Regarding the main hull, the concept of submerged spar buoy with tension legs is adopted. The structure above the sea surface should be minimized. Therefore, the side project areas and the water plane areas which are affected from strong winds and high waves respectively are small enough to maintain a stability of the machine even in case of big typhoon.
The heat exchanger such as the vaporizer and the condenser for the OTEC engine should be incorporated inside the upper and upwelling pipe and the hydrodynamic loss of the sea water flow should be minimum. New configuration and arrangement should be needed for the OTEC engine.
In Table 2, we propose the particulars of two different size DOW upwelling machines. One is an experiment scale, having 4m diameter impeller for introduction and confirmation of the effects, and the other is an ultimate scale having 50m diameter impeller which can be manufactured only in the biggest shipbuilding facility for the super large tanker (VLCC).
6. FEASIBILITY STUDY
In this chapter, the effects such as increase of the primary production and fish production etc. by using the ultimate size DOW upwelling machine are studied in the case of setting up the machine in "the sea of desert".
In "the sea of desert", we assume that the nutrient-salt density of DOW is 20 times of the surface water. The surface/DOW mixing rate of the machine is 2/1.
Then, the nutrient-salt density of the mixing water is;
(1*2 + 20*1)/3 = 7.33
about 7 times of surface water.
The primary production of "the sea of desert" is assumed about 30 (gC/m2/year)4). All mixed water is assumed to be diffused within the layer of sunlight. The primary production per m2 and the nutrient-salt density is assumed to be proportional.
Then, the increase of the primary production per m2 is;
30*(7 - 1) = 180 (gC/m2/year)
The thickness of the layer of sunlight is assumed 100 m, and all the water within the layer is assumed to be replaced by the mixed water. And, the discharge capacity of the mixed water per year is;
90 M (m3/day)*365 = 32,850 M (m3/year).
Then, the area of fishing ground is;
32,850 M/100 = 330 M (m2/year).
This area is the same as about 20 km diameter circle.
So that, the increase of the primary production by the machine is;
180*330M*10-6 = 60 K (ton C/year)
This means the carbon of 60,000 (ton C /year) is fixed by photosynthesis. From this result we expect that the machine is also very effective for the decrease CO2 in the air through the absorption of CO2 into the ocean. But we have to consider the DOW has dissolved CO2 which has been accumulate by the bacteria in course of decompose the organic matter into inorganic.3) This issue should be clarified quantitatively to estimate global warming by increase of CO2 anyway.
Regarding the production of fishes, the reference should be made to J. Ryther's report.5) Generally, the production efficiency of fishes in the upwelling sea area is very much higher than the other sea area such as coastal sea and open sea, because the size of phytoplankton is very big and the food chain steps is very short. From the Table 3,5) we can know that the ratio between fish production and primary production in the upwelling sea area is;
(120*106) / (0.1*109) = 1.2
