High Efficiency Polymer based Direct Multi-jet Impingement Cooling Solution for High Power Devices

Liquid jet impingement cooling is an efficient cooling technique where the liquid coolant is directly ejected from nozzles on the chip backside resulting in a high cooling efficiency due to the absence of the TIM and the lateral temperature gradient. In literature, several Si-fabrication based impingement coolers with nozzle diameters of a few distributed returns or combination of micro-channels and impingement nozzles. The drawback of this Si processing of the cooler is the high fabrication cost. Other fabrication methods for nozzle diameters for ceramic and metal. Low cost fabrication methods, including injection molding and 3D printing have been introduced for much larger nozzle diameters (mm range) with larger cooler dimensions. These dimensions and processes are however not compatible with the chip packaging process flow. This PhD focuses on the modeling, design, fabrication and characterization of a micro-scale liquid impingement cooler using advanced, yet cost efficient, fabrication techniques. The main objectives are: (a) development of a modeling methodology to optimize the cooler geometry; (b) exploring low cost fabrication methods for the package level impingement jet cooler; (c) experimental thermal and hydraulic characterization and analysis of the fabricated coolers; (d) applying the direct impingement jet cooling solutions to different applications

Electronics Thermal Management in Information and Communications Technologies: Challenges and Future Directions

This paper reviews thermal management challenges encountered in a wide range of electronics cooling applications from large-scale (data center and telecommunication) to smallscale systems (personal, portable/wearable, and automotive). This paper identifies drivers for progress and immediate and future challenges based on discussions at the 3rd Workshop on Thermal Management in Telecommunication Systems and Data Centers held in Redwood City, CA, USA, on November 4–5, 2015. Participants in this workshop represented industry and academia, with backgrounds ranging from data center thermal management and energy efficiency to high-performance computing and liquid cooling, thermal management in wearable and mobile devices, and acoustic noise management. By considering a wide range of electronics cooling applications with different lengths and time scales, this paper identifies both common themes and diverging views in the thermal management community

Characterization and Modeling of Two-Phase Heat Transfer in Chip-Scale Non-Uniformly Heated Microgap Channels

A chip-scale, non-uniformly heated microgap channel, 100 micron to 500 micron in height with dielectric fluid HFE-7100 providing direct single- and two-phase liquid cooling for a thermal test chip with localized heat flux reaching 100 W/cm2, is experimentally characterized and numerically modeled. Single-phase heat transfer and hydraulic characterization is performed to establish the single-phase baseline performance of the microgap channel and to validate the mesh-intensive CFD numerical model developed for the test channel. Convective heat transfer coefficients for HFE-7100 flowing in a 100-micron microgap channel reached 9 kW/m2K at 6.5 m/s fluid velocity. Despite the highly non-uniform boundary conditions imposed on the microgap channel, CFD model simulation gave excellent agreement with the experimental data (to within 5%), while the discrepancy with the predictions of the classical, "ideal" channel correlations in the literature reached 20%. A detailed investigation of two-phase heat transfer in non-ideal micro gap channels, with developing flow and significant non-uniformities in heat generation, was performed. Significant temperature non-uniformities were observed with non-uniform heating, where the wall temperature gradient exceeded 30°C with a heat flux gradient of 3-30 W/cm2, for the quadrant-die heating pattern compared to a 20°C gradient and 7-14 W/cm2 heat flux gradient for the uniform heating pattern, at 25W heat and 1500 kg/m2s mass flux. Using an inverse computation technique for determining the heat flow into the wetted microgap channel, average wall heat transfer coefficients were found to vary in a complex fashion with channel height, flow rate, heat flux, and heating pattern and to typically display an inverse parabolic segment of a previously observed M-shaped variation with quality, for two-phase thermal transport. Examination of heat transfer coefficients sorted by flow regimes yielded an overall agreement of 31% between predictions of the Chen correlation and the 24 data points classified as being in Annular flow, using a recently proposed Intermittent/Annular transition criterion. A semi-numerical first-order technique, using the Chen correlation, was found to yield acceptable prediction accuracy (17%) for the wall temperature distribution and hot spots in non-uniformly heated "real world" microgap channels cooled by two-phase flow. Heat transfer coefficients in the 100-micron channel were found to reach an Annular flow peak of ~8 kW/m2K at G=1500 kg/m2s and vapor quality of x=10%. In a 500-micron channel, the Annular heat transfer coefficient was found to reach 9 kW/m2K at 270 kg/m2s mass flux and 14% vapor quality level. The peak two-phase HFE-7100 heat transfer coefficient values were nearly 2.5-4 times higher (at similar mass fluxes) than the single-phase HFE-7100 values and sometimes exceeded the cooling capability associated with water under forced convection. An alternative classification of heat transfer coefficients, based on the variable slope of the observed heat transfer coefficient curve), was found to yield good agreement with the Chen correlation predictions in the pseudo-annular flow regime (22%) but to fall to 38% when compared to the Shah correlation for data in the pseudo-intermittent flow regime

