Thesis (M.S.)--Ohio University, August, 1990. / Title from PDF t.p.

Thesis (M.S.)--Tennessee Technological University, 2009. / Title from title page screen (viewed on July 20, 2010). Bibliography: leaves 59-62.

Thesis (M.S.)--University of Wisconsin--Madison, 1966. / eContent provider-neutral record in process. Description based on print version record. Bibliography: l. 44-45.

Cost-effective liquefaction of gases at cryogenic temperatures requires a combined approach of designing efficient refrigeration cycles to generate cooling capacity and designing efficient liquefaction processes to utilize that capacity. This dissertation addresses both approaches for improvement of the liquefaction process. Magnetic refrigeration employing the magnetocaloric effect of ferromagnetic materials has been identified as potentially more efficient and cost-effective than conventional refrigeration systems. One magnetic cycle that shows promise for efficiently achieving cooling over large temperature spans is active magnetic regenerative refrigeration (AMRR). In this cycle the magnetic material serves the dual functions of work input and thermal regeneration, however the operation is complex with coupled fluid, thermal, and magnetic phenomena and a clearer understanding of the regenerative operation is required. Models to elucidate the flow characteristics of the regenerative heat exchangers of rotary AMRR and Gifford-McMahon (GM) systems using a commercially available computational fluid dynamics (CFD) software package are described. Theoretical results are presented to qualify and quantify the effect of maldistributed flow within regenerators. Experimental results of an improved regenerator for the GM system based on the CFD flow simulations are presented. Efforts to develop an improved AMRR thermal model using the commercial package are also described. The second approach for the design of efficient liquefiers addresses a drawback of the usual embodiment of the AMRR cycle, namely, the provision of cooling at a single temperature which necessitates that cryogenic designs have multiple stages providing cooling over a range of discrete temperatures for an efficient liquefaction process. Use of multiple stages leads to increased expense and complexity. A simple, inexpensive plumbing change of the flow through the regenerator of a single-stage device can significantly increase the overall liquefaction capacity compared to the usual flow configuration making additional staging unnecessary. This dissertation describes the alternative flow arrangement, known variously as “bypass flow,” “permanent flow,” or “DC flow,” which is suitable for all passive and active regenerative refrigeration cycles used as liquefiers. Theoretical results showing increased liquefaction capacity when bypass flow is employed are given for active magnetic regenerative and Gifford-McMahon systems. Experimental results are presented for a single-stage GM refrigerator modified for bypass flow which demonstrates increased liquefaction capacity. / Graduate

The wide fluctuations that occur in the aggregate electrical demand of a generating utility are punitive with respect to total system efficiency. Demand side management techniques have been applied to reduce such fluctuations including the conversion of electrical energy to thermal energy during periods of low demand for use during peak demand periods. For thermal processes requiring energy above ambient temperature it is feasible to use sensible heat due to the existence of stable storage mediums and efficient methods of heating at the high temperatures required. However where energy is required below ambient temperatures, efficiency of cooling limits the use of sensible heat, hence latent heat storage has been adopted. Conventional cold storage systems use ice banks to store cooling energy at 0°C in order to capture the high latent heat of fusion of water. The rate of discharge for such stores is limited by thermal resistance in the store and the thermal capacity of secondary coolants (such as glycol solutions). This investigated the use of hydrophilic materials to overcome the limitations of current cold-storage technology. Such materials have the capacity to absorb and retain up to 95% by mass of water (or other aqueous solutions) regardless of how the materials is subdivided. Furthermore the thermal properties of the polymers in their hydrated state resemble those of the free hydration fluid, including any phase transitions. By supporting the hydrated materials in a non-freeing, non-aqueous fluid the resultant mixture provides a medium for cold storage that can be pumped and used at the point of load, and is not limited by the thermal resistance of an encapsulating material. Three aspects concerning the utilisation of hydrophilic materials for thermal engineering applications have been investigated; (i) the physical properties of the materials in their hydrated state, (ii) methods of fluidising material in a high density store, and (iii) the heat transfer properties of hydrophilic based slurries while undergoing phase transition. Material tests have shown that currently available hydrophilic materials have thermo- physical properties that depend principally upon the hydrating fluid, regardless of particle size, and are stable over long periods (>3years). Suitable hydration fluids can lower the temperature of the phase transition thus extending their potential as storage mediums beyond those of ice-based technologies. Novel materials, of very high water content (95%) have been produced and investigated. These appear to be very suitable for thermal storage because they increase the maximum achievable energy densities of a fluidised storage system and potentially reduce cost. A number of thermal storage devices to utilise hydrophilic based slurries have been designed and evaluated. The resultant devices has been shown to provide a means of taking hydrophilic materials to, and from, a packed bed and feeding them at a controlled rate into a fluid stream. The thermal charge/discharge rates of such a device are limited only by the choice of external heat exchange systems. An experimental apparatus has been designed to investigate the effects of phase change particles on the heat transfer properties of flowing mixtures. The results have shown that (i) at temperatures above the phase transition temperature the presence of the particles causes an increase in the measured heat transfer coefficient for concentrations above 10% by volume, (ii) there is a significant interaction of particles at the heat transfer surface, and (iii) that under high flow rate conditions, with phase change occurring, heat transfer coefficients are considerably enhanced (ie 80%) above those of the support fluid when used alone or with non-active particles. Further work is recommended to extend this study to produce an engineering prototype storage system for trial evaluation.

