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The performance of two innovative collector-loop heat exchangers used in pumped circulation solar water heaters was investigated experimentally and numerically, and TRNSYS simulation models were developed for evaluating long-term performance. The heat exchangers evaluated are a narrow gap mantle on a vertical tank and a falling film system in a standard gas hot water tank. The falling film system is based on minor changes to a mass produced tank and does not require the addition of a special purpose heat exchanger. The heat exchangers were assessed for a range of operating conditions to quantify the overall heat exchanger UAhx value and the effect of thermal stratification in the tank. Flow visualisation experiments and CFD modelling were also performed to provide detailed understanding of the operation characteristics of the heat exchangers. For each heat exchanger, the measured and computed collector loop side heat transfer coefficients were correlated by developing new Nusselt number versus Reynolds and Prandtl number functions. New heat transfer correlations were developed for both types of heat exchanger and have been implemented into full solar water heater simulation models in TRNSYS. Predictions of tank stratification conditions in each heat exchanger were in good agreement with experimental data. Compared to a standard direct circulation system, the annual performance of the mantle system and falling film system are 8% and 18% less respectively. The decrease in system performance is due to the heat exchanger penalty and reduced thermal stratification in the storage tank, however they have the added features of freeze protection and suitability for hard water areas. They are also cheaper to manufacture than convectional heat exchange systems. The annual performance of a falling film solar water heater was shown to be affected by de-stratification if an in-tank electric booster was used. However, improved performance can be achieved if an advanced switching controller is used to modulate the flow rate such that the collector return temperature is always higher than the temperature in the top of the tank.

Last leaf includes a list of publications co-authored by the author during the preparation of this thesis. / Includes bibliographical references (leaves 179-187). / xiv, 188 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / A novel and reliable method for heat exchanger network synthesis is proposed.The prime objective has been the elimination or reduction of drawbacks inherent in both evolutionary methods and mathematical programming methods while retaining the adevantages of both methods. / Thesis (Ph.D.)--Adelaide University, Dept. of Chemical Engineering, 2001

The study of thermoacoustic effects is a relatively new area, particularly in application to thermoacoustic engines. For thermoacoustic engines to be commercially viable, there are still many aspects to be investigated, not only practical aspects but also at the fundamental level of physics. Particularly lacking is research on heat exchangers in thermoacoustic engines, despite the fact that this is one of the most important components, for which a design methodology does not yet exist. The primary aim of this work was to investigate the design methodology for heat exchangers in thermoacoustic devices to improve their efficiency. In this work, second law analysis was chosen as the design methodology and was applied to a simplified model of heat exchangers in thermoacoustic engines and its validity was examined. However, for the analysis to be useful to design practical devices, further knowledge of the heat transfer mechanism in oscillatory, compressible flow, and on the development of boundary layers under such conditions are required. This is not currently available for thermoacoustic devices. The commercial software PHOENICS was used to investigate this oscillatory heat transfer problem numerically. To test the capability of the software for simulating thermoacoustic phoenomena, two dimensional standing waves and thermoacoustic couples were simulated at various operating conditions and geometries, including conditions very close to those at heat exchangers in thermoacoustic engines. The results were compared with existing analytical solutions and the results of numerical simulations from others and showed that PHOENICS is capable of simulating thermoacoustic effects. However, the accuracy of second order effects, such as heat flux induced by thermoacoustic effects, was limited by the capability of PHOENICS and the results should be interpreted with this in mind. Energy and flow fields from thermoacoustic couple simulations were investigated from plots of energy vectors, energy lines, instantaneous velocity fields, particle traces and energy dissipation.The dependence of such quantities on plate spacing, plate length and Mach numbers are presented. One important result from these test which is relevant to the design of regenerators or heat exchangers in thermoacoustic engines was that a net heat pumping effect appears only near the edges of thermoacoustic couple plates, within about a particle displacement distance from the edges. Also it was observed that the energy dissipation near the plate is proportional to the plate surface area but increases quadratically as the plate spacing is reduced. The results also indicated the presence of larger scale vortical motion outside the plates which disappeared as the plate spacing was reduced. The presence of such vortical motion did not seem to influence the heat transfer to the plates. In order to simulate heat exchangers in thermoacoustic engines without simulating the whole device, boundary conditions representative of those near the ends of the regenerator plate were considered and tested. Although in some test cases, the simulation converged to a solution with minimal energy imbalances, there was a major discontinuity in the energy flux vectors near the boundary. Further investigations (both numerical and experimental) are required to provide further insight into the boundary conditions which need to be specified for future simulations of heat exchangers in thermoacoustic engines.

Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2008. / Committee Chair: Srinivas Garimella; Committee Member: David Sanborn; Committee Member: Sheldon Jeter.

Thesis (Ph. D.)--Mechanical Engineering, Georgia Institute of Technology, 2007. / Committee Chair: King, William; Committee Member: Allen, Mark; Committee Member: Brand, Oliver; Committee Member: Glezer, Ari; Committee Member: Joshi, Yogendra.