الفهرس 
Chapter 1 introductionOnly 14 pages are availabe for public view
 |  | from | 156 |  |  |
| | | from | 156 | | |
Abstract
Improvement of the receiver performance is one of the effective methods to improve the performance of parabolic trough solar collector (PTC). In the present work, PTC with a two-gate aluminum helical screw-tape, inserted into an evacuated tube (ET) receiver, is designed and manufactured. The inserted helical screw-tape configuration helps to increase the heat transfer rate between the heat transfer fluid (HTF) / water and the evacuated tube surface by using the two-pass fluid flow and also by generating a swirl flow. This configuration may be considered as a counter-flow heat exchanger which decreases the temperature difference along the receiving element. The effects of water flow rate variation on the water outlet temperature and the performance of the collector are studied. The experiments are performed at flow rates of 10, 12, 16, 20, and 25 l/h. Also, numerical simulations using the commercial CFD software ANSYS CFX 17.1 are performed. This study aims to construct a numerical model which simulates an evacuated tube, the receiving element in a parabolic trough concentrating system, with non-uniform heat flux. A semi-empirical equation that gives the heat flux distribution around the evacuated tube solar collector is deduced. During the simulation runs, the effects of incident solar radiation variation, water flow rate and materials of helical screw on the outer surface temperature and Nusselt number are studied. During this study, the heat flux ranged from 800 W/m2 up to 1200 W/m2 with step 200 W/m2. For every heat flux, different water flow rates ranged from 10 l/h to 50 l/h with step 10 l/h, in addition to 75 and 100 l/h are tested. Based on the investigation results of a parabolic trough solar collector with two-gate helical screw tape inserts, a parametric study is performed on Banias power station, Syria. The effect of replacing the existing low pressure feed water heaters with a solar heating system is investigated at different electrical loads (68, 102, 136, and 170 MW) and different flow rates (10, 20, 25, 50, and 100 l/h). The solar field is assumed to give the same temperature after the low pressure feed water heater. A counter flow heat exchanger with an effectiveness of 0.8 was assumed to exchange the heat from the solar field to the power plant feed water. A comparison between the thermal efficiency and fuel consumption of this power station at different part loads of (68, 102, and 136 MW) with and without solar field is performed to assess the degree of enhancement. The results of the present study show that the maximum daily efficiency of the PTC is 69% at 20 l/h while the minimum daily efficiency is 59.5% at 16 l/h. The heat removal factor and the overall heat loss coefficient of the system are 0.843 and 9.64 W/m² °C, respectively. It is also found that the helical screw core enhances the solar collector performance during cloudy periods by compensating the effect of the large instantaneous variation of the incident solar radiation where it works as a thermal storage element. Also, it is found that the total thermal energy of Banias power station increases while the fuel consumption decreases at replacing the low pressure feed water heaters with a solar heating system for different power loads (68, 102, and 136 MWe). The yearly estimated saving in the amount of used fuel, and gases reduction of (CO2 and SO2) increase with increasing the power load of the Banias station when replacing the low pressure feed water heaters by the proposed solar heating system for different power loads (68, 102, and 136 MW).