Evaluation of thermosyphon flat plate collector as heat source for a Solar Liquid Piston Pump (SLPP)

The Flat Plate Solar Collector operating in the thermosyphon mode has been suggested as a possible heat source for the Solar Liquid Piston Pump CSLPP). So far, this proposal has not been investigated As part of a cooperative project between the International Development Research Centre (IDRC), Canada and the Department of 4echanical Engineering, University of Science and Technology (UST), Kumasi to develop and evaluate the SLPP, the flat plate solar collector has been investigated as a heat source for the SLPP. • In the present work, a computer simulation model based on Huang and Hsieh’ s model for a thermosyphon solar water heating system (TSWH) and suitable experiments have been developed and used to evaluate the transient arid long-term performance of the double glazed flat plate collector operating in a thermosyphon loop, including the SLPP evaporator coil. The main components of the Thermosyphon Solar Water Heating System (TSWH) which are the flat plate collector arid storage tank were also locally designed and constructed as part of the work. As an input to the simulation, the optical and thermal performance characteristics of one each of single- and double- glazed flat plate collectors were determined using the ASKRAE 93-77 standard test method. These were found to be FRno = 0. 707 + 0. 044 and FRUL= 13.901 ± 8.241 for the single glazed collector and 0. 495 + 0. 046, 7.81 ± 4.704 for the double glazed collector respectively. Also frictional heads of the SLPP evaporator coil and the TSWH have been directly measured. The frictional losses in the evaporator coil were found to be go times higher than those in the isolated TSWH. The selected simulation model was programmed in Fortran IV and validated using experimental results obtained by Huang and Hsieh. This model which used a storage tank volume -collector area (V/A) ratio of 125 litres/ma and a time step of 15 minutes, treated the 250 litre storage tank as stratified into S sections. The model however, was unable to simulate satisfactorily the flow rates and collector water temperatures for the present experimental system which used a small V/A ratio of 11litres/rn2. In order to improve on the model, variations in the time step and number of tank sections were independently investigated for the thermosyphon system without the SLPP evaporator coil. The results indicated that the small storage tank could be treated as fully mixed and a time step of at most 6 minutes could be used in the simulation. Using the modified model, the simulated collector inlet and outlet temperature results compared favour ably with those obtained from the experimental system performance tests before the mid—day hours while those after mid-day indicated negative flowrates which were not in agreement with the experimental results. The simulated flowrate results were about 30% lower than those obtained experimentally while the simulated collector water temperatures were 15% lower than those measured. Sensitivity analysis indicated that FRUL is more sensitive to the collector performance as compared with FRno Simulation results of the long-term performance of the SLPP using the monthly average daily meteorological data of Navrongo one of the towns in Northern Ghana with very high solar energy intensity showed that the hot water temperature of 80 – 90oC required by the SLPP could be generated by using a double glazed flat: plate controller for nearly 5 hours in a day in that hot months of January, February, March and April. However, the flowrate requirement of 0.02kg/m2 couldn’t be met

Source: KNUST