Engineering Thermodynamics, Heat Transfer and Fluid Flow in Natural and Industrial Processes

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Authors: Luca Piancastelli, Eugenio Pezzuti, Stefano Cassani
Abstract: The primary task in DI (Direct Injection) diesel engines design is the fulfilment of the required emission limits. This result should be achieved with acceptable power-to-rpm diagrams, acceptable fuel consumption, acceptable power density and affordable purchase and maintenance expenses. The most common approach to fulfil these requirements is the downsizing. In this case a significant increase in the crankshaft speed and boost pressure is unavoidable. In this way, an improvement in airflow through the redesign of the intake and exhaust geometry is obtained. Unfortunately, duct design is extremely difficult due to “Mach lock”. A further important boundary condition is due the injector inertia. The dynamic response improves with small injectors due to the Newton’s second law. Small injectors designed for unitary power of 15 to 70 HP are extremely common. Therefore, most of the research is centered on these injectors. Furthermore, their small inertia favors better opening and closing time. Nozzles number and position is also greatly influential on combustion performance. The larger surface of the spray reduces the gasification time of the droplets. For these reasons, multiple injectors systems may be used in large high pressure HSDI-CR (High Speed Direct Injection – Common Rail) diesels. Multi injection was commonplace in relatively large old diesels. This paper proposes new intake duct geometries for modern two-injectors-per-cylinder truck-size engines. For this purpose a new promising, patented concept is introduced. The study includes flow simulations during the intake phase. This patented geometry induces the presence of two extremely strong swirls approximately centered to the injectors, with excellent swirl coefficient and high flow rate. The use of swirl generators on the manifolds avoids the necessity to design helical intake ducts. This patented approach simplifies head design. Moreover, using a VG (Variable Geometry) arrangement for the volutes (swirl generators) it is possible to tune the swirl index at the optimum for every crankshaft velocity and every load. In this way, the vehicle fuel consumption is also reduced.
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Authors: Janke Venkata Ramana Reddy, Vangala Sugunamma, N. Sandeep
Abstract: Present study deals with the impact of cross diffusion on Casson fluid flow in the presence of Lorentz force. Flow is caused by the exponential stretching of surface in two lateral directions. The influence of space dependent varying heat sink/source is also contemplated. The basic governing equations are first converted into system of ODEs and then solved using an efficient numerical procedure namely R.K. based shooting technique. From the solution we found that flow is affected by some physical parameters like Casson parameter, non uniform heat parameters, Soret and Dufour numbers etc. Hence the impact of such parameters on velocity, temperature and concentration profiles is shown via plots. Further the friction factor, local Nusselt and Sherwood numbers are also calculated and given in tables. Results indicate that an increase in the Casson parameter enhances the temperature and concentration fields. Dufour and Soret numbers have tendency to enhance temperature and concentration fields respectively.
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Authors: Prathi Vijaya Kumar, S. Mohammed Ibrahim, Giulio Lorenzini
Abstract: Magnetohydrodynamic non-Newtonian fluid flow over a stretching sheet with intermittent thickness under multifarious slips is appraised. Williamson fluid pattern is incorporated in this discussion. The energy and concentration equations are confederated with the repercussion of Soret and Dufour. We endorsed homotopy analysis method (HAM) to collocate the solutions of ODE. The graphical and tabular results for velocity, temperature, concentration, friction factor, heat and mass transfer rates when (Newtonian fluid) and (non-Newtonian fluid-Williamson fluid) are secured and discussed in detail.
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Authors: Mohammad Alhuyi Nazari, Mohammad Hossein Ahmadi, Giulio Lorenzini, Heydar Maddah, Morteza Fahim Alavi, Roghayeh Ghasempour
Abstract: The thermal conductivity of nanofluids depends on several factors such as temperature, concentration, and temperature. These parameters have the most significant effect on thermal conductivity compared with other factors. In the present study, the accuracy of trained Perceptron neural network with 10 neurons and three input variables including size of nanoparticles, temperature, and concentration is evaluated. The sum of squared errors and the correlation coefficient of the trained neural network are equal to 0.99293 and 0.00031, respectively.
