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II. TEM Primary Uses

As solid-state energy converters, TE modules (TEMs) have several advantages over competing technologies.

These advantages include high reliability potential, noise-free operation, vibration-free operation, scalability, orientation-independence and compactness (high energy density). Based on these advantages, TEMs have come to dominate certain applications, and new benefits continue to emerge.

Five primary uses of TEMs underlie these countless applications.



A. Large Delta T


In many situations, the object being cooled generates little or no heat. In these cases, the combination of TE cooling and thermal insulation produces large temperature differences. For a hot side around room temperature, temperature differences of about 72°C and 125°C can be achieved by single-stage and multi-stage TECs, respectively. COP is low when a TEC is operated near its maximum °T, but this can be acceptable when the heat load is small.

 

B. Heat Pumping


When DT can be kept low, TECs can pump heat with a COP near or exceeding. Common designs can pump about 30 W across a 30°C DT at a COP near. Innovative high-watt density designs can match the cooling capacity of several such standard modules in a single (40mm) 2 module.

 

C. Temperature Stabilization


The low thermal mass and fast response time of TECs, combined with an appropriate control loop, provides precise temperature control. In relatively stable thermal environments, TECs achieve 0.01°C temperature stability. Such extreme stability is difficult to achieve by other means.

D. Heating & Cooling


While vapor-compression systems can only cool, TEC systems can seamlessly switch between heating and cooling. This feature is important for thermal cycling, or when seasonal temperature changes require dual functionality. Thermal cycles can be driven aggressively by compact TEC designs.

E. Power Generation



Waste Heat Recovery


A typical automobile converts about one-quarter of the combusted fuel energy to useful work, while the remaining energy escapes as waste heat through the radiator and engine exhaust. The American manufacturing industry as a whole does a better job of utilizing energy, but still roughly one-third of the energy consumed escapes as heat to the atmosphere or to cooling systems.

Waste heat recovery recaptures this lost heat for conversion into electrical power. As researchers attempt to address this task, TE conversion continues to emerge as a prime candidate for waste heat recovery applications. 

Not all waste heat streams are good candidates for thermoelectric waste heat recovery. Since thermoelectric efficiency is a function of temperature difference, most low-grade waste heat applications, at temperatures below 200°C, are not good candidates for waste heat recovery. The conversion efficiencies will be too low to provide adequate payback (e.g., three years) for the thermoelectrics, associated heat exchangers and other hardware.
 
Higher energy waste streams, such as automobile engine exhaust, have larger temperature differences and yield higher conversion efficiencies. Higher temperatures require higher temperature thermoelectric materials with higher figures of merit (ZTs) over the temperature range of interest. Lead tellurides, skutterudites, clathrates, magnesium silicides and others are all candidate materials for these applications.


Direct Generation

 
Thermoelectric power generation utilizes a temperature gradient and heat flow in order to produce useful power output.
 
Direct thermoelectric power generation (direct generation) means creating a heat flow and temperature difference with the primary intent of producing power by TE conversion. In most cases, the heat comes from combustion of a hydrocarbon fuel (butane, propane, diesel, JP-8) or from the decay of a radioactive isotope. 

For direct generation applications, efficiency is paramount – not only the TEG efficiency, but also the overall system efficiency. Combustion efficiency, recuperation of the exhaust gases, system heat losses, fan power consumption, pump power and electronics/power conditioning losses all impact system efficiency. As for the TEG, high efficiency follows from maximizing the temperature difference across the TEG and the average device ZT over that temperature difference. 

Due to the extremely high-energy content of hydrocarbon fuels, even a modest TEG efficiency can yield an energy density several times greater than Lithium-ion batteries, provided the design properly manages the combustion process and balance-of-plant power consumption. This advantage opens the door for many long-life, smaller power sources for a variety of applications, including soldier electronics power.


Co-Generation

 
The U.S. military uses self-powered tent heaters that employ TEGs. In these heaters, most of the combustion energy passes through TEGs, converting it to a cooler temperature suitable for space heating. The remaining energy either converts to electricity or remains available for heating. The TEGs drive the blower and other electronics and can supply surplus power to an outlet. We call this type of application “co-generation.”

Thermoelectric co-generation mirrors thermoelectric waste heat recovery in many ways, except with certain distinctions. The differences appear in four characteristics of the applications:

Waste Heat Recovery

  • Fuel combusted to produce work
  • Required heat exhaustion at a certain rate and typically at > 300°C
  • TEG system is thermally in parallel with the customary exhaust path
  • Energy savings must cost-justify TEG system usage ($/watt)


Co-Generation

  • Fuel combusted to provide heat
  • Required heat downgraded before delivery
  • TEG system is in the primary heat path
  • Portability and wireless installation cost justify the TEG system


While cost per watt is less important in co-generation than in waste heat recovery, volume and weight of the TEG system are critical. Due to greater efficiency, high-temperature TEGs often prove a better choice than bismuth telluride-based TEGs in both cases.


          Typical Co-Generation Applications

  • Self-powered tent (space) heaters
  • Self-powered home heating systems
  • Mosquito catchers (fuel burned to make CO2)



Energy Harvesting

 
Energy harvesting is the process of converting ambient energy from the environment into useable electric energy to power small electronic devices. Energy harvesting technology from II-VI Marlow captures available thermal energy and converts it to usable electricity to perpetually power sensors or other low power micro devices.

