Showing papers on "Film temperature published in 2021"

Thermal Characteristics Study of the Bump Foil Thrust Gas Bearing

Abstract: In this paper, a thermo-hydrodynamic model of the bump foil thrust gas bearing is developed, which solves the coupled gas film three-dimensional energy equation, non-isothermal Reynolds equation, and the foil deformation equation. The effects of bearing speed, thrust load, and external cooling gas on the bearing temperature field are calculated and analyzed. The test rig of foil thrust gas bearing was built to measure the bearing temperature under different working conditions. Both simulation and experiment results show that there exist temperature gradients on the top foil both in the circumferential and radial directions. The simulation results also shows that the top foil side of the gas film has the highest temperature value in the entire lubrication field, and the position of highest temperature moves radially inward on the thrust plate side as the rotor speed increases. The gas film temperature increases with the increasing rotor speed and bearing static load, and rotor speed has greater effects on the temperature variation. Cooling air flow passing through the bump foil is also considered in the simulations, and the cooling efficiency decreases as the mass of gas flow increases.

Analysis of stability of two-phase flow mechanical seal with spiral groove under high speeds

Abstract: A thermo-hydrodynamic model was introduced by considering fluid film phase change to analyze the stability of a spiral groove mechanical seal under high speeds. The Reynolds equation, energy equation and heat conduction equation were solved using the finite difference method. Two kinds of phase state stability criteria and fluid film temperature or pressure distributions in each phase state were studied. Different phase states of fluid film and phase state stability of such a spiral groove mechanical seal under variable operating and geometry conditions were analyzed. The results show that vapor mass fraction volume ratio vs sealed fluid temperature (κ-Tf) curve and film pressure coefficient versus sealed fluid temperature (Km-Tf) curve can be used as phase state stability criteria which can predict the range of instability, stability and quasi-stability of a spiral groove mechanical seal. But the Km-Tf curve is more suitable for practical engineering applications. It is found that a significant change in pressure distribution will bring about instability of a spiral groove mechanical seal. The sudden change of film pressure distribution usually occurs when the leakage flow medium in the interface is in the transition phase from quasi-liquid to quasi-vapor where κλ=0 = κ0<λ<1 and κλ=1 = 0. Optimized design of a spiral groove mechanical seal will improve its stability during the phase change from liquid phase state to vapor phase state.

Effect of operating parameters on water film properties of transpiring wall reactor

Abstract: Transpiring wall reactor can effectively minimize reactor corrosion and salt deposition problems, which seriously hinder the commercialization of supercritical water oxidation. In this work, methanol was selected as organic matter, and the influences of key operating parameters on water film properties and organic matter removal were investigated mainly via numerical simulation. The results show that methanol conversion could be higher than 99% and hardly affected by various feed and transpiration water parameters. The highest value of reactor center temperature significantly increased by about 300 K as feed preheating temperature changed from 673 K to 823 K. Decreasing feed flow rate, feed concentration, feed preheating temperature and transpiration water temperature, and increasing transpiration intensity reduced water film temperature but raised coverage rate, which are beneficial to forming excellent water film with good corrosion and salt deposition resistance. These findings can provide significant reference for the optimization of reactor operating parameters.

Initial dynamic thermal dissipation modes enhance heat dissipation in gold nanoparticle–polydimethylsiloxane thin films

Abstract: Plasmonic nanocomposite materials have exhibited value for applications ranging from biological hyperthermia to optical sensing and waveguiding. Energy absorbed from incident irradiation can be re-emitted as light or decay into phonons that propagate through the surrounding material and increase its temperature. Previous works have examined steady-state thermal dissipation resulting from irradiated plasmonic nanocomposites. This work shows heat dissipation in the first few seconds can significantly exceed that during subsequent steady state, depending on film geometry, nanoparticle diameter and concentration, laser irradiation power, and position within and adjacent to the irradiated spot. Films of lower thickness containing 16 nm gold nanoparticles (AuNPs) irradiated at 13.5 mW laser power showed highest enhancement and tunability of the dynamic thermal mode within and adjacent to the irradiated spot. Measured initial nanocomposite film temperature in or near the irradiated spot exceeded that resulting from constant bulk film thermal dissipation. These results improve understanding of cooling dynamics of resonantly irradiated nanocomposite materials and guide development of devices with enhanced thermal dissipation dynamics.

