Cooling techniques for high density electrical components and electronic devices have been studied heavily in recent years. The advancements in the electrical/electronic industry have required methods of high heat flux removal. Many of the current electrical components and electronic devices produce a range of heat fluxes from 20 W/cm2 – 100 W/cm2 . While parallel flow cooling systems have been used in the past, jet impingement is now more desirable for its potential to have a heat transfer coefficient 3-5 times greater than that of parallel flow at the same flow rate. Problems do arise when the jet impingement is confined and a cross flow develops that interacts with impinging jets downstream leading to a decrease in heat transfer coefficient. For long heated surfaces, such as an aircraft generator rotor, span wise fluid management is important in keeping the temperature distribution uniform along the length of the surface. A detailed simulation of the heat/mass transfer on a three-layer impingement/effusion cooling system has been conducted. The impingement jet fluid enters from the top layer into the bottom layer to impinge on the heated surface. The spent fluid is removed from the effusion holes and exits through the middle layer. Three different effusion configurations were used with effusion diameters ranging from 0.5 mm to 2 mm. Temperature uniformity, heat transfer coefficients, and pressure drops were compared for each effusion diameter arrangement, jet to target spacing (H/d), and rib configuration. A Shear Stress Transport (SST) turbulence fluid model was used within ANSYS CFX to simulate all design models. Three-layer configurations were also set in series for long, rectangular heated surfaces and compared against traditional cooling methods such as parallel internal flow and traditional jet impingement models. The results show that the three-layer design compared to a traditional impingement cooling scheme iii over an elongated heated surface can increase the average heat transfer coefficient by 75% and reduce the temperature difference on the surface by 75%. It was shown that for a three layer design under the same impingement geometry, the average heat transfer coefficient increases when H/d is small. The inclusion of ribs always provided better heat transfer and centralized the cooling areas. The heat transfer was increased by as much as 25% when ribs were used. The effusion hole arrangement showed minimal correlation to heat transfer other than a large array provides better results. The effusion holes’ greatest impact was found in the pressure drop of the cooling model. The pressure losses were minimal when the effective area of effusion holes was large. This minimizes the losses due to contraction and expansion.

Electrohydrodynamic (EHD) micropumps have been developed and used in many diverse applications such as in microscale liquid cooling and various microfluidic systems. The objective of this research is to investigate different methods of enhancing the performance of ion drag EHD micropumps. In particular, the effect of electrode surface topology, applied electric field and doping agent in the dielectric liquid were investigated. The effect of 3D sharp features on the electrodes on charge injection in HFE 7100 as dielectric fluid was studied under an applied DC electric field. Micro and nano-scale features with high aspect ratio were developed on smooth copper electrodes by chemical etching or through electrophoretic deposition of single walled carbon nanotube (SWCNT). The spacing between the electrodes was kept at 250 µm. A reduction factor of 5 was achieved for SWCNT electrodes compared to the smooth case for the onset of charge injection. This study was then extended to determine its effects on the performance of ion drag EHD micropumps with 100 pairs of interdigitated electrodes. The emitter electrodes (20 µm) were half the width of the collector electrodes (40 µm), with one pump having an inter-electrode spacing of 120 µm and the other with 40 µm. Each micropump had a width of 5 mm and a height of 100 µm. SWCNT was deposited on the emitter electrodes of the micropump to generate a maximum static pressure of 4.7 kPa at 900 V, which is a 5 fold increase compared to the pump with smooth electrodes. Flow rate at no back pressure condition was improved by a factor of 3. The effect of Ferrocene as a doping agent in the working fluid HFE 7100 was studied under DC voltages. A maximum static pressure of 6.7 kPa was achieved at 700 V with 0.2% weight based doping agent, 11 times higher than when there was no doping agent at the same applied voltage. When there was no back pressure the pump generated a maximum flow rate of 0.47 mL/min at 700 V with 0.05% doping agent which is 9 times greater than with no doping agent. The effect of pulsed voltage on the performance of ion drag EHD micropump has been studied to exploit the displacement current at the sudden change of applied voltage magnitude. A range of pulse repetition rate and duty cycle were found to significantly enhance the pump performance. Static pressure generation was up to 75% and 88% greater at an optimal pulse repetition rate and duty cycle, respectively, compared to the average of the two DC levels. The effect of external flow on the discharge characteristics of an injection micropump was studied with DC volts. Higher discharge current and lower threshold voltage for the onset of charge injection in case of co-flow compared to the static case was observed. There was an optimum flow rate to generate maximum current for both co and counter-flow cases. / Thesis / Doctor of Philosophy (PhD)

Micro-Cooling, Heating and Power (CHP) is the decentralized generation of electricity in which normally wasted heat is recovered for use in heating and cooling of the space. A micro-CHP demonstration facility is needed to showcase the system and allow for experiments to be performed. This thesis illustrates the steps taken for the installation and instrumentation of a Micro-CHP (Cooling, Heating, and Power) demonstration facility. Equipment sizing was performed by creating an accurate building model and performing a transient building analysis. Temperature, pressure, flow rate, and relative humidity are measured in order to determine accurate energy balances through each piece of equipment in the micro-CHP system. The data is collected using a number of LabView subroutines while a Visual Basic program was developed to display the information.

