Category Archives: micro-channel heat sink

White Paper: Microchannel Heat Sink Application in IGBT Modules

Traditionally the IGBT modules were cooled by forced air-cooled heat sinks. Air-cooled heat sinks are still good thermal management solutions for low-power and less temperature-restricting IGBT modules. However, the high-power IGBT modules are exclusively cooled by liquid-cooled heat sinks, also known as cold plates. Learn more about their application in this white paper (PDF, download, no registration needed): Download it here

Engineering White Paper: White Paper: Microchannel Heat Sink Application in IGBT Modules
A microchannel heat sink (also known as a cold plate) can be used to cool high power IGBT

EE Times Features ATS Article, “Heat Removal with Microchannel Heat Sinks”

We’d like to note to our followers here of our blog that ATS’ own Dr. Bahman Tavassoli has had an article published in EE Times entitled, “Heat Removal with Microchannel Heat Sinks”. Here’s a snippet so  you know what Dr. Tavassoli is covering:

For high performance CPUs, graphics cards, power amplifiers and other devices, air-cooling has proven ineffective at dissipating high heat fluxes. Heat transfer methods such as heat pipes, vapor chambers, nanomaterials, liquid cooling and miniature refrigeration systems have been attracting more interest.

The rest of our article covers the “whys” and “hows”. If your considering liquid cooling, then this article on microchannel heat sinks is a must read!

You can reach the article at EE Times here: “Heat Removal with Microchannel Heat Sinks

What are Leading Edge Strategies to Cool Laptop Computers and Cramped Computing Spaces? (part 2 of 2)

In part 1 of our 2 part series on leading edge strategies to cool laptop computers and cramped computing spaces, we primarily covered Vapor Compression Refrigeration Systems. In part 2 we’ll finish up our two part series by examining Miniature Scale Diaphragm Compressors and Micro-Channel Heat Sinks.

Miniature Scale Diaphragm Compressors
The researchers at Purdue have developed tiny compressors that pump refrigerants using penny-sized diaphragms, mainly of two contoured conductive planes that serve as electrodes. These planes are separated by dielectric insulation layers and a gas/refrigerant gap. As a voltage potential is applied between the electrodes, the electrostatic force deforms the diaphragm and pulls the diaphragm towards the electrode on the chamber wall. The contour of the compression chamber causes a progressive and continuous zipping action of the diaphragm until the membrane mates with the entire chamber wall. At the end of the compression strokes, the compression volume has almost zero dead space and the flexible diaphragm provides perfect rectification. Thus, the pressure of the refrigerant inside the chamber rises. The refrigerant flow in and out of the compressor chamber is controlled by suction and discharge flapper mini-valves. Target operational parameters for the miniature compressor are a heat removal of 200 W, pressure head of 750 kPa, pressure ratio of 2 and flow rate of 3000 ml/min. The targeted dimensions of the diaphragm compressor are 80 mm in diameter and 20 mm in height.

Although the new technology seems promising, there are still several challenges. One complication is that many diaphragms must operate in parallel in order to pump a large enough volume of refrigerant for the cooling system. One possible solution is to stack the diaphragms within the system small enough to fit inside a laptop. The design can be optimized using computational methods, which enables the engineers to determine how many diaphragms to use and how to stack them, either in parallel to each other or in series. By stacking in one direction, the pressure might increase. While stacking in the other direction, the necessary volume would be able to be pumped. Another major challenge is to manufacture the compressors at a low cost.

Miniature Diaphragm Compressor SchematicFigure 9 – Miniature Diaphragm Compressor Schematics [4]

Micro-Channel Heat Sinks
Another research project at Purdue is focusing on heat transfer in microchannel heat sinks, which circulate coolant through numerous channels about three times the width of a human hair. The micro-channel heat sink is a copper plate containing numerous grooves 231 microns wide or about three times as wide as a human hair and 713 microns deep. Figure 10 [5] shows Purdue researchers testing their microchannel heat sinks.