Diode laser modules based on laser-machined, multi-layer ceramic substrates with integrated water cooling and micro-optics

This thesis presents a study on the use of low temperature co-fired ceramic (LTCC) material as a new platform for the packaging of multiple broad area single emitter diode lasers. This will address the recent trend in the laser industry of combining multiple laser diodes in a common package to reach the beam brightness and power required for pumping fibre lasers and for direct-diode industrial applications, such as welding, cutting, and etching. Packages based on multiple single emitters offer advantages over those derived from monolithic diode bars such as higher brightness, negligible thermal crosstalk between neighbouring emitters and protection against cascading failed emitters. In addition, insulated sub-mounted laser diodes based on telecommunication standards are preferred to diode bars and stacks because of the degree of assembly automation, and improved lifetime. At present, lasers are packaged on Cu or CuW platforms, whose high thermal conductivities allow an efficient passive cooling. However, as the number of emitters per package increases and improvements in the laser technology enable higher output power, the passive cooling will become insufficient. To overcome this problem, a LTCC platform capable of actively removing the heat generated by the lasers through impingement jet cooling was developed. It was provided with an internal water manifold capable to impinge water at 0.15 lmin-1 flow rate on the back surface of each laser with a variation of less than 2 °C in the temperature between the diodes. The thermal impedance of 2.7°C/W obtained allows the LTCC structure to cool the latest commercial broad area single emitter diode lasers which deliver up to 13 W of optical power. Commonly, the emitters are placed in a “staircase” formation to stack the emitters in the fast-axis, maintaining the brightness of the diode lasers. However, due to technical difficulties of machining the LTCC structure with a staircase-shaped face, a novel out-plane beam shaping method was proposed to obtain an elegant and compact free space combination of the laser beam on board using inexpensive optics. A compact arrangement was obtained using aligned folding mirrors, which stacked the beams on top of each other in the fast direction with the minimum dead space

Energy Efficient Two-Phase Cooling for Concentrated Photovoltaic Arrays

Concentrated sunlight focused on the aperture of a photovoltaic solar cell, coupled with high efficiency, triple junction cells can produce much greater power densities than traditional 1 sun photovoltaic cells. However, the large concentration ratios will lead to very high cell temperatures if not efficiently cooled by a thermal management system. Two phase, flow boiling is an attractive cooling option for such CPV arrays. In this work, two phase flow boiling in mini/microchannels and micro pin fin arrays will be explored as a possible CPV cooling technique. The most energy efficient microchannel design is chosen based on a least-material, least-energy analysis. Heat transfer and pressure drop obtained in micro pin fins will be compared to data in the recent literature and new correlations for heat transfer coefficient and pressure drop will be presented. The work concludes with an energy efficiency comparison of micro pin fins with geometrically similar microchannel geometry

Investigation of a Novel Thermoelectric Cooler for Building/Infrastructure Application

