Prediction of Thermo-Physical Properties of TiO2-Al2O3/Water Nanoparticles by Using Artificial Neural Network

In this paper, an artificial neural network is implemented for the sake of predicting the thermal conductivity ratio of TiO2-Al2O3/water nanofluid. TiO2-Al2O3/water in the role of an innovative type of nanofluid was synthesized by the sol–gel method. The results indicated that 1.5 vol.% of nanofluids enhanced the thermal conductivity by up to 25%. It was shown that the heat transfer coefficient was linearly augmented with increasing nanoparticle concentration, but its variation with temperature was nonlinear. It should be noted that the increase in concentration may cause the particles to agglomerate, and then the thermal conductivity is reduced. The increase in temperature also increases the thermal conductivity, due to an increase in the Brownian motion and collision of particles. In this research, for the sake of predicting the thermal conductivity of TiO2-Al2O3/water nanofluid based on volumetric concentration and temperature functions, an artificial neural network is implemented. In this way, for predicting thermal conductivity, SOM (self-organizing map) and BP-LM (Back Propagation-Levenberq-Marquardt) algorithms were used. Based on the results obtained, these algorithms can be considered as an exceptional tool for predicting thermal conductivity. Additionally, the correlation coefficient values were equal to 0.938 and 0.98 when implementing the SOM and BP-LM algorithms, respectively, which is highly acceptable. View Full-Tex

Heat transfer through converging-diverging channels using adomian decomposition method

This study consists of proposing a new mathematical method to develop a new model for evaluating thermal distributions throughout convergent-divergent channels between non-parallel plane walls in Jeffery Hamel flow. Subsequently, dimensionless equations that govern temperature fields and velocity are numerically tackled via the Runge–Kutta-Fehlberg approach based on the shooting method. Additionally, an analytical study is performed by applying an effective computation technique named Adomian Decomposition Method. Determining the effect of Reynolds and Prandtl numbers on the heat transfer and fluid velocity inside converging/diverging channels can be mentioned as the fundamental purpose of this research. Based on the results obtained for dimensionless velocity and thermal distributions, a supreme match can be observed between numerical and analytical results indicating the adopted ADM method is valid, applicable, and has great precision.https://www.tandfonline.com/loi/tcfm20pm2021Mechanical and Aeronautical Engineerin

Numerical calculations of the thermal-aerodynamic characteristics in a solar duct with multiple V-baffles

The study aimed to enhance the heat transport by improving the hydrodynamic structure of the system by changing and restructuring the duct’s internal geometry. Modern fins, of the shape ‘V’, have been proposed with different dimensions, and they are periodically arranged over the duct surfaces. The most important steps of this research are the change in the V-fin attack-angle (40°–80°), length (Hb/2, 3Hb/4, Hb, 5Hb/4 and 3Hb/2), and separation length (Ds/2, 3Ds/4, Ds and 5Ds/4), as well as the flow rate (6 × 103–3 × 104). The study yielded an optimum case for a 40-degree attack-angle, with a factor of thermal enhancement of 2.163 for the highest value of Reynolds number. On the other hand, improving the length of the V-fins or decreasing in the space between them, increases the flow strength by enlarging the recycling cells, which reflects on the hydrodynamic behavior, and changes the heat transfer. The presence of this new model offins also highlights a hydrothermal improvement ranging between 1.196 and 23.779 percent compared to the previously indicated models, reflecting the effectiveness of the new system of solar heat exchangers with air V-finned ducts.https://www.tandfonline.com/loi/tcfm20pm2020Mechanical and Aeronautical Engineerin

Experimental investigation of heat transfer and exergy loss in heat exchanger with air bubble injection technique

The main aim of this study is to evaluate thermal performance and exergy analysis of a shell-and-tube heat exchanger with a new technique called air bubble injection. The study has been carried out with different parameters such as flow rate, fluid inlet temperature, and different air injection techniques. The air has been injected at different locations such as the inlet of pipe, throughout the pipe, and in the outer pipe of the heat exchanger. Based on the results, the performance of the heat exchanger enhances with an increase in the flow rate and the fluid inlet temperature. The exergy loss and dimensionless exergy loss increase with a rise in the flow rate. The maximum and dimensionless exergy losses are obtained at a maximum flow rate of 3.5 l min−1. With the air bubble injection in the heat exchanger, it has been observed that the temperature difference increases, which leads to an increase in the exergy loss. The injecting air bubbles throughout the tube section shows that minimum dimensionless exergy is 27.49% concerning no air injection.http://link.springer.com/journal/109732021-08-28am2020Mechanical and Aeronautical Engineerin

Thermodynamic and economic analysis of performance evaluation of all the thermal power plants : a review

Surging in energy demand makes it necessary to improve performance of plant equipment and optimize operation of thermal power plants. Inasmuch as thermal power plants depend on fossil fuels, their optimization can be challenging due to the environmental issues which must be considered. Nowadays, the vast majority of power plants are designed based on energetic performance obtained from first law of thermodynamic. In some cases, energy balance of a system is not appropriate tool to diagnose malfunctions of the system. Exergy analysis is a powerful method for determining the losses existing in a system. Since exergy analysis can evaluate quality of the energy, it enables designers to make intricate thermodynamic systems operates more efficiently. These days, power plant optimization based on economic criteria is a critical problem because of their complex structure. In this study, a comprehensive analysis including energy, exergy, economic (3-E) analyses, and their applications related to various thermal power plants are reviewed and scrutinized.The National Natural Science Foundation of China, Hubei Provincial Natural Science Foundation of China, Key Project of ESI Discipline Development of Wuhan University of Technology and the Scientific Research Foundation of Wuhan University of Technology.https://onlinelibrary.wiley.com/journal/20500505am2020Mechanical and Aeronautical Engineerin

