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Evaporators separate liquids from solutions. For maximum efficiency, designers reduce the temperature difference between the heating and heated media using multiple-stage evaporators. This efficiency requires increased size and bulk. A vendor claimed its thermal compression evaporator achieved high efficiency with only two stages. It did not function as claimed. This project investigated the evaporator's design to identify its problems and propose an alternative design with a minimized footprint. The analysis showed theoretical flaws and design weaknesses in the evaporator, including violation of the first law of thermodynamics. An alternative thermal compressor design was created through computational fluid dynamics using spreadsheet methods developed in house, aided by the software product FLUENT. Detailed component sizing was done using the software product HYSYS. The proposed redesign achieved four to one efficiency with two stage thermal compression, using one half of the space of a traditional system of similar performance.

Pas de résumé / As one of the key components in the modern propulsion system, compressor plays an important role on the performance of the aero-engine. Flow near the endwall in the compressor is complex and corner separation which generates at the corner region by the blade suction surface and the endwall is an inherent flow structure in the blade passage. As a reduction of the compressor performance can be caused by the corner separation especially at off-design and multi-stage conditions. Understanding the mechanism and also control of the corner separation is an effective approach to enhance the compressor stability. Mechanism and control methods of the corner separation in the cascade passage have been investigated in this thesis, following contents are included: l. Simulation by the RANS methods on a highly-loaded PVD cascade has been conducted. The numerical method used is verified by the comparison with the experiment. The topology analysis, overall performance and the flow characteristics of the corner separation are analyzed. The effects of some aerodynamic parameters such as the solidity, aspect ratio and blade fillet on the corner separation have also been studied. 2. The control effects of one active control method by the boundary layer suction and two passive control methods by the slot at the root of the blade and the hub clearance on the corner separation in PVD cascade are studied and compared systematically. The slot configuration on the blade combined under the influence of the aerodynamic parameters have also been conducted in order to know the cascade performance by the aerodynamic parameters under the introduction of the control method. 3. Optimization of the slot configuration at 4° incidence angle is conducted on the NACA65 cascade of LMFA in Lyon. The optimized slotted cascade is verified by the experiment at three incidence angle. 4. DDES method based on the SST k - ω model is used to simulate the optimized NACA65 slotted cascade. The turbulent characteristics in the corner separation and slot jet flow are analyzed, such as the turbulent anisotropy and the velocity spectra. 5. The study of the slot configuration on the corner separation is carried out on a realistic fan stator with high loading and high Mach number. The feasibility and effectiveness of this passive control method in the practical engineering are verified.

An axial compressor for a domestic appliance can be designed to be smaller than an equivalent centrifugal compressor. However, the performance of such a compact axial compression system is limited by increased viscous losses and reduced flow turning at low Reynolds numbers ($Re$). In domestic appliance compressors, $Re$ is typically in the range $10^4$ - $10^5$. Although the aerodynamics of isolated aerofoils operating at these $Re$ have been studied extensively, the flow fields within low $Re$ axial compressors have not been investigated in detail. This dissertation aims to develop an improved understanding of loss variation at low $Re$ and to explore how the losses can be reduced through design changes. Experiments on a 5 times scaled-up single stage axial compressor have been conducted across a range of $Re$ of $10^4$ - $10^5$. The flow field has been characterised using detailed area traverses with a miniaturised five-hole probe at the rotor inlet, rotor exit and stator exit and a miniature hot-wire at the rotor exit. The probe was specifically designed and calibrated for the scale of the experiments and methods to improve the accuracy of the measurements have been applied including a probe geometry correction. The traverse experiments were performed at the design operating condition ($\phi=0.55$ and $Re= 6\times10^4$) and at a condition close to stall for a datum stage design, a stage with an improved stator design and two stators with compound lean. It was found that losses in the rotor were greater than the stator losses across the whole range of $Re$. As expected, the loss decreased with increasing $Re$ for both the stator and rotor. The losses were also increased by three-dimensional flow, with typical loss coefficients at the hub and tip of the blade rows in the range of $20-30\%$. A major contributor to the rotor loss was an unexpected hub separation that increased in size as $Re$ was reduced. At higher $Re$, the major loss sources were the rotor tip leakage, the stator wake and the stator hub separation. The results indicate that an improved stator design that accounts for the actual, measured, rotor exit flow field at low $Re$ could reduce the $Re$ at which blade row losses start to rise dramatically as well as reduce the loss across all $Re$. The improved stator design was better matched to the radial distribution of rotor exit flow angle, which led to a decrease in stator loss across all $Re$. For all stator designs, however, the measured stage stall margin was identical at all $Re$. This, along with the increase in velocity deficit in the rotor tip region at off-design indicates that stall occurred in the rotor and was neither $Re$ nor stator design dependent. The introduction of compound lean to the the stator design had the expected result of decreasing the endwall corner separation loss and increasing midspan losses. The experiments have shown that there was a loss increase in both the midspan and casing region much greater than the corresponding decrease in the stator hub. Also the mass flow redistribution in the experiments was larger that the redistribution predicted by the CFD. Three-dimensional RANS computations at low $Re$ of the same designs as experimentally studied were also conducted in order to investigate the predictive accuracy of industry standard CFD. The simulation results predicted the overall loss distribution but overestimated the end-wall losses and failed to capture the drop in stage performance at low $Re$. The differences with the experiments were caused by the inherent limitations of a fully turbulent solver that cannot reproduce transitional flow-features. Similarly to the experiments, there was no stall margin dependency on $Re$ in the simulations. This thesis has shown that with axial compressors designed specifically for low $Re$, the $Re$ at which the losses start increasing exponentially can be shifted from $10\times10^4$ to $ 4\times10^4$. The loss increase is predominantly caused by the rotor hub corner separation.

This thesis presents a thermodynamic model for a screw chiller and cooling tower system for the purpose of developing an optimized control algorithm for the chiller plant. The thermodynamic chiller model is drawn from the thermodynamic models developed by Gordon and Ng (1996). However, the entropy production in the compressor is empirically related to the pressure difference measured across the compressor. The thermodynamic cooling tower model is the Baker & Shryock cooling tower model that is presented in ASHRAE Handbook - HVAC Systems and Equipment (1992). The models are coupled to form a chiller plant model which can be used to determine the optimal performance. Two correlations are then required to optimize the system: a wet-bulb/setpoint correlation and a fan speed/pump speed correlation. Using these correlations, a "quasi-optimal" operation can be achieved which will save 17% of the energy consumed by the chiller plant.

Air compressor systems play a large role in modern industry. These compressors can account for a significant portion of a manufacturing facility’s electric consumption and any increase in efficiency can lead to economic benefits. Air compressors are sensitive to ambient conditions, as evidenced by the fact that compressing cooler and drier air decreases the amount of work required to compress the air. A thermodynamic model of an air compressor system was developed and several cases were run by using both vapor compression and absorption cycle chillers to cool and dehumidify the inlet air. The results show that the performance increases as much as 8 percent for the compressor system with absorption inlet cooling and as much as 5 percent when using vapor compression inlet cooling. Climates with higher humidity and temperatures can see the most benefits from inlet air cooling and dehumidification.

In todays highly maneuverable jet aircraft designs, aircraft are required to have a propulsion system that can operate during sudden accelerations and rapid changes in angle-of-attack. Consequently, the compressor of the jet engine occasionally must operate at low-flow rates and rapid changes in inlet conditions. The high angle-of-attack and low-flow regime of compressor operation is often plagued by rotating stall and surge. Rotating stall and surge can result in loss of engine performance, rapid heating of the blades, and severe mechanical stresses. Traditional methods for suppressing rotating stall and surge only partially protect against rotating stall or reduce compressor efficiency. The objective of this research is to design a stall suppression system that will introduce oscillatory blowing into one of the rotor blade (stall suppression blade). This oscillatory blowing method has been tested on a wing section in a wind tunnel and has shown to increase the stall angle-of-attack by several degrees.\cite{gilarranzetal02} This increase in stall angle-of-attack will eliminate stall cells as they form in the compressor. The goal of this research is to design a single stage axial compressor that will incorporate the new oscillatory blowing stall suppression system; moreover, this research will design, build, and test a scaled down version of this suppression system.

This thesis presents a thermodynamic model for a screw chiller and cooling tower system for the purpose of developing an optimized control algorithm for the chiller plant. The thermodynamic chiller model is drawn from the thermodynamic models developed by Gordon and Ng (1996). However, the entropy production in the compressor is empirically related to the pressure difference measured across the compressor. The thermodynamic cooling tower model is the Baker & Shryock cooling tower model that is presented in ASHRAE Handbook - HVAC Systems and Equipment (1992). The models are coupled to form a chiller plant model which can be used to determine the optimal performance. Two correlations are then required to optimize the system: a wet-bulb/setpoint correlation and a fan speed/pump speed correlation. Using these correlations, a "quasi-optimal" operation can be achieved which will save 17% of the energy consumed by the chiller plant.

In this research, a multi-agent approach was applied to the design of a large axial flow compressor in order to optimise performance and to greatly enlarge the useful operating range of the machine. In this design a number of distributed software/hardware agents co-operate to control the internal geometry of the machine and thereby optimise the compressor characteristics in response to changes in flow conditions. The resulting machine is termed an ‘Intelligent Geometry Compressor’ (IGC). The design of a multi-agent system for the IGC was carried out in three main phases, each supported by computer simulation. In the first phase a steady-state model of the IGC was developed in which global control of the variable geometry is achieved by a single agent. This was used to help identify specific requirements for performance and the underlying parametric relationships. The subsequent phases incorporated additional agents into the machine design to meet these requirements. Initially, agents were deployed to optimise the settings of individual rows of stator vanes. In the final phase, the MAS was extended to incorporate agents into the machine design for the control of individual stator vanes. Simulation results were obtained which demonstrate the effectiveness of the intelligent geometry compressor in achieving delivery pressure regulation over a wide range of steady-state operating conditions whilst optimising overall machine efficiency and avoiding the occurrence of stall. Some of the implications for the physical design of an IGC arising from the MAS concept were briefly considered. The experience of the research supported by the specific results and observations from many simulation trials, led to the conclusion that multi-agent systems can provide an effective and novel alternative approach to the design of an intelligent geometry compressor. By implication, this conclusion may be extended to other intelligent machine applications where similar opportunity to apply a distributed control solution exists.