        Energy Harvesters from II-VI Marlow

  • Utilize our bulk material thermoelectric power generators built using II-VI Marlow proprietary processes to deliver maximum power and efficiency
  • Draw upon our vast experience in thermoelectric modeling to provide:
    • Optimal thermal matching with small natural convection heat sinks, and
    • Optimal electrical matching to the latest state-of-the-art, low-voltage step-up and power management circuits
  • Geared to incorporate energy storage technology such as a rechargeable a Li-Ion battery, long-life thin film batteries or super-capacitors, allowing for wireless employment without ever changing batteries.

The result is low-cost, optimized, robust power solutions from II-VI Marlow that provide maximum power at small temperature differences.  Available differences of less than 5°C are enough to provide usable power for customer applications.

 


Wireless Sensor Applications

 

Employ wireless sensors in locations where hard wiring and changing batteries is impractical. This essentially free energy source creates a maintenance-free solution and can last the lifetime of the application. Inherently reliable, thermal energy harvesting solutions act as the foundation for a stand-alone wireless sensor network.

For more information, download our FREE white paper on Energy Harvesting for Wireless Sensors.

         General Applications 

  • Building automation: HVAC, gas, lighting, electricity, air quality/detectors
  • Aviation: Commercial, military
  • Military: Monitoring and intelligence gathering, battlefield and wearable soldier trackers
  • Industrial Plants and Refineries: Monitor, process, test and measurement equipment and pipelines
  • Security: Home, commercial, perimeters, border
  • Consumer Electronics: Cell phones, wearable devices, GPS trackers, etc.
  • Infrastructure: Bridges, buildings, dams, levees, pipelines, water/sewer
  • Railway and train car monitoring


        Advantages of Thermoelectrics

  • Easy installation
  • Zero maintenance
  • Small, compact, rugged design
  • Environmentally conscious solution
  • Energy saving
  • Low initial cost
 

F. Applications by Market


Industrial, Consumer

 

Industrial is the fastest-growing market for II-VI Marlow products. This growth is driven by personal comfort climate control and small-scale refrigeration. Typical customer priorities are cost, reliability, efficiency, size and form factors. II-VI Marlow addresses these priorities by working with the customer on application analysis and product design. From there, our versatile manufacturing and tailored inspection and testing ensure customer satisfaction. 

              Consumer Products

  • Portable Food/Beverage Containers
  • Chilled Water Dispensers
  • Beer/Wine Cabinets
  • Small Refrigerators
  • Personal Comfort Cooling/Heating

 

               Industrial

  • Harsh Environment Protection for Critical Components
  • Computer Microprocessors and Robotics
  • Cabinet Cooling
 

2. Telecommunications


The highest performing materials, proficiency with specialty solders, quality-minded manufacturing processes, our drive to miniaturization and unparalleled customer service are the keys to our success in the telecommunications market. Traditional TECs and our microTECs serve the various telecommunications applications, which include:

  • 980nm and 1480nm Pump Lasers
  • Digital Transmission Lasers
  • Planar Lightwave Circuits
  • Optical Channel Monitors
  • CATV Transmission Lasers
  • Avalanche Photodiodes
  • Wavelength Lockers

 

3. Defense, Space, Photonics 


II-VI Marlow is the dominant provider of thermoelectric coolers and assemblies for defense, space and photonics related applications in the U.S. and Europe. II-VI Marlow TECs have helped man see the distant reaches of the universe aboard the Hubble Telescope and provided refrigeration capability to the astronauts aboard the Space Shuttle and the International Space Station. The military services employ II-VI Marlow TECs in guidance systems, infrared cameras, range finding and target systems whether day or night. II-VI Marlow commitment to quality has resulted in the proven performance of its TECs in the harshest battle conditions as well as in the demanding environment of space. II-VI Marlow thermoelectric coolers and assemblies are used in the following defense, space and photonic applications:

  • Space Stations
  • Shuttle Refrigerators/Freezers
  • Star Trackers
  • Space Telescope Cameras
  • Cooling Infrared Sensors
  • Cooling Laser Diodes
  • Thermal Reference Sources-Black Body
  • Naval Navigation
  • Guidance Systems
  • Threat Warning
  • Police Tracking and Night Vision


Our military and high-reliability devices can be manufactured by certified manufacturing personnel in accordance with the soldering requirements of ANSI J-STD-001.

4. Medical Applications/Instruments


II-VI Marlow is the established leader in the medical market and can provide the optimal thermoelectric solution for your medical application. Whether you need accurate temperature control for analytical instrumentation or rapid thermal cycling for DNA replication, we will match a highly reliable thermoelectric solution to your system’s requirements. II-VI Marlow will develop an integrated thermoelectric engine assembly to meet your specific medical applications. We use the best materials, design criteria and construction techniques to ensure medical-grade quality and reliability.

  • DNA / PCR Thermal Cycling (Real Time)
  • Blood Analysis
  • Immuno Essay
  • Diagnostic Medical Equipment
  • Blood Vessel, Heart & Eye Surgery
  • Cosmetic Surgery
  • Life Science
  • Chemical Analysis
  • Tissue Preparation & Storage
  • Photonics Imagery
  • Molecular Analysis
  • Scientific Research
  • Physical Therapy
 

5. Automotive


The automotive industry is a rapidly expanding area of demand for thermoelectric cooling modules. II-VI Marlow has pursued two primary areas for automotive customers: temperature controlled seats and cup holders. In the seat application, thermoelectric technology provides the ability to switch easily between heating and cooling. The same is true for cup holders. Dual cup holders are also available – one beverage cools while the other is heated using the same thermal energy. II-VI Marlow Automotive Product Development Team – combined with our low-cost, high-quality Vietnam factory – provides our customers with a unique capability to meet the difficult automotive requirements while providing competitive pricing.

  • Automotive Seat Cooling/Heating
  • Cup Holders
  • Automotive Night Vision
  • Waste Heat Recovery