Global Thermal Effects Research Articles

Numerical and experimental investigation of textured journal bearings for friction reduction

This work investigates the mechanisms for friction reduction in textured journal bearings. The measured friction of laser-etched connecting-rod big-end shells was compared with a non-textured reference under engine-like conditions. Experiments covered several working conditions, and the friction and lubricant film temperatures were measured for three texture configurations. The origin of the verified friction reduction was explored using a numerical model that simulates the hydrodynamic lubrication and global thermal effects. The simulation results accurately matched the friction measurements, revealing that the microscopic mechanisms of reduction in lubricant shear stress and effective viscosity due to texture-induced cavitation act simultaneously to reduce the friction coefficient for the textured shells. The findings have practical applications for the optimal design of textured hydrodynamic bearings.

Research on Thermal Characteristics of Internal Ventilated Paths in Compact Medium High- Voltage Motor Based Fluid Network Decoupling

Aiming at the problem that it is difficult to model and analyze the thermal effect of large motors as a whole, a method based on fluid network decoupling is proposed to solve the global thermal effect of large motors. Taking YJKK500-4 2500-kW compact medium-sized high-voltage motor as an example, combined with the internal structure and the actual size of the motor, and using the flow-heat coordination mechanism and the fluid network, the whole internal ventilated paths of motor are divided into four equal pressure regions: end, stator-rotor, end, and internal fan according to the magnitude of pressure. The reasonable basic assumptions and boundary conditions are selected to link each region, which can avoid the problem that the inlet boundary condition is difficult to give. After that, the internally ventilated paths are modeled and analyzed, and the fluid flow and temperature in each region of the internally ventilated paths are obtained. Combined with the experimental data, the calculation results are all within the error. The rationality and correctness of the method used in the paper are confirmed, which solves the problem that the ordinary computer cannot calculate the huge model of large motor and provides a basis for the calculation of similar motor in the future.

Investigation of global thermal effect of large fused silica surface figuring using inductively coupled plasma

Inductively coupled plasma (ICP) machining at atmospheric pressure has been used widely in fabrication of optical elements. However, the non-convergence caused by the global thermal effect is regarded as an inevitably issue for applying ICP to figure large fused silica optical surface. In this paper, according to the detailed investigation of the surface temperature distribution of the global thermal effect, a new method of round-trip repetitive tool path is proposed as a convenient way to balance the global thermal effect for making large fused silica surface error rapidly convergence. Experiment result shows that a work-piece with a size of 200 × 200 × 20 mm3 is successfully figured with this method. Result demonstrates that this method can realize rapid convergence for large fused silica optical surface. The presented study can provide convenient technical guidance of efficient fabrication for large fused silica optics by ICP surface figuring.

A numerical study on heat-recirculation assisted combustion for small scale jet diffusion flames at near-extinction condition

In order to prove the existence of heat-recirculation (through burner wall) assisted flame stabilization mechanism for miniaturized jet diffusion flames, a series of two-dimensional axisymmetric numerical computations are performed for methane–air flames over a sub-millimeter (constant inner diameter of 0.8mm) jet. A skeletal mechanism including 17 species and 58 steps is employed for the chemical kinetics and detailed transport properties are considered. Burner is considered as thermally conductive and chemically inert. Heat fluxes responsible for heat recirculation (feedback) (Qre) and heat loss (Qloss) through the burner surfaces are calculated respectively from the numerical results. An effective excess-enthalpy (H) is defined and used to measure the global thermal effect of the burner on the flame. A wide range of fuel jet velocities (V, from the minimum value to sustain a steady state flame to 3.2m/s) for different burners with various thermal conductivities (kb, from 1.0W/m-K to 100W/m-K, which covers most of the realistic burner materials) and wall thicknesses (cb, from 0.2mm to 0.8mm) are considered in this work. The results show that, as V increases, the ratio of Qre to Qloss monotonically increases, resulting in a critical fuel jet velocity Vc, above which Qre exceeds Qloss and thus the heat recirculation effect could cancel out the heat loss effect by the presence of the burner. Further, it is suggested that the Vc can be reduced by reducing kb and cb, hence, heat-recirculation assisted combustion is found to be promoted at near extinction condition under such burner system. Flame temperatures are significantly elevated as kb or cb decreases at near extinction conditions, revealing that the extinction limit in fuel jet velocity can be extended under specific condition. Computations are then conducted for flames of hydrogen and dimethyl ether to examine the fuel dependence. It is indicated that the flame–burner thermal interaction is influenced by both physical properties of the fuel (Sc number) and chemical kinetics. For the fuels with Sc > 1, such as dimethyl ether (Sc = 1.2), flame is readily to be lifted, resulting in negligible flame–burner interaction (H ≈ 0). For the fuels with Sc < 1, such as methane (Sc = 0.7) and hydrogen (Sc = 0.2), chemical kinetics that dominating the flame base structure becomes the key factor. Due to the flame–burner attachment, an extremely high H can be expected for a hydrogen jet diffusion flame to achieve excess-enthalpy combustion at certain condition. Overall, this study implies that, given the narrow operation flow rate range restrained by the quenching and the blow off limits in a premixed combustion system, heat recirculation assisted stable combustion could be possible in a relatively wider flow rate (power output) range by choosing a diffusion combustion mode.

