Tanya Kirilova Gachovska

Enhanced Anthocyanin Extraction from Red Cabbage Using Pulsed Electric Field Processing

This study was conducted to evaluate the effect of pulsed electric field (PEF) treatment on anthocyanin extraction from red cabbage using water as a solvent. Mashed cabbage was placed in a batch treatment chamber and subjected to PEF (2.5 kV/cm electric field strength; 15 micros pulse width and 50 pulses, specific energy 15.63 J/g). Extracted anthocyanin concentrations (16 to 889 microg/mL) were determined using HPLC. Heat and light stabilities of the control and PEF-treated samples, having approximately the same initial concentrations, were studied. PEF treatments enhanced total anthocyanin extraction in water from red cabbage by 2.15 times with a higher proportion of nonacylated forms than the control (P < 0.05). The heat and light stabilities of the PEF-treated samples and control samples were not significantly different (P > 0.05). Practical Application: An innovative pretreatment technology, pulsed electric field processing, enhanced total anthocyanin extraction in water from red cabbage by 2.15 times. Manufacturers of natural colors can use this technology to extract anthocyanins from red cabbage efficiently.

Ultraviolet and Pulsed Electric Field Treatments Have Additive Effect on Inactivation of E. coli in Apple Juice

Apple juice inoculated with Escherichia coli ATCC 23472 was processed continuously using either ultraviolet (UV), high-voltage pulsed electric field (PEF), or a combination of the PEF and UV treatment systems. Apple juice was pumped through either of the systems at 3 flow rates (8, 14, and 20 mL/min). E. coli was reduced by 3.46 log CFU/mL when exposed in a 50 cm length of UV treatment chamber at 8 mL/min (2.94 s treatment time with a product temperature increase of 13 degrees C). E. coli inactivation of 4.87 log CFU/mL was achieved with a peak electric field strength of 60 kV/cm and 11.3 pulses (average pulse width of 3.5 mus, product temperature increased to 52 degrees C). E. coli reductions resulting from a combination treatment of UV and PEF applied sequentially were evaluated. A maximum E. coli reduction of 5.35 log CFU/mL was achieved using PEF (electrical field strength of 60 kV/cm, specific energy of 162 J/mL, and 11.3 pulses) and UV treatments (length of 50 cm, treatment time of 2.94 s, and flow rate of 8 mL/min). An additive effect was observed for the combination treatments (PEF and UV), regardless of the order of treatment (P > 0.05). E. coli reductions of 5.35 and 5.30 log CFU/mL with PEF treatment (electrical field strength of 60 kV/cm, specific energy of 162 J/mL, and 11.3 pulses) followed by UV (length of 30 cm, treatment time of 1.8 s, and flow rate of 8 mL/min) and UV treatment followed by PEF (same treatment conditions), respectively. No synergistic effect was observed.

A Real-Time Thermal Model for Monitoring of Power Semiconductor Devices

A RC thermal network with temperature dependent thermal conductivities and heat capacitances is used to calculate the junction temperature of IGBT in a device model realized in Simulink. The collector current, IC, collector-emitter voltage, VCE, and the case temperature, TC, measured during the cycling, are used as input parameters of the Simulink model. The model is compared with a constant thermal conductivity and heat capacitance model (RC network) and verified experimentally using a thermo-sensitive electrical parameter method. Including the temperature dependent parameters results in an improvement of accuracy for determining the junction temperature compare to the model with constant thermal conductivity and heat capacitance.

Modeling, Simulation, and Validation of a Power SiC BJT

This paper presents a physics-based model of a silicon carbide bipolar junction transistor and verification of its validity through experimental testing. The Fourier series solution is used to solve the ambipolar diffusion equation in the transistor collector region. The model is realized using MATLAB and Simulink. The experimental results of static operation and also the simulated and experimental results of switching waveforms are given.

Monitoring IGBT's health condition via junction temperature variations

Insulated gate bipolar transistor (IGBT) failures are a major issue in modern power electronics applications. Two most dominated failure mechanisms of IGBTs are solder fatigue and bond wire wear-out. This paper proposes a new method to online monitor an IGBTs health condition by using the instantaneous junction temperature variation between present and the first operating cycles of the IGBT with the same operating current. In this work, the instantaneous junction temperature of an IGBT is estimated from a thermal network model. The proposed method is validated by experimental results obtained from accelerated aging tests for IGBTs.

