Mohsen Motahari

ABSTRACT Contact heat transfer between curvilinear contacts has gained much attention due to its highly complex nature. There is still no thorough study for satisfactory calculation of curvilinear contact heat transfer using theoretical or physics‐based models. On the other hand, using the existing data, machine learning provides a powerful technique, capable of forecasting the thermal contact conductance (TCC) for different materials. In the present research, heat transfer between contacting curvilinear surfaces is calculated using the inverse solution, then the efficiency of adaptive neurofuzzy inference system (ANFIS) and radial basis function (RBF) neural network in estimating the rate of heat transfer through these surfaces based on the input–output data acquired by the inverse method and based on experimental study is investigated. The basis of this analysis is based on the temperatures measured from sensors located in specific areas of two surfaces in contact in a laboratory setup. Using the measured temperatures and the inverse method, the transient temperature function between curvilinear contacts is calculated. For the ANFIS, different training functions are used to train the network, and the best function is selected. The results show that the ANFIS using the dsigmf input function and linear output function can predict the TCC through curvilinear contacts with the root mean square error of 0.007. However, the error of RBF neural networks is 0.0059 less than the error of the ANFIS model for thermal contact prediction. Compared with other published works, the proposed networks perform better than group method of data handling–type neural networks. The ANFIS and RBF‐type networks perform well in estimating the rate of contact heat transfer between curvilinear contacts. However, the RBF‐type neural networks perform best. This investigation presents efficient and accurate strategies for estimating TCC applicable in aerospace, automotive, and manufacturing industries.

Introduction Nowadays, spraying method is used in plant nutrition to optimize the use of chemical fertilizers and reduce environmental hazards. With the foliar solution, the elements are quickly transferred to the plant and delivered to the branch, leaf, or fruit. Surveys show that increase performance per unit area is one of the most important things that has attracted the attention of many researchers. The first requirement for high performance is high dry matter production per unit area. Some experiments have shown that increasing the amount of carbon dioxide in the air can increase yield, accelerate flowering and accumulate carbohydrates in plants. One of the solutions to increase carbon dioxide concentrations in plants is to use compounds such as ethanol and methanol. Therefore feeding plants with alcohols such as ethanol and methanol as carbon sources is one of the appropriate methods to increase their quantitative and qualitative properties. Materials and Methods Due to the importance of peppermint (Mentha piperita L.) in the production of valuable secondary metabolites, and also the effect of ethanol and methanol on some morphological and physiological parameters of this plant, a pot experiment was conducted in factorial based on completely randomized design with three replications in the research greenhouse of Shahed University in 2018. Foliar treatments included different concentrations of 0, 15, 30 and 45% ethanol, methanol and combine them that was done in three stages. The studied traits were plant height, number of leaves per plant, biological yield, chlorophyll a, chlorophyll b, total chlorophyll, carotenoid, flavonoid, essential oil percentage, essential oil yield and protein percentage. Data analysis was performed using SAS statistical software (version 9.2) and mean treatments were compared by LSD test. Also charts were drawn by excel software. Results and Discussion The results showed that the simple effects of ethanol and methanol on plant height, biological yield, flavonoid content, essential oil percentage, essential oil yield and protein percentage were significant but their interactions were not significant. Ethanol 45% had the most effect on percentage and yield of essential oil and protein percentage. But the use of 15% ethanol treatment had the highest value in other traits (plant height, total phenol and flavonoids), which was at a statistical level with 45% methanol treatment. Also interaction between ethanol and methanol on leaf number per plant, chlorophyll a, chlorophyll b, total chlorophyll and carotenoid was significant at 1% probability level. The highest number of leaves per plant and chlorophyll a (29.55 µg/g fresh leaf weight) was observed in the combination of 15% ethanol and 15% methanol, while the highest amount of chlorophyll b (20.86 µg/g fresh leaf weight) and total chlorophyll (49.85 µg/g fresh leaf weight) was related to the combined application of 15% ethanol and 45% methanol. Conclusion Foliar spraying is one of the methods of fertilization and supply of nutrients to plants that due to high absorption rate nutrients can be made available to plants in the shortest time. The results of this study showed that all the studied traits were significantly affected by one or more of the ethanol and methanol treatments. Therefore, the foliar application of ethanol and methanol as carbon sources has an important role in improving the qualitative and quantitative parameters of peppermint.