Macroscopic aspects of the Unruh effect

Macroscopic concepts pertaining to the Unruh effect are elaborated and used to clarify its physical manifestations. Based on a description of the motion of accelerated, spatially extended laboratories in Minkowski space in terms of Poincaré transformations, it is shown that, from a macroscopic perspective, an accelerated observer will not register with his measuring instruments any global thermal effects of acceleration in the inertial (Minkowskian) vacuum state. As is explained, this result is not in conflict with the well-known fact that microscopic probes used as thermometers respond non-trivially to acceleration if coupled to the vacuum. But this response cannot be interpreted as the effect of some exchange of thermal energy with a gas surrounding the observer; in fact, it is induced by the measuring process itself. It is also shown that genuine equilibrium states in a uniformly accelerated laboratory cannot be spatially homogeneous. In particular, these states coincide with the homogeneous inertial vacuum at sufficiently large distances from the horizon of the observer and consequently have the same (zero) temperature there. The analysis is carried out in the theory of a free massless scalar field; however the conclusion that the Unruh effect is not of a macroscopic thermal origin is generally valid.

Performance degradation in scratched journal bearings

In this work, performance degradation in scratched journal bearings is evaluated by means of numerical simulations. A hydrodynamic numerical model with global thermal effects is employed (lubricant temperature and viscosity are assumed to be uniform). A very fine mesh is used, which allows a deterministic representation of a large number of circumferential scratches of various sizes and rectangular cross-shape. The severity of the scratches is quantified using four parameters: their depth, the extent of the scratched region, the density of the scratches and the position of the scratched region with respect to the bearing mid-plane. The influence of each of these parameters is studied independently. In order to evaluate bearing performance degradation, several operating parameters are computed, including minimum film thickness, average oil temperature and maximum hydrodynamic pressure. Lastly, charts are presented showing the evolution of the different bearing operating parameters as a function of the scratch severity, allowing the identification of critical scratch configurations that can lead to bearing damage.

Modular Thermal Sensors in Temperature-Gated TRP Channels

A group of ion channels in the TRP family, the so-called thermal TRP channels, exhibit unprecedentedly strong temperature dependence, some of which reach Q10 > 100 as compared to 2-3 for typical enzymatic reactions. The strong thermal sensitivity of these channels arises because their gating involves large enthalpy changes between closed and open. To quantify the energetics of gating, we applied optically generated submillisecond temperature jumps to directly measure the temperature-dependent activation kinetics. The data show that the opening of TRPV1, for example, is accompanied with an enthalpy change of ∼100 kcal/mol, five times the energetic changes in voltage- or ligand-dependent gating. To gain insights on the energetic source, we analyzed single-channel and macroscopic kinetics of temperature-dependent gating, both showing that temperature has localized effects on specific gating components. Furthermore, the perturbation of membrane compositions, which altered the physical properties of lipids such as temperature-dependent phase transitions, did not abolish temperature activation of the channel. Thus the thermal sensitivity of the channel appears to be intrinsic to the channel itself, most likely arising from a specific protein domain rather than integration of global thermal effects. Using systematic chimeric analysis, we uncovered a proximal N-terminal region to be crucial for temperature sensing in heat-activated TRPVs. Changing this region both successfully transferred thermal sensitivity to temperature-insensitive isoforms and profoundly altered thermal sensing in temperature-sensitive wild-type channels. Swapping other domains including the whole transmembrane core, the C terminus, and the rest of the N terminus had little effect on the large enthalpy of gating. These results support that thermal TRP channels contain modular thermal sensors for their activation by temperature.

Modular thermal sensors in temperature-gated transient receptor potential (TRP) channels

The molecular basis of the thermal sensitivity of temperature-sensitive channels appears to arise from a specific protein domain rather than integration of global thermal effects. Using systematic chimeric analysis, we show that the N-terminal region that connects ankyrin repeats to the first transmembrane segment is crucial for temperature sensing in heat-activated vanilloid receptor channels. Changing this region both transformed temperature-insensitive isoforms into temperature-sensitive channels and significantly perturbed temperature sensing in temperature-sensitive wild-type channels. Swapping other domains such as the transmembrane core, the C terminus, and the rest of the N terminus had little effect on the steepness of temperature dependence. Our results support that thermal transient receptor potential channels contain modular thermal sensors that confer the unprecedentedly strong temperature dependence to these channels.

