In order to study dropwise condensation on a metal plate, the method for controlling a tiny dew droplet deposited on a
copper plate has been developed by using scattered laser light. The method employed the proportional control
combined with shifting movement by an integrator to control the intensity of the scattered laser light constantly. Also,
the control simulation of the method has been developed to confirm the usefulness of the method and the simulated
three-dimensional shape of controlled dew droplet was obtained with the control action. A tiny thin dew droplet, of
which the diameter was of handreds micrometers and the mass was about 10-7 g, was controlled in the atmosphere at
room temperature for 60 minutes at the preset level of the intensity of scattered laser light and the three-dimensional
shape of the controlled dew droplet was shown from the interference fringes.
Tiny droplets deposited on a copper plate were controlled and measured by a developed control technique and by using a simplified optical apparatus, white light and laser light. The technique employs the proportional control combined with shifting movement by an integrator. The droplets were controlled constant for thirty minutes at the preset level of the intensity of scattered light in a control circuit. The droplets were almost a hemisphere form in initial condensation at room temperature and were few tens micrometers in diameter. The controlled mass of a dew droplet was obtained from the volume of its shape and was of the order of 10-8 g.
In this paper, the technical training for fabricating the laser diode and photodiode modules and also assembling the electronic drives for the both modules is described from a view point of student technical training to study fundamental technology of optical fiber telecommunications. First, the students assembled the both modules using small parts and adjusted the optic axis of laser light from a source with an accuracy of a few micrometers so that the laser light efficiently enters the core of an optical fiber cable. The characteristics of the modules such as the spatial intensity distribution of emitted laser light, the relationship between the input laser power and the output current of a photodiode were measured to evaluate the fabricated modules. Second, two electronic analogue circuits of the drives used for the modules were assembled to study about typical optronics devices such as laser diode and photodiode, the functions of the circuits in the drives and how they are used in combination with the optical fiber telecommunications technology. Lastly, the fabricated modules and the assembled drives were tested by transmitting the test image using an optical fiber cable.
In order to improve the initial and the response times of the Laser Dew-Point Hygrometer (LDH), the measurement simulation was developed on the basis of the loop computation of the surface temperature of a gold plate for dew depostition, the quantity of deposited dew and the intensity of scattered light from the surface of the plate at time interval of 5 sec during measurement. A more detailed relationship between the surface temperature of the plate and the cooling current, and the time constant of the integrator in the control circuit of the LDH were introduced in the simulation program as a function of atmospheric temperature. The simulation was more close to the actual measurement by the LDH. The simulation results indicated the possibility of improving both the times of teh LDH by the increase of the sensitivity of dew and that of the mass transfer coefficient of dew deposited on the plate surface. It was concluded that the initial and the response times could be improved to below 100sec and 120 sec, respectively in the dew-point range at room temperature, that are almost half of the those times of the original LDH.
A simple ionization absolute humidity gauge was developed in the present study. It consisted of a parallel plate ionization chamber with a radioactive alpha-ray source for supplying ion pairs to measure absolute humidity in air and an operational amplifier circuit for measuring the ionization current of the order of 10-12 A produced by alpha-particles. A sealed alpha-ray soure, 241Am, was used. The size of the gauge was 50 mm in diameter and 130mm in length. The distance between the two electrodes in the chamber was set at 15 mm which was enough longer distance than the maximum range of attenuated alpha-particles from the source and the wall effect on the ionization current was removed. The ionization current of the gauge was measured at various humidities in a range from 0 g/m3 to 25 g/m3 and temperatures in the range from 20°C to 40°C under the atmospheric pressure. It was shown that the ionization current is inversely proportional to the absolute humidity because a decrease in the ionization current is caused by the absolute amount of water vapor contained in the air. From the relationship between the absolute humidity and the ionization current, it was found that the absolute humidity could be measured with a sensitivity of 0.4 g/m3 that is equal to 3% in relative humidity at 20°C. The continual measurement of absolute humidity was carried out to confirm the performance of the gauge.
In order to measure the total mass per unit area of dew droplets deposited on a metal plate in the dew-point hygrometer, the shape of a dew droplet deposited on a copper plate was measured accurately by using an interference microscope that employed a phase-shift technique. The microscope was constructed by adding a piezoelectric transducer to an usual interference microscope. A simple method that uses a conventional speaker horn and an optical fiber cable was introduced to depress speckle noise. The shape of a dew droplet deposited on the copper plate surface with 0.1 μm in average roughness was measured with an accuracy of ±3nm. The mass of a dew droplet could be calculated numerically from the volume of its shape and was of the order of 10-9 g. The total mass of dew droplets deposited per unit area and the deposition velocity were obtained under a gentle wind. The total mass was the order of 10-5 g/cm2 at the beginning of deposition and the deposition velocity was ranged from 2x10-6 to 6x10-5 g/cm2.min.
A simple sensor for measuring the air density in the atmospheric pressure has been developed using a usual optical fiber cable and a radioactive alpha-ray sour. The air density wuld be measured with an accuracy of ±4x10-6g/cm3 in the range from 1.07 X 10-3g/cm3 to 1.309 X10-3 g/cm3. Coupling the two air density sensors has also developed the absolute humidity sensor.
Small dew droplets, which deposited on the mirror surface of a copper plate, were measured by using an interference microscope to evaluate the quality of dew deposited on the mirror surface of the dew-point hygrometer. A He-Ne laser of 10 mW and an optical fiber cable of 3 mm in diameter and 120 cm in length were used as a light source and an optical guide to the microscope. The fiber cable was shaken slightly with an acoustic speaker to reduce speckle noise in the interference images. A shape of dew droplet deposited on the mirror surface of the copper plate was obtained from the interference fringes, and the mass thickness of dew droplets was also obtained by numerical calculation of the volumes of each dew droplet deposited and was of the order of 10-5 g/cm2. The deposition velocities of dew on the surface under slow wind velocity were also measured.
Pyrolytic graphite (HOPG) surfaces coated with gold particles of nanometer scale size have been studied to demonstrate the possibility of obtaining additional chemical surface data by obsery ing photon emission from the STM tunnel contact.
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