May 12, 2012

Carbon nanotubes increase heat transfer of nanofluid coolants by 15%

Nanohex is the world’s largest collaborative project for the research and development of nanofluid coolants, NanoHex comprises of a consortium of 12 leading European companies and research centres. The €8.3 million project has been funded by the Seventh Framework Programme grant.

Led by Siemen’s AG, the NanoHex nanofluids will be applied to the cooling system of Insulated Gate Bipolar Transistors (IGBT), the power electronics modules used for the traction of high speed trains.

Power electronics control of the flow of power, shaping the supplied voltage by means of semiconductor devices such as IGBTs. Power electronics can help to increase the energy efficiency of equipment and processes that use electrical power and thus, the development boundaries of large electric drives are being continuously pushed to produce more powerful, reliable, durable, smaller, lighter, and less costly power electronics products. Current liquid cooling systems are limited as to how efficiently they may transfer heat without looking to increase in size or incorporate active refrigeration.

Data Centres account for 2% of global carbon emissions, a figure equal to that of air travel, with almost half of the energy consumed utilised for cooling.

An efficient cooling system is however, essential for a data centre, as thermal stress can directly impact performance, reducing throughput and reliability, and increasing the chance of electrostatic discharge, which may damage the equipment.

The NanoHex nanofluid will be applied to the cooling system of computer servers, racks and/or cabinets. Using a custom built cold plate, the coolant could be circulated through the data centre cabinets, adjacent to the server blades, in order to directly draw heat away from the processing chips. As several companies already use water as a coolant, there is a market for direct replacement, as well as a new cooling system.

The efficient removal of heat from computer servers, racks and cabinets would ease the demand for air conditioning in the server room decrease the size of chilling units and improve the performance of the system. All of which provide considerable cost savings.

International Journal of heat and mass transfer - Enhanced thermal conductivity of ethylene glycol with single-walled carbon nanotube inclusions

In the present work, we report measurements of the effective thermal conductivity of dispersions of single-walled carbon nanotube (SWNT) suspensions in ethylene glycol. The SWNTs were synthesized using the alcohol catalytic chemical vapour deposition method. Resonant Raman spectroscopy was employed to estimate the diameter distribution of the SWNTs based on the frequencies of the radial breathing mode peaks. The nanofluid was prepared by dispersing the nanotubes using a bile salt as the surfactant. Nanotube loading of up to 0.2 vol% was used. Thermal conductivity measurements were performed by the transient hot-wire technique. Good agreement, within an uncertainty of 2%, was found for published thermal conductivities of the pure fluids. The enhancement of thermal conductivity was found to increase with respect to nanotube loading. The maximum enhancement in thermal conductivity was found to be 14.8% at 0.2 vol% loading. The experimental results were compared with literature results in similar dispersion medium. Experimental results were compared with the Hamilton–Crosser model, the Lu–Lin model, Nan’s effective medium theory and the Hashin–Shtrikman model. Effective medium theory seems to predict the thermal conductivity enhancement reasonably well compared to rest of the models. Networking of nanotubes to form a tri-dimensional structure was considered to be the reason for the thermal conductivity enhancement.

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