Feasibility analysis of a two-phase solar thermal water heater

Alkarak, Hesham Mellad (2015) Feasibility analysis of a two-phase solar thermal water heater. Masters thesis, Memorial University of Newfoundland.

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Abstract

Experiments were conducted to measure the heat transfer characteristics of nonboiling two-phase segmented flow in a solar thermal collector. The solar thermal collector was manufactured to have a serpentine flow path (residential serpentine deign) and the diameter of collector pipe was 0.0109 m. The working fluids used in the experiments were water, ethylene glycol and air. Single phase water was examined first, and the results were used as a basis for comparison for the water-air two-phase flow results. Two-phase experiments using ethylene glycol-air and single phase ethylene glycol were then conducted. The flow rates of the water-air and ethylene glycol-air phases were varied between a range of values during each experiment and the system pressure and temperatures were recorded at each combination of flow rates. The experimental data was used to calculate the number of variables, such as the heat transfer rate Q , temperature difference between the entrance and exit of the solar thermal collector [delta]T , average bulk temperature b T , the time required for raising the temperature inside the tank from 25℃ to 70℃, and the energy gained from the tank E . It has been shown that the heat transfer enhancement of two-phase flow system was better than the single phase flow system. Several experiments were conducted to study the effects of liquid void fraction αl. The effect of liquid void fraction showed that the heat transfer rate was highest in all experiments when the liquid void fraction was 0.5, while the heat transfer rate was at its lowest value when the liquid void fraction was 0.79. The effect of void fraction was found to be a controlling factor due to its impact on liquid slug length, which in turn affects the heat transfer rate. Finally, the four two-phase experiments were compared with single phase flow experiment. The result illustrated that the two-phase flow system was better than the single phase flow system.

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