Effect of liquid drainage on heat transfer from a heated surface to flow of aqueous foam

Abstract: According to global studies, application of macro aqueous foam flow as a coolant seems promising and complex at the same time. Research of the heat transfer between a heated horizontal flat surface at the bottom of the channel and a longitudinal flow of aqueous foam was performed in this investigation. The distribution of the foam temperature in various cross-sections along the heated surface was found experimentally. A significant change in temperature was observed only in the bottom 1/4 part of the cross-section. The liquid drained from foam and formed a moving film which covered the heated surface. The inflow of lower temperature liquid into the film of drained liquid inhibited the intensive increase in film temperature. This influenced the character of cooling intensity of the heated surface. Analytically obtained formulas to calculate the amount of liquid draining from the foam and the developed methodology were verified in the experimental research.

The influence of thermal effects on the breakup of thin films of nanometric thickness

Abstract: We apply a previously developed asymptotic model (J. Fluid. Mech. 915, A133 (2021)) to study instabilities of free surface films of nanometric thickness on thermally conductive substrates in two and three spatial dimensions. While the specific focus is on metal films exposed to laser heating, the model itself applies to any setup involving films on the nanoscale whose material parameters are temperature-dependent. For the particular case of metal films heated from above, an important aspect is that the considered heating is volumetric, since the absorption length of the applied laser pulse is comparable to the film thickness. In such a setup, absorption of thermal energy and film evolution are closely correlated and must be considered self-consistently. The asymptotic model allows for a significant simplification, which is crucial from both modeling and computational points of view, since it allows for asymptotically correct averaging of the temperature over the film thickness. We find that the properties of the thermally conductive substrate -- in particular its thickness and rate of heat loss -- play a critical role in controlling the film temperature and dynamics. The film evolution is simulated using efficient GPU-based simulations which, when combined with the developed asymptotic model, allow for fully nonlinear time-dependent simulations in large three-dimensional computational domains. In addition to uncovering the role of the substrate and its properties in determining the film evolution, one important finding is that, at least for the considered range of material parameters, strong in-plane thermal diffusion in the film results in negligible spatial variations of temperature, and the film evolution is predominantly influenced by temporal variation of film viscosity and surface tension (dictated by average film temperature), as well as thermal conductivity of the substrate.

Power Law Lubricant Consistency Variation with Pressure and Mean Temperature Effects in Roller Bearing

Abstract: The present paper squarely aims to scrutinize the normal velocity of a hydrodynamic lubrication of roller bearings. The changes that happen in lubrication consistency due to pressure and temperature are shown in figures and tables. Further, hydrodynamic lubricant pressure, film temperature, mean film temperature, load and traction for different consistency index n and squeezing velocity q are calculated and compared with the previous results. Those results are positively agreed with the previous findings.

Effect of Al2O3 nanoparticle additives on the performance characteristics of rough journal bearings

Abstract: This paper investigates the influence of Al2O3 nanoparticle additives on static and dynamic characteristics of water-lubricated rough journal bearings under thermo-hydrodynamic lubrication (THL). The time-dependent modified Reynolds equation and the approximated adiabatic energy equation have been formulated and solved numerically with boundary conditions and initial conditions. The results are presented for dimensionless maximum film pressure, dimensionless maximum film temperature, dimensionless minimum film thickness, eccentricity ratio, attitude angle, dimensionless friction force, spring constants, damping coefficients and mass parameters for both journal bearings with transverse roughness patterns and with longitudinal roughness patterns under a dimensionless load of 7. The results show that journal bearings with Al2O3 nanoparticle additives tend to significantly increase load carrying capacity and minimum film thickness by decreasing both the eccentricity ratio and temperature rise for longitudinal roughness patterns. For journal bearings with longitudinal roughness patterns and lubricated with Al2O3 nanoparticle additives, the stability region tends to increase.

