Digitized by Kansas Correctional Industries

Thesis (M. Sc.)--University of Hong Kong, 2002. / Includes bibliographical references (leaves 58-59).

No description available.

Nowadays Solar Energy is one of the engineering fields most exploited, due to the ongoing need to developing new technologies based on renewable energy or improving the existing ones. One particular application of this kind of energy is Solar Cooling, which consist in generating cold from the heat received from the Sun. A common installation of solar cooling requires solar collectors, an absorption/adsorption chiller, fan coils, piping, valves and pumps. It calls for a minimal preventive maintenance which should allow keeping operating conditions within certain limits.The aim of this work is to analyze the viability of the installation of a solar cooling system in a roof. It has been chosen the Building 45 of the University of Gävle (Hus 45) as a pattern design. It was built in 2008, thirteen years after Högskolan i Gävle was inaugurated. This building uses electric compression coolers for its cooling demand. According to their heating demand, this is solved by using District Heating.This work is focused on the determination of the cooling demand of this particular building and the proposal of a solar cooling system that could supply it. Calculating the cooling demand means applying most of the concepts learnt during the whole speciality of the degree, like thermal loads in buildings. This calculation has been possible by using IDA ICE, which is a software that allows the user to develop a new construction through defining all structure parameters. After having defined all the contour conditions, the simulation shows all kinds of parameters in detail, in particular, the cooling demand of the respective building. Moreover, creating a new solar cooling system for this building means reviewing all the concepts related to refrigeration cycles and solar energy that have been learnt during the intensification. To do it, it has been necessary to use POLYSUN, another program that let the user to create solar thermal systems, photovoltaic systems or any other installation for getting heating, cooling or hot water.In addition, another important point to discuss is the usage of a solar cooling system based on absorption/adsorption technology instead of using photovoltaic as a way of providing to the current cooling units.The simulation about the cooling demand of the building shows that for covering the 95,22% of the operation hours (within the study), it is required to solve a cooling peak demand of 100 kW, which is in terms of energy a value of 68437,6 kWh. Regarding the designs of the solar cooling systems, two variants have been analyzed. While the first one is based on using the absorption technology, the second one has two subdivided proposals: a stand-alone photovoltaic system and a net metering installation. The absorption system could cover the cooling demand with the exception of July. The viability of this installation is questioned because of the low operation hours of the absorption machine, which is not working as it was expected since it is the cooling tower who really carries out the cooling function. On the other hand, the stand-alone system allows the building to cover all of its cooling demand, but the system is oversized and no profitable within a period of 30 years although it supposes a reduction of 100% in CO2 emissions, which is obvious since this option considers an electrical consumption from the grid of 0 kWh. Finally, the net metering system is probably the best option for covering the cooling demand of this building, as it has the shorter pay-back (18 years), the less visual impact when the solar modules are installed on the roof and requires less maintenance.Since there are no advantages in using an absorption machine for a cooling system in a Swedish climate, the next step would be analysing a system like the one proposed into another climate, where the solar radiation has more influence, thus, the absorption machine could work because of the inlet water (coming from the solar loop) is hot enough.

In heavy-duty disc brake systems, braking is a transient, non-linear and asymmetrical thermo-mechanical process. Surface cracking, rather than wear, is the major factor limiting the brake disc's life. The disc material (cast-iron), heat transfer boundary conditions and pad-disc frictional reactions are characteristically non-linear and asymmetrical during the friction process. Non-uniform deformation and surface cracks in brake discs result from the accumulation of excessive residual stress/strain. During braking processes, many factors affect the distributions of the residual stress and strain in discs, and hence the propagation of the surface cracks. The disc material, structure and boundary conditions are three of the crucial aspects. From the structure, a brake disc could be either solid or ventilated. In practice, solid structures always have higher anti-cracking performance than the same class of ventilated designs. However solid discs cost more material and have lower cooling efficiency. This thesis presents an improved finite element analysis for heavy-duty disc brakes and identifies design improvements. As the friction pads slide against the disc's surfaces continuously, the thermal and mechanical loads are functions of time and spatial coordinates. A 3-D asymmetrical finite element model was developed to achieve more accurate simulations of the thermo-mechanical behaviour of brake discs during braking processes. A non-linear inelastic material model for cast-iron was employed in the FE model. Permanent plastic stress and strain fields were predicted and analysed for multi-stop drag operations. The residual stress/strain fields in the discs are investigated to understand the differences between solid and ventilated discs in terms of the cracking resistance ability. Several engineering solutions are recommended for optimising the performance of the disc brake system. _ The thesis is organized in five chapters. Chapter One introduces the background concepts about the commercial disc brake system. In this part, the brake structure, material and previous researches are reviewed. The goals for this investigation are also summarised at the end of this chapter. Chapter Two introduces the general finite element modelling knowledge, procedures and the modelling boundary conditions and material models. Chapter Three presents an analysis of the disc brakes thermo-mechanical behaviour and the affecting factors. Chapter Four is focused on the residual stress field prediction and cracking behaviour analysis. The project conclusions and further research recommendations are presented in Chapter Five.

A computer assisted design model, developed for undergraduate students to teach the basic principles of humidification design, is developed and presented. Beginning with the development of the differential equations, the conversion to numerical code is presented, followed by a series of applications to mechanical draft in cooling towers, natural draft cooling towers, and packed columns. Extensions of the program to other uses is also discussed. Several calculation options are presented which allow students to understand the effect of design options at a practical level. A user's manual, flow charts, program listing, and other design information are also included. / Graduation date: 1991

Thesis (Ph. D.)--University of Queensland, 2002. / Includes bibliographical references.

The deterioration of freshly harvested horticultural crops can be minimised by precooling prior to storage. This technique of quickly cooling the produce does not only increases the shelf life, but it also reduces the size of the refrigeration system needed for storage facility. Vacuum cooling is an effective method of precooling leafy vegetables, but has a major drawback of requiring substantial initial capital investment. Thus, vacuum coolers are generally limited to large-scale or co-op operations where the initial investment can be spread across a large quantity of produce. / The conventional philosophy behind precooling design is to establish systems to cool produce as quickly as possible; this concept is more so with vacuum coolers. By changing certain design criteria of a vacuum cooler, it may be possible to reduce the capital cost of vacuum coolers by reducing the rate of vacuum. Though the time to cool the produce may be increased, the reduction in the size of the vacuum pump and the refrigeration system, and hence the capital cost of the cooler, may be beneficial to small-scale producers who can not justify the large expenses incurred when purchasing a conventional system. / Experiments were performed on a modified vacuum cooler in which the rate of vacuum could be controlled. The cooling characteristics, including the temperature distribution and mass loss, and the lettuce quality were determined for different rates of vacuum. A relationship between the speed of the vacuum and the peak product refrigeration load was developed and tested with experimental data. The results suggest that slower vacuum coolers can be successfully designed and built for small-scale operations.

No description available.

Thesis (Ph. D.)--University of Stellenbosch, 2003. / Includes bibliographical references. Also available via the Internet.