Purdue Researchers Testing Micro-Channel Heat Sink Figure 10 – Purdue Researchers Testing Micro-Channel Heat Sink [5]

Currently the researchers at Purdue are seeking to characterize and predict the enhancement due to boiling heat transfer provided by randomly roughen the surfaces in micro-channel heat sinks. Some results indicate that increasing the surface roughness by a factor of 3 yields a 30% enhancement in the amount of heat that can be removed while keeping the heat sink temperature constant. Further increases in surface roughness appear to be of little additional benefit.

There has been a lot of research in the feasibility and operational performance of small scale vapor-compression system. One promising area is the microchannel heat exchanger, which circulates coolant through numerous channels about three times the width of a human hair. Another promising area is a micro-diaphragm compressor. As the challenge of heat removal from more powerful electronic chips in smaller form shape, small scale vapor-compression system might be a promising solution.

Reference:

1. Review Core Duo vs. Core 2 Duo, NotebookCheck website http://www.notebookcheck.net/Review-Core-Duo-vs-Core-2-Duo.2404.0.html

2. Mongia R. et al., Small Scale Refrigeration System for Electronics Cooling within a Notebook Computer, Proceedings SEMITHERM XXII, March 2006, San Clara, pp.751-758

3. Miniature Refrigeration System for Electronics Cooling, Minicool website http://www.minicool.co.uk/project.html

4. CTRC Breakthroughs, CTRC website https://engineering.purdue.edu/CTRC/research/breakthroughs.php

5. Purdue Miniature Cooling Device Will Have Military, Computer Uses, ScienceDaily website http://www.sciencedaily.com/releases/2005/04/050414173948.htm

6. Miniature Cooling Device, California Science & Technology News website http://www.ccnmag.com/article/miniature_cooling_device

7. Trutassanawin S. et al., Experimental Investigation of a Miniature-Scale Refrigeration System for Electronics Cooling, CTRC Research Publications, Sept. 2006, pp.678-687.

8. Chiriac V., Chiriac F., Optimized Refrigeration Vapor Compression System for Power Microelectronics Cooling, Proceedings of Clima 2007 WellBeing Indoors.

What are Leading Edge Strategies to Cool Laptop Computers and Cramped Computing Spaces? (part 1 of 2)

If you’ve ever kept a laptop computer on your lap for any extended length of time, you know how hot they can get. Cramped computing spaces, such as microTCA, PC104 and custom small form factors can have much the same effect where the chassis is small and close to the components. In the case of laptops, a laptop heat sink with heat pipes abutting a metal chassis can be a solution to transfer the heat from the CPU, chipset and other components. In the case of cramped (or more politely, small form factor computing) heat sinks, larger fans and ducted airflow are some default choices. However, leading edge thermal management developments can provide some unique approaches to cooling these use cases. Our two part article here will cover three in particular.

As integrated circuits (ICs) have to provide increased functionality and computational power through a greater number of transistors in smaller and smaller packages, the removal of the heat dissipated by these electronic chips has become a serious challenge in the design of portable and other space-limited electronics devices. The cooling of these electronic chips in notebook computers is especially challenging due to the notebooks small footprint. Currently, heat pipes, as shown in figure 1 [1], are used to transport the heat from the high power components to a remote heat exchanger. The heat is then dissipated to the air passing through the remote exchanger. However, the heat dissipation using a heat pipe is approaching an asymptotic limit for the size restrictions of a notebook-shape form.

heat sink with heat pipe for a laptop computerFigure 1 – Heat Pipe Cooling in Existing Notebook Computer [1]

Alternative cooling approaches have been investigated to achieve the required dissipation rates, while satisfying the required reliability and cost considerations. These methods are thermoelectrics and refrigeration. Given the small cooling capacity and low efficiency of thermoelectrics, a refrigeration system is the only viable method to further increase the heat dissipation of high power components in notebook computers. Refrigeration cooling allows high heat flux dissipation at low junction temperatures, which will increase microprocessor performance at lower operating temperatures and increase chip reliability. However, refrigeration cooling also increases the size, complexity and cost of the cooling system. The complexity would increase the uncertainties in the system reliability.

Vapor Compression Refrigeration System

A basic vapor-compression refrigeration system consists of four major components: an evaporator, a compressor, a condenser and a throttling device.  Figure 2 [2] shows a schematic of a vapor-compression refrigeration system. The main heat transfer mode of the vapor-compression refrigeration cycle is evaporation/condensation of the refrigerant.

Vapor-Compression Refrigeration System Figure 2 – Vapor-Compression Refrigeration System Schematic [2]

When the refrigerant enters the evaporator, it evaporates due to the low pressure and absorbs heat from the evaporator at a constant temperature. Then, the vapor refrigerant travels through the compressor, which increases the pressure of the refrigerant. After the compressor, the vapor refrigerant condenses in the condenser due to the high pressure and rejects heat to the condenser at constant temperature. The refrigerant then travels through a throttling device, which reduces the liquid refrigerant pressure. The low pressure liquid refrigerant re-enters the evaporator and restarts the cycle. Figure 3 [2] shows the thermodynamic state point diagram of a vapor compression cycle.

Figure 3 - Vapor Compression Cycle Thermodynamic State Point Diagram [2]

Figure 3 – Vapor Compression Cycle Thermodynamic State Point Diagram [2]

For electronic cooling, the evaporator would be directly attached to the high power electronic chip, absorbing the chips heat dissipation. The heat dissipation would be rejected to the ambient environment through the air-cooled condenser. Figure 4 [3] shows the schematic of the vapor-compression cycle within a computer.

Schematic of a Miniature Refrigeration SystemFigure 4 – Schematic of a Miniature Refrigeration System [3]

Recently, there have been a lot of studies that aim to further investigate the feasibility of the refrigeration system for electronics cooling. Studies of vapor compression systems and system simulation were directed at electronics cooling in laptop computers. One such study was conducted by Mongia, Masahiro, and DiStefano. The small-scale refrigeration system, within the study, included a compressor, cold plate, condenser and throttling device. These components were specially designed, such that the entire cooling system can be incorporated within a notebook form factor. Figure 5 [2] shows the schematic of the entire system with temperature and pressure measurement points.

Small Scale Refrigeration System Schematic

Figure 5 – Small Scale Refrigeration System Schematic [2]

Iso-butane was chosen as the working fluid. The cold plate and condenser contain microchannels to efficiently transfer heat to and from the refrigerant.  Prototypes of each of the components were built and tested in order to assess their individual performance. Figure 6 [2] shows a complete form factor loop that was also built and tested to determine the system feasibility and overall performance. The test results, as shown in Figure 7 [2], show that this system can achieve a coefficient of performance (COP) > 2.25 at a moderate temperature rise. The thermal resistance of this system ranges from 0.28 – 0.7 °C/W. Figure 8 [2] shows the cooling loop within a notebook.

 photo of Small Scale Refrigeration Form Factor Figure 6 – Complete Small Scale Refrigeration Form Factor Loop[2]

Results from Small Scale Refrigeration Study

Figure 7 – Results from Small Scale Refrigeration [2]

Small Scale Refrigeration System within a Notebook

In part two we’ll cover Miniature Scale Diaphragm Compressors and Micro-Channel Heat Sinks.

Reference:

1. Review Core Duo vs. Core 2 Duo, NotebookCheck website http://www.notebookcheck.net/Review-Core-Duo-vs-Core-2-Duo.2404.0.html

2. Mongia R. et al., Small Scale Refrigeration System for Electronics Cooling within a Notebook Computer, Proceedings SEMITHERM XXII, March 2006, San Clara, pp.751-758

3. Miniature Refrigeration System for Electronics Cooling, Minicool website http://www.minicool.co.uk/project.html

4. CTRC Breakthroughs, CTRC website https://engineering.purdue.edu/CTRC/research/breakthroughs.php

5. Purdue Miniature Cooling Device Will Have Military, Computer Uses, ScienceDaily website http://www.sciencedaily.com/releases/2005/04/050414173948.htm

6. Miniature Cooling Device, California Science & Technology News website http://www.ccnmag.com/article/miniature_cooling_device

7. Trutassanawin S. et al., “Experimental Investigation of a Miniature-Scale Refrigeration System for Electronics Cooling”, CTRC Research Publications, Sept. 2006, pp.678-687.

8. Chiriac V., Chiriac F., “Optimized Refrigeration Vapor Compression System for Power Microelectronics Cooling”, Proceedings of Clima 2007 WellBeing Indoors.