metals in different cold plate designs.

Table 1. Compatibility Match-ups of Common Cold Plate Metals and Cooling Fluids [1]

The choices of cold plate coolants will obviously have varied properties. Some of the differences between fluids are less relevant to optimizing cold plate performance, but many properties should be compared. Tables 2 and 3 show the properties of some common coolants.

Tables 2 and 3. Comparisons of Properties of Typical Electronic Coolants. [4]

An excellent review of common cold plate fluids is provided by Lytron, an OEM of cold plates and other cooling devices. The following condenses fluid descriptions taken from Lytron’s literature. [5]

The most commonly used coolants for liquid cooling applications today are:

  • Water
  • Deionized Water
  • Inhibited Glycol and Water Solutions
  • Dielectric Fluids

Water – Water has high heat capacity and thermal conductivity. It is compatible with copper, which is one of the best heat transfer materials to use for your fluid path. Facility water or tap water is likely to contain impurities that can cause corrosion in the liquid cooling loop and/or clog fluid channels. Therefore, using good quality water is recommended in order to minimize corrosion and optimize thermal performance.

If you determine that your facility water or tap water contains a large percent of minerals, salts, or other impurities, you can either filter the water or can opt to purchase filtered or deionized water. [5, 6]

Deionized Water – The deionization process removes harmful minerals, salts, and other impurities that can cause corrosion or scale formation. Compared to tap water and most fluids, deionized water has a high resistivity. Deionized water is an excellent insulator, and is used in the manufacturing of electrical components where parts must be electrically isolated. However, as water’s resistivity increases, its corrosivity increases as well. When using deionized water in cold plates or heat exchangers, stainless steel tubing is recommended. [5, 7]

Inhibited Glycol and Water Solutions – The two types of glycol most commonly used for liquid cooling applications are ethylene glycol and water (EGW) and propylene glycol and water (PGW) solutions. Ethylene glycol has desirable thermal properties, including a high boiling point, low freezing point, stability over a wide range of temperatures, and high specific heat and thermal conductivity. It also has a low viscosity and, therefore, reduced pumping requirements. Although EGW has more desirable physical properties than PGW, PGW is used in applications where toxicity might be a concern. PGW is generally recognized as safe for use in food or food processing applications, and can also be used in enclosed spaces. [5, 8]

Dielectric Fluid – A dielectric fluid is non-conductive and therefore preferred over water when working with sensitive electronics. Perfluorinated carbons, such as 3M’s dielectric fluid Fluorinert™, are non-flammable, non-explosive, and thermally stable over a wide range of operating temperatures. Although deionized water is also non-conductive, Fluorinert™ is less corrosive than deionized water. However, it has a much lower thermal conductivity and much higher price. PAO is a synthetic hydrocarbon used for its dielectric properties and wide range of operating temperatures. For example, the fire control radars on today’s jet fighters are liquid-cooled using PAO. For testing cold plates and heat exchangers that will use PAO as the heat transfer fluid, PAO-compatible recirculating chillers are available. Like perfluorinated carbons, PAO has much lower thermal conductivity than water. [5, 9]

Conclusion

Water, deionized water, glycol/water solutions, and dielectric fluids such as fluorocarbons and PAO are the heat transfer fluids most commonly used in high performance liquid cooling applications.

It is important to select a heat transfer fluid that is compatible with your fluid path, offers corrosion protection or minimal risk of corrosion, and meets your application’s specific requirements. With the right chemistry, your heat transfer fluid can provide very effective cooling for your liquid cooling loop.

References
1. https://www.aavid.com/product-group/liquidcoldplates/fluid
2. http://semi-therm.org/wp-content/uploads/2017/04/How-to-design-liquid-cooled-system.pdf
3. Mohapatra, Satish C., “An Overview of Liquid Coolants for Electronics Cooling,” ElectronicsCooling, May 2006.
4. http://www.calce.umd.edu/whats_new/2012/Presentations/David
%20Saums%20PPt.pdf
5. http://www.lytron.com/Tools-and-Technical-Reference/Application-Notes/The-Best-Heat-Transfer-Fluids-for-Liquid-Cooling
6. https://www.thereadystore.com/5-gallon-collapsible-water-container
7. https://www.amazon.co.uk/IONISED-WATER-Mineralised-Deionised-Distilled/dp/B00X30JKGY/ref=pd_lpo_vtph_263_tr_t_2?_encoding=UTF8&psc=1&refRID=QNAM8H7J8R1AEDP8W5FF
8. http://www.rhomarwater.com/products/catalog/envirogard-heat-transfer-fluid-antifreeze
9. http://www.skygeek.com/anderol-royco-602-cooling-fluid.html

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.

