Abstract: In this paper, we present a modeling of planar structures under dynamic loading containing stationary cracks in order to determine the dynamic stress intensity factor (DSIF). This parameter will be evaluated by using the eXtended Finite Element Method (XFEM) coupled with two different techniques, namely the technique of displacement jump and that of interaction integral. A comparison between the two approaches is discussed. Moreover, the effects of crack orientation and damping material on the DSIF variation are tested. The good correlation of the obtained results for the treated examples with the literature ones demonstrates the effectiveness, accuracy and robustness of the computer software developed in this study.
Abstract: Thermal management system (TMS) design is considered to be a key technology for advanced aero engines and supersonic or hypersonic propulsion systems. In this paper, the concepts of coupling flow and thermodynamic networks are proposed for TMS design. In this method, the propulsion system is considered to be a zero-dimensional flow system. Components, subsystems and hence the entire engine system can be modelled using some basic flow and thermodynamics networks. The platform for TMS design, ThermalM, is developed based on this model. As an example, modelling for a Turbine Based Combined Cycle (TBCC) thermal management system is described. Performance of the fuel heat exchanger in the network is discussed in detail. With the TMS design technology, performance of the advanced propulsion system can be analysed.
Abstract: The current paper is principally dedicated to the study of geometry and frequency effects for internal spur gears heated by induction. The overall work is realized by the simulation efforts performed on Comsol multi-physics software. The 3D model used during this study is built basing on coupling between Maxwell’s and heat transfer equations. This model is used to calculate the temperature profile in the gear in function of machine parameters. The module and the frequency are varied to determinate their effects. In fact, two gears having the same external diameter but different modules are exploited during this study and the frequency is varied from low to high level. The obtained results allow understanding the effect of module and frequency on the final temperature distribution. Finally, the optimal frequency value permitting to have the best temperature profile is found.
Abstract: This paper presentsa sensitivity study using a Comsol3D model simulation for spur gear heated by induction process. Based on an adequate formulation and taking into account the material properties, a multi-physics 3D model is built to calculate the final temperature distribution determinate according the machine parameters and some geometrical factors (coil width and gap between coil and gear). Since the hardness profile is affected by thermal historic during heating, the surface temperatures are deeply analyzed versus the initial current density and the heating time using medium (MF) and high frequencies (HF). Finally, the sensitivity of hardness profile with the machine parameters variation isinvestigated using various statistical tools applied to the obtained results. The obtained results exhibits the main machine parameters and theirs effects on the hardness profile.
Abstract: This paper presents numerical investigations on melting of phase change material using paraffin wax inside a double pipe heat exchanger. Numerical simulations are performed for melting of phase change material (PCM) in annulus while the inner pipe has two or four longitudinal fins and the results compared with inner bare tube. The aim of this study is to understand the PCM melting behaviors by observing the natural convection currents movement and melting fronts formation. It is concluded that melting performance of PCM can be significantly improved by applying longitudinal fins on the inner tube.
Abstract: The hot-wire anemometer is a famous thermal transducer for turbulence measurements. The fundamental principle of hot-wire anemometer is based on the convective heat transfer, since the heat transfer is directly proportional to the temperature difference between the sensor and the fluid, hence ambient temperature variations are one of the most important error sources in the measurements with the hot-wire anemometers. Many methods have been proposed to compensate for the ambient temperature variations. In such methods the effect of temperature drift is only considered and the effect of Nusselt number is ignored. In the present research the effect of air flow temperature variations on the response of constant temperature anemometer has been studied experimentally. Furthermore, with the basis of air flow velocity and ambient temperature variations, the percentage errors in velocity measurements have been estimated. Finally, based on achieved results, an accurate method has been proposed to compensate the air flow temperature variations.
Abstract: This study developed the pre-heating device which heats the water by using the exhaust gases from gas-operated hot-water heater. Thus the temperature of water is raised at an exit of the pre-heating device. The pre-heated water is then transport to the gas-operated hot-water heater to increase the water temperature which is used for showers. Thus, the thermal performance is enhanced with the pre-heating device. The overall performance of the absorption heater system is analyzed by finite element analysis. The different types of pre-heating devices are simulated for the thermal performance. Other important considerations for producing the pre-heating devices are the bending-tube technology and manufacturing cost. The appropriated design of pre-heating device is selected for producing. Thus the performance and testing of pre-heating devices will be carried out.
Abstract: In this study 3 geometry for ONAN cooling system of power transformers are numerically simulated with (Perforated nomex) and without insulating papers (Netting tape). Geometries are A, RA, and R type. The A type has just axial channels. The RA type has radial and axial channels but there are no baffles to drive the flow into radial channels. The R type is like the RA type but with baffles. Insulating paper used in this study has some holes to cause some vortex in flow to increase heat transfer. The CFD code used is Fluent 6.3. To simulate flow in natural convection mode, Boussinesq model and pressure inlet and outlet boundary conditions are used. Results show that the most effective geometry is the one with baffles that drive flow in radial channels in addition to axial channels. Streamlines near the holes in papers show that that height of holes is too small to affect heat transfer and, so, the comparison between geometries with and without paper shows the types without paper have higher heat transfer coefficients.
Abstract: Gas-steam launching system with water injection in block can overcome the problem of horizontal or large-angle launching, and gets more and more value in recent years. Based on the characteristic of launching system, the model was built with several assumptions, which could provide reference and technique for developing the new launching system. And the generator result was verified by the experimental one. The interior ballistic characteristics were researched by calculation result under different deep and injection water mass conditions. The comparison of the simulation results and theory analysis indicates the model was rational and valid, and different launching deep and cooling water mass had effect on ballistics, more water can cool down the silo, but also brings more energy loss, and deeper launch needs more energy, so good design is required to fit the parameters demand in all respects.
Abstract: This paper presents a numerical investigation on the effect of thermal anisotropy of the top layer alloy on heat transfer and lubricant depletion on the disk surface in a heat-assisted magnetic recording (HAMR) system. The disk consists of multilayer structures and a thin layer of lubricant on the top surface. Cases under different laser powers and initial lubricant film thicknesses are examined. The top-layer alloy thermal anisotropy does show non-negligible effect on the heat transfer and lubricant depletion. With the top-layer alloy being more anisotropic, higher temperature increase and lager lubricant depletion can be observed on the disk surface. The results also show that the thermal anisotropy effect is more significant under a lower laser power but nearly keeps no much difference under different initial lubricant film thicknesses. Thus it is of importance to include the thermal anisotropy effect of the top-layer Co-alloy when simulating the heat transfer and lubricant depletion in practical multilayer HMAR systems, especially for the cases under the condition of lower laser power, as the effect cannot be neglected under such conditions.