In this research, the efficiency of multilayer perceptron (MLP) and radial basis function (RBF) neural networks in estimating the remaining useful life (RUL) of angular contact ball bearing based on acoustic emission signals are investigated. To capture the bearing acoustic emission signals, an appropriate laboratory setup is used. Acoustic emission signal processing is carried out in the time and frequency domain and 102 different features are extracted. Prognostic feature selection have been used to reduce the dimension of the extracted features. Applications of the different training algorithms in MLP neural network are compared for bearing RUL prediction. The results indicate that acoustic emission is a good method for bearing RUL prediction. Mobility, Square-mean-root, and Count are the best time domain features based on the used feature selection method. Also, the Frequency center, Signal power, and F60 are the best frequency domain features. It was shown that between different backpropagation training algorithms for MLP neural net, Levenberg Marquardt has the lowest SSE error of 7.86 for the prediction of bearing remaining useful life based on frequency domain features. Moreover, comparison of RBF and MLP neural networks shows that RBF neural networks presents the best performance with SSE error of 2.85.

In this paper, different geometries and arrangements of vortex generators for improving the heat transfer performance of heat sinks have been studied. The effect of different parameters including the inclination angle of vortex generators and the distance between them are also investigated on heat transfer performance of heat sinks. Numerical computations are done based on the finite volume method and they have been validated with available experimental data which were in accurate compatible with each other with RMSE error of less than 6%. According to the obtained outcomes, between rectangular, triangular and symmetrical NACA0012 vortex generator, heat sink with NACA0012 vortex generator has the best thermal performance. On the other hand, heat sink with rectangular vortex generator has the highest fluid flow pressure drop. So, using rectangular vortex generator with heat sink needs a fan with the highest power. Also, the results show that thermal resistance of the heat sink decreases with Reynolds number increase. Also, heat sink pressure drop increases with Re number enhancement. Meanwhile, the pressure drop rate is more sensible in higher Reynolds numbers.

Hydrothermal gasification is a thermochemical; process that operates at a temperature range of 800-1000 C, in order to convert solid and liquid feedstocks into chemicals or clean gaseous fuel known as syngas. In this research, an Aspen plus model of heavy oil was developed to investigate the effect of operating conditions and a CO2 sorbent (CaO) on gas composition and gasification efficiencies. An increase in CaO/F ratio from 0.5 to 1.0 greatly reduced amount of produced CO2 and increased H2 due to positive performance of carbonation reaction in conversion of CO2 to CaCO3. Carbon Conversion Efficiency (CCE) initially increased by raising CaO/F, and then it is relatively decreased by a further increase in CaO/F.

Pyrolysis is a thermal process where organic materials such as biomass and oil are decomposed and lighter materials such as gas, vapor, liquid products, and char are produced. The aim of this study was to investigate the pyrolysis behavior of sewage sludge in different operating conditions. Using a fixed bed, the influence of some important parameters such as pyrolysis temperature, heating rate, particle size, and N2 flow rate on product yields was studied. Results showed that with increase in temperature from 400 to 700°C, the char yield decreased from 30.1 to 7.50%, while the gas yield increased from 35.8 to 52.4%. The gas yield also increased from 46.9 to 49.1% as the heating rate increased from 20 to 60°C/s, while the oil yield increased from 45.2 to 46.8% as heating rate increased to 40°C/s and then the increase leveled off.

In this paper, a complete literature review for thermal contact between fixed and periodic contacting surfaces and also thermal contact between exhaust valve and its seat in internal combustion engines is presented. Furthermore, the effects of some parameters such as contact pressure, contact frequency, the contacting surfaces topography and roughness, curvature radius of surfaces, loading–unloading cycles, gas gap conductance and properties, interface interstitial material properties, surfaces coatings and surfaces temperature on thermal contact conductance are investigated according to the papers presented in this field. The reviewed papers and studies included theoretical/ analytical/experimental and numerical studies on thermal contact conductance. In studying the thermal contact between exhaust valve and its seat, most of the experimental studies include two axial rods as the exhaust valve, and seat and the one ends of both rods are considered at constant and different temperatures. In the experimental methods, the temperatures of multi-points on rods are measured in different conditions, and thermal contact conductance is estimated using them.