Cold Plates for IGBT and Power Electronics from Advanced Thermal Solutions   For information on ATS Cold Plates, visit our Cold Plate page at https://www.qats.com/Products/Liquid-Cooling/Cold-Plates

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Posted in Cold Plates, Liquid Cooling

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Cold Chains: How Various Industries Keep Products Cold During Shipping

Posted on October 19, 2017 by | 9 comments

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

A cold chain is a series of packaging, shipping, and distribution steps, all conducted at controlled temperatures. A successful cold chain keeps products within their required temperature ranges even when shipping between continents or hemispheres. Cold maintenance preserves the optimal shelf lives of produce, seafood, frozen food, pharmaceuticals, and other products that must be kept constantly chilled or frozen to maintain their quality.

Cold Chains

Fig. 1. Components in a KoolTemp Insulated Container from Cold Chain Technologies. [1]

About 70% of all food consumed in the United States is handled by cold chains. Without proper cooling or freezing, most of this food would show signs of perishing before reaching its end user and could potentially be inedible and unsafe.

For pharmaceuticals, consider a vaccine supply shipped to a third world country without a cold chain infrastructure. Excess exposure to heat could make the vaccine inactive and, even worse, this may not be discovered until after the shots have been distributed.

It is critical for shipping parties (food companies, drug companies, et al.) to have sufficient scientific knowledge of their products and the environments they will travel through before reaching the end users. With that knowledge in hand, the cold chain can accommodate almost every product that must ship under cold temperatures.

Fig. 2. There Are Four Temperature Range Standards Commonly Used to Designate Optimal Transport Temperatures in the Cold Chain. [2]

Cold transportation and storage standards have been developed by the U.S. as well as countries in Europe and Asia. Guidelines are also provided by the World Health Organization (WHO). The most common temperature standards in the food cold chain are “banana” (13°C), chill (2°C), frozen (-18°C) and deep frozen (-29°C); each is related to specific product groups. These standards are mainly used in the produce (agricultural) industry.

For vaccines and other pharmaceuticals, the cold chain must be compatible with labeled instructions such as “Store in a refrigerator, 2°C to 8°C (36°F to 46°F),” or “Store in a freezer, -25°C to -10°C (-13°F to 14°F).”

Food and pharma providers apply science to make products that will better withstand warmer temperatures. But most of these products must still be kept cold or frozen once they are packaged and shipped out. Poor temperature conditions or delays of an in-shipment food product or a drug can damage that product enough so it loses any market value or utility. [3]

Fig. 3. An Insulated Box Liner from IPC Helps Keep Produce Cool During Shipment. [4]

The pharmaceutical industry factors in potential temperature fluctuations during transit and storage. For many of pharma products, there is an MKT (mean kinetic temperature). This is a “thermally equivalent” temperature that degrades the same amount of a drug as degraded by the different temperatures during a particular period of time. [5]

MKT is a complex calculation with many data points. Per Wikipedia, the mean kinetic temperature can be expressed as shown in Figure 4:

Fig. 4. The Mean Kinetic Temperature (MKT) Expresses the Effect of Temperature Fluctuations During Storage and Transit of Perishable Goods. [6]

Here is a simple analogous example of working out an MKT:

A dozen eggs sat:

  • In a 20°C room for two hours.
  • In a 2°C refrigerator for four hours.
  • And on a 25°C loading dock for one hour.

Using MKT, a company can calculate that the temperature profile of the eggs was “thermally equivalent” to storing them at 10.096°C for seven hours. [7]

Cold Chain Packaging

Ensuring that a shipment will remain within a temperature range for an extended period of time comes down largely to the type of container and the refrigeration method. Duration of transit, the size of the shipment, and the outside temperatures experienced are all important in deciding the type of packaging. Examples of packaging used in shipping range from small insulated boxes that require dry ice or gel packs, rolling containers, or a 53-foot truck with its own refrigeration unit.

