Category Archives: Particle Image Velocimetry (PIV)

Implementation conditions of the solar pond project

2.1 Research on the over-wintering technology of fish in the seawater solar pond

The area of the solar pond is 6000 m2 and the gradient is in 1.8. The interior of the pond is trapezium-structured, in which there are three contrast districts. The water is 4m deep in district □, 3.5m deep in district □ and 3m deep in district □. See fig 4

During the process of designing and constructing the pond, optimizing and simulating the ecological environment suitable for fish in seawater is attached importance to. In the temperature-preserving area, trapezium-shaped structure is adopted to provide fish with the convenience and freedom to choose suitable Living space. It is because that a large quantity of poisonous gas is accumulated continuously in the high-temperature zone during the operation of the solar pond.

Bulldozers, digging machines and slurry pumps are combined to work to construct the solar pond. The underground depth of the pond is 3.5m and upground depth is 0.5m. The upper slope of the pond is protected by cement board. The treatment of leakage-prevention is not adopted at the bottom of the pond, thus the underground brine is adopted to be poured into the solar pond and the salt concentration is regulated and controlled at about 25%o. The depth of water poured in pond for the fist time should be suitable for raising and managing young aquatic products, then go on pouring in water to 3/4 of the depth of the pond and should maintain the water level. When water temperature drops to 15°C,(It happens during the first-ten-day period of November) People should pour fresh water into the pond of about 20cm to 30cm, then pay attention to the change in weather. Fresh water of 20cm to 30cm should be poured into the pond before the cold current or at the time of the cold current. The depth of the fresh water should reach 60cm to 80cm when December arrives.

The crux of the safe working of the seawater solar pond is to maintain the existence of salt gradient and to upkeep good physico-chemical, biological factors of the heat-preserving areas. Fresh water should be added timely once the solution of the surface mixes. In winter, the ice surface

should be kept clean and accumulated snow is strictly forbidden in order not to affect photosynthesis and the effects of integrating and preserving heat.

In order to study and explore the law of change in physico-chemical factors in the seawater solar pond, water temperature, salt concentration, dissolved hydrogen, PH and so on are monitored regularly. See graph

Form the winter of 2001 to the spring of 2002, the working conditions of the seawater solar pond is fine and the salt gradient is controlled well. The temperature reaches 10.0”C, which is 4.0”C higher than the lowest working temperature. It meets the demand of the over-wintering of cultivation objects in the seawater of warm water kind in the Northern Part of China.

However, the physico-chemical target of the lower convective zone of solar pond exceeds limits, especially, the dissolved bydrogen in the water drops to zero. In the year of 2002, several measures were taken to improve the content of the dissolved hydrogen and better the water quality at the bottom.1) Develop and install the underwater hydrogen-increase devices at the interior of the solar pond.2) Design water circulating plastic pipeline at the bottom of solar ponds. The problems of water changing foul and low dissolved hydrogen are solved successfully through the two above-mentioned measures and the output of the over-wintering fish achieves 250kg per mu.

Numerical Model

The set of coupled partial differential equations and the boundary conditions described in the previous section are converted to algebraic equations by means of finite-volume techniques using rectangular meshes on a staggered arrangement. Diffusive terms at the boundaries of the control volumes are evaluated by means of second-order central differences, while the convective terms are approximated by means of the high-order SMART scheme [13], with a theoretical order of accuracy between 1 and 3.

The domain where the computations are performed and a schematic of the mesh adopted is shown in Fig. 1b. The mesh is represented by the parameter n. According to Fig.1b, 1.5n*n* n control volumes are used (for example, when the problem is solved on 30 * 20 * 20 control volumes, it means n = 20). The numerical solutions have been calculated adopting a global /г-refinement criterion. That is, all the numerical parameters (numerical scheme, numerical boundary conditions, etc.) are fixed, and the mesh is refined to yield a set of numerical solutions. This set of numerical solutions have been post-processed by means of a tool based on the Richardson extrapolation theory and on the concept of the Grid Convergence Index (GCI) [4][5]. When the numerical solutions are free of programming errors, convergence errors and round-off errors, the computational error is only due to the discretization. The tool processes a set of three consecutive solutions in the /і-refinement. The main output is an estimate of the uncertainty of the numerical solutions due to discretization, the. Only solutions with order of accuracy between 1 and 3 GCI less than 1percent and Richardson nodes higher than 60 percent are considered. The mesh is intensified near the two plates using a tanh-like function with a concentration factor of 2 [10], in order to properly solve the boundary layer. This aspect is indicated in the Fig. 1b with solid triangles at the boundaries intensified.

The resulting algebraic equation system was solved using SIMPLE algorithm [2], and the iterative convergence procedure was truncated when relative increments of the computed Nusselt number in the last 50 iterations dropped below 0.0001%.

Approximate cost of the hybrid solar system

Investment

The following costs have to be considered, [11] : Ci=2673 Euros for air solar collectors, C2=1203 Euros for water storage tank, C3=1093 Euros for Trombe wall, C4=890 Euros for solar still, C5=6500 Euros PV system. The total cost of the equipment is C’=12539 Euros.

Installing cost is roughly C’’=C’/4=3100 Euros.

Total cost (equipment + installing) is Csun=15639 Euros.

Investment payback

Taking into account the electricity price in Romania, cl=0.06Euro/kWh, in 2003, the total useful energy supplied by the hybrid systems would cost yearly CL=694.7 Euros/year. If we do not take into account the rate of interest, the investment Csun would be paid back in a time T=Csun/cl=24.9 years. The life time of the installations is roughly t’’=40 years, that means the solar energy user would benefit from free energy during т1=15 years.

If the state supported VAT, the costs of the suggested solar system for a small or medium sized stock raising farm would be only C’sun=12668 Euros. The investment payback time would be reduced to only t2=20 years. In this case the solar energy user will benefit from free energy during 20 years.

Conclusions

The suggested solar system satisfies the requirements of the possible users by:

• Indoor air heating at the required thermal level.

• Water heating

• Water distillation

• Air ventilation

• Space illumination

Small and medium sized stock raising farms could be organised by modules. Each module would have lairs of one hundred young animals each. A part of the modules would be experimental and another part would be reference modules. The modules organised like reference modules would be energy supplied by means of conventional tools. The experimental modules would be energy supplied both by conventional and RES tools. The monitoring of energy consumption and expenses based on RES and conventional energy would allow the users to choose the most convenient way for their specific activity. The new RES legislation initiated by the Government could facilitate the implementation of RES (e. g. by exemption from taxes).