Protein denaturation in whole milk treated by pulsed electric field

Increased consumer awareness of quality and safety issues require that new methods of food processing are developed. The pulsed electric field (PEF) is an emerging non-thermal method with much potential. The objective of this study was to investigate protein denaturation in whole milk treated with PEF. The whole milk was exposed to the electric field intensity ranging from 18 to 22 kV cm-1 and the number of pulses ranging from 0 to 80 at room temperature (about 20oC). The results of this study proved that milk proteins of whole milk were partially denatured when applying PEF treatments. Electric field intensity and the number of pulses all influenced protein denaturation of whole milk. The extent of protein denaturation of whole milk was determined by their thermal behavior using differential scanning calorimetry (DSC) and by their fluorescence intensity changes using fluorescence spectroscopy (FS). Both apparent enthalpy and transition temperatures of PEF-treated whole milk were modified by PEF. The milk protein was denatured about 25% with PEF treatment at electric field intensity 22 kV cm-1 and the number of pulse 80. Fluorescence intensity decreased at longer numbers of pulses. These effects of PEF on milk proteins in whole milk may have significant implications for properties of products made from PEF-treated milk.

A real-time thermal model for monitoring of power semiconductor devices

A resistance-capacitance (RC) thermal network with temperature-dependent thermal conductivities and heat capacitances is used to calculate the junction temperature of insulated-gate bipolar-transistor modules using a device model realized in Simulink. The collector current IC, collector-emitter voltage VCE, and the case temperature TC measured during the cycling are used as input parameters of the proposed model. The proposed model is easier to implement compared with the thermosensitive electrical parameter (TSEP) method, and it is compared with an RC network with constant thermal conductivity and heat capacitance model and experimentally verified by using a TSEP method. The results of the proposed model show an improvement of the accuracy for determining the junction temperature compared with the model with constant thermal conductivity and heat capacitance.

Modeling Bipolar Power Semiconductor Devices

Abstract Download Free Sample This book presents physics-based models of bipolar power semiconductor devices and their implementation in MATLAB and Simulink. The devices are subdivided into different regions, and the operation in each region, along with the interactions at the interfaces which are analyzed using basic semiconductor physics equations that govern their behavior. The Fourier series solution is used to solve the ambipolar diffusion equation in the lightly doped drift region of the devices. In addition to the external electrical characteristics, internal physical and electrical information, such as the junction voltages and the carrier distribution in different regions of the device, can be obtained using the models. Table of Contents: Introduction to Power Semiconductor Device Modeling / Physics of Power Semiconductor Devices / Modeling of a Power Diode and IGBT / IGBT Under an Inductive Load-Switching Condition in Simulink / Parameter Extraction

Inactivation of E. Coli affected by medium conductivity in pulsed electric field

Pulsed electric field PEF is effective in inactivating microorganisms in liquids such as saline water, phosphate buffer, milk and others. PEF treatment efficacy is influenced by number of parameters. Medium conductivity has been a subject of investigation because of the contrary reports. Present study was undertaken to systematic evaluate the effect of medium conductivity on the inactivation of E. coli. The experiments were conducted on E-coli innoculted phosphate buffer (2 to 4.5 mS/cm) in a continuous-flow co-field treatment chamber with an applied electric field strength of 60 kV/cm and 50 Hz pulse frequency. In the first set of experiments, the effect of medium conductivity on E-coli inactivation was evaluated at 49 μs treatment time. In the second set of experiments, the effect of medium conductivity was evaluated at constant specific energies of 54, 77 and 135 J/mL. For the same treatment time, the microbial inactivation was higher in the buffer with higher electivity conductivity. Sub-lethal injury to E. coli. was observed in buffer PEF treatment. Even though the treatment times were different there was no significant effect of on the microbial inactivation to the different conductivity medium when the same specific energy was applied.

Modeling and simulation of a SiC BJT

The objective of this study was to develop a physics-based model of a SiC BJT and verify its validity through experimental testing. Two physical models were considered: a lumped charge model and the Fourier series solution used to solve the ambipolar diffusion equation (ADE). These models were realized using Matlab and Simulink. The simulation and experimenatl results of static and switching waveforms are given.