With the enormous building/infrastructure construction in advanced and emerging economies, the energy demand and carbon emissions from building/infrasturcture continues to rise. Buildings/infrastructure construction sectors contributed to 30% of global energy consumption and 27% of total energy emissions. To align with the carbon net zero scenario, carbon footprint from building need to more than halve by 2030, which requiring significant efforts on adopting clean and efficient technologies applicable to all end-uses. For energy consumption of modern building, heating, ventilation, and air-conditioning (HVAC) system play a critical role, which accounts for 40% of total building consumption and 70% of landlord consumption.Thermoelectric coolers (TECs) are highly dependable, scalable, and noiseless devices. Beyond their conventional use, TECs have been investigated for a wide range of applications, including waste heat energy harvesting, electronics cooling, wearable device technology, power generation, and more. Numerous researches have unveiled their substantial potential in both domestic and industrial sectors, particularly in distributed building air conditioning. However, the cooling/energy performance of the TECs faces challenges in terms of building structures embedding, which limits its application. In particular, the integrated structure of TEC makes it difficult to dissipate heat to outside of building.To overcome these challenges, the proposed research aims to investigate a novel TEC air cooler which has a number of distinguished innovations: (1) First-of-its-kind trial in separating hot and cold ends enabling placement of one side of TEC to outside of the building and another side of TEC to inside of building, thus creating an increased temperature gradient between the ends and increased cooling capacity. Furthermore, separated TEC makes it possible to be integrated with the building façade. (2) Initiative optimization of the TEC geometries enables the enhanced energy performance and cooling capacity that makes the TEC more building applicable; (3) Pioneering full-day case studies of TEC performance illustrates the applicability and adaptation of the coolers across different climatic conditions of the world.This thesis employs a fundamental approach that integrates both theoretical and experimental analyses. The methodology comprises an exhaustive literature review, a conceptual design phase, mathematical analysis, model development, validation, and an in-depth examination of performance and thermal characteristics for thermoelectric geometry optimization. Furthermore, the thesis includes a conceptual design phase, mathematical analysis, model development, experimental testing, model validation, performance analysis, and real-climatic condition case studies.Trials on the separated configuration TEC indicate that the specialist TEC, when applying 10 K temperature difference and 5A of current, led to reduction in cooling capacity by 5.6% compared to the integrated TEC, varying from 7.13 W to 6.76 W. However, the TEC device height will be doubled. While sacrificing a small portion of cooling capacity, the TEC’s application scenarios have been significantly broadened. It is noteworthy that separated-TEC configuration exhibits excellent cooling power density. The cooling capacity per unit area could exceed 15 kW/m2 under high current (I=5A), even at low current (I=0.5A), it is up to 500 W/m2.Geometry optimization of the TEC reveals that the proposed design excels in both cooling performance and thermal-mechanical characteristics. The study demonstrates that under specified conditions, the truncated cone-shaped module (g) exhibits a noteworthy improvement in cooling capacity. In comparison to a traditional TEC, the cooling capacity from 0.1429 W increases to 0.1557 W, when operating at a temperature difference of 50 K, marking an 8.9% enhancement. This translates to a rise in the overall TEC device's cooling capacity from 18.15 W to 19.78 W. Additionally, the 'g' module, characterized by its absence of corners or edges, effectively reduces the peak von Mises stress.A number of case studies were undertaken. The results show that, by introducing the separated-configuration structure, the unit cooling capacity of TEC system increases from 16.66 W/m2 to 18.82 W/m2 by 13%, while the cooling surface temperature is reduced by 0.2 °C.This research shows that the TEC geometry optimization and separated TEC configuration create an opportunity to allow the TEC to be well integrated into a building. The cooling performance of the TEC could be improved by establishing the optimal geometry and its proper connection and configuration

PERFORMANCE OF A MICROCHANNEL-THERMOELECTRIC POWER GENERATOR WITH ALUMINA-IN-WATER NANOFLUIDS AS COOLANTS

In the past two decades, the rapid advancement of military aircraft in terms of performance and power consumption in order to accomplish evermore demanding missions has introduced new challenges, namely, having to conserve of non-renewable petroleum, minimize carbon emissions, and accomplish more mission per unit energy. This thesis describes the work done to evaluate the performance of a renewable-energy device termed the microchannel-thermoelectric power generator (MC-TEPG), which uses alumina-in-water nanofluids as coolants, that is intended to replace or supplement current non-renewable power supplies such as battery packs in order to contribute to overcoming the abovementioned challenges. The MC-TEPG recovers waste heat internally generated by motors of military aircraft and converts it to usable electric power via the Seebeck effect. This thesis studies nanofluid flow and heat transfer in the MC-TEPG microchannels, and thermoelectric power generation under varying conditions. Current results show MC-TEPG feasibility and suggest future promise