M.Ing. / Wet compression versus dry compression in heat pumps working with pure refrigerants or nonazeotropic mixtures is investigated in this paper. In total 34 pure refrigerants as well as 31 nonazeotropic binary mixtures at different concentrations are considered. This resulted in approximately 300 different mixtures being analysed. The pure refrigerants were analysed for three different heating applications found in practice: the heating of swimming pool water, heating air for interior space heating, and the heating of water for domestic use. The investigation was conducted with cycle analyses calculating performances at different wet and dry compressor inlet values. Use was made of thermodynamic refrigerant properties calculated from a computer database. It was concluded that for both pure and non-azeotropic refrigerants analysed, all those with re-entrant saturation vapour lines produce better heating COP's when the refrigerant is superheated before entering the compressor. Only a few of the refrigerants with bell-shaped T-s curves, consistently produce higher heating COP's when wet compression is used. However, their heating capacities decreased while the compressor displacement rates increased. It was concluded that in general dry compression is more favourable than wet compression. From the few exceptions that do exist, some manage to produce very high COPh's while retaining competitive heating capacities. A by-product of this study is that, from the vast amount of refrigerant mixtures analysed, valuable knowledge was gathered regarding refrigerants not commonly used in the applications considered

M.Ing. / Wet compression versus dry compression in refrigeration cycles working with pure refrigerants or non-azeotropic mixtures is investigated in this paper. In total 34 pure refrigerants as well as 31 non-azeotropic binary mixtures are considered. This resulted in approximately 300 different mixtures being analysed. The pure refrigerants and refrigerant mixtures were analysed for one cooling application, namely that of spatial air conditioning at an evaporating temperature of 7°C, and a condensing temperature of 50°C. The investigation was conducted with cycle analyses calculating performances at different wet and dry compressor inlet values. Use was made of thermodynamic refrigerant properties calculated from a computer database. It was concluded that for both pure and non-azeotropic refrigerants analysed, all those with re-entrant saturation vapour lines produce better cooling COP's when the refrigerant is superheated before entering the compressor. Only a few of the refrigerants with bell-shaped T-s curves consistently produce higher cooling COP's when wet compression is used. However, their cooling capacities decreased while the compressor displacement rates increased. It was concluded that in general dry compression is more favourable than wet compression. From the exceptions that do exist, some manage to produce relatively high COP c 's while retaining competitive cooling capacities. A by-product of this study is that, from the vast amount of refrigerant mixtures analysed, valuable knowledge was gathered regarding refrigerants not commonly used in the applications considered.

No description available.

Thesis (M.S.)--Missouri University of Science and Technology, 2009. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed April 14, 2009) Includes bibliographical references (p. 201-203).

Thesis (M.S.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 195-198). Also available on the World Wide Web.