Tag Archives: thermal management

2012 coolingZONE Summit Preview: Thermal Measurement and Experimental Design in Electronic Systems

ATS’ Qpedia is the official media sponsor of the 2012 coolingZONE Business and Technology Summit August 27-30 in Cambridge, MA. We sat down with Dr. Kaveh Azar who will be presenting the Pre-Summit Short Course “Thermal Measurement and Experimental Design in Electronics Cooling” and “State of the Art in Thermal Management – From Vacuum Tubes to Super Computers” as the Summit. In this interview, Dr. Azar discusses why education is so important in the electronics cooling industry and the crucial issues he will discuss at coolingZONE this August.

Qpedia:

Hi my name is Andrea and I’m coming to you from Qpedia Thermal eMagazine. Qpedia is the official media sponsor for the 2012 coolingZONE Summit in August. I’m with Dr. Kaveh Azar hoping to ask a few questions about the thermal management community in general and his upcoming short course on August 27th.

Dr. Azar:

Thank you Andrea, I’m glad to be here.

Qpedia:

Dr. Azar, you have served as an organizer, general chair, and keynote speaker at countless conferences, and have always played an active role in the thermal management community. Why do you think education is so important in this field?

Dr. Azar:

Andrea this is a very good and insightful question. Thermal management obviously as we all know is a critical juncture point for the successful launch of any electronics cooling product. Either we are new to the field or have come from school, when I say new to the field it could have been a seasoned engineer that comes to an electronics company with a mechanically engineering background or electrically engineering background and has given the responsibility of thermal managing of electronics systems. The unfortunate part of it is we are not really exposed to a specific field in electronics cooling. Not that there is new heat transfer or fluid dynamics, we are all exposed to the fundamentals in our graduate studies, but when we get to electronics cooling there are some very unique parameters that make it very difficult. These stem from awkward geometry, multiple materials, multiplicity of heat sources on a board and as a result of it some of the traditional problems we have seen in our thermal management classes in school that we have been exposed to in school may not necessarily apply. Therefore, those of us who have gone through this education by the school of hard knocks have being have an obligation to come back and education people who are coming to the field new, weather from school or as an engineer in a role with new responsibilities. We have to share our experiences and exposures to the people that we have had in electronics cooling to those that are going to be involved. Those are the little nuggets that make the problem much easier to solve than going just going to a heat transfer or thermodynamics class. So the problem is very difficult to solve and education, especially education with experience is very important to share and help the new people coming into the field solve their thermal problems.

Qpedia:

Thank you. On August 27th, you will be giving a one day short course on “Thermal Measurement and Experimental Design in Electronic Systems”. Could you please give a short overview on what you will be presenting?

Dr. Azar:

Absolutely. Here on this board, just to give an example of why a course like this is of value to any thermal or mechanical engineer in electronics cooling, if you look at this board, you see a multiplicity of geometries, power sources, different packaging, plastic molded packages, metal packages, connectors, the way heat sink attach with clips and as a thermal engineer I have the responsibility to come back and see if this device is going to be functional in the application this board will reside. This board could be sitting vertical, horizontal, or faced down depending on what the configuration is. We have all of these very powerful computational analysis tools but at the end of the day we have to verify our solution. So you have run your CFD simulation, you have done your analytical modeling, but now you need to know whether it is correct or not. To be able to calculate the temperature of this device, I need to know what the air and temperature velocity are and possibly the pressure drop. So in this course we are going to look at the component, board, and system level for how to measure thermal parameters. This includes: temperature, velocity, pressure, and heat flux and also learning about flow visualization which is very important.

Qpedia:

Thank you. Why is thermal measurement so important?

Dr. Azar:

At the end of the day, we have to verify. There is nothing like measurement. It is dangerous to produce data, but at the end of the day people believe data verses simulation and modeling. And when we do measurement often times it is very difficult to do the simulation and we don’t have an exact answer as to what is happening. Assume for instance, for the sake of discussion this is a telecommunications board, and we have multiple boards sitting in an environment or even a single board facing down or up in a natural convection or mild force convection. These are very difficult problems especially with the complex geometry that you see and I need to verify my simulation. I have these powerful tools that I have purchased , I have my answer, I want to send my product out but I need to see whether my answers are correct or not. Because if I don’t have a correct answer, I could jump into a whole different cooling capacity that I could cool this with a simple fan and heat sink. If my simulation is wrong, if I didn’t set the correct boundary conditions, if I didn’t verify my answer, where the measurement will come into the picture to help, it’s going to cause me to go consider a higher capacity cooling system and a higher capacity cooling system will cost more. It is a very competitive market and we want to make sure that every aspect of our solution is minimized as far is cost is concerned so we can get our products out to the market as cost effective as possible and as reliable obviously.

