Greener equipment – thermal management revisited
With the raft of green initiatives being pushed through the electronics industry; the amount energy still wasted in the equipment is surprising.
Better and more efficient thermal management is an important factor for green designs. In this article we take look at improvements in active and passive product and design.
AC Fan efficiency
A traditional 120 x 38mm AC fan typically uses a shaded pole motor which has hardly changed in design for years. Such a fan will produce typically:
50 Cubic feet per minute (CFM)
Typical maximum static pressure of 0.06 inches of water.
More importantly it also consumes around 15W of power
In other words a piece of equipment already not efficient enough to operate at a safe temperature without forced cooling has to waste another 15W to run the fan.
Shaded pole technology is not likely to improve as it is difficult to improve the wire wrapping process these motors use. When this type of motor is used in a fan it creates a relatively large hub area when compared to DC motor types.
Size for size this means the amount of space for the impeller is limited when compared to a DC fan. The result is lower potential airflow and static pressure.
A further limitation is that the AC fans powered direct from the mains cannot provide signalling to report fan performance or a fault.
What are the alternatives?
There are fans which can deal with the above application that are smaller and consume less than half the power consumed by traditional AC fans.
The above 120mm application could be addressed by a more efficient 92 x 25mm fan which gives similar airflow, higher static pressure and only uses 4-5W of power.
These high efficiency fans use new technology which allows improved motor-wire wrapping process. This results in a smaller motor, higher torque and bigger impeller blades. The impeller surface area offers nearly twice the airflow of the traditional AC fans.
The lower power consumption vs. performance is therefore substantial and contributes to compliance to greener demands.
These fans also have options to monitor fan motor speed. They also have standard thermal cut outs to extend service life.
More efficient DC fans
There have also been developments to improve the efficiency of DC fans recently. The more efficient DC fans now use a three-phase motor technology for low power consumption. This new design also reduces the rotor size and makes available more impellor blade surface area. Again the surface area gives better airflow and better flow concentration.
Compared to conventional fans with similar rotation speeds, the above design improvement consumes around 50 per cent less power.
Further benefits of these new fans are far less vibration, longer fan life and better sound quality. The new hub designs further improve EMI and protection from the environment.
For companies seriously looking to produce more eco friendly equipment; these fans with this technology should be considered.
Other design considerations to improve efficiency
Heat dissipation by conduction to equipment exterior and then radiation via heat-sinks/fins is another well known method to minimise fan size or eliminate their use.
YEG Powerline has also been able to help customers improve design in this area.
The key to the most efficient heat transfer from an electronic component to a heat sink is minimal air gap between mating surfaces. These air gaps are tiny; however, air is a poor conductor of heat. Presence of any gaps no matter how small will affect thermal transfer efficiency. Normally a thermal interface material is used to minimise this and is also used where electrical isolation is required.
Optimal selection of a good thermal interface material is important. There have been many good developments in this area. New materials are announced frequently. Therefore designers should keep up to date with what is available.
There are a wide range of thermal interface materials on the market. These take the form of sheets, gap fillers, thermal compounds or greases. YEG Powerline has found that sheets or gap filler in custom shapes are getting more popular because of ease of use.
Thermal sheets and gap filler are developed for best thermal, electrical, mechanical and physical properties. Each application will have different priorities in relation to these properties, e.g. highest thermal conductivity with the electrical breakdown voltage of less importance. In every application the optimal trade off of these properties will need to be carefully selected.
Interface material with the smoothest surface finish and best selection for other properties will be most successful. A smooth surface finish at the start will require less material compression, less assembly force and therefore easier installation.
YEG Powerline has found increased demand for thermal conducting material with adhesive on both sides popular in LED applications. This is to replace messy pastes or greases where ease of installation is important with reasonable thermal conductivity.
Manufacturers or solution providers with specialist knowledge of thermal management are a valuable partner for OEMs to design and make greener products.
For more information please contact:
Scott Lacey, Divisional Manager - YEG Powerline
Email: scott.lacey@youngelectronics.com
Tel: +44 (0)1494 753500
Fax: +44 (0)1494 753501
Or visit the company’s website at www.yegpowerline.co.uk
YEG Powerline is a division of:
Young Electronics Group
Coronation Road,
Cressex Business Park,
High Wycombe.
HP12 3TA
England
12th Apr 2010