Hiromu Baba

Spectral calculation of the thermal performance of a solar pond and comparison of the results with experiments

This paper deals with a method and the result of the spectroscopic calculation on heat balance of a salt-gradient solar pond under the conditions of spectral solar radiation. Furthermore, reflection of the ray incident upon the surface of the pond water, refraction of the rays within the salt-water layer and diffusion of salt in the pond water are considered. On the other hand, in order to make a clear mechanism of the heat collection and heat storage of the solar pond, we conducted an indoor experiment and a numerical analysis on a small scale model of the salt-gradient solar pond with 2 m2 surface area and 1.6 m depth, under the incident rays from a Xe-lamp solar simulator. According to the above experimental analysis, we made a simulation model of thermal performance for a solar pond and carried out the calculation from the heat balance. We found that the simulation calculations correspond well to the experimental results, so that our thermal simulation model and method might be correct. We also did the thermal calculation by changing the incident rays from a Xe-lamp into natural ray (Moon’s spectrum) and Halogen lamp. As a result, it was found that the temperature distributions in the solar pond were notably different due to spectral characteristics of the incident ray. Therefore, the spectroscopic consideration for thermal performance of any solar pond is necessary to obtain a correct solution under the spectral incidence with special wavelength distributions.

Experiment and analysis of practical-scale solar pond stabilized with salt gradient☆

Abstract A large-scale solar pond with salty water was constructed in the suburbs of Kitami in 1985. Its performance has been measured and analyzed by the authors after that. The solar pond body is circular of 44 m diameter, and the pond water is of 3 min total depth. After, 15 months, the depth of the salt gradient zone (S.G.Z.) was thinned by 10 cm in the top and by 20 cm in the bottom due to convection of the top and bottom zones. The temperature in the convective storage zone (C.S.Z.) reached 70°C, its maximum, at the beginning of September in 1985, however, it was not as high in 1986 due to contamination of the pond water. The temperature of the storage zone was reduced from November to April due to ice covering on the pond surface. The collected heat yielded largely and the collection efficiency reached more than 30% in summer, but decreased to negative values in winter. The thermal performance of the solar pond was predicted by a simulation calculation, and the calculated result compared well with the measurements.

Experimental study about erosion in salt gradient solar pond

An experimental study was executed using a small model pond to examine the erosion phenomenon on the gradient zone of a solar pond. By means of observing the flow pattern of the heat reserve zone, it was made clear that the erosion was caused by naturally occurring convection, which is based on the vertical temperature difference in the heat reserve zone. In other words, the ruling factor in erosion is the vertical temperature difference in the heat reserve zone. With regards to a real solar pond, a policy was proposed which suppresses erosion velocity by controlling the ponds operating conditions while keeping the temperature gradient of the non-convection zone (NCZ) as large as possible and making the vertical temperature difference in the heat reserve zone small. On analysis, the rational modification was effected by the Grashof number Gr, which is a dimensionless number and shows the influence of the flotage on the speed field and the temperature field. As a result, it was found that the modified dimensionless Grashof number explains the erosion velocity of the gradient zone well. Moreover, the function of the correlation between the erosion velocity and the modified Grashof number was obtained by regression calculation and could estimate the erosion condition of the gradient zone quantitatively.

Development of electrolyte solution concentration measurement system and application in solar pond

In order to measure the concentration of an electrolyte solution, especially the salt gradient in a solar pond in which the salinity is changed continually, the C.E.T. sensor and its special circuit were developed on the basis of the electroconductivity-temperature measurement method, by which the salt gradient could be measured quickly at any experimental site. Based on a thorough analysis of the conventional sensor with needle electrodes, the C.E.T. sensor effectively overcame the fault (wall-approach-effect) of the conventional sensor with a special structure formed by several cylindrical electrodes and a shield plate on the top. Here, the circuit was designed to obtain high S/N signals and a relation function with a high multiple correlation coefficient of 0.998 was obtained to adapt the wide ranges of concentration 0∼20 wt% and temperature 10∼80°C on measuring electrolyte-solution concentration. The applicability of the C.E.T. sensor was verified and a new design and measurement method was described in this research.

Analysis and experiment of the performance of a flat-plate solar collector considering the wavelength dependence

Abstract Taking into consideration the wavelength dependence of the spectral radiative characteristics of an absorbing plate and a transparent plate which are the main components of a flat-plate solar collector, the performance of the solar collector was analysed from the viewpoint of te heat balance on the absorbing and transparent plates based mainly on the radiation heat transfer under the steady state. Two sorts of hand-made solar collectors with selective and non-selective wavelength characteristics were constructed to compare the analytical result with a long-term experiment outdoors. The calculations compared well with the measurements for both the selective and the non-selective collectors, and it was thus shown that the prediction method could generally be applied to evaluate the collectors performance.

Spectral and Total Transmittances of Sodium Chloride and Potassium Chloride Water Solutions.

We describe the measurements of spectral transmittance and the calculations of the total transmittance for sodium chloride and potassium chloride water solutions. The spectral transmittance of NaCl and KCl water solutions over the infrared and nearby regions increases with increasing salinity. In the visible region, the spectral transmittance of NaCl w-s increases slightly, while that of KCl w-s decreases with increasing salinity. The total transmittance of the two salt water solutions can also be calculated by means of an integral method and a simple 5-partition method over 0∼3 m water depth. The simple method is of practical use to calculate the total transmittance for a conventional solar pond, because the rate of error between the two methods is about 10% at shallow depth and 0% at 3 m depth.