PhD Theses

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Browsing PhD Theses by Author "Chami, Francis Augustine"

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    Investigation of performance characteristics of multi-phase thermal pump
    (University of Dar es Salaam, 2004) Chami, Francis Augustine
    A multi-phase thermal pump has been investigated. Basically the pump is a metal tube, which on one end has separate water and steam inlets and a water outlet on the other end. Non-return valves are employed on all inlets and outlet. Experimental methods coupled with mathematical modeling were done. The results indicated that the discharge head of the pump increased linearly with steam pressure. The temperature of the inlet water influenced significantly the volumetric discharge rate. The discharge rate increased with steam pressure to a maxima and decreased thereafter, for a given inlet water temperature. Except for very low steam pressures, the discharge volume per stroke of the pump was found to be higher than the volume of the smaller cylinder, an observation that did not support the sudden expansion theory of operation of the pump with two cylinders. Further investigations of the pump to establish operating characteristics for steam gauge pressure between 0.05 and 0.5 bar indicated the existence of substantial suction head and a maximum developed head was measured. Entry and exit losses accounts were made of the developed head. The process of pumping was found to be a sensitive one and highly dependent on heat transfer from the steam. Both heat loss through the pump walls and to the water being pumped contributed in creating conditions for condensation and this in turn initiated the filling of the pump with water ready for another pumping stroke. Experiments were conducted to find the influence of operating parameters on the performance of the pump, with the focus on the optimum parameters for a given condition. Observation of the results revealed that pump diameter did not have significant influence on the flow rate. It was also observed that each pump has at least one common cycle time where different discharge heads produced the same flow rate. Modeling of the pump has revealed the existence of dimensionless parameters that influence the operation of the pump. These are Reynold’s, Prandtl’s dimensionless numbers and length to diameter ratio of the pump. Conditions necessary for the reversal of the pump caused by the involved forces have been established. A novel idea has been worked out on the application of the multi-phase thermal pump in refrigeration system. This idea has introduced a new refrigeration system to the refrigeration industry, which involved a principle different from that of conventional refrigeration systems. A coefficient of performance (COP) of 8.3 and the overall heat energy balance of the system has been calculated and a working model has been produced. Recommendations are made for more efforts to be directed in the application of the pump in the refrigeration industry using different environmentally friendly refrigerants and improving the system.