Forced convection heat transfer and pressure drop for a horizontal cylinder with vertically attached imperforate and perforated circular fins

In this study, the effect of holes placed on perforated finned heat exchangers on convective heat transfer experimentally investigated. Six millimeter-diameter holes were opened on each circular fin on a heating tube in order to increase convective heat transfer. These holes were placed on the circular fins in such a way as to follow each other at the same chosen angle. The holes created turbulence in a region near the heating tube surface on the bottom of the fin. Some experiments were then performed to analyze the effect of this turbulence on heat transfer and pressure drop. These experiments were carried out at six different angular locations in order to determine the best angular location. In addition, a perforated finned heater was compared with an imperforate finned heater to observe the differences. In the cases of the Re above the critical value, Nusselt numbers for the perforated finned positions are 12% higher than the Nusselt numbers for the imperforate state. Moreover, a correlation has been obtained between the Re and Nu in the Re number above the critical value and the Re below the critical value. Meanwhile, correlations regarding pressure drops in the flow areas have been obtained.     

Liquefaction/Solubilization of Low-Rank Turkish Coals by White-Rot Fungus (Phanerochaete chrysosporium)

Microbial coal liquefaction/solubilization of three low-rank Turkish coals (Bursa-Kestelek, Kütahya-Seyitömer and Mu?la-Yata?an lignite) was attempted by using a white-rot fungus (Phanerochaete chrysosporium DSM No. 6909); chemical compositions of the products were investigated. The lignite samples were oxidized by nitric acid under moderate conditions and then oxidized samples were placed on the agar medium of Phanerochaete chrysosporium. FTIR spectra of raw lignites, oxidized lignites and liquid products were recorded, and the acetone-soluble fractions of these samples were identified by GC-MS technique. Results show that the fungus affects the nitro and carboxyl/carbonyl groups in oxidized lignite sample, the liquid products obtained by microbial effects are the mixture of water-soluble compounds, and show limited organic solubility.     

Thermal analysis of borogypsum and its effects on the physical properties of Portland cement

Borogypsum, which consists mainly of gypsum crystals, B₂O₃ and some impurities, is formed during the production of boric acid from colemanite, which is an important borate ore. In this study, the effect of borogypsum and calcined borogypsum on the physical properties of ordinary Portland cement (OPC) has been investigated. The calcination temperature and transformations in the structures of borogypsum and natural gypsum were determined by differential thermal analysis (DTA), thermogravimetric analysis (TGA) and X-ray diffraction (XRD) techniques. Thermal experiments were carried out between ambient temperature and 500 °C in an air atmosphere at a heating rate of 10 °C min⁻¹. After calculation of enthalpy and determination of conversion temperatures, borogypsum (5% and 7%), hemihydrate borogypsum (5%) and natural gypsum (5%) were added separately to Portland cement clinker and cements were ground in the laboratory. The final products were tested for chemical analysis, compressive strength, setting time, Le Chatelier expansion and fineness properties according to the European Standard (EN 196). The results show that increasing the borogypsum level in Portland cement from 5% to 7% caused an increase in setting time and a decrease in soundness expansion and compressive strength. The cement prepared with borogypsum (5%) was found to have similar strength properties to those obtained with natural gypsum, whereas a mixture containing 5% of hemihydrate borogypsum was found to develop 25% higher compressive strength than the OPC control mixtures at 28 days. For this reason, utilization of calcined borogypsum in cement applications is expected to give better results than untreated borogypsum. It is concluded that hemihydrate borogypsum could be used as a retarder for Portland cement as an industrial side. This would play an important role in reducing environmental pollution.     

Investigation of H2S gas sensing performance of Ni:WO3 films at room temperature: nickel precursor effect

Journal of Materials Science: Materials in Electronics - In this work, pure and nickel-doped WO3 films were produced by chemical bath deposition on In-doped SnO2 (ITO) substrates without annealing...     

Pyrolysis Kinetics of Asphaltite by Thermal Analysis

Pyrolysis properties and kinetic analysis of asphaltite were investigated by means of thermogravimetry (TG) and derivative thermogravimetry (DTG). Thermal experiments were carried out from ambient temperatures to 1000°C in nitrogen atmosphere at different heating rates. TG/DTG curves showed that the decomposition proceeds through two steps with DTG peaks corresponding to the weight loss obtained. Kinetic analysis of the asphaltite decomposition steps was carried out under non-isothermal conditions. Coats-Redfern method was used to analyze the TG data for determination of kinetic parameters. Activation energies (E_a) and pre-exponential factors (k_o) were calculated for different heating rates and compared.     

Approximating signals by fast impulse sampling

An impulse sampler multiplies an input signalu by a periodic delta impulse train of period . If is small, then the output signal of the sampler (or filtered versions thereof) can be used as an approximation ofu. Ifu belongs to the Sobolev spaceH ^s with s>1/2, then the output is inH ^–s. Our main result is that as the sampling period becomes small, the impulse sampler approximates the identity in the operator norm fromH ^s toH ^–s (we also give the rate of convergence). We obtain related approximation results in theL ² norm, which refer to the situation when filters are connected before and after the impulse sampler (as usually happens in engineering applications). We generalize our results to distributions on ⁿ and indicate applications to control theory for distributed parameter systems.     

Pyrolysis Kinetics of Asphaltite by Thermal Analysis

Abstract

Pyrolysis properties and kinetic analysis of asphaltite were investigated by means of thermogravimetry (TG) and derivative thermogravimetry (DTG). Thermal experiments were carried out from ambient temperatures to 1000°C in nitrogen atmosphere at different heating rates. TG/DTG curves showed that the decomposition proceeds through two steps with DTG peaks corresponding to the weight loss obtained. Kinetic analysis of the asphaltite decomposition steps was carried out under non-isothermal conditions. Coats-Redfern method was used to analyze the TG data for determination of kinetic parameters. Activation energies (E _a ) and pre-exponential factors (k _o ) were calculated for different heating rates and compared.