Advanced Thermal Solutions, Inc. (ATS) has released a new thermal test instrument, the iFLOW-200, which assesses the thermal and hydraulic characteristics of cold plates in electronics cooling. It can be used to simulate a wide range of conditions to optimize a cold plate’s performance before it is commercialized or prior to its use in an actual application.
The iFLOW-200 measures coolant temperatures from 0-70°C with the high accuracy of ± 1°C. Differential pressure of the coolant in the cold plate is measured up to 103,000 Pa (15 psi), with the precise accuracy of ± 1%. Distilled water is used as the reference coolant. For test comparisons, the systems coolingVIEW software can also calculate thermal resistance and pressure drop as a function of flow rate for selected liquids.
The instrument system includes a pair of K-type thermocouples for measuring temperature changes on the cold plate surface. Temperatures are monitored on the coolingVIEW interface.
The iFLOW-200 system features easy set up and operation to save time when evaluating different cold plate models. Designed for accuracy and convenience, the iFLOW-200 simply requires setting the starting and ending coolant flow rates, and choosing the dwell time, pumping power and other parameters. These are easily done on any PC using the systemd user-friendly application program.
The iFLOW-200 system features separate controller and hydraulics enclosures with USB connections. The hydraulic package includes a fluid level indicator, coolant inlets and outlets from/to the cold plate under test, ports for surface temperature thermocouples, and a fluid cooling system for its internal heat exchanger. The iFLOW-200 is also ideal for testing alternative liquids.
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-info@coolingzone.com or 508-329-2021.
ATS, Advanced Thermal Solutions, Inc. will present technical webinars on electronic cooling topics in July, August and September 2012. Each of these free events will provide engineering-level training in a key area of modern thermal management.
Here are the different webinar topics and presentation times:
Using Thermal Interface Materials to Improve Heat Sink Thermal Performance
July 26, 2012 at 2:00 p.m. ET
To cool hotter components, engineers are using larger fans and heat sinks, and increasing surface areas. These hardware enhancements can add significantly to design costs. In many cases, cooling performance can be improved by using a higher performance interface material between the case and the heat sink. Participants will learn the importance of lowering thermal resistance using thermal interface materials, or TIMs, and the different kinds of TIMs available from the market.
Air Jet Impingement Cooling
August 23, 2012 at 2:00 p.m. ET
Ongoing increases in power in devices such as processors and IGBTs mean that higher capacity cooling methods are needed to remove excess heat. One such method is the jet impingement of a liquid or gas onto a surface on a continuous basis. Lab experiments at ATS have shown up to a 40% improvement in cooling achieved using this method. This webinar will explore jet impingement cooling theory, implementation and best practices.
LED Thermal Management in Commercial and Consumer Lighting Applications
September 27, 2012 at 2:00 p.m. ET
Excess heat directly affects both short-term and long-term LED performance. The short-term effects are color shift and reduced light output, while the long-term effect is accelerated lumen depreciation and thus shortened useful life. Participants will learn how to diagnose and solve thermal issues in consumer and commercial LED applications.
Each of these one-hour online tutorials will include detailed visuals, real world examples, instructions, definitions and references. Audience questions will be answered by the presenters during and after the presentation. One or more ATS PhD-level thermal engineers will be presenting live.
There is no cost to attend these ATS webinars, but virtual seating is limited. Registration is available online at http://www.qats.com, or by calling 1-781-949-2522.
To maintain operation, the heat must flow out of a semiconductor as such a rate as to ensure acceptable junction temperatures. This heat flow encounters resistance as it moves from the junction throughout the device package, much like electrons face resistance when flowing through a wire. In thermodynamic terms, this resistance is known as conduction resistance and consists of several parts. From the junction, heat can flow toward the case of the component, where a heat sink may be located. This is referred to as ÎJC, or junction to case thermal resistance. Heat can also flow away from the top surface of the component and into the board. This is known as junction to board resistance, or ΘJB.
Source: JESD51-2, Integrated Circuits Thermal Test Method – Natural Convection, JEDEC, March 1999.
ΘJB is defined as the temperature difference between the junction and the board divided by the power when the heat path is from junction to board only. To measure ΘJB, the top of the device is insulated and a cold plate is attached to the board edge (Figure 1). This is the true thermal resistance, which is the characteristic of the device. The only problem is that, in a real application one does not know how much power is being transmitted from different paths.
Due to the multiple heat transfer paths within a component, a single resistance cannot be used to accurately calculate the junction temperature. The thermal resistance from junction to ambient must be broken down further into a network of resistances to improve the accuracy of junction temperature prediction. A simplified resistor network is shown in Figure 2.
As board layouts become denser, there is a need to design optimized thermal solutions that use the least amount of space possible. Simply put, there is no margin to allow for over-designed heat sinks with tight component spacing. Accounting for the effect of board coupling is an important part of this optimization. The possibility for using an oversized heat sink exists only if the junction to case heat transfer path is considered.
To ensure a 105°C junction temperature at 55°C ambient a typical component (see Table 1) needs a heat sink resistance of 2.05°C/W (if we ignore board conduction). When board conduction is taken into account, the actual junction temperature could be as low as 74°C, assuming the board temperature is the same as the air temperature. This indicates a heat sink that is larger than necessary.
From this example, it is clear that all heat transfer paths from the component junction must be considered. Using just the ΘJC and ΘCA values can lead to a larger than optimal heat sink and may not accurately predict operating junction temperatures. Using the proposed correlation can also predict junction temperature when the board temperature is known from experimentation, as shown in Figure 3.
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.