Qpedia:

Thank you. Can you tell us a little about the live demo you plan on giving?

Dr. Azar

Yes, Andrea. As some of you may know, we have developed a whole host of thermal test instruments at ATS. We use these on a regular basis for characterization and consulting work that we do with a variety of clients and I have always believed that it is of immense value to see an experiment in progress. I can sit here and talk about hot wire anemometers, laser doppler velocimetery, heat flux gauges, etc. but when you see it in operation you have a totally different appreciation for some of the challenges we have to face in order to collect good data. In the previous question I mentioned that people believe data and they don’t believe analysis. So the data that you generate has to be as accurate as possible. The live demo will show you the challenges and the issues we confront when we have to do a clean measurement. You can see how this equipment is used, for someone who has never done this before it may be very difficult to imagine what a hot wire anemometer is, how it works, and what the challenges are. Granted it’s a sensor but there are errors associate in that and when you put it in an experiment you can see where the errors are and how to eliminate it when you do a measurement. So the demo will encompass all of this and give an accurate description of measurement is all about.

Qpedia:

Thank you. What do you hope that attendees to take away from this short course?

Dr. Azar:

My greatest hope, first of all, is that they get a good understanding of what measurement is all about. Secondly, that they get a good understanding that measurement is not a game. It is a very detailed process. For me to be a good experimentalist I have to be a good analyst and I hope to convey this very strongly to the people who participate. Last but certainly not least is for people to understand the tools that are available for measurement so when you go back to your offices and you have to conduct a measurement or you see data being collected, you have a chance of judging what to look for, what the pertinent parameters are so you select the right instrument, place it in the right location, and when you look at the data you question the validity of the data even though you may have put it together yourself as you would question your results from analysis and simulation. If those three items are accomplished, which they have been in the past and hopefully we can again, then I think we are going to have a very successful course for our participants and obviously very gratifying for those of us who are giving the course.

Qpedia:

I agree! Dr. Azar thank you very much for your time. We look forward to seeing you at the 2012 coolingZONE Summit, August 27-30, in Cambridge, Massachusetts.

Dr. Azar:

Thank you Andrea for giving me the opportunity to talk with you and the audience.

Visit www.coolingzone.com to see the full list of topics, short courses, exhibitors, and speakers that will be at the 2012 Summit.
Register by July 31, 2012 to receive a 15% discount. Contact coolingZONE at cz-[email protected] or 508-329-2021.

New Benchtop Wind Tunnel Tests Boards and Components at Elevated Temperatures

The CLWT-115 research quality, closed loop wind tunnel from ATS provides a convenient, accurate system for thermally characterizing PCBs and individual components at controlled temperatures from ambient to 85°C.

Advanced Thermal Solutions, ATS has introduced the CLWT-115 wind tunnel which allows engineers to evaluate the effects of elevated temperatures on component and PCB response and reliability. The new research quality, closed loop wind tunnel provides a convenient, accurate system for thermally characterizing PCBs and individual components at controlled temperatures from ambient to 85°C.

The CLWT-115 wind tunnel produces high quality, low turbulence air flows of up to 5 m/s (1000 ft/min). When customized, it can generate flows up to 50 m/s (10,000 ft/min) using optionally available orifice plates. The clear Lexan test section lets the user view the test specimen and allows for flow visualization.

Unlike open loop wind tunnels, the CLWT-115 recirculates internal air. This allows the system heater to quickly warm the air to a specific temperature. The testing of boards and components in hot air is a requirement in some NEBS and other standards. The precise controls and temperature range of the CLWT-115 wind tunnel allows its use for testing heat sink performance and for calibrating air and temperature sensors.

The complete wind tunnel fits on most lab benches and is powered from standard AC outlets. It has a smaller footprint than traditional, closed loop wind tunnels or environmental test chambers.

The wind tunnel’s test section can be accessed from the top door or sides for mounting and repositioning of boards, components and sensors. Internal rail guides provide an easy mechanism to install test specimens of different sizes (e.g., PCB, heat sink).

Instrument ports (6) are provided in the side walls of the test section for placing temperature and velocity sensors such as thermocouples, Pitot tubes and hotwire anemometers.

For more information about the CLWT-115 benchtop wind tunnel, visit Qats.com or call 1-781-949-2522.

Performance Differences between Fan Types Used for Electronics Cooling

Billions of fans are now in use for active cooling of PCBs and other hot electronic components. An article in Qpedia, the thermal e-magazine from Advanced Thermal Solutions, Inc., (ATS), explores the two most common types of fans used in electronics cooling: the radial (or centrifugal) fan and the axial fan.

