providing support to users of our tas software introduces us at harvard thermal to a wide variety of thermal problems. because our software is relatively easy to use and inexpensive, we get a very diverse user base.

we do have full time thermal analysts using the software who have been doing analysis for many years. we also have a significant number of users who are not full time thermal analysts, have engineering degrees and probably took a heat transfer course in college. they may have the understanding of heat transfer or at least have the ability to learn it but lack the understanding of how to thermally analyze a problem.

this, like most other specialties, comes with experience. a good intentioned engineer will purchase a tool like tas to save their company lots of money in consulting services. he or she may go to a training class to learn the mechanics of using the tool. armed and raring to go they dive in and start creating models. within a short period of time, their model may get overwhelming or they can't figure out where to begin.

this series of articles will discuss the thermal design process. they will not discuss the equations used to calculate temperatures but rather the process used. they will discuss how to understand the problem, decipher what your goals are, figure out where the problem areas are and how to address them.

they will discuss the thermal design process generically as well as relate them to very specific cases. the cases will be based on those i have encountered. because this is a developing series, i am looking to our readers to provide cases that they would like addressed.

the majority of my experience is in the thermal analysis of electronic systems. they range from gallium arsenide (gaas) rf amplifiers at the sub-micron level, to details of electronic components, to air and conduction cooled printed circuit boards to system level analysis which may be a 250 million dollar radar system.

i will discuss the process you would go through to calculate the gaas channel temperature when mounted in a transmit/receive module operating in a millisecond pulsed mode, which is in turn mounted to a liquid cooled cold plate on which are mounted many other components, which is cooled in parallel with 800 other identical cold plates, which is in an antenna structure the size of a tractor trailer.

where do you begin?

i will discuss how to perform hand calculations to better understand the problem. how to break the problem into logical, manageable parts and share boundary conditions will be discussed. how to recognize where to concentrate to improve the thermal design will be addressed. the three modes of heat transfer will be discussed. their relative importance for specific case will be addressed. the question of accuracy will be addressed.

how accurate do you really have to be for your problem? a military system requires accuracy to ensure long life and reliability. when calculating the temperature of a lamp fixture for your house, you may want the bezel to below safe touch temperatures and internals to be below wire insulation ratings.

how accurate you need the answers to be is just one of the many criteria that goes into, understanding the problem, selecting the software tools for the job and how to perform the thermal analysis.

the question of accuracy will also be addressed with respect to software tools, empirical formulas and testing. comparing thermal test data with analytical predictions will be discussed. most of the time, thermal test measurements are taken as reality.

if you are confident in your analysis, the only reason why test results and predictions do not agree is because the test conditions do not replicate the analysis. it is that simple. ways of determining differences between tests and predictions will be discussed. the use of well-defined tests during the design process to provide specific data not obtainable through other means will be discussed.

the goal is to provide the readers with a template to be used during the thermal design of a system. the template will provide a methodology for understanding the problem, planning how to analyze the problem, and solving the problem. there are always many ways of achieving the same goal. i encourage feedback from our readers.

other opinions, suggestions and ideas on the subject will only help the series be more beneficial to our readers. this electronic format provides the perfect forum for this somewhat interactive series. i look forward to writing this series of articles and also look forward to hearing from you.

about david rosato: david rosato received a bsme from the university of massachusetts in 1977 and a msme from worcester polytechnic institute in 1981. dave worked as a thermal analyst for raytheon company for 15 years. while at raytheon dave developed a general-purpose thermal modeling tool. in 1994, he started harvard thermal to market the software. as a principal engineer, he left raytheon in 1996 to grow the business on a full time basis. today dave is president of harvard thermal, developer of the tas software and providers of thermal analysis services. he has over 20 years of thermal analysis experience mostly in military and commercial electronics.

about tim fleury tim manages the engineering services side of harvard thermal. prior to starting at hti in 2000, tim was a principal engineer at raytheon company in the analysis section. he has over 22 years of experience in the thermal analysis of military and commercial electronics.