On the Stability of Particle–Particle Interaction during Gravitational Settling

The elevated energy demand and high dependency on fossil fuels have directed researchers’ attention to promoting and advancing hydraulic fracturing (HF) operations for a sustainable energy future. Even though previous studies have demonstrated that the proppant suspension and positioning in slickwater play a vital role during the shut-in stage of the HF operations, minimal experimental work has been conducted on the fundamental proppant–proppant interaction mechanisms, especially a complete mapping of the interactions. This study utilizes high-speed imaging to provide a 2D space- and time-resolved investigation of two-particle (proppant models: 2 mm Ø, 2.6 g·cm−3) interactions during gravitational settling in different initial spatial configurations and rheological properties. The mapping facilitates the identification of various interaction regimes and newly observed particle trajectories. Pure water results at a settling particle Reynolds number (Rep) ~ 470 show an unstable particle–particle interaction regime characterized by randomness while altering pure water to a 25% (v/v) water–glycerin mixture (Rep ~ 200) transitions an unstable interaction to a stable prominent repulsion regime where particles’ final separation distance can extend up to four times the initial distance. This indicates the existence of Rep at which the stability of the interactions is achieved. The quantified trajectories indicate that when particles are within minimal proximity, a direct relation between repulsion and Rep exists with varying repulsion characteristics. This was determined by observing unique bottle-shaped trajectories in the prominent repulsion regimes and further highlighted by investigating the rate of lateral separation distance and velocity characteristics. Additionally, a threshold distance in which the particles do not interact (or negligibly interact) and settle independently seems to exist at the normalized 2D lateral separation distance

On the Stability of Particle–Particle Interaction during Gravitational Settling

The elevated energy demand and high dependency on fossil fuels have directed researchers’ attention to promoting and advancing hydraulic fracturing (HF) operations for a sustainable energy future. Even though previous studies have demonstrated that the proppant suspension and positioning in slickwater play a vital role during the shut-in stage of the HF operations, minimal experimental work has been conducted on the fundamental proppant–proppant interaction mechanisms, especially a complete mapping of the interactions. This study utilizes high-speed imaging to provide a 2D space- and time-resolved investigation of two-particle (proppant models: 2 mm Ø, 2.6 g·cm−3) interactions during gravitational settling in different initial spatial configurations and rheological properties. The mapping facilitates the identification of various interaction regimes and newly observed particle trajectories. Pure water results at a settling particle Reynolds number (Rep) ~ 470 show an unstable particle–particle interaction regime characterized by randomness while altering pure water to a 25% (v/v) water–glycerin mixture (Rep ~ 200) transitions an unstable interaction to a stable prominent repulsion regime where particles’ final separation distance can extend up to four times the initial distance. This indicates the existence of Rep at which the stability of the interactions is achieved. The quantified trajectories indicate that when particles are within minimal proximity, a direct relation between repulsion and Rep exists with varying repulsion characteristics. This was determined by observing unique bottle-shaped trajectories in the prominent repulsion regimes and further highlighted by investigating the rate of lateral separation distance and velocity characteristics. Additionally, a threshold distance in which the particles do not interact (or negligibly interact) and settle independently seems to exist at the normalized 2D lateral separation distance

Moisture Estimation in Cabinet Dryers with Thin-Layer Relationships Using a Genetic Algorithm and Neural Network

Nowadays, industrial dryers are used instead of traditional methods for drying. When designing dryers suitable for controlling the process of drying and reaching a high-quality product, it is necessary to predict the gradual moisture loss during drying. Few studies have been conducted to compare thin-layer models and artificial neural network models on the kinetics of pistachio drying in a cabinet dryer. For this purpose, ten mathematical-experimental models with a neural network model based on the kinetic data of pistachio drying were studied. The data obtained was from a cabinet dryer evaluated at four temperatures of inlet air and different air velocities. The pistachio seeds were placed in a thin layer on an aluminum sheet on a drying tray and weighed by a scale attached to the computer at different times. In the neural network, data was divided into three parts: Educational (60%), validation (20%) and testing (20%). Finally, the best mathematical-experimental model using a genetic algorithm and the best neural network structure for predicting instantaneous moisture were selected based on the least squared error and the highest correlation coefficient

Exergy and economic analyses of replacing feedwater heaters in a Rankine cycle with parabolic trough collectors

Fossil fuels are exhaustible and their consumption causes environmental problems. As a result, renewable energy resources, specifically solar energy, should be utilized more to overcome the aforementioned issues. The biggest problem with renewable energy utilization is that their capital cost is very high. To tackle this problem, renewable energies should be coupled with conventional energy systems to lower the initial investment. In this paper, a parabolic trough collector is coupled with a conventional Rankine cycle to increase output power of the system by replacing its closed feedwater heaters. Also, to be able to use the system during the nights, a thermal storage system is added to the cycle. A complete energy, exergy and economic analyses are performed on the system and the results are compared with the base case condition. The results show that by using the proposed system, net generated power of the plant increases by 8.14%. Also, exergy analysis shows that in both cases boiler has the highest rate of exergy destruction. In general, due to huge amount of losses in the collector, exergy efficiency of the system decreases. Finally, economic analysis shows that simple payback time of the system equals to 1.5 years which is very low. Keywords: Parabolic trough collector, Rankine cycle, Energy analysis, Exergy analysis, Economic analysi