The difference between the axial fan and radial fans can be divided into two parts, namely geometry and fluid dynamics.

An axial-flow fan has blades that force air to move in a parallel direction to the shaft around which the blades rotate. For a radial fan, the air flows in on a side of the fan housing, then turns 90 degrees and accelerates, due to centrifugal force as it exits the fan housing. These differences in air flow direction have design implications. For example, a radial fan can blow air across a PCB more efficiently, and use less space, than mounting an axial fan to blow air down onto a board.

The fluid flow rate through an electronics system, e.g., enclosure, is determined by the intercept between the fan and system curves that plot the air pressure drop over volumetric flow rate. A system’s air flow curve can be calculated using 1D fluid mechanics, or it may require the use of high performance CFD or experimental data. In general, for the same power and rotation speed, the radial fan can achieve a higher pressure head than an axial fan. However, an axial fan can achieve a higher maximum flow rate than a radial fan.

In theory, this same approach applies when using two fans in series or in parallel. When the fans are in series, the maximum flow rate should stay the same as for the single fan, but the maximum pressure head doubles. When using two fans in parallel, the maximum pressure head should remain the same as for the single fan, but the flow rate doubles. In real situations, though, the fans may interfere with each other, thus providing lower than expected results. Thus, actual experimentation is typically needed.

Download the Full ATS White Paper Performance Differences Between Fans and Blowers and Their Implementation

An Instrument for Measuring Air Velocity, Pressure and Temperature in Electronics Enclosures

For engineer-level thermal management studies, the iQ-200 instrument from Advanced Thermal Solutions, Inc, ATS, can simultaneously measure air velocity, air pressure and the temperature of components and surrounding air at multiple locations inside electronic systems. This enables users to obtain full and accurate profiles of components, heat sinks, PCBs and other electronics hardware to enable more effective thermal management.

Developed by Advanced Thermal Solutions, Inc., ATS, the iQ-200 system simultaneously captures data from up to 12 J-type thermocouples, 16 air/velocity sensors, and four pressure sensors.

The thermocouples provide surface area temperature measurements on heat spreaders, component packages, housing hardware, and elsewhere to track heat flow or detect hot spots. Temperature data is tracked from -40 to 750°C. The sensors (available separately) measure both air temperature and velocity at multiple points allowing a detailed analysis of airflow.

Candlestick Sensor from ATS

Thin, low profile ATS candlestick sensors can be easily positioned throughout a system under test and measure airflow from -10 to +6°C. Air velocity is measured from natural convection up to 6 m/s (1200 ft/min). The iQ-200 can be factory modified to measure airflow to 50 m/s (10,000 ft/min) and air temperature up to 85°C. Four differential transducers capture pressure drop data along circuit cards, assemblies and orifice plates. Standard pressure measurement capabilities range from 0- 1,034 Pa (0 – 0.15 psi).

The ATS iQ-200 system comes preloaded with user-friendly iSTAGE application software which effectively manages incoming data from the various sensor devices, and allows rich graphic presentation on monitors and captured on videos or documents. The iQ-200 connects via USB to any conventional PC for convenient data management, storage and sharing.

More information on the iQ-200 system from ATS can be found on Qats.com (http://www.qats.com/products/Temperature-and-Velocity-Measurement/Instruments/iQ-200/2632.aspx), or by calling 781-769-2800.

The Principal Methods for Measuring Thermal Conductivity in Electronics Cooling Studies

A paper by Advanced Thermal Solutions, Inc., ATS, compiles the major methods used by engineers for measuring thermal conductivity. In all, the paper describes and compares 17 proven methods for measuring thermal conductivity in electronics.

In one section of the paper, these methods are grouped according to the time dependence of the heat applied to the sample. Each method is classified under steady-state, periodic or pulsed. Another section compares the performance of each thermal conductivity measurement method, and provides an idea of sample size and preparation, and the operator skill required. There is also a list of the equipment typically needed to conduct each of these thermal tests.

According to the ATS article, the wide choice of methods may first appear to be a disadvantage. However, once understood for their application-specific benefits the advantages become evident. Materials to be tested, part geometry and part test temperatures will usually be the primary criteria.

As always, the relative cost and expected level of accuracy will also be important factors. Avoiding complicated boundary conditions, irregular part geometry, difficult heater placement/construction and encouraging the difficult task of one-dimensional heat flow will greatly simplify the measurement process. Multiple benefits will result from reducing the cost and assembly difficulty of the experimental set-up while avoiding those errors often introduced when attempting to construct complicated analytical/mathematical models.