Fig. 5. Canadian Vaccine Storage and Handling Guidelines for Immunization Providers. [8]

The major cold chain technologies used for providing a temperature controlled environment during transport involve a range of materials and vehicles. Below is a quick summary [9]

Dry ice – Solid carbon dioxide is about -80°C and is capable of keeping a shipment frozen for an extended period of time. It is widely used for the shipping of pharmaceuticals, dangerous goods, and foodstuffs and in refrigerated unit load devices for air cargo. Dry ice does not melt, instead it sublimates when it comes in contact with air. [10]

Gel packs – Large shares of pharmaceutical and medicinal shipments are classified as chilled products. This means they must be stored in a temperature range of 2-8°C. The common method to provide this temperature is to use gel packs, or packages that contain phase-changing substances that covert from solid to liquid and vice versa to control an environment. Depending on the shipping requirements, these packs can either start off in a frozen or refrigerated state. Along the transit process they melt to liquids, while at the same time capturing escaping energy and maintaining an internal temperature. [11]

Eutectic plates – These are also known as cold plates. The principle is similar to gel packs, but the plates are filled with a liquid and can be reused many times. Eutectic plates have a wide range of applications, such as maintaining cold temperature for rolling refrigerated units. They can also be used in delivery vehicles to keep temperature constant for short periods of time. [12]

Liquid nitrogen – An especially cold substance at about -196°C, it is used to keep packages frozen over a long period of time. Liquid nitrogen is commonly used to transport biological cargo such as tissues and organs. It is considered a hazardous substance for the purpose of transportation. [13]

Quilts – These are Insulated pieces that are placed over or around freight to act as a buffer against temperature variations and to maintain a relatively constant temperature. Using quilts, frozen freight will remain frozen for a longer time period, often long enough to make the usage of more expensive refrigeration devices unjustifiable. Quilts can also be used to keep temperature sensitive freight at room temperature while outside conditions can substantially vary (e.g. during the summer or the winter). [14]

Reefers – Their name derived from ‘refrigeration’, reefers are temperature controlled, insulated vans, small trucks, semi-trailers or standard ISO containers. They are specially designed to allow temperature-controlled air circulation maintained by an attached and independent refrigeration plant. A reefer is therefore able to keep the cargo temperature cool and even warm. The term reefer increasingly applies to refrigerated 40-foot ISO containers with the dominant size being 40 high-cube footers (45R1 being the size and type code). A reefer carries around 20-25 tons of refrigerated cargo and is fully compatible with the global intermodal transport system, which implies a high level of accessibility to markets around the world. [15]

The first reefer ship for the banana trade was introduced in 1902 by the United Food Company. This enabled the banana to move from an exotic fruit that had a small market, because it arrived in markets too ripe, to one of the world’s most consumed fruit. Its impact on the reefer industry was monumental.

Conclusion

It takes time and coordination to efficiently move a shipment and every delay can have negative consequences, notably if this cargo is perishable. The greater the physical separation, the more likely freight can be damaged in one of the transport operations involved. Some goods can be damaged by shocks while others can be damaged by undue temperature variations.

For a range of goods labeled as perishables, particularly produce, quality also degrades with time. Ensuring that cargo does not become damaged or compromised in shipment, businesses in the pharmaceutical, medical and food industries are increasingly relying on the cold chain.

A recent industry forecast sees the global cold chain market growing by 7% every year, reaching $340 billion by 2025. [16]