In this study, a CFD model of entrained-flow gasification of petroleum residue proposed to simulate the effects of some critical parameters such as equivalence ratio and system pressure on carbon conversion efficiency, tar yield, hydrogen concentration, and higher heating value of the syngas. It is a 2D model and steady state, which can be used as a general model to evaluate the performance parameters of other fuels (coal, biomass, and municipal solid wastes) during gasification process. Results showed the equivalence ratio has a negative effect on the higher heating value of the syngas and a positive impact on the gasification efficiency. It also found that the carbon conversion efficiency strongly depends on the equivalence ratio and gasification temperature. The model validated against experimental observations and found to be in good agreement.

Gasification is a clean technology to convert fuels to high-quality syngas in presence of a gasifying agent. In this study, an Aspen Plus model of heavy oil gasification was developed to produce the hydrogen rich syngas. Effect of some parameters such as gasification temperature and steam/fuel ratio on the hydrogen yield and was investigated. Results showed that the temperature plays a major role in the process; higher temperatures produce the higher hydrogen content. It was also found that the operation under high steam/fuel ratio can cause a significant increase in the hydrogen yield. The modeling results were compared with the experimental data available in the literature and found to be in good agreement.

Pyrolysis, so-called devolatilization, is one of the first steps of all thermochemical processes occurring in an inert atmosphere. The authors discuss the main kinetic features of heavy oil pyrolysis, on the basis of the data derived m from a TGA analysis and by using a kinetic model. The samples were heated over a range of temperature from 400 K to 430°C at various heating rates between 10 and 80°C/min. Experimental results showed that the effect of time is considerable in the case of tar conversion, compared to char and gases.

Kinetic study on pyrolysis of petroleum residue was carried out by an accurate Arrhenius type equation at heating rate of 0.5–30.0°C/min under nonisothermal conditions. The influence of some critical parameters including temperature, heating rate and activation energy on mass conversion was evaluated. The apparent activation energies for during the pyrolysis process were in the range of 198–361 kJ/mol at various mass conversions of 5–94%. The reaction temperature was introduced as the most important parameter for the improvement of mass conversion, compared to that of other parameters. The pyrolysis of petroleum residue was occurred in a broad temperature range, from 150–650°C, yielding 33 wt% unpyrolyzed residue. It also was found that an increase in heating rate has a minor impact in the process. Model predictions were compared with experimental data, which showed fully good agreement.

A heavy oil gasification model that can predict the hydrogen yield has been developed for a high pressure circulating fluidized bed. The model is based on the Aspen Plus package, which is a professional software for simulation of thermal process. To illustrate the effects of the steam/fuel ratio and temperature, several conditions have been examined. The results show that the gasification temperature plays a major role in the process. As gasification temperature increases from 600 to 800°C, the production of hydrogen increases dramatically. The influence of steam/fuel ratio (0.50–0.80) is also considerable, but shows a constant rate at the higher steam/fuel. Simulation results were validated against experimental data available in the literature.

Combustion is a highly efficient technology for energy conversion of biomass materials, municipal wastes, and fossil fuels. In this study, combustion tests of two petroleum residues (P1, P2) in a batch type fixed-bed reactor were presented for different operating conditions. The effects of air flow rate (50–70 L/min) on the combustion parameters (gas temperature and carbon conversion) were performed. Additionally, the influence of fuel flow rate on the environmental characteristics (NOx emissions) was evaluated. The experimental results demonstrated that air flow rate is the most important factor in the process; a higher air fuel rate contributed to higher NOx emissions and gas temperature. It also was found that the NOx emissions increase dramatically when the air flow rate increases.

In this study, an input stream of symmetrical supersonic inlet with boundary layer suction has been investigated by using of two-dimensional full Navier−Stokes equations. The analysis has been performed for three various Mach numbers. The main purpose of this study is reduction of adverse pressure gradient for performance improvement of supersonic air-intake. At this paper, the upper leading edge has been considered round because the sharp leading edge cannot withstand the high thermal loading in supersonic flow. The results show that the high pressure gradient across the crossing shock waves has been minimized by the use of boundary layer suction. So, the input mass flow rate to air-intake has been increased. Viscose and non-viscose Turbulent flow analysis has been done by McCormack explicit method. Modeling of turbulent flow has been done with Wilcox k-ω two equations model. The results have been compared with the prestigious experimental papers at the end.