Bulk Temperature Rise Research Articles

The importance of cell uptake in photothermal treatments mediated by biomimetic magnetic nanoparticles

Biomimetic magnetic nanoparticles (BMNPs) mediated by MamC have proven to be photothermal agents able to allow an optimized cytotoxicity against tumoral cells when used simultaneously as drug nanotransporters and as hyperthermia agents. However, it remains unclear whether BMNPs need to be internalized by the cells and/or if there is a threshold for internal Fe concentration for the photothermal therapy to be effective. In this study, three different situations for photothermal treatments have been simulated to disentangle the effect of BMNPs cell uptake on cell viability after photothermal treatments. Human hepatoblastoma (HepG2) cell line was treated with suspensions of BMNPs, and protocols were developed to have only intracellular BMNPs, only extracellular BMNPs or both, followed by photothermal exposure of the treated cell cultures. Our data demonstrate that: (1) Although the heating efficiency of the photothermal agent is not altered by its location (intra/extracellular), the intracellular location of BMNPs is crucial to ensure the cytotoxic effect of photothermal treatments, especially at low Fe concentration. In fact, the concentration of BMNPs needed to reach the same cytotoxic effect following upon laser irradiation of 0.2 W/cm2 is three times larger if BMNPs are located extracellularly compared to that needed if BMNPs are located intracellularly; (2) For a given location of the BMNPs, cell death increases with BMNPs (or Fe) concentration. When BMNPs are located intracellularly, there is a threshold for Fe concentration (∼ 0.5 mM at laser power intensities of 0.1 W/cm2) needed to affect cell viability following upon cell exposure to photothermia. (3) Bulk temperature rise is not the only factor accounting for cell death. Actually, temperature increases inside the cells cause more damage to cell structures and trigger cell death more efficiently than an increase in the temperature outside the cell.

Multiple mesoscopic hotspot mechanisms model and its applications in drop impact hazard simulations

ABSTRACT Due to the complex stress state (shearing, compression, friction, etc.) of the charged polymer-bonded explosives (PBXs) under accidental drop impact loading, a physical model is needed to describe the hotspot formation and ignition responses to predict the safety of PBXs. A mechanical-thermal-chemical-coupled model incorporating microcrack and microvoid-related damage followed by ignition, which is predicted based on an innovative defect-related ignition criterion of effective inelastic work, is developed to evaluate PBX charge hazards under drop impact loading. The results show that (i) microcrack hotspots play a critical role in the total temperature under low-velocity (<175 m/s) drop impact loading. Under high-velocity (>175 m/s) drop impact loading, microvoid hotspots become the dominant position owing to the timescale of the microvoid hotspot formation being shorter (~10 μs), (ii) the bulk temperature rise can be ignored for its insignificant contribution to the calculation of total temperature, and (iii) a defect-related criterion model is established which is suitable for determining threshold velocity for dropped PBX charge ignition occurrence. The simulated pressure and defect-related ignition response of PBXs are in good agreement with the tests performed by China Academy of Engineering Physics.

Sliding wear response of ultrasonic-assisted stir-squeeze cast Al-Zn(-Mg) alloy/ZrO2p composite: wear mechanism and subsurface deformation

The character of hard ZrO2p in dry sliding wear of Al-Zn(-Mg) alloy was investigated in the cast and heat-treated conditions using a pin-on-disc wear tester at fixed sliding speed (3.5 m s−1) and varying applied pressure (0.5–2.125 MPa), giving special accentuation on the response parameters such as seizure resistance, wear rate, and bulk temperature rise. Hardness behavior was also studied for the same concerning materials in accordance with ASTM standards. The composites exhibited enhanced hardness, wear and seizure resistance, and greater temperature rise over the alloy. Indeed, the wear rate at preliminary stages increased with increasing applied pressure up to a transition limit beyond which it upsurged abruptly to greater value at the seizure pressure. Heat treatment also significantly improved the hardness, and resistance to wear and seizure. Amongst, heat-treated composite embedded with 4% ZrO2p yielded the highest hardness of 180 HV and seizure pressure of 2.125 MPa, respectively. The deformation in the subsurface was examined in terms of microhardness variation along the depth perpendicular to the worn surface. It was detected that the presence of ZrO2p not only enhanced the seizure resistance but also effectively hampered the extent of subsurface deformation at the seizure. The wear mechanism was prevalently governed through the establishment of the mechanically mixed layer (MML), oxide layer, cracking, and deformed subsurface.

An experimental study on dynamic deformation and ignition response of a novel propellant under impact loading

Investigations on high-energy and low-vulnerability propellants can provide a guarantee for improving the power and safety of solid rocket motors. In the present study, mechanical-thermal coupled responses were recorded by a high-speed infrared thermal imaging systems. The dynamic compressive properties and damage-ignition response mechanism under high strain rates of a novel type of propellant were studied, using a split Hopkinson pressure bar apparatus. The experimental results suggested that the mechanical properties of the novel propellant, in terms of yield stress, initial compressive modulus, and ultimate stress, were greatly affected by the loaded strain rate. The stress-strain responses exhibited an initial linear elasticity region, followed by yielding, and then a subsequent strain hardening or softening stage (plateau region), which was strongly dependent on the strain rate. It was found that the yield stress and ultimate stress increased with the strain rates. Moreover, the ignition response was accentuated at higher strain rates, resulting in an earlier and more intense ignition. According to the high-speed images and the post-test SEM images, the critical strain rate for ignition is 4500 s−1. Finally, by calculating the bulk and local temperature rise (considering the friction mechanism), it is clear that the dominant ignition mechanism of the novel propellant is the friction which is macroscopically represented as viscous shear flow.

Synergistic effects of iron and hexagonal-Boron Nitride additions in copper-based composites for braking application

This paper explores the addition of h-BN and iron to Cu-based brake pads on the performance benefits. It also investigates the effect of graded layering by synthesizing three and four-layer brake pads by powder compaction and sintering route. The top one or two layers are made of Cu-based composite containing Fe, h-BN, and W, while the middle layer is pure Cu and, bottom steel plate. Two different compositions were explored for the composites by varying Fe content. From the two composite compositions, brake pads with single-layer composite or two-layer composite were synthesized. Characterization of brake pad specimens was carried out using density measurements, optical microscopy, scanning electron microscopy, energy dispersive spectroscopy. The brake pads were subjected to simulated braking tests at braking energy/cycle of 60, 96, and 136 K Joules. Wear rate, coefficient of friction, stopping distance, stopping time, and hardness were measured and compared among other brake pads. The brake pad containing single-layer Fe rich Cu composite showed the best performance in the simulated braking tests. EDS analysis of wear debris shows the formation of iron