Thermal Facts and Fairy Tales: Not Always Efficient

Reducing the power required to cool electronics has significant cost advantages and quantifying the potential improvements of one technology over another is a frequent theme in current electronics cooling literature.  Developing life cycle cost models and assessing the current and projected future cost benefits of different thermal management technologies is a worthwhile activity, especially for large thermal management systems.   Related it seems that thermal engineers have a desire to not be wasteful.  If we find a useful purpose for waste heat, then we feel better about increasing system efficiency where the system may now include more than the electronics.  An example would be preheating fuel or air used for power generation or supplying hot coolant for building heating needs.  Provided that the energy recovery doesn’t significantly impact the performance of the thermal management system, energy recovery most likely makes sense.  Conversely, energy recovery considerations can become too dominant since the efficiency of the recovery system is dependent on interacting with the electronics at higher temperatures.  Increasing the electronics temperature just to allow increased recovery is not likely to be a beneficial trade.

The fact of this column is that as a general rule, thermal engineers desire to be efficient.  This applies to the cooling systems we help design as well as the design and analysis processes themselves.  Our bosses like for us to be more efficient and may even use some metrics to assess our efficiency over time.  Usually, though, finding a good metric to measure design and analysis productivity improvements is hard and somewhat subjective.  The fairy tale portion of this column is that we can eliminate all of the inefficiency from our daily jobs.  This does not mean that minimizing inefficiency isn’t a good goal or that finding a good performance measure and using it to drive a desired improvement isn’t  worthwhile.

Invariably, we often do not fully understand the problem we are asked to solve.  In these cases, there is probably some educational benefit to constructing a model that focuses on the less significant details but the overall process can be inefficient.  Other times, we reasonably understand the physics of the problem but may not have a complete understanding of other aspects such as cost and schedule.  With better  computers and software training, we can build faster and more complex models but often something happens and we revise our predictions.  If the revision was the result of better interaction with our team members, then it might be unfair to say the initial work was wasted and in fact the design process may be working well.  I have come to realize that not every bit of engineering effort is immune from revision (or even the occasional start over from scratch) but that doesn’t deter me from striving to have a more efficient process.  At least a portion of being more efficient is related to knowledge sharing and more specifically, this column.

Thermal facts and fairy tales as a regular column began as a replacement for the technical data column after we had written columns on most of the thermal properties of interest to thermal engineers.  This is the 12th column and the prior columns are listed in Table 1.   As editors, we have covered some of these “fairy tales” to help our readers become more efficient in their daily jobs.  We also hope that this column has challenged some of your thinking and motivated you to better understand electronics cooling.  Similar to the technical data column, at some point, the list of thermally relevant fairy tales will be exhausted and this column may evolve further.  We welcome our readers input relative to this topic and feel free to contact us.