H. Peter J. de Bock

Investigation and application of an advanced dual piezoelectric cooling jet to a typical electronics cooling configuration

In recent years, electronics have significantly reduced in size at maintained or increased functionality. This trend has led to an increased demand for more capable thermal management solutions at smaller scales. However, miniaturization of conventional fan and heat sink cooling systems introduces significant size, weight and efficiency challenges. In this study the flow performance of a novel thin form-factor cooling solution, the advanced dual piezoelectric cooling jet (DCJ), is evaluated. A DCJ is a micro-fluidic device that disturbs the boundary layer over a hot component and hence increases heat transfer. The design of an equivalent fan-curve experiment is described in detail. A first ever fan curve for a bimorph DCJ device is presented. This is coupled to a thermal performance analysis using an experiment simulating thin profile consumer electronics.

EXPERIMENTAL INVESTIGATION OF MICRO/NANO HEAT PIPE WICK STRUCTURES

The performance of electronic devices is limited by the capability to remove heat from these devices. A heat pipe is a device to facilitate heat transport that has seen increased usage to address this challenge. A heat pipe is a two-phase heat transfer device capable of transporting heat with minimal temperature gradient. An important component of a heat pipe is the wick structure, which transports the condensate from the condenser to the evaporator. The requirements for high heat transport capability and high resilience to external accelerations leads to the necessity of a design trade off in the wick geometry. This makes the wick performance a critical parameter in the design of heat pipes. The present study investigates experimental methods of testing capillary performance of wick structures ranging from micro- to nano-scales. These techniques will facilitate a pathway to the development of nano-engineered wick structures for high performance heat pipes.Copyright

On the charging and thermal characterization of a micro/nano structured thermal ground plane

As power densities in electronic devices have increased dramatically over the last decade, advanced thermal management solutions are required. A significant part of the thermal resistance budget is commonly taken up by the heat spreader, which serves to reduce the input heat flux and connect to an increased area for heat removal. Thermal ground planes are devices that address this issue by utilizing two-phase heat transfer achieving higher effective thermal conductivities than conventional solid heat spreaders. This study describes the need for and design of a charging station to accurately dispense the working fluid and a thermal characterization experiment to characterize performance. The design study includes detailed analysis of accuracy and validation of the setup.

Development and Experimental Validation of a Micro/Nano Thermal Ground Plane

Heat pipes are commonly used in electronics cooling applications to spread heat from a concentrated heat source to a larger heat sink. Heat pipes work on the principles of two-phase heat transfer by evaporation and condensation of a working fluid. The amount of heat that can be transported is limited by the capillary and hydrostatic forces in the wicking structure of the device. Thermal ground planes are two-dimensional high conductivity heat pipes that can serve as thermal ground to which heat can be rejected by a multitude of heat sources. As hydrostatic forces are dependent on gravity, it is commonly known that heat pipe and thermal ground plane performance is orientation dependent. The effect of variation of gravity force on performance is discussed and the development of a miniaturized thermal ground plane for high g operation is described. In addition, experimental results are presented from zero to −10g acceleration. The study shows and discusses that minimal orientation or g-force dependence can be achieved if pore dimensions in the wicking structure can be designed at micro/nano-scale dimensions.Copyright

Evaluation on Use of Thermoelectric Devices for Electronics Cooling

As Thermoelectric devices are getting cheaper and more powerful in cooling, these devices are getting more popular for electronics cooling applications. However, due to the additional heat production inside the thermoelectric device, the application of a TE-cooler might not always be appropriate. In some applications, use of thermoelectric devices or coolers might cause higher temperature rises on heat generating electronics than conventional cooling solutions. To authors’ best knowledge, there exists no literature that studies whether thermoelectric cooling is better than traditional convective cooling without Thermoelectrics. This study aims to evaluate the performance and effectiveness of thermoelectric cooling for electronics. Two figures of merit are proposed, to compare performances of conventional and thermoelectric cooling techniques. An attempt is made to derive this figure of merit analytically with assumptions reflecting common electronics applications. Selective case studies will be presented based on constant heat flux and constant temperature difference.Copyright

Particle image velocimetry study on dual cooling jet flows

With the advance of the Internet of Things (IoT), electronics are becoming more prevalent in applications outside the traditional consumer electronics environment. Current electronic systems are often challenged by operation at extreme low temperature, high temperature, rapid cycling temperature, vibration, or dust-filled environments. Typical systems for these environments are natural convection cooled and sealed to protect the interior electronics from the exterior environment but this has as consequence that efficient heat removal is challenging, limiting electronics capability. Application of fans is often considered to negatively impact reliability. Dual Cool Jet (DCJ) is a variant of variable orifice synthetic jet(VO-SJ) consisting of piezo actuated metal disks that are mechanically configured to form a miniature thin form factor air mover. The DCJ does not require bearings or a DC motor making the air mover potentially lower cost and more reliable, making it an attractive candidate for electronics in harsher environments. DCJ produces a pulsing jet of high velocity air flow, imparting momentum on the adjacent fluid creating series of counter rotating vortex pairs. The flow field produced by a DCJ has been numerically studied and has proven to be a complex function of the transient aero-mechanical interaction between the disks and the internal air volume. This study provides a unique insight in the air flow field of a DCJ by publishing time-resolved particle image velocimetry and displacement measurement results. These results show that the variable orifice nature of DCJ (2.5X area change) plays a key role in generating a difference between ingestion and expulsion velocity of as much as 8x, resulting in a new flow generated by the device. The study explores the effect of DCJ actuation frequency and its effect on the flow characteristics. The results aid to better understand the application of synthetic jets like DCJ and further help to advance future technology applications.

An Efficiency Entitlement Study for Thermoelectric Generators

Recent developments in thermoelectric materials and systems have led to renewed interest in thermoelectric devices for power generation. Operating conditions of the heat source and heat sink are essential in evaluating the conversion efficiency of such thermoelectric generator systems. This study provides a method for evaluating efficiency entitlement for thermoelectric power generation when thermoelectric material properties and system operating conditions are specified. The efficiency entitlement in closed form solutions for the most commonly used thermoelectric power generation configurations are presented followed by results and discussion.Copyright