DRYING OF ZUCCHINI AND CARROT SLICES: INFLUENCE OF TISSUE STRUCTURE ON MASS TRANSFER PARAMETERS

The present work aimed mainly at investigating the influence of tissue structure on dehydration characteristics of zucchini and carrot. Microwave power levels of 100, 350, 550 and 750 W used to dehydrate the samples with thicknesses of 3, 5, 7 and 9 mm. The results showed that moisture removal from the slices occurred in a short accelerating period at the process beginning followed by a falling rate period. The moisture diffusivity increased with both increasing microwave power and the samples thickness where the average values for zucchini and carrot slices changed from 1.17×10-8 to 9.42×10-8 and from 0.73×10-8 to 5.51×10-8 m2 s-1, respectively. The average activation energy for zucchini and carrot slices varied in the range of 1.22–1.68 and 1.57–1.84 W g-1, respectively and decreased with increasing samples thickness.

Co-Combustion Studies of Low-Rank Coal and Refuse-Derived Fuel: Performance and Reaction Kinetics

In connection to present energy demand and waste management crisis in Pakistan, refuse-derived fuel (RDF) is gaining importance as a potential co-fuel for existing coal fired power plants. This research focuses on the co-combustion of low-quality local coal with RDF as a mean to reduce environmental issues in terms of waste management strategy. The combustion characteristics and kinetics of coal, RDF, and their blends were experimentally investigated in a micro-thermal gravimetric analyzer at four heating rates of 10, 20, 30, and 40 °C/min to ramp the temperature from 25 to 1000 °C. The mass percentages of RDF in the coal blends were 10%, 20%, 30%, and 40%, respectively. The results show that as the RDF in blends increases, the reactivity of the blends increases, resulting in lower ignition temperatures and a shift in peak and burnout temperatures to a lower temperature zone. This indicates that there was certain interaction during the combustion process of coal and RDF. The activation energies of the samples were calculated using kinetic analysis based on Kissinger–Akahira–Sunnose (KAS) and Flynn–Wall–Ozawa (FWO), isoconversional methods. Both of the methods have produced closer results with average activation energy between 95–121 kJ/mol. With a 30% refuse-derived fuel proportion, the average activation energy of blends hit a minimum value of 95 kJ/mol by KAS method and 103 kJ/mol by FWO method.

Kinetics of walnut shells through Pyrolysis Assessed as an alternative Bio-fuel

Biomass residues have potential to be used as an alternative solid fuel for various processes, also will be responsible for the optimization of the pyrolysis reaction processes, giving insight into the pyrolysis mechanisms and aiding in engineering efforts. There are different methods for production of bio-fuel from biomass residues; however before the production of bio-fuels from biomass it is important to understand their thermal degradation and kinetics. In the present work the Kinetics studies of four different walnut shells, namely, paper (PSW), thin (TSW), medium (MSW) and hard (HSW) shelled walnuts have been studied. Thermal degradation behaviour of walnut shells is investigated using thermogravimetric analysis (TGA) under three different heating rates (30, 60 and 100 0Cmin−1 ) in an oxidizing atmosphere to understand the kinetic behavior. Kissinger–Akahira–Sunose (KAS) and Ozawa–Flynn–Wall (OFW) methods were used to estimate the kinetic parameters such as Pre-exponential factor (R) and average activation energy (Ea ) using TGA data of active zone. The average activation energy of biomass obtained from PSW, TSW, MSW and HSW using KAS method were 198.25, 184.21, 180.93, and 152.79 kJ mol−1 , respectively. Whereas by OFW method the values were found to be 204.10, 186.28, 188.39 and 153.78 kJ mol−1 respectively. Thus the present investigation may be useful for its use as a renewable energy source and potential candidate for fuel production by thermo-chemical processes.

Kinetic Analysis of Co-Firing of Corn Stalk and Paper Sludge Using Model-Fitting and Model-Free Methods

The combustion kinetics of corn stalk (CS), paper sludge (PS), and their mixture were studied by thermogravimetric analysis (TGA) using one model-fitting method (Coats–Redfern (CR)) and four model-free methods, namely, Flynn–Wall–Ozawa (FWO), Kissinger–Akahira–Sunose (KAS), Starink, and Friedman methods. TGA experiments were carried out at three different heating rates (10, 20, and 30 °C min−1) and with different weight percentages of PS in the mixture (0%, 20%, 50%, 80%, and 100%). The comprehensive combustion characteristic index decreases with an increase in the weight percentage of PS in the blends and increases with the increasing heating rate. Significant interactions occur in the co-firing of the blends containing 20% and 50% of PS. The co-firing kinetic parameters determined by the CR method show relatively high reliability due to the high correlation coefficient obtained from the linear fitting. The values of average activation energy determined by the model-fitting method are generally lower than those calculated from model-free methods. The co-firing of the blends containing 20% of PS shows the highest comprehensive combustion characteristic index and the lowest average activation energy based on the model-free methods.