A mathematical model for vaporization of explosive thin film in active detection techniques

Abstract: When detecting explosive traces by optical remote methods based on recording the vapors, it is essential to know the applicability limits of these techniques. The amount of a vaporized explosive depends on the vaporization kinetics, which, in turn, relies on the physicochemical properties of the explosive, film weight and thickness, ambient air temperature, and film temperature. In active detection techniques, the explosive film temperature on the surface of objects may be higher than the air temperature due to special heating devices. In this case, the questions on how the quantity of matter available for detection is about to change and how much energy has to be consumed to heat up the film can be answered by mathematical modeling. The mathematic model is based on the Hertz–Knudsen–Langmuir equation that describes the vaporization rate of matter with mass transfer between the surface and surrounding air, which is taken into account. In an elaboration of the mathematical model, we introduced previously the temperature difference between the film and ambient air, which is now taken into consideration. The basic parameters influencing the film vaporization rate, and their variation range, were identified. The kinetic parameters of vaporization of thin films of some explosives with a quantity of matter typical of a fingerprint were estimated. The weight of matter in air during vaporization of explosive thin films in a wide range of parameters under study was calculated. Conclusions were made of the applicability limits of the developed standoff detection methods for trace explosives.

Multiparameter Determination of Thin Liquid Urea-Water Films

Abstract: In this work, wavelengths were determined for the robust and simultaneous measurement of film thickness, urea concentration and fluid temperature. Film parameters such as film thickness, film temperature and the composition of the film are typically dynamically and interdependently changing. To gain knowledge of these quantities, a measurement method is required that offers a high temporal resolution while being non-intrusive so as to not disturb the film as well as the process conditions. We propose the extension of the FMLAS method, which was previously validated for the film thickness measurement of thin liquid films, to determine temperatures and concentrations using an adapted evaluation approach.

Experimental and numerical investigation of ethanol film cooling

Abstract: Within a Belgian-German GSTP project, an experimental setup was designed, manufactured and tested to provide data on the behaviour of a shear-driven liquid film. The tests were performed on a flat plate in a rectangular duct using ethanol as film coolant at DLR’s vitiated hot air facility M11. In addition to standard measurement equipment comprising thermocouples and pressure sensors, nonintrusive measurement techniques were applied to acquire additional data of the film. The Von-Karman-Institute for Fluid Dynamics provided in-situ film temperature measurement using a dedicated laser-induced fluorescence setup. DLR performed background-oriented Schlieren measurements to record information on the film thickness. The experimental data was used by ArianeGroup and Numeca International to validate different software tools to describe the heat flux to the film and its dry-out. While ArianeGroup used its film cooling model implemented in the Rocflam3 code, Numeca performed VOF simulations using its updated Fine™/Open flow solver.

Modelling of carbon nanotube film based temperature sensor: thermal emission and gas discharge.

Abstract: The carbon nanotube film based ionized temperature sensor is sensitive to gas temperature, and shows good sensitivity compared with other temperature sensors. But it is still unclear about the effect of carbon nanotube film on thermal emission and gas discharge at different temperatures. In this article, we established a gas discharge model of the carbon nanotube film temperature sensor. Field assisted thermal emission is simulated at the tip of carbon nanotubes by analysing the field enhancement effect and effective work function. Ionization collision, excitation, recombination collision, Penning ionization and quenching of argon are considered in order to obtain the interaction of various particles at different temperature. The current density-temperature characteristic of the temperature sensor was obtained at 24-80 V. The increase of the working voltage is helpful to improve the output current and sensitivity of the temperature sensor. Response time of the sensor will not change in the temperature range of 293-373 K. However, the change of temperature will affect the current density, secondary electron emission and reaction rate. In addition, the sensor has different temperature sensitivity in Argon and Helium. The above simulation results are helpful to understand the role of carbon nanotube film and temperature sensitivity of the ionized sensor. It can also be used to study and improve the sensitivity of this type of sensor.

Effect of fluid inertia force on thermal elastohydrodynamic lubrication of elliptic contact

Abstract: A non-Newtonian thermal elastohydrodynamic lubrication (TEHL) model for the elliptic contact is established, into which the inertia forces of the lubricant is incorporated. In doing so, the film pressure and film temperature are solved using the associated equations. Meanwhile, the elastic deformation is calculated with the discrete convolution and fast Fourier transform (DC-FFT) method. A film thickness experiment is conducted to validate the TEHL model considering the inertia forces. Further, effects of the inertia forces on the TEHL performances are studied at different operation conditions. The results show that when the inertia forces are considered, the central and minimum film thicknesses increase and film temperature near the inlet increases obviously. Moreover, the inertial solution of the central film thickness is closer to the experimental result compared with its inertialess value.