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Authors: Mojtaba Mirzaei, Mohammad Hossein Ahmadi, Mahyar Ghazvini, Ehsan Sobhani, Giulio Lorenzini, Nima Khalilpoor
Abstract: The expenses, which caused by pollution and limited fossil resources, have convinced scientists to concentrate on renewable resources such as biological waste. Conversion of bio-waste to syntheses gas produces higher heating values in comparison to conventional bioenergy production methods. To produce energy from bio waste, it is important to study on existing technology and using CHP and gas turbines. In this paper a plan for producing electricity and heat at the same time by using bio waste has been proposed. This plan provides a method to produce hybrid gas (combined gas) by using solid bio-waste of Tehran in two forms of wet and dry as a renewable energy resource and steam in a fixed bed gas reactor. This gas is a combination of Hydrogen, Carbon monoxide, Carbon dioxide Water and some amount of Methane. Selected temperature and pressure for the reactor respectively is1900 [˚F] and 390 [Psi]. As indicated in the results, the best air and steam combination entering fixed bed reactor among 60 different combinations for dry waste is 0.2% of entering fuel volume for steam 0.25% of entering fuel volume for air heating value for this combination is 6471 [BTU/lb]. Furthermore, for the steam volumes of 1.5% to 0.9%, the percentage of H2 in the syngas increases by enhancing the volume of air content.
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Authors: G. Vinod Kumar, S. Vijaya Kumar Varma, R.V.M.S.S. Kiran Kumar
Abstract: The present investigation has put a focus on the hydromagnetic boundary layer unsteady flow of a nanofluid over a stretching sheet. A new heat flux model named Cattaneo-Christov is applied as the substitution of classical Fourier’s law. Buongiorno’s model is incorporated. The coupled non-linear transformed equations are solved numerically by using shooting technique with MATLAB bvp4c package. The obtained results are presented and discussed through graphs and tables in detail. Our results reveal that the unsteady parameter reduces all the three boundary layer thickness. The thermal relaxation parameter exhibits a non-conducting nature that makes the decline in fluid temperature.
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Authors: M. Krishna Murthy
Abstract: Magnetohydrodynamic (MHD) three dimensional boundary layer flow of Casson fluid over an unsteady exponentially stretching sheet with slip conditions is studied. The governing partial differential equations are transformed into ordinary differential equations using similarity transformations and are solved numerically using shooting technique. The effects of pertinent parameters on velocity and temperature distributions are shown in graphically. The skin friction coefficient and the Nusselt number are computed numerically. We noticed that Casson parameter increases then the velocities and temperature decrease.
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Authors: Bujula Ramadevi, Janke Venkata Ramana Reddy, Vangala Sugunamma
Abstract: Through this article, we presented a comparative study for the MHD non- Newtonian fluid flow past a stretching sheet using Cattaneo-Christov heat flux model. The flow equations and the related convective boundary conditions have been altered as dimensionless ODEs by suitable similarity transformations. Further, these are resolved by employing fourth order Runge-Kutta method along with shooting technique. The influence of all flow regulating parameters on velocity, thermal and mass diffusive boundary layers are perceived through graphs. Also the variation in skin friction, mass and heat transfer coefficients for the same parameters are perceived via numerical values. The velocity of the flow past a linear stretching sheet is higher than that of the flow past a non-linear stretching sheet. But heat transfer performance in the flow via non-linear surface is better than that of flow via linear surface.
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Authors: Bijjanal Jayanna Gireesha, K. Ganesh Kumar, N.G. Rudraswamy, S. Manjunatha
Abstract: This article deals with the combined effects of viscous dissipation and convective condition on 3D flow, heat and mass transfer of a nanofluid over a stretching sheet by considering gyrotactic microorganism. Appropriate transformations yield the nonlinear ordinary differential systems. The resulting nonlinear system has been solved. Role of substantial parameters on flow fields as well as on heat, mass and microorganism transportation rates are determined and conferred in depth through graphs. It is found that, the larger values of bio-convection Schmidt number decreases the microorganisms profile.
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