الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
The thermal performance of a heat-pipe evacuated-tube solar collector is investigated in the present study under various operating conditions and arrangements. Hot water is targeted at a relatively high inlet temperature of 60-90 ℃ that is commonly utilized in solar driven systems such as solar cooling and desalination systems. A mathematical model for the system was developed and validated experimentally under weather conditions of Alexandria, Egypt. The theoretical model of the collector is enhanced by considering the effect of the thermal mass of the system, hence the maximum relative error between the experimental and theoretical results was reduced from 12.5% to 4.4%. The effects of the inlet water and ambient temperatures, number of evacuated-tubes, water mass flow rate, and solar irradiance on both the exit water temperature and the collector efficiency were all considered in extensive investigations. The results showed that the collector performance was strongly affected by all the above parameters but with different manners. At certain values of the water mass flow rate and solar irradiance, the exit temperature increases with the increase in the number of series evacuated-tubes reaching a specified number above which the increase in the exit water temperature will be insignificant. In addition, a new generalized expression for predicting the collector efficiency was derived based on the mathematical model results to be used in calculating the exit water temperature at different operating and climatic conditions and different number of evacuated tubes. The deduced expression has been also validated experimentally for different series and parallel arrangements. charts for the optimum number of evacuated-tubes are produced at different climatic and operating conditions. Effects of the solar irradiance, mass flow rate and temperature rise on the minimum number of tubes and the corresponding arrangement are investigated and discussed. Finally, the optimization tactic used in the present study reveals that considerable energy savings and reduced initial costs for the solar-driven applications can be achieved.