Mudtorlep Nisoa

Development of High Voltage High Frequency Resonant Inverter Power Supply for Atmospheric Surface Glow Barrier Discharges

High-voltage high-frequency power supply using voltage-fed load resonant inverter with a series-compensated resonant inductor has been developed for efficient atmospheric surface glow barrier discharges(ASGBD). It produces a controllable frequency and sinusoidal alternating voltage output. The maximum output voltage is about 6 kV peak to peak. Resonant power converter can be tune easily to the resonant frequency of the load. Operating frequency varies according to the load and voltage level typically in the range of 10 kHz and 1 MHz range. The output voltage is controlled by using pulse width modulation technique. The power supply developed in this paper is applied successfully for ozoniser that can produce high concentrate ozone by using ASGBD for agricultural industry applications.

Development of a compact permanent magnet helicon plasma source for ion beam bioengineering

A compact helicon plasma source was developed as a millimeter-sized ion source for ion beam bioengineering. By employing a stacked arrangement of annular-shaped permanent magnets, a uniform axial magnetic flux density up to 2.8 kG was obtained. A cost effective 118 MHz RF generator was built for adjusting forward output power from 0 to 40 W. The load impedance and matching network were then analyzed. A single loop antenna and circuit matching elements were placed on a compact printed circuit board for 50 Ω impedance matching. A plasma density up to 1.1 × 10(12) cm(-3) in the 10 mm diameter tube under the magnetic flux density was achieved with 35 W applied RF power.

Chemical deterioration and discoloration of semi-dried tilapia processed by sun drying and microwave drying

ABSTRACT Drying methods can affect the chemical deterioration and discoloration of fish muscle. This study aimed to monitor the effect of microwave drying at different effective powers in comparison with sun drying on the physicochemical changes of semidried tilapia. Lipid deterioration, protein oxidation and discoloration of semidried tilapia (Oreochromis niloticus) muscle processed by sun drying and microwave drying were investigated. Results of the study revealed that the pH of microwaved tilapia was higher than that of the sun-dried tilapia (p < 0.05) and the pH increased with increasing microwave power (p < 0.05). The sun drying possessed higher degree of lipid oxidation as indicated by thiobarbituric acid-reactive substances (TBARS) with a greater level of lipolysis when compared to microwave drying (p < 0.05). Higher protein carbonyl content was in microwaved tilapia compared to sun-dried one (p < 0.05) and this content increased with increasing microwave power (p < 0.05). Sun drying resulted in a brown discoloration correlated with the highest metmyoglobin formation (p < 0.05), whereas microwave drying, particularly with high power, caused a green discoloration of semidried tilapia as revealed by a negative a* value with a significantly decreased redness index (p < 0.05). Therefore, lipid deterioration, protein oxidation and discoloration of semidried tilapia muscle were strongly influenced by drying methods.

Color and hardness of durian chips irradiated by controlled low power microwave

Durian cv. Monthong was dried by using controlled low power microwave at atmospheric pressure. Although the hardness of durian chips was higher than that obtained from microwave drying in vacuum, it was comparable to the hardness of conventional products. According to Hunter Lab color parameters, durian surfaces became lighter but their yellowness was decreased after the microwave drying. Compared between 16 and 27 W irradiations, the higher power led to the increase in lightness and yellowness. Cross-sectional micrographs revealing the porous structure confirmed that a lower hardness was obtained in the case of 16 W.

Development of compact high voltage switched mode power supply for microwave plasma sources supply for low pressure plasma

Although microwave induced plasmas are well known as high efficiency plasma sources, their uses in laboratories are limited since the microwave power systems are complicated and expensive. The output power of commercially available low-cost microwave ovens is fixed and discontinuous resulting from the high voltage doubler topology of the magnetron tube power supply. In this paper, a high voltage switched mode power supply of forward topology has been developed for continuous microwave power radiation. The forward converter can generate a no-load high voltage output maximum of 7 kV. When driving the magnetron tube, the microwave output power could be varied from 0 to 35 W while the high voltage output level was constantly regulated at -3.4 kV. A microwave induced plasma system was setup to investigate the plasma produced. A low pressure argon plasma was produced with only 2 W over a wide range of pressures.

Effect of Strong Correlation of Mg2+-doped into Cr3+ Sites of CuCrO2 on Thermoelectric Properties

This study aims to investigate the strong correlation effect of spin and charge carriers for the Mg2+-substituted into Cr3+ sites of CuCrO2 delafossite on thermoelectric properties. The CuCr0.98Mg0.02O2 sample was synthesized by a solid state reaction. The starting powder CuO, Cr2O3 and MgO were ball milled with poly vinyl alcohol solution for 24 h. The ball milled powder was pressed and sintered in air atmosphere at temperature 1050 C for 6 h. The crystal structure was characterized by XRD, TGA, XPS and the thermoelectric properties were measured at high temperature. The XRD displayed peaks of the pure phase CuCrO2 structure as hexagonal delafossite-type structure space group: Rm. The Seebeck coefficient of the samples displayed positive sign as p-type (hole) conductor. The XPS results displayed Mg2+, Cu1+, Cr3+ and Cr4+ ion states. The Mg2+ induced mixed-valance Cr3+/Cr4+ states resulting in enhanced Seebeck coefficient due to a strong correlation of the spin-entropy. The experimental results of Seebeck value were close to calculated results by the extended Heikes formula confirming of the strong correlation effect. In addition, the Mg-doped CuCrO2 resulted in increased electrical conductivity and reduced thermal conductivity with increasing temperature. These indicate that the Mg2+-substituted for Cr3+ of CuCrO2 delafossite enhance the thermoelectric properties.

Preliminary numerical study of Thailand Plasma Focus II (TPF-II) design

In this work, we use the Lee model to predict the plasma parameters, such as plasma temperature and pinch duration, in the 3.37 kJ DPF device, called “Thailand Plasma Focus-II (TPF-II).” This numerical result is then used to optimize the electrode parameters for the maximum production rate of 18F. The crossing point of pinch duration and pinch temperature is considered to obtain the appropriate electrode length, anode radius and gas gap between anode and cathode. The gas gap between both electrodes is indicated in ratio between cathode radius and anode radius, c. The results show that the best values of c, anode radius and electrode length are 1.48, 1.2 cm and 26.1 cm, respectively, in which the plasma pinch temperature, peak current and pinch duration of 0.76 keV, 207 kA and 8.725 ns can be obtained.