References
1. http://www.coldchaintech.com
2. https://people.hofstra.edu/geotrans/eng/ch5en/appl5en/cc_temperature_standards.html
3. https://people.hofstra.edu/geotrans/eng/ch5en/appl5en/ch5a5en.html
4. https://www.pinterest.com/pin/309481805617481264
5. http://www.pharmaguideline.com/2013/12/mean-kinetic-temperature-mkt-in-stability.html
6. https://en.wikipedia.org/wiki/Mean_kinetic_temperature
7. http://www.madgetech.com/kbase/software/mean-kinetic-temperature.html
8. https://www.canada.ca/en/public-health/services/publications/healthy-living/national-vaccine-storage-handling-guidelines-immunization-providers-2015.html
9. https://people.hofstra.edu/geotrans/eng/ch5en/appl5en/ch5a5en.html
10. https://www.pharmaceuticalonline.com/doc/cold-chain-dry-ice-data-logger-libero-ti-d-0001
11. https://ipcpack.com/products/gel-packs/
12. http://coolpac.com/eutectic-plates/
13. http://www.antechscientific.com/a/About_Us/News/2015/0403/2.html
14. http://qsales.com/essential_grid/palletquilt/
15. http://ashjoecoldchain.blogspot.com/
16. http://www.businesswire.com/news/home/20170607005554/en/Global-Cold-Chain-Market-Analysis-Trends-2014-2016

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.

9 Comments

Posted in Cold Chains, Consulting

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What is Geothermal Cooling and Heating Technology and How Does it Work

Posted on September 6, 2017 by | 12 comments

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

If you cross-sectioned the Earth, it would show a multi-layered structure with a solid iron core spinning in a sea of liquid iron and sulfur. You would also find great quantities of flowing heat starting at the very center and moving outward.

The flow of heat from Earth’s interior to the surface is estimated at 47 terawatts, i.e. 47 trillion watts, and comes from two main sources in roughly equal amounts: the radiogenic heat produced by the radioactive decay of isotopes in the mantle and crust and the primordial heat left over from the formation of the Earth 4-1/2 billion years ago.

In a recent study, scientists estimated the temperature of the center of the Earth at 6,000°C (10,800°F) – about as hot as the surface of the sun. [2]

Geothermal Cooling

Fig. 1. Earth’s Outermost Layer, the Crust, and Comprises Just 1% of Our Planet’s Mass. [2]

In fact, more than 99% of the inner Earth is hotter than 1,000°C (1,800°F). Unlike the sun, the Earth is much cooler at its outer crust and on its outside surface. But even at cooler temperatures, the shallow depths of the Earth’s crust provide a geothermal resource for both heating and cooling structures built above the ground.

By drilling deeper down, but still within the crust, much higher temperatures can be harnessed to help generate power that can in turn provide industrial and even community-wide levels of heating and cooling. High-temperature geothermal heat has tremendous potential because it represents an inexhaustible, and virtually emissions-free, energy source. [3]

Geothermal Cooling

Fig. 2. Simple Diagram of Near Surface Heating and Cooling Geothermal System. [4]

Near Surface Heating and Cooling Systems

The ground absorbs nearly half of the solar energy the planet receives. As a result, the Earth remains at a constant, moderate temperature just below its surface year-round. However, air temperature varies greatly from summer to winter, making air source (traditional) heating and cooling least efficient when you need it the most. [5]

Geothermal heat pumps take advantage of the moderate temperatures typically found at shallow depths to boost efficiency and reduce the operational costs of architectural heating and cooling systems. Unlike conventional heating and air conditioning systems, which use the outside air to absorb and release heat, geothermal systems use heat pumps to transfer heat from below the surface.

Geothermal Cooling

Fig. 3. Four Basic Types of Geothermal Heat Pump System Shown in a US Department of Energy Illustration. Open Loop Systems Can Use Either a Man-made or Natural Water Reservoir. [6]

The pumps connect to closed loops of plastic pipes buried either horizontally or vertically in the ground below the frost line (about 100-200 meters), where the temperature is consistently between 40-80°F depending on location. Called ground loops, the underground pipes are filled with water and sealed tight except where they are connected to the geothermal heating and cooling system inside the building.

In winter, water running through the loops will absorb heat from the ground and pipe it into the home, while the system will run in the opposite direction to keep things cool during the scorching summer months. The pipes are connected to a heat pump and water heater inside the house and users can control the indoor climate through a smart thermostat.

