The purpose of this thesis was to gain an understanding of the thermodynamics within a recently designed boiler, called the Henry Steamer. It is a forced circulation water tube boiler which can employ a modern, accurate control system. This enables the boiler to be small and compact. However previous design and optimisation of the Henry Steamer was performed using a trial and error method. The design of the boiler exists in its present state from years of evolving through a trial and error approach. This is not preferred and as such the objective of this thesis was to define the thermodynamics of the Henry Steamer boiler. Once the thermodynamics had been explored and trends could be seen, it was important to obtain an explanation for these results. Observing trends is beneficial, however gaining an understanding and explaining the cause of these trends is of greater importance.
To determine the thermodynamics of the system, experiments were performed measuring the temperature and pressure at specific points for various parameter settings. The parameters that were varied included volumetric flow rate, firing rate of the burners and the outlet pressure of the steam. These measurements gave an understanding of the thermodynamic system within the Henry Steamer. However limitations were found with only measuring temperature and pressure. At two of the most critical points in the system the fluid existed as a two-phase flow. Temperature and pressure both remain constant for a two-phase flow regardless of the steam quality.
To rectify this problem and approximately quantify the steam quality in the two-phase flow, two additional experiments were performed. These experiments included a combustion analysis and a measurement of the fuel flow rate. The temperature of the exhaust stack was also measured for the various parameter settings. From this data the total heat absorbed by the fluid could be determined. This allowed thermodynamic models to be created giving an estimate of the final steam quality in the two-phase flow.
Two types of thermodynamic models were created; ideal models of the systems and an actual model based on the measured data. The ideal models were used to observe the theoretical effects of varying the parameters on a T-s diagram. The ideal model is also used as a comparison against the actual model. By identifying significant differences in the ideal and actual models recommendations were made to improve the Henry Steamer system.
The analysis of the data demonstrated the effect of varying the flow rate, firing rate and steam outlet pressure. Initially it was believed that steam could not exist in the coil, as the resulting heat transfer reduction could cause boiler failure. From the data analysis and literature review this statement can now be clarified. In actual fact two-phase flow with a steam quality greater than 85% has the potential to cause damage to the boiler coil. On comparing the ideal and the actual thermodynamic models the following deficiencies were found in the actual system. The role of the expansion orifice is to maintain the pressure within the coil and create a significant pressure drop at the orifice. However the measured values only indicated a small pressure drop across the orifice. It is believed that this was a result of insufficient reduction in the orifice causing a pressure drop to occur over a distance up stream. This results in a lower final steam quality than what would occur if the pressure drop at the orifice was greater.