1,721,057 research outputs found
Modelling and simulation of direct steam injection for tomato concentrate sterilization
No full textDirect steam injection (DSI) is a sterilization technique which is often used for high viscosity fluid food when the preservation of the quality characteristics and energy efficiency are the priority. In this work an apparatus for the sterilization of tomato concentrate has been analyzed by means of multidimensional CFD (Computational Fluid Dynamics) models, in order to optimize the quality and safety of the treated food. A multidimensional two-phase model of steam injection inside a non-newtonian pseudoplastic fluid was adopted to evaluate the thermal history of the product and the steam consumption during the target process. Subsequently CFD analysis has been extended to examine the effects of the different process parameters (sterilization temperature, steam flow rate, radial and axial temperature profiles, nozzle geometry) on the resulting product. Result obtained are in agreement with available data acquired in industrial plant
One-Dimensional Fluid Dynamic Modeling of a Gas Bladder Hydraulic Damper for Pump Flow Pulsation
No full textSimulation approaches for the study of the oil flow rate distribution in lubricating systems with rotating shafts
No full textThis study addresses the issue of predicting the distribution of lubricant flow through the outlets of a rotating
shaft used in vehicle power transmission. A typical geometry with closely spaced rows of holes, suitable for the
lubrication of multi-disk clutches, was considered. Both lumped parameter and computational fluid dynamics
approaches were applied and compared. The test rig for model validation was designed with a variable speed shaft
featuring an axial oil inlet and three equally spaced pairs of radial outlet holes. The main characteristic of the
experimental facility is the possibility to selectively measure the flow rates through each outlet. It was found that the
three-dimensional model based on the multiple reference frame approach provides a reliable prediction of how the
flow rate is distributed. Generally, the flow rate is lower through the outlet closest to the inlet and is maximum at the
farthest exit. The flow distribution is minimally affected by the shaft speed. The influence of geometric parameters
on making the flow distribution more uniform was studied. It was found that a better flow balance is obtained with
a low ratio between the diameter of the radial holes and that of the axial channel. The results obtained offer bestpractice
guidelines for accurately simulating comparable systems, in order to optimize reliability of the mechanical
transmission and energy efficiency of the flow generation uni
Experimental methods for measuring the viscous friction coefficient in hydraulic spool valves
Full text linkIn hydraulic components, nonlinearities are responsible for critical behaviors that make it difficult to realize a reliable mathematical model for numerical simulation. With particular reference to hydraulic spool valves, the viscous friction coefficient between the sliding and the fixed body is an unknown parameter that is normally set a posteriori in order to obtain a good agreement with the experimental data. In this paper, two different methodologies to characterize experimentally the viscous friction coefficient in a hydraulic component with spool are presented. The two approaches are significantly different and are both based on experimental tests; they were developed in two distinct laboratories in different periods of time and applied to the same flow compensator of a pump displacement control. One of the procedures was carried out at the Fluid Power Research Laboratory of the Politecnico di Torino, while the other approach was developed at the University of Parma. Both the proposed methods reached similar outcomes; moreover, neither method requires the installation of a spool displacement transducer that can significantly affect the results
Modelling and validation of cavitating orifice flow in hydraulic systems
No full textCavitation can occur at the inlet of hydraulic pumps or in hydraulic valves; this phenomenon should be always avoided because it can generate abnormal wear and noise in fluid power components. Numerical modeling of the cavitation is widely used in research, and it allows the regions where it occurs more to be predicted. For this reason, two different approaches to the study of gas and vapor cavitation were presented in this paper. In particular, a model was developed using the computational fluid dynamics (CFD) method with particular attention to the dynamic modeling of both gaseous and vapor cavitation. A further lumped parameter model was made, where the fluid density varies as the pressure decreases due to the release of air and the formation of vapor. Furthermore, the lumped parameter model highlights the need to also know the speed of sound in the vena contracta, since it is essential for the correct calculation of the mass flow during vaporization. A test bench for the study of cavitation with an orifice was set up; cavitation was induced by increasing the speed of the fluid on the restricted section thanks to a pump located downstream of the orifice. The experimental data were compared with those predicted by CFD and lumped parameter models
A Two-Zone Diesel Engine model for the Simulation of Marine Propulsion Plant Transients
No full textAbstract: The paper presents a mathematical model for the dynamic analysis of turbocharged diesel engines for use in computer simulations of ship propulsion plants.
The engine description is based on a two-zone combustion model which allows a detailed calculation of the thermodynamic processes inside the cylinders and an evaluation of exhaust gas emissions. The thermodynamic study of the in-cylinder phenomena is combined with an analysis of the dynamic behaviour of the turbocharger and of the intake and exhaust systems (intercooler, manifolds, etc.).
The procedure has been validated by comparisons with both experimental data obtained by the engine Manufacturer and theoretical results supplied by a phenomenological combustion code. Despite the good accuracy of the results obtained, the computational time is kept reasonably short. This is an important feature, because the engine simulator is part of a broader code, already developed by the authors, simulating the whole propulsion system of a ship
Energy Comparison between a Load Sensing System and Electro-Hydraulic Solutions Applied to a 9-Ton Excavator
Full text linkWith the increasingly stringent regulations on air quality and the consequent emission limits for internal combustion engines, researchers are concentrating on studying new solutions for improving efficiency and energy saving even in off-road mobile machines. To achieve this task, pump-controlled or displacement-controlled systems have inspired interest for applications in offroad working machines. Generally, these systems are derived from the union of a hydraulic machine coupled to an electric one to create compact components that could be installed near the actuator. The object of study of this work is a 9-ton excavator, whose hydraulic circuit is grounded on load sensing logic. The validated mathematical model, created previously in the Simcenter Amesim© environment, represents the starting point for developing electro-hydraulic solutions. Electric components have been inserted to create different architectures, both with open-and closed-circuit layouts, in order to compare the energy efficiency of the different configurations with respect to the traditional load sensing system. The simulations of a typical working cycle show the energy benefits of electrohydraulic solutions that allow for drastically reducing the mechanical energy required by the diesel engine and, consequently, the fuel consumption. This is mainly possible because of the elimination of directional valves and pressure compensators, which are necessary in a load sensing circuit, but are also a source of great energy dissipations. The results show that closed-circuit solutions produce the greatest benefits, with higher energy efficiencies than the open-circuit solution. Furthermore, closed-circuit configurations require fewer components, allowing for more compact and lighter solutions, as well as being cheaper
Evaluation of tooth space pressure and incomplete filling in external gear pumps by means of three-dimensional cfd simulations
No full textThe paper presents the computational fluid dynamics simulation of an external gear pump for fluid power applications. The aim of the study is to test the capability of the model to evaluate the pressure in a tooth space for the entire shaft revolution and the minimum inlet pressure for the complete filling. The model takes into account the internal fluid leakages and two different configurations of the thrust plates have been considered. The simulations in different operating conditions have been validated with proper high dynamics transducers measuring the internal pressure in a tooth space for the entire shaft revolution. Steady-state simulations have been also performed in order to detect the fall of the flow rate due to the incomplete filling of the tooth spaces when the inlet pressure is reduced. It has been demonstrated that, despite the need of a compromise for overcoming the limitation of considering fixed positions of the gears' axes and of the thrust plates, significant results can be obtained, making the CFD approach very suitable for such analyses
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