There are four basic configurations for geothermal heat pump ground loops. Three of them are closed-loop systems that use a self-contained water and an anti-freeze solution. The open-loop system uses ground water or water from a well. [6]

Geothermal Cooling

Fig 4. Geothermal Pumps Can Efficiently Heat and Cool Homes and Commercial Buildings. [7]

Newer geothermal systems can be installed at shallower depths, less than 50 feet. Even at these levels, the ground can provide a heat source in colder weather and serve as a cooling heat sink when surface temperatures are hot. [8]

There are several providers of geothermal heating and cooling systems. Google’s parent company, Alphabet, is among them with its newly created startup, Dandelion. Originally conceived at X, Alphabet’s innovation lab, Dandelion is now an independent company offering geothermal heating and cooling systems to homeowners, starting in the northeastern U.S. [9]

To put in the ground loops, Dandelion uses its “clean drilling technology” to dig a few small holes in the yard, each only a few inches wide. Then a technician will install the other components inside the house, and the system should be up and running in two or three days. After that, the only regular maintenance is an air filter change every six to 12 months.

Deeper Down Geothermal Systems

The Kola borehole, on Russia’s Kola Peninsula is the deepest mankind has ever drilled into the Earth’s crust. After nearly 15 years of boring, the hole was 12,262 meters (40,230 feet) – over 12 kilometers or 7.6 miles deep. At that depth, the temperature was 185°C (356°F). [10]

Geothermal Cooling

Fig. 5. Very Hot, Deep Underground Thermal Energy Can Convert Water to Steam to Power Turbine Generators in Power Plants. [11]

Even at half that depth, there can be much more heat than a near-surface geothermal system can access. The Norwegian company Rock Energy wants to be an international leader in high power geothermal heat and energy. A pilot plant has been planned for Oslo that will collect heat from 5,500 meters deep. The high temperatures from this depth can heat water to 90-95°C (194-203°F) and can be used in district heating plants. [12]

Rock Energy is planning to drill two wells, an injection well where cold water is pumped down, and a production well where hot water flows back up. Between these will be so-called radiator leads that connect the wells. The water is then exchanged with water in a district heating plant managed by the Norwegian power company Hafslund. [13]

Geothermal Cooling

Figure 6. Water is Superheated by Deeply Located Hot Rocks and Pumped to the Surface Where It Converts a Separate Liquid to Turbine-Driving Steam. [14]

A hot dry rock system potentially allows geothermal energy to be captured from hot rocks, 3-5 km (1.8-3.1 miles) underground. In operation, cold water is pumped at high pressure down into the very high-temperature, fractured hot rock. The water becomes superheated as it passes through the rock on its way to the extraction boreholes.

In Figure 6, the diagram of a hot dry rock system shows hot water emerging from the borehole and directed through a heat exchanger. After giving up its heat, the cooled water is recycled back down the injection borehole in the hot rock bed. The working fluid, a low boiling point liquid, circulating through the secondary circuit of the heat exchanger is vaporized by the heat extracted from the well water and used to drive the power plant’s turbines. [14]

At both shallow depths and miles down, the Earth offers thermal energy that can harnessed for heating, cooling and power generation. Compared to most other processes, geothermal energy is cleaner, continuous and, as technology advances, a low cost alternative to fossil fuels or to solar and wind-powered systems.

References
1. https://en.wikipedia.org/wiki/Earth%27s_internal_heat_budget
2. https://www.geokraftwerke.de/en/geokraftwerke/geothermal-energy/geothermics.html
3. https://www.sciencedaily.com/releases/2015/10/151023094414.htm
4. http://www.coolingzone.com/index.php?read=1279
5. http://www.climatemaster.com/residential/how-geothermal-works/
6. https://www.pinterest.com/pin/524387950340721445/
7. https://www.geoexchange.org/geothermal-101/
8. https://en.wikipedia.org/wiki/Geothermal_heat_pump
9. https://dandelionenergy.com/
10. https://en.wikipedia.org/wiki/Kola_Superdeep_Borehole
11. http://photonicswiki.org/index.php?title=Survey_of_Renewables
12. https://www.qats.com/cms/2017/04/25/industry-developments-district-cooling-systems/
13. https://www.sintef.no/en/latest-news/energy-underfoot-/
14. http://www.mpoweruk.com/geothermal_energy.htm

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.

12 Comments

Posted in District Cooling, Geothermal Cooling, heat pipe, Thermal Industry News

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