Raghav Mahalingam

Air cooled heat sinks integrated with synthetic jets

This paper discusses the development of active air-cooled heat sinks using synthetic jet ejector arrays for high power dissipation electronics. The heat sinks typically consist of a plate fin heat sink augmented with a synthetic jet module such that each fin is straddled by a pair of synthetic jets thereby creating a jet ejector that entrains cool ambient air upstream of the heat sink and discharges it into the channels between the fins. The present work characterizes three configurations of active integrated heat sinks designed for around 100 W power dissipation levels with respect to power dissipation, thermal effectiveness and package weight and volume. The flexibility of adapting synthetic jets for different heat sink designs is demonstrated by changing the relative orientation of the entrained and discharged air flow for the different cooling module designs, indicating the potential for controlling and utilizing limited air flow in spatially constrained environments. The performance of the heat sinks is assessed using an Intel thermal die instrumented with thermocouples. Using air temperature and velocity measurements the thermal effectiveness of heat sinks is compared with an off-the-shelf heat-sink-fan combination as well as with a steady flow past the heat sink. The jets generate an airflow in the range of 3-5 CFM, resulting in /spl sim/25 Watts/CFM for each device with a thermal effectiveness as high as 60-70%.

Design and Characterization of a Heat Sink Cooled by an Integrated Synthetic Jet Matrix

A novel active heat sink design has been implemented using a matrix of integrated synthetic jets. In previous synthetic jet heat sink designs, cooling air is entrained upstream of the heat sink and is driven along the length of the fins resulting in a significant rise in the air temperature and corresponding drop in stream wise heat transfer effectiveness. In the new design, synthetic jets emanate from the base of the fins so that the induced jets and more importantly the entrained (cooling) ambient air flow along the fin height. The significantly shorter flow path ensures rapid purging and replacement of the heated air with cool entrained air. Furthermore, in the matrix design the jets are spread uniformly throughout the heat sink such that all fin surfaces are subjected to the same airflow. The velocity field of the active heat sink is mapped using particle image velocimetry (PIV) and the configuration that maximizes the volume flow rate through the fins is investigated. Thermal performance is characterized using a surrogate heater and embedded thermocouple sensors. The thermal performance of identical heat sinks cooled by the two synthetic jet approaches is compared

A Modular Stackable Concept for Heat Removal From 3-D Stacked Chip Electronics by Interleaved Solid Spreaders and Synthetic Jets

A design for cooling 3-D stacked chip electronics is proposed using solid heat spreaders of high thermal conductivity interleaved between the chip layers. The spreaders conduct heat to the base of an advanced synthetic jet cooled heat sink. The stack conduction was investigated parametrically through computational modeling. The effect of the power dissipated, the heat transfer coefficient applied to the peripheral surface, the spreader thickness, spreader thermal conductivity, and the shape of via holes in the spreader were modeled. Results show that for moderate power dissipations, 5 W in each 27times38 mm layer, a 250 mum thick copper heat spreader would conduct heat adequately. In order to remove the heat from the edges of a five-layer stack and transfer it to the ambient air, a novel active heat sink design has been implemented using a matrix of integrated synthetic jets. In previous synthetic jet heat sink designs, cooling air is entrained upstream of the heat sink and is driven along the length of the fins, resulting in a significant rise in the air temperature and corresponding drop in streamwise heat transfer effectiveness. In the new design, synthetic jets emanate from the base of the fins so that the induced jets, and more importantly the entrained (cooling) ambient air, flow along the fin height. The significantly shorter flow path ensures rapid purging and replacement of the heated air with cool entrained air. Furthermore, in the matrix design the jets are spread uniformly throughout the heat sink such that all fin surfaces are subjected to the same airflow. The velocity field of the active heat sink is mapped using particle image velocimetry (PIV) and the configuration that maximizes the volume flow rate through the fins is investigated. Thermal performance is characterized using a surrogate heater and embedded thermocouple sensors. The thermal performance of identical heat sinks cooled by the two synthetic jet approaches is compared.

Forced Air Cooling With Synthetic Jet Ejectors

This paper discusses the concept of synthetic jet ejectors for forced air cooling and some practical implementations of the same. Synthetic or “zero-mass-flux” jets, unlike conventional jets, require no mass addition to the system, and thus provide means of efficiently directing airflow across a heated surface. Because these jets are zero net mass flux in nature and are comprised entirely of the ambient fluid, they can be conveniently integrated with the surfaces that require cooling without the need for complex plumbing. A synthetic jet ejector mechanism for obtaining high heat transfer rates at low flow rates is discussed. Synthetic jet ejectors consist of a primary “zero-mass-flux” unsteady jet driving a secondary airflow through a channel. Several practical implementations of synthetic jets are introduced from low form factor, low power spot cooling applications to high heat dissipation applications and flow bypass control where synthetic jets are used to enhance fan performance.© 2005 ASME

Low-Profile Synthetic Jet Cooling for Portable Computers

This paper explores the novel technique of forced synthetic jet cooling within high-aspect ratio ducts that can be accommodated within low-profile electronic systems. A synthetic jet is an intense, small-scale turbulent jet that is synthesized directly from the fluid in the system in which it is embedded and is formed when fluid is alternately sucked and ejected from the cavity by the motion of a diaphragm bounding the cavity, so that there is no net mass addition to the system. This feature obviates the need for input piping or complex fluidic packaging and makes synthetic jets ideally suited for the low-profile geometries of portables. In the current work, a simple configuration of a 2-D synthetic jet ejector in a rectangular channel is used to ascertain the flow and thermal performance curves, overall thermal resistance and effectiveness for the synthetic jet ejector channel flow.Copyright