A performance analysis of an OTEC system using the Uehara cycle is carried out when the mass fraction of ammonia, the temperature difference of heat source, and the performance of the heat exchanger are changed. The thermal efficiency of the Uehara cycle becomes larger when the temperature difference between the inlet and outlet of warm sea water is smaller.As the mass fraction w5 of ammonia is larger, the thermal efficiency of the Ueharacycle is larger because the extraction rate of the turbine ω is increased.The mass fraction of ammonia greatly depends on the performance of the plate type regenerator.
Titanium and its alloys, possessing high resistance against corrosion, are being specially adopted in a modern salt producing plant for an evaporator, which however could cause a galvanic attack against conventional materials within the plant due to insufficient insulation. This study investigated the electrochemical properties of titanium and Monel, an example of a less noble metal, in a salt-producing environment.Monel showed stable corrosion potential and relatively small anodic polarization resistance while the corrosion potential of titanium became gradually nobler with immersion time.The potential difference between titanium and Monel reached about 0.4 V after 5 days.The apparent cathodic polarization resistance for titanium increased slightly with immersion time, though the potential rage in which cathodic current appeared was extended.The cathodic current density on titanium held at constant potential was increased when the boiling solution under reduced pressure was exposed to air.Similarly the galvanic current between titanium and Monel responded to a smaller value of atmosphere in the brine under reduced pressure and a larger value when exposed to air.The galvanic current was controlled by the cathodic polarization resistance and increased as the area ratio of cathode against anodic increased. The recommended value of insulation resistance was calculated based on an equivalent circuit.
In this paper, an experimental study of upward jet flash evaporation is carried out to clarify the effect of the nozzle diameter on the evaporation phenomenon and also to obtain empirical equations representing the area of influence by the upward flash evaporation from one nozzle. The nozzles are made of stainless tubes with internal diameters of 52, 83 and 107 mm.The temperature of the inlet superheated water is 24, 30 and 35°C.The mean velocity of the inlet superheated water varies from 1.2 to 2.7m/s.The horizontal temperature distribution is measured by 10 thermoresistances at 25 locations along the jet axis between 0 mm and 600 mm from the nozzle exit. The results of the experiment show that the temperature of superheated water drops quickly in the case of flash evaporation with a nozzle of larger diameter.By the dimensionless arrangement, two major empirical equations are obtained to estimate the area of influence by the flash evaporation from one nozzle.Using these equations, the designers can calculate the size of the flash chamber and the optimal interval of the nozzles for the upward jet flash desalination plant.