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Data centres are an integral part of today's technology. With the growing demand for data centers to meet computational needs, there is pressure to decrease data center-related costs. By reducing the amount of power needed to cool servers, the overall power consumption can be decreased. Efficient cooling of data centres involves meeting temperature constraints while minimizing power consumption. By exploring the opportunities that may be available through controlling multiple cooling units, we can avoid issues such as overcooling (some parts of the data center being cooled more than necessary) or warm air recirculation (return of exhausted hot air to inlets of servers). Currently, in data centres with more than one cooling unit, each of the cooling units is controlled independently. This mode of operation results in each cooling unit needing to be set for the worst case, which results in over cooling and is not energy efficient. Coordinating cooling units has the potential to decrease the power consumption of a data centre by eliminating this over cooling. Furthermore, coordinating with workload management may help mitigate cooling unit power consumption. This research is concerned with exploring what is feasible within the options discussed above. It contains two main parts. In the first part, we present an algorithm to minimize power consumption of cooling units while keeping all the server cores below a temperature threshold. In the second part of this thesis, we derived a data-driven model for server outlet temperature. / Thesis / Master of Science (MSc)

Surveillance of countries' borders is of greatest interest to monitor to detect enemies. Saab's radar aircraft has air, ground and sea surveillance capabilities and is characterized by the large radar that attaches to the fuselage of the aircraft. When designing future aircraft and unmanned vehicles, weight and energy efficiency are sensitive parameters to consider. The weight of aircraft and its equipment has an important impact on, among other things, fuel consumption and thus how long they can stay in the air. In addition, all mission equipment must be provided with cooling to avoid overheating. The aim of this study has been to analyze and evaluate existing refrigeration systems in some of Saab's radar aircraft during various operational scenarios and also review alternative designs for future vehicles and carbon dioxide as future cooling media. The refrigeration systems Environmental Control System and Mission Air Cooling System ensure that cabin and cockpit areas are tempered and pressurized and that all heat generated in the equipment is transported away and out to the surrounding atmosphere as a heat sink. The Environmental Control System uses ambient air as media. Compressed air is drained from engines or an auxiliary power unit and supplies the refrigeration system with air. The Mission Air Cooling System is a conventional refrigeration machine with R134a as the refrigerant. The existing cooling circuit absorbs heat in the evaporator which is placed in the air distribution where the air circulates and cools the equipment. The refrigerant then transports the heat to the surrounding atmosphere. Carbon dioxide as a refrigerant has been used since the 19th century. With the ongoing phasing out of conventional refrigerants, R134a included, carbon dioxide is starting to become relevant again. Despite carbon dioxide's good heat transfer properties, there is a major challenge regarding the high-pressure conditions, which places demands on the components of the refrigeration system. Carbon dioxide can reduce pressure losses and dimensions of components and pipelines as well as reduce installation weight. The performance of the refrigeration systems has been evaluated based on their coefficient of performance and how much energy from the engine corresponds to the amount of fuel that the refrigeration systems require. Pressure, temperature and enthalpy conditions were developed in a simulation program, alternatively previous calculation templates were reused to calculate heat transfers and work in each refrigeration system. In addition, the installation weights of the refrigeration systems in relation to each other were provided in order to be able to analyze these against other parameters, such as performance and complexity, for future aircraft and unmanned vehicles. An alternative construction in the Mission Air Cooling System was investigated where the air distribution is excluded and instead the cooling circuit is led all the way to the devices. The evaporator thus functions as a cooling plate. The calculations for a carbon dioxide machine were carried out using research articles. For the Environmental Control System, it turned out that the design of the air intake together with the air velocity profile in some cases generates low mass flows, which causes abnormal heat exchanges and temperature conditions in the cabin and cockpit. The Mission Air Cooling System had better performance in terms of coefficient of performance but has a long chain of energy conversions required for the electricity supply which contributes to energy losses. Calculations carried out for a carbon dioxide machine resulted in the compressor's displacement being able to be reduced by 89\%. Finally, based on the analyses and calculations carried out, a section is presented that explains which parameters should be considered for future designs for unmanned vehicles, as well as a figure that can be seen as an example of a system structure. The system structure is a conventional refrigeration machine with carbon dioxide as the refrigerant. Based on the analyses made regarding the installation weight and the performance of the refrigeration systems, it is likely that the presented system structure also contributes to the lowest weight and is an example of a refrigeration system in future aircraft and vehicles.

Engine development has been in the direction of increased turbine inlet temperatures to improve efficiency and power output. Secondary flows develop as a result of a near-wall pressure gradient in the stagnating flow approaching the inlet nozzle guide vane as well as a strong cross-passage gradient within the passage. These flow structures enhance heat transfer and convect hot core flow gases onto component surfaces. In modern engines it has become critical to cool component surfaces to extend part life. Bypass leakage flow emerging from the slot between the combustor and turbine endwalls can be utilized for cooling purposes if properly designed. This study examines a three-dimensional slot geometry, scalloped to manipulated leakage flow distribution. Statistical techniques are used to decouple the effects of four geometric parameters and quantify the relative influence of each on endwall cooling levels and near-wall total pressure losses. The slot geometry is also optimized for robustness across a range of inlet conditions. Average upstream distance to the slot is shown to dominate overall cooling levels with nominal slot width gaining influence at higher leakage flow rates. Scalloping amplitude is most influential to near-wall total pressure loss as formation of the horseshoe vortex and cross flow within the passage are affected. Scalloping phase alters local cooling levels as leakage injection is shifted laterally across the endwall. / Ph. D.