الفهرس | Only 14 pages are availabe for public view |
Abstract This investigation introduced the construction, operation, and the test results of a solar concentrator with dual axis sun tracking utilizing for milk pasteurization. Modified satellite dish was employed as a solar concentrator. The process of milk pasteurization partitioned into two separated loops; one of both is for water heating by solar energy, the other one is for milk heating by hot water, the two loops become in contact by a heat exchanger. The sun tracking system was simple and low cost electromechanical setup. The control is more required with using the solar energy whereas the solar energy varies significantly with the time of the day, day of the year, and weather conditions. This temporal mismatch between the solar energy and the energy demand for pasteurization leads to uniformity of energy flow through the system thus may leads to corruption of milk. Therefore, it is necessary to have control strategy of the system to maximize the utility of the solar energy, and to ensure that the milk has pasteurized efficiently, and allows to quickly respond to different operating conditions. So, the work includes representation of control scheme. Powering the system is a hybrid scenario wherein the solar energy is used standalone as power source when it is sufficient to the demand load, whilst the electric grid energy is used as auxiliary source when the solar energy is insufficient. If the solar energy is insufficient, the remaining energy for pasteurization is supplied automatically from an auxiliary electric heater to reduce the time required for pasteurization. The solar power is based on using of the two forms of solar energy; photovoltaic and thermal. The solar thermal energy is transferred to the milk through the heat exchanger using pump. While the solar photovoltaic cells are used to power the pump, cooler, electronics, and control circuits. Also, the work is concerned to analysis of thermodynamic behavior of the system based on the basics of thermodynamics and heat transfer.Thermodynamics is useful to describe how the system responds to changes in the inputs, as well as to describe the interactions between the system and its subsystems and the surrounding, leading to predict the performance of system. And, evaluation of the system was done in a view of the thermal efficiency, the efficiency of pasteurization, and the financial cost. The conclusions of this investigation are: 1. the milk reached to the pasteurization temperature 73 ˚C in average time was depend on the value of solar radiation, the milk took about 92, 110, and 123 seconds at radiation values 1000 to 1100, 900 to 1000, and 800 to 900 W/m2, at respectively; 2. the productivity was varied depended on the value of solar radiation, the productivity was about 9, 8, and 7.5 L/h at radiation 1000 to 1100, 900 to 1000, and 800 to 900 W/m2, at respectively; 3. the percentage of solar energy usage was about 20 % at radiation value less than 400 W/m2, while it was about 60 % at radiation value less than 800 W/m2, and 100 % of solar energy at radiation value larger than 800 W/m2; 4. the difference between the maximum and minimum heat energy ∆E in the heat exchanger was about 265 kJ/kg at clear sky, while ∆E was about 150 kJ/kg when the sky was non-clear; 5. using the sun tracking device increased the cumulative daily heat gain by approximately 59 %; 6. the thermal efficiency decreased with the increasing of solar radiation. The average overall thermal efficiency was about 41 %; 7. the cost by solar energy was about 0.01 LE/L, while it was about 0.04 LE/L by the conventional energy for cost of energy; 8. the solar technique may be saving about 75 % of the costs of energy;9. the samples of the pasteurized milk were negative for ALP test, thus it means that the milk has been properly pasteurized by the system. It can be recommended that: 1- Improving the performance of the components of the system; the quality of reflection, the absorber, the accuracy of tracking, insulation, and the heat exchanger. 2- Use of such designed system to pasteurize water and juices. |