Superplastic Deformation and Dynamic Recrystallization of a Novel Disc Superalloy GH4151

The superplastic deformation of a hot-extruded GH4151 billet was investigated by means of tensile tests with the strain rates of 10−4 s−1, 5 × 10−4 s−1 and 10−3 s−1 and at temperatures at 1060 °C, 1080 °C and 1100 °C. The superplastic deformation of the GH4151 alloy was reported here for the first time. The results reveal that the uniform fine-grained GH4151 alloy exhibited an excellent superplasticity and high strain rate sensitivity (exceeded 0.5) under all experimental conditions. It was found that the increase of strain rate resulted in an increased average activation energy for superplastic deformation. A maximum elongation of 760.4% was determined at a temperature of 1080 °C and strain rate of 10−3 s−1. The average activation energy under different conditions suggested that the superplastic deformation with 1 × 10−4 s−1 in this experiment is mainly deemed as the grain boundary sliding controlled by grain boundary diffusion. However, with a higher stain rate of 5 × 10−4 s−1 and 1 × 10−3 s−1, the superplastic deformation is considered to be grain boundary sliding controlled by lattice diffusion. Based on the systematically microstructural examination using optical microscope (OM), SEM, electron backscatter diffraction (EBSD) and TEM techniques, the failure and dynamic recrystallization (DRX) nucleation mechanisms were proposed. The dominant nucleation mechanism of dynamic recrystallization (DRX) is the bulging of original grain boundaries, which is the typical feature of discontinuous dynamic recrystallization (DDRX), and continuous dynamic recrystallization (CDRX) is merely an assistant mechanism of DRX. The main contributions of DRX on superplasticity elongation were derived from its grain refinement process.

Study on Mechanism of Low Temperature Co-Pyrolysis of Duckweed and Flame Coal

Co-pyrolysis characteristics of long flame coal mixed with duckweed in different proportions were studied by using TG. And the kinetic parameters was also figured out by using the method of Coats-Redfern. It was exhibited significant synergistic effect created more the light component between duckweed and coal during co-pyrolysis, The pyrolysis rate of flame coal is much smaller than biomass, and the starting pyrolysis temperature of flame coal is higher than biomass. The kinetic analysis indicated that the pyrolytic processes can be described as first order reactions model. The average activation energy of duckweed and coal was 39.14kJ/mol and 46.43kJ/mol , and with the increasing of the duckweed proportion, pyrolysis activation energy was decreased.

The Mathematical Model and Emperiences Algorithm of Activation Energy of Mixed Wastes

Through the single center of gravity mixture experiment design, the thermogravimetric combustion experiments of the cotton, easy chopsticks, food bags and its mixed components were done. Then the combustion characteristics curves of thermogravimetric and thermogravimetric differntial, and each group point average activation energy were obtained by above experiments. Using three Scheffe polynomial and the average activation energy of each waste component combustion, we get the activation energy calculation empirical formula of mixed waste combustion empirical formula. Through the three vertices of gravity method mixed waste combustion test, the experimental results of mixed waste activation energy fit well with the activation energy calculated from empirical formula. The activation energy calculated from empirical formula is correct, therefore, can be used to calculate the empirical formula derived from mixed waste activation energy. Application of this method has important guiding significance to the design of waste incinerator actually works and the waste combustion adjust.

Pyrolytic Characteristics and Kinetics of Xanthoceras Sorbifolia Oil

The pyrolytic characteristics and kinetics of Xanthoceras sorbifolia oil were investigated pyrolysis in indifferent atmosphere and at heating rates of 10, 20 and 30 °C min-1 in an inert atmosphere. The most probable mechanism function and activation energy pre-exponential factors were calculated by the Popescu, FWO and KAS methods. Three stages appeared during pyrolysis: moisture evaporation, primary devolatilization and residual decomposition. Significant differences in the average activation energy, thermal stability, final residuals and reaction rates of the X. sorbifolia oil were observed. Stage II of the X. sorbifolia oil could be described by the Avramic- Erofeev equation 20 (n=4). The average activation energy of X. sorbifolia oil was 353 kJ mol-1