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dc.contributor.advisorStorm, C.P.
dc.contributor.authorVan Niekerk, Steven Cronier
dc.date.accessioned2021-11-30T12:25:28Z
dc.date.available2021-11-30T12:25:28Z
dc.date.issued2021
dc.identifier.urihttps://orcid.org/0000-0002-0905-1993
dc.identifier.urihttp://hdl.handle.net/10394/38075
dc.descriptionPhD (Mechanic Engineering), North-West University, Potchefstroom Campusen_US
dc.description.abstractThe diffusion-absorption refrigerator was patented by Von Platen and Munters (1926). The conventionally low coefficient of performance and the high driving temperature have been the focus of most research since its conception. Previous research pertaining to diffusion-absorption component modifications, mathematical models, alternative fluid options and transient experimental simulations are reviewed to determine the drawbacks and performance improvement opportunities. In order to apply the diffusion-absorption technology to domestic applications, it is necessary to increase the coefficient of performance and decrease the required driving temperature. The design and optimisation discused in this thesis are therefore for the thermodynamic cycle rather than the diffusion-absorption components. A lower driving temperature will enable the effective application of solar thermal power since more low-grade heat can be absorbed at lower temperatures. A mathematical model was constructed to evaluate the influence of operating parameters on the diffusion-absorption system performance. This model is validated against experimental results reported by Ersöz and Najjaran. From the parametric evaluation, opportunities are identified to increase the system coefficient of performance and lower the driving temperature requirement. In summary the contribution of the endeavours and outcomes of this thesis are devising methods to mitigate the negative effects of varying ambient conditions and the optimisation of non-standard operating parameters. Methods to enable the realisation of these opportunities were identified and the integration thereof, into the diffusion-absorption system, is discussed. These methods are afforded by the residential use of the diffusion-absorption system and will enable supply to both heating and refrigerating applications. The main supporting system is the use of a radiant heat rejection with a cold storage system to improve the condenser and absorber temperatures. This enables the negative influence of interdaily and seasonal ambient temperature fluctuations to be dampened while the condenser temperature is decreased. A reduction in condenser temperature results in a lower system pressure, a lower generator temperature and a higher evaporator heat gain that result in an increased coefficient of performance. Consideration is given to the stable continuous operation of the diffusion-absorption system and the supporting systems necessary to realise this for an inherently intermittent solar supply. The use of compound parabolic collectors is proposed to absorb solar thermal energy during daytime while thermal storage systems are proposed to distribute the heat applied to the diffusionabsorption system. This enables the diffusion-absorption system to be proportionally smaller than a system operating only during the day. The strong solution concentration (xss = 0.6171) is optimised to maximise coefficient of performance with functional constraints specified by the supporting systems and the high and low temperature yield requirements for domestic appliances as well as bubble pump flow regime considerations. Refrigeration and heat pump coefficients of performance are respectively maximised at 0.703 and 1.703 for a generator bubble pump driving temperature of 72.3 °C, while heating and refrigerating yields can effectively be applied for domestic use. The diffusionabsorption driving temperature is sufficiently reduced to enable effective solar thermal powering. A feasibility evaluation was done on the residential application of a solar thermal powered diffusion-absorption system for a typical family of four. It is reported that a diffusion-absorption system with a continuous 1102 W heat input (solar thermal) to the generator bubble pump would be able to supply the essential heating and refrigerating appliances throughout the year. A highlevel return on investment (ROI = 10.84 years) calculation deemed the proposed system financially feasible and options to reduce the ROI are discussed. Novel contributions made in this thesis include the mathematical model constructed in such a way that fundamental principles and flow regime constraints are included and that the optimisation of non-standard operating conditions is enabled. The constant condenser outlet temperature operation of the diffusion-absorption system is the main contribution made in this thesis. This is enabled through the residential integration and the application of a radiant heat sink system with cold storage. The operational stability and performance of the diffusion-absorption system are increased by the optimisation of identified non-standard operating conditions and the driving temperature is decreased thereby. This enables the effective solar thermal powering of the diffusion-absorption system while the solar thermal heat store enables continuous stable 24-hour operation. A refrigerant expansion tank is thermodynamically designed to maintain the bubble pump and diffusion-absorption performance irrespective of seasonal fluctuations. Future recommendations are made for further development of the identified supporting systems. It is also recommended that detailed component mechanical design is done to build on previous research and that, provided the necessary funding, the proposed diffusion-absorption system is constructed and experimentally tested.en_US
dc.language.isoenen_US
dc.publisherNorth-West University (South Africa).en_US
dc.subjectAqua-ammoniaen_US
dc.subjectDiffusion-absorptionen_US
dc.subjectHeat pumpen_US
dc.subjectMathematical modelen_US
dc.subjectOptimisationen_US
dc.subjectRefrigerationen_US
dc.subjectResidentialen_US
dc.subjectSeasonalen_US
dc.subjectSolar thermalen_US
dc.subjectThermodynamic cycleen_US
dc.subjectThermodynamic designen_US
dc.titleDesign and optimisation of a solar thermal powered Aqua-Ammonia diffusion-absorption heat pump cycle under seasonal variance for residential useen_US
dc.typeThesisen_US
dc.description.thesistypeDoctoralen_US
dc.contributor.researchID10706003 - Storm, Christoffel Philippus (Supervisor)


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