A novel hybrid heat-pipe solar collector/CHP system—Part II: theoretical and experimental investigations
Introduction
A hybrid heat pipe solar collector/CHP system has been developed based on the integration of a number of innovative components including a hybrid heat pipe solar collector, a turbine, a boiler, condensers and pumps [1]. The design and construction of the system are described in Part I of this paper. This paper describes the evaluation of its performance by a combination of theoretical modelling and experimental testing.
Section snippets
Analysis of the thermodynamic cycle and heat transfer
Fig. 1 shows the schematic layout of the system, and Fig. 2 indicates the thermodynamic cycle using T(temperature)-s(entropy) chart. The system uses a typical Rankine cycle powered by both solar and gas energy. High temperature hot water generated by the boiler/collector unit is used to heat and vaporize the refrigerant (either n-pentane or HFE-7100), resulting in a change of state from 1 (under-saturated liquid) to 2 (saturated vapour) or 2′ (super-heated vapour). The vapour, at a high
Experimental testing
Experimental testing was also carried out on the prototype system. The heat pipe solar collector was mounted outside the test building on the campus of the University of Nottingham, adjacent to a shed housing the boiler. The collector, in conjunction with the boiler, was operated to supply heat for the domestic micro CHP system. The exhaust flue gas from the boiler was intended to direct across the flow channels fitted to the backside of the solar collector to enhance its heat transfer, and
Comparison of theoretical and experimental results
A comparison was made between the theoretical and experimental results for the impulse-reaction turbine system, and the results are shown in Fig. 24. Both the theoretical analysis and testing were carried out at approximately the same evaporation and condensation pressures for the purpose of comparison. It was found that there were significant differences between the experimental results and the theoretical values. The major reasons for these are as follows:
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The real thermodynamic process
Energy and environmental effects—simple analysis
A simple analysis to determine the energy and environmental benefits of the proposed system has been carried out by comparing the primary energy consumption of the proposed system with that of conventional heat and electricity supply systems. The results are outlined in Table 5. The investigation assumed that the system was incorporated with four collector units and operated at 40% of the hours in the whole year on a full load basis. The conventional systems were assumed to operate on the same
Conclusions
A theoretical analysis was carried out to investigate the thermodynamic and heat transfer characteristics of the hybrid CHP system. The system was assumed to operate on a typical Rankine cycle which was powered by both solar and gas energy through utilization of a solar collector and gas boiler. It was found that the electricity efficiency increased and the heat efficiency decreased when the evaporation pressure increased, and the condensation pressure remained the same. However, the
Acknowledgements
The authors would like to acknowledge the financial support provided by the European Commission, under the Energy, Environmental and Sustainable Development Programme, for this research work.
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