Wall and fluid inlet temperature effect on heat transfer in incompressible laminar oscillating flows

This paper deals with the problem of oscillating flows occurring in devices such as Stirling or thermoacoustic engines and refrigerators. Since the global governing equations cannot be solved, the authors propose to introduce a few simplifications; the most simplifying reduction is that the fluid is assumed to be incompressible. However, specific attention is paid to describing the flow characteristics that's why the Lagrangian formalism which allows the individual study of each fluid particle is adopted. Thereby each particle contribution to global thermal effects can be evaluated and the gas temperature profiles along the exchanger can be computed. Various situations are presented including the case of a non-uniform temperature at the wall and a phase lag between pressure and temperature at the fluid entrance. The efficiency of the wall to fluid thermal exchange is analyzed. The authors show that this exchange depends upon two important parameters: the geometric ratio between the exchanger length and the particle oscillating displacement, and a thermal parameter “ β”, governing the temperature profiles and related to the Prandtl number, the operating frequency and the phase lag between the instantaneous heat flux and the wall to fluid temperature difference.

Global thermal and dynamical perturbations due to Cretaceous mantle avalanche

The numerical models of mantle convection agree to depict avalanches behaviour according to the level of endothermicity of the spinel → perovskite phase change. Their potential effects on the global thermal and dynamical states of the mantle have been computed thanks to a numerical code, which takes into account both the 400-km exothermic and the 660-km endothermic phase changes. The cycle followed by the avalanches is: local layering, destabilization of the 660-km thermal layer, travelling and spreading on the core, and reappearing of the local layering. Therefore, mantle convection is characterized by quiet periods of partial layering embedded in catastrophic events. During the avalanche, the amplitude of the surface velocity is multiplied by two, which would imply an enhanced plate tectonic and ridge activities. The global thermal effects of the avalanche are compatible with a high mantle temperature and an acceleration of Earth's rotation during the Cretaceous. They also offer a coherent explanation to locate the origin of mantle plumes both within the CMB and just below the transition zone.

Cretaceous length of day perturbation by mantle avalanche

These last 10 years, numerical models of mantle convection have emphasized the role of the 670 km endothermic phase change in generating avalanches that trigger catastrophic mass transfers between upper and lower mantle. On the other hand, scientists have emphasized the concomitance of large-scale worldwide geophysical and tectonic events, which could find their deep thermal roots in the huge mass transfers induced by the avalanches. In particular, the paleontological records show two periods of length of day (l.o.d.) shortening between 420 and 360, and 200 and 80 Myr BP. This last event is synchronous with a strong true polar wander and a global warming of the upper mantle. In order to study the potential effects of the avalanche on the main component of the Earth’s rotation, the Liouville equation has been solved and the l.o.d. evolution has been calculated from the perturbations of the inertia tensor. The results show that the inertia tensor of the Earth’s is mainly sensitive to the global transfers through the 670 km discontinuity. The l.o.d. perturbations will be synchronous with the global thermal effects of the avalanche. These theoretical results allow proposing a self-consistent physical mechanism to explain periods of the Earth’s rotation acceleration. Within this context, the l.o.d. shortening during the Cenozoic and Cretaceous brings one more clue to the possible participation of a mantle avalanche in generating the concomitant large scale events which have occurred during this very particular period of the Earth’s history.

5615556 Free-piston vuilleumier heat pump

This paper deals with the problem of oscillating flows occurring in devices such as Stirling or thermoacoustic engines and refrigerators. Since the global governing equations cannot be solved, the authors propose to introduce a few simplifications; the most simplifying reduction is that the fluid is assumed to be incompressible. However, specific attention is paid to describing the flow characteristics that's why the Lagrangian formalism which allows the individual study of each fluid particle is adopted. Thereby each particle contribution to global thermal effects can be evaluated and the gas temperature profiles along the exchanger can be computed. Various situations are presented including the case of a non-uniform temperature at the wall and a phase lag between pressure and temperature at the fluid entrance. The efficiency of the wall to fluid thermal exchange is analyzed. The authors show that this exchange depends upon two important parameters: the geometric ratio between the exchanger length and the particle oscillating displacement, and a thermal parameter “β”, governing the temperature profiles and related to the Prandtl number, the operating frequency and the phase lag between the instantaneous heat flux and the wall to fluid temperature difference.

Effect of the thermodynamic affinity of plasticizers for polyvinyl chloride on the heat of its interaction with fillers

A microcalorimeter of the Calvé type has been used to determine the heats of swelling of PVC in four plasticizers and heats of wetting by the latter of chalk, kaolin and Aerosil and the heats of the interaction of plasticized PVC with these fillers. It is shown that the energy interaction of PVC with the filler is due to the competing influence of its heats of swelling in the plasticizers and the heats of wetting by the latter of the fillers. For identical thermodynamic affinity of the plasticizers for PVC the global thermal effect of the interaction of plasticized PVC with filler is more negative the greater the heat of wetting by the plasticizer of the filler. For identical heats of wetting by the plasticizers of the PVC filler the worse PVC interacts energetically with the filler, the greater the thermodynamic affinity of the plasticizer and the greater the heat of swelling of PVC.