الفهرس 
General outlook on situation of energy in EgyptOnly 14 pages are availabe for public view
 |  | from | 105 |  |  |
| | | from | 105 | | |
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.