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Enhanced Cooling of Oil Based Transformers and Other Heat Generating Equipment with NanoParticle Suspensions
Nanometer-sized, low-cost, readily- available, particulate nanodiamond is used as an additive to the mineral oil used in electrical power transformers and other oil-cooled electrical equipment to enhance the thermal conductivity [TC] and dielectric properties of the oil without compromising the oil's required electrical insulation, such that failures are suppressed, oil life is greatly extended and load boundaries are elevated. This could extend transformer life and allow increases to transformer MVA ratings.
The concept of introducing additives to cooling media to enhance thermal conductivity is not new; e.g., conventional antifreeze enabling cooling systems to be more efficient. However, the idea of adding particles to cooling media for cooling efficiency enhancement is less intuitive, but has been known since the 1970's. Nanodiamond was chosen as the preferred additive material for electrical equipment because it is an inert, dielectric oil-compatible material that is dispersible and readily suspended in transformer oil.
This technology uses commercially-available nanometer-sized, low cost sp3 carbon (diamond matrix) particles, i.e., particulate nanodiamond (ND) as an additive to transformer mineral oil (XO) to enhance the TC and dielectric properties of the oil. With the addition of this property-enhancing, cost-effective dispersion, the TC can be directly raised without compromising the oil's required electrical insulation. Thus, failures are suppressed, oil life greatly extended, load boundaries elevated, and it offers the potential to extend transformer life and allow increase to their MVA ratings.
Vanderbilt researchers have created mixtures of nanodiamond in trans- former oil (NDXO) and, in cooperation with the Tennessee Valley Authority, have observed enhancements of greater than 70% in TC and a reduced susceptibility to arcing in test mixtures of NDXO. A transformer test bed comprised of two matched load 25KW transformers, one with NDXO, and the other with standard cooling oil, has been operated successfully under fully-loaded (25KW) conditions. In these tests, the core of the NDXO transformer was observed to operate more than 25°F cooler than the control transformer. The technology is also applicable to numerous other heat transfer applications.
Potential Market Size
In several industries such as power transmission and transportation, efficiency gains are constrained by limitations in cooling systems. It is estimated that the U.S. market for products based on the present technology as applied to power transformers could be $50-100M annually, and perhaps twice that globally. With a significant amount of dedicated development work, this technology could be applied to parts of the engine cooling market, opening up a market opportunity worth $1-2B.
Current Competitive Products
Currently, petroleum-based mineral oil is the dominant material in use, but has lower TC. Commercially available, but much less used soy-based mineral oil has a more competitive TC.
Previous studies by the Electric Power Research Institute (EPRI) indicated that a thermal conductivity (TC) enhancement of transformer oil of a modest 5% would result in significant cost savings to the electrical power generation and distribution infrastructure. The oil used to cool operating transformers has served the industry well, but suffers from excessive maintenance replacement costs, environmental jeopardy and catastrophic failure incidence directly traceable to overheating. Transformer oil itself is a very poor thermal conductor; hence local hot spots lead to cracking of the oil's molecular composition and insulation collapse (corona). Nanosize particles that are suspended in liquids will increase the overall TC and do so in much more than an additive manner. Several researchers conducted tests on nanoparticle suspensions and found a significant increase in thermal conductivity with very small particle volume fraction (less than 1.0%) a result that is much higher than that predicted by traditional theory.
It is estimated that $1-2M and 18 months is needed to move the technology from present prototype stage to a commercializable position. This will advance the technology to the point where it can be exploited by an existing company or become the foundation to launch a startup company. The nanodiamond additive is available commercially. Capitalization would be needed to handle mixing and QC. This could be done in a relatively simple and small chemical plant of ~20-30K square feet; plant and facilitization of $2-4M. Nonrecurring examples of $1-2M over a 12 month period is anticipated for process finalization and qualification. Critical in the implementation path is a user who can accept and apply the product in real situations, providing essential to safety and benefits. Dr. Davidson's lab has such companies engaged.
Vanderbilt researchers have established a transformer test bed and are testing two 25KW utility transformers, one with NDXO cooling fluid, and the other a control, operated simultaneously, and are collecting operational data such as temperature-load profiles.
- Document the interdependency of TC:suspension:viscosity that meets the requirements of all three concurrently.
- Finalize the existing well developed connection to volume suppliers.
- Stirrers, pumps and other equipment and procedures are installed and can prepare ~2O gallon NDXO mixtures and add them to beta transformers. Finalize procedures to suppress sedimentation and develop the NDXO concentrate that is added directly to larger volumes with simple mixing.
- Upscale transfer to a larger test bed; outfit large power transformers, ideally near Nashville, with NTDXO, using Vanderbilt as test advisors/consultants.
The soy oil is noted for its thermal conductivity enhancement but is considered 'novelty'/expensive by the users (similar to ethanol fuel on a smaller scale). An additive concept as is NDXO (ND plus either petroleum mineral oil or soy-based oil) could gain acceptance.
This product would require the users to add another ingredient to their existing 'comfortable' system. There is reluctance by the transformer users to change the status quo. The establishment of a reputable beta user and use data is essential.
Intellectual Property Status
Two U.S. patents, 6,858,157 and 7,390,428, have been issued and are held jointly with TVA. Other patents are pending. Inventors are professors at major institutions with a track record of competent science and other applied inventions.!doctype>