/library/oar/handle/123456789/103487 2025-11-07T07:48:53Z 2025-11-07T07:48:53Z /library/oar/handle/123456789/129307 2024-11-27T09:28:16Z 2022-01-01T00:00:00Z

Title: An efficient HVAC design for research laboratories Abstract: Laboratories are very energy-intensive buildings and hence have a high carbon footprint. The aim of this dissertation was to improve the heating, ventilation and air conditioning (HVAC) design of such laboratories so as to make the system more efficient. This dissertation reviewed HVAC equipment available on the local market was reviewed to determine whether the equipment found was suitable for laboratories whilst still being compliant with applicable standards. The literature review was then followed by simulations conducted on Design Builder™ simulation software. The aim of the simulations was to reduce and/or reuse HVAC energy supplied to the indicated zones, in turn reducing the electrical energy required by the overall system. A superseded pre-existing 3D model was altered to match the final design of the University of Malta SLC Conservation and Heritage Labs. This included both a structural update and an HVAC systems update. The model HVAC system was divided into two setups. The first setup accounted for the HVAC systems utilised within non-laboratory zones, whilst the second HVAC setup was designed for laboratory zones. This was done because the ventilation from these two setups cannot be allowed to mix. The simulations accounted for population within the zones (including expected physical activity of the occupants, amount of clothing worn by occupants and the switching schedule) and the required HVAC performance to maintain the desired thermals, humidity level and ventilation flow rate. Initially the simulations, were used to determine the most suitable technologies for the considered case study. Once the variables were individually analysed a final simulation was run to identify the best energy reduction that can be obtained for the University of Malta SLC Conservation and Heritage Labs for the HVAC systems under consideration. The final simulation yielded an 8.9% improvement for the cooling demand and a 28.7% improvement for the heating demand. This equates to an overall reduction in the annual demand of 14.8%. In conclusion, the study provides a very much needed first look at lab energy consumption. Furthermore, the dissertation has a lot of potential for future studies to advance an already improved HVAC system Description: M.Sc.(Melit.)

2022-01-01T00:00:00Z /library/oar/handle/123456789/103724 2022-11-16T14:52:14Z 2022-01-01T00:00:00Z

Title: Testing emissions and other parameters from vehicles driven on the chassis dynamometer Abstract: The driving conditions in the Maltese islands are characterised by frequent stopping due to traffic and traffic lights, and also by inclined roads. These conditions have an impact on both fuel consumption and emissions, providing differing results when compared to highway conditions. The New European Drive Cycle (NEDC), which has been used by regulatory bodies to certify vehicles’ compliance to regulations regarding emissions, fails to replicate the usual driving conditions within Malta, especially the inclines. The aim of this dissertation was to investigate the effect of positive road grades and frequent stopping on the fuel consumption and emissions of two vehicles, both Dacia Sandero Stepways, one being Euro 6 certified and the other Euro 5 certified. The Diesel Particulate filter (DPF) regeneration process for these vehicles was also tested and discussed. Testing was carried out through use of the chassis dynamometer within the Thermodynamics laboratory. Initially, LabVIEW was used in order to extract real time data through the vehicles’ OBD-II port through an ELM327. A heated line was also designed and installed in order to be able to also make use of the Fourier Transform Infrared spectroscopy (FTIR) emissions bench. The FTIR emissions bench was then used in order to obtain more detailed data regarding the tailpipe emissions from both vehicles. The drive cycles used were taken from trips carried out in Malta, and were chosen in order to replicate a variety of driving conditions. The driving conditions during these drive cycles varied from completely flat with no stops to inclined with stops. It was found that the inclines and stops resulted in increases in both emissions and fuel consumption. The latter’s increase was more significant, with NOx emissions reaching up to 17 times higher (0.51g/km compared to 0.03g/km) during an inclined drive cycle with stops. The fuel consumption was 123% higher, when comparing the same two drive cycles. Furthermore, the stop start feature, present in most modern cars, was found to be most useful when it comes to decreasing CO2 and fuel consumption but was found to have minimal effect in Nitrogen Oxides (NOx) reduction when AdBlue is used. The DPF regeneration process was found to be dependant mostly upon the pre DPF and coolant temperatures, reaching levels of 500-700°C and 80-100°C respectively. Furthermore, post injection was confirmed to be one of the primary methods of increasing pre DPF temperature on the tested vehicles. The Euro 6 certified vehicle was found to be compliant with regulations regarding NOx and CO2 emissions when tested on flat conditions. However, the emissions exceeded the limit substantially when an incline and stops are introduced into the drive cycle, exceeding by 537% and 103% for NOx and CO2 emissions respectively. AdBlue injection was found to be an effective NOx aftertreatment method. The Euro 5 compliant vehicle, which does not use AdBlue, emitted up to 27 times more NOx than the Euro 6 compliant vehicle (0.03g/km compared to 1.10g/km during a flat drive cycle test). Description: B.Eng. (Hons)(Melit.)

2022-01-01T00:00:00Z /library/oar/handle/123456789/103722 2022-11-16T13:11:37Z 2022-01-01T00:00:00Z

Title: Conceptual aero-cooling designs for high-pressure turbines in jet engines Abstract: This thesis starts off by providing a thorough literature review of state-of-the-art existing high-pressure turbine architectures and other theoretical cooling technologies whose working principles have only been investigated outside the context of application to the high-pressure turbine. Following the compilation of a substantial amount of information pertaining to the barriers to further gains in turbojet engine efficiency, principal engine sources of failure and their mechanisms, and existing and potentially applicable thermal stress ameliorating technologies, a meticulous validation process is performed to create a robust CFD framework capable of reliably simulating the effects of various cooling technologies within a rotor-stator cavity. An analytical approach has been taken to lay a solid foundation on which the validation process is built. The computed flow and heat transfer characteristics of a simple rotor-stator cavity are compared with previous experimental and numerical studies. The results are used to interpret the heat-transfer patterns observed in the validation. A simple verification procedure for the structural analysis follows. Several proof-of-concept designs for minimising thermal gradients during flight operation have been modelled and compared following the encouraging assessment of the impact of heat transfer modelling on high-pressure turbine discs via the validation and verification processes. A number of geometry-based modifications that would require significant changes to the disc and/or system structure are first proposed and scrutinised. Upon the establishment of a combination of a TWD with concentric rib flow turbulators at the bore as an adequate design to continue developing, some alterations to the operating conditions are then perused. Although the premise of the present study lies within the conceptual design stage, the adopted approach is not unlike a typical TRL method used in industry, where once any major geometrical modifications are finalised, any additional improvements may only be carried out via altering the operating conditions. A brief pilot study to investigate potential model comparison approaches to reduce the computational resources required during the conceptual design stage follows. Initiated by exploring the possibility of establishing a relation such that further comparisons between different models could simply be made based on the temperature differences in lieu of performing a transient FEA computation every time. Description: B.Eng. (Hons)(Melit.)

2022-01-01T00:00:00Z /library/oar/handle/123456789/103721 2022-11-16T13:10:31Z 2022-01-01T00:00:00Z

Title: Optimisation of the VRF test rig to eliminate oil trapping in the evaporator Abstract: Refrigeration is a hot topic when the summer months arrive on the Maltese Islands. The refrigeration cycle is dealt with during the thermodynamics lectures. However, without practical knowledge of the subject, it is difficult to envision how the process works. In this final year project, the VRF test rig in the thermodynamics labs was optimised due to trapping oil in evaporator. An oil separator was added to the system to aid in the oil return to the compressor due to the design of the heat exchangers. The caps at each end of the heat exchangers were re-manufactured from acrylic to add better transparency to the rig. Moreover, sensors on the system, such as the flow and temperature sensors, had faults with interpretation of the data. As a result, the flow sensor was redesigned such that it can read the small flow rates generated by the Aspen 4-24-0000X compressor. The electrical circuit was rebuilt, such that a 5 volts, voltage regulator was added, to eradicate the loss in power to the +5 volts power line, connecting the temperature sensors. The installation of submersible water pumps was also required to be able to drain the new glass water tanks. The water tanks were changed since plastic crazing and yellowing were noted at the beginning of the year. The control algorithm for the rig was altered to accommodate the new Ethernet shield. A GUI was created such that it can be accessible over the web. The GUI was designed with features to manually control the system by varying the speed of the compressor and EEV steps. Testing concerning the rig’s capacity with the flow rate of water was performed. The COP of the system could be obtained which later on was cross-checked with the performance chart of the system. The results obtained were all on a positive note, as long as the speed of the compressor is below 5500RPM, since prolonged duration at the mentioned speed would result in an abrupt motor lock. The transparent heat exchangers also helps in giving a better understanding of the Vapour Compression cycle used in most domestic and commercial A/C units. Description: B.Eng. (Hons)(Melit.)

2022-01-01T00:00:00Z