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New avenues of decreasing environmental impacts and increasing the efficiency of HVAC systems are constantly being explored in the race to reduce carbon emissions and global warming. These new avenues have led to the exploration of the use of carbon dioxide as a refrigerant in refrigeration applications. Many researchers have also investigated ways to reduce the power consumption of compressors, which is typically the main source of power draw for HVAC systems. One theoretical process to achieve this is through isothermal compression. This thesis explores the idea of isothermally compressing CO2 by using a liquid piston and integrated gas cooler to achieve higher efficiencies with this transcritical cycle. A test facility was designed, sized, constructed, and calibrated to emulate the suction and discharge conditions of a typical CO2 system for air conditioning applications. A prototype of the liquid piston and integrated gas cooler chamber was designed and constructed as well. A simulation model was built in Engineering Equation Solver in order to properly design the gas cooler chamber. Other critical components have been carefully chosen to ensure smooth operation of the system. Results show isothermal efficiencies of up to 82.7% during steady-state operation and an isothermal efficiency of 91.2% during steady-state operation with the additional help of evaporative cooling. Comparing this to other conventional compressors give up to 34.2% absolute improvement in the isothermal compressor efficiency. These results show sufficient performance to warrant the design of a fully working prototype despite efficiency/capacity tradeoffs in the system. Challenges had been encountered such as the loss of refrigerant through the liquid piston, which will be accounted for in the next prototype. Discussion of the next prototype includes the use of a double-acting piston and a smaller tubed fractal heat exchanger design.

Magnesium alloys offer a wide range of applications in modern lightweight structures, although the correct forming parameters need to be found to reach a good combination of fine microstructure and the required mechanical properties. Several discrete and statistical methods have been proposed to simulate the dynamic recrystallization process and adopted to study microstructural evolution. However, the materials parameters necessary to develop these models are not widely available. Hence, industrial evaluation of these parameters is complex, unpractical for several types of material and time consuming for daily industrial applications. In that way, the thermomechanical behavior and grain size evolution modeling of the AZ31 alloy are proposed using isothermal compression data. Parameters to calculate coupled stress–strain–temperature parameters, dynamic recrystallization, volume fraction and grain size were obtained from the stress–strain curves. Then, the data were input in Deform-3D software to simulate the hot deformation process and verify with experimental data the consistency of the values obtained. Measured grains size agreed with the conducted modeling, showing the reliability of strain–stress and grain size data on predicting dynamic recrystallization phenomena., Postprint (author's final draft)

A hydraulic air compressor (HAC) is a no moving parts compressor that uses hydropower to compress air that is inducted through a Venturi effect. The solubility of gases in water increases with pressure and provides a means for the dissolved gas to bypass the air-water separator and reduce the compressed air yield of a HAC. The model developed and fully described herein extends the approach of Chen and Rice (1983) to allow for a multiplicity of gas mixtures, predicts the compressed air yield reduction from gas solubility, and predicts the compressed air yield improvement by increasing the liquid temperature and the presence of pre-dissolved salts. The model simulated multiple scenarios that adjust the parameters that are known to affect air absorption in the downcomer and returns results consistent with the expected behaviour in each scenario. One of such scenarios was the simulation of the downcomer of the Ragged Chutes HAC installation. The results were compared with the single data point of oxygen concentration in compressed air delivered by a HAC and results from an equilibrium solubility model available in the literature. Under the same conditions, the model described herein predicts a concentration of oxygen of 0.181 mol/mol, a value that is 2.3% higher than the equilibrium condition. In order to match the results of the equilibrium model, the mass diffusivities of nitrogen, oxygen, argon and carbon dioxide needed to be artificially increased from their reported values in the literature by a factor of 2000. This suggests that the solubility kinetics are important to consider in the design of a HAC when predicting the compressed air yield but if the equilibrium assumption is adopted the estimate of compressed air yield will be conservative.

A hydraulic air compressor (HAC) is a no moving parts compressor that uses hydropower to compress air that is inducted through a Venturi effect. The solubility of gases in water increases with pressure and provides a means for the dissolved gas to bypass the air-water separator and reduce the compressed air yield of a HAC. The model developed and fully described herein extends the approach of Chen and Rice (1983) to allow for a multiplicity of gas mixtures, predicts the compressed air yield reduction from gas solubility, and predicts the compressed air yield improvement by increasing the liquid temperature and the presence of pre-dissolved salts. The model simulated multiple scenarios that adjust the parameters that are known to affect air absorption in the downcomer and returns results consistent with the expected behaviour in each scenario. One of such scenarios was the simulation of the downcomer of the Ragged Chutes HAC installation. The results were compared with the single data point of oxygen concentration in compressed air delivered by a HAC and results from an equilibrium solubility model available in the literature. Under the same conditions, the model described herein predicts a concentration of oxygen of 0.181 mol/mol, a value that is 2.3% higher than the equilibrium condition. In order to match the results of the equilibrium model, the mass diffusivities of nitrogen, oxygen, argon and carbon dioxide needed to be artificially increased from their reported values in the literature by a factor of 2000. This suggests that the solubility kinetics are important to consider in the design of a HAC when predicting the compressed air yield but if the equilibrium assumption is adopted the estimate of compressed air yield will be conservative.

It is well known that the isothermal compression is an ideal process to consume least power for compressor. The isothermal compression can't be really reached, but can be approached by decreasing the discharge temperature during compression. For this purpose, a cooling system has been built in the paper. Firstly, an innovative circulation system has been built to absorb the heat generated by compression, which is segregated from the refrigeration circulation system. The principle and the structure are introduced. Then, the experimental has been conducted. Based on the experimental, the following results has be obtained: The cooling capacity increased by 1.3%; for the experimental condition, discharge temperature of the gas reduced by 10℃, input power reduced by 4.1%, and COP increased by 5.2%.

It is well known that the isothermal compression is an ideal process to consume least power for compressor. The isothermal compression can't be really reached, but can be approached by decreasing the discharge temperature during compression. For this purpose, a cooling system has been built in the paper. Firstly, an innovative circulation system has been built to absorb the heat generated by compression, which is segregated from the refrigeration circulation system. The principle and the structure are introduced. Then, the experimental has been conducted. Based on the experimental, the following results has be obtained: The cooling capacity increased by 1.3%; for the experimental condition, discharge temperature of the gas reduced by 10℃, input power reduced by 4.1%, and COP increased by 5.2%.