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Project

Development of Microvalves for High-Performance Cooling of Microelectronics

Driven by miniaturization and the continuing increase in clock speed and data transfer, power dissipation in many electronic components has exceeded the limits of conventional cooling methodologies, such as fan-blown air cooling. Given the expected increase in power density, microprocessor designers have identified cooling as one of the major challenges forthe next decade. Similar needs arise from the further development of other electronic devices such as Light Emitting Diodes (LED), where futuregenerations of high light-output multichip LED modules are being developed for general and automotive illumination applications as well as for power electronics. Hence, there is a tremendous need for innovative cooling technologies. One of the most important factors in reducing the lifetime of micro-electronic components is the high operation temperature and thermal cycling. Liquid cooling has been identified as one of the mostpromising solutions in reducing the operation temperature of high powerelectronics. Liquid cooling is often not optimized, leading to excess of cooling and large temperature variations over the IC. If the coolant is allowed to boil in the cooling channels, the heat transfer coefficientis increased with one order of magnitude. The problem of phase transition regime is the boiling instability.
A solution of these problems isaddressed by implementation of valves in the cooling system. For single-phase systems they have the role of maintaining a more uniform temperature over the IC and to reduce the pumping power. For two-phase systems the valve purpose is to maintain the most optimum boiling conditions.
A comparative study of different actuation principles was performed to identify the best actuation technology applied for chip cooling valves which meet the cooling requirements targeted in this PhD project. This classifies the valve size between the micro and macro-scale, a field which has been mainly overlooked by prior research and potentially promising applications have not been yet explored. It is for the first time that valves are especially designed for chip cooling applications. The principal requirements for the mechanical valves are the following: no leakage to the environment, low power consumption, continuous and proportional flow control, low cost, fast response time, small size and high reliability.
The most promising actuation technology found for single-phase flow is thermopneumatic actuation. Based on this principle, a valve has been designed manufactured and tested on a cooling system. The valve actuation is performed by the thermal expansion of a liquid  (actuation  fluid)  which,  at  the  same time, actuates the valve and provides feed-back sensing. The thermopneumatic valve shows a novel actuation principle that combines the advantages of zero power consumption, small size compared with the high flow rate, and low manufacturing costs. This valve has the major advantage that it can be used together with any heat sink used for microelectronic cooling. Its small size and its independence from external energy make it suited for portable devices. No electrical connection, no wires and no electronic control are needed, increasing its simplicity and reliability. A maximum flowrate of 38 kg/h passes through the valve for a heat load up to 133 W. The valve is able to reduce the pumping power by up to 60 % and has the capability to reduce the temperature variation over the IC with up to 24 %.
The most suitable actuation principle found for two-phase cooling is electro- magnetic actuation for large bandwidth, large forces, relatively high strokes and low manufacturing cost. The electromagnetic valve uses the reluctance actuation principle. It makes use of a pilot valve to reduce the size and the required actuation force. The emphasis is placed on a compact planar design to fit in planar devices. A pressure balance design allows operation at high system pressures. Because the pressure balance is used to drive the valve, an analytical and numerical model has been developed to predict the pressure distribution over the valve. The pilot valve has also been modelled as well and linearised using the results obtained from the model. The results of the model havebeen successfully validated by measurements. The valve is capable to control a flow rate up to 15 kg/h. This flow rate is sufficient to remove a heat input of 133 W equivalent with a heat flux of 500 W/cm2 at a temperature difference of 20 deg. C. Its equilibrated design allows a pressure drop control of up to 100 kPa at maximum system pressures of 600 kPa.Compared with the latest research published in literature and the latest developments in industry, this electromagnetic valve classifies on topof the list when it comes to the following combined properties in a single package: high speed proportional control, compact dimensions, high flow rates at low pressure drop, high reliability and low manufacturing cost.
This research demonstrates the need for valves and the benefits of using valves in high performance cooling systems.
Date:9 Sep 2008 →  17 Sep 2013
Keywords:Microvalves, micro-cooling
Disciplines:Manufacturing engineering, Other mechanical and manufacturing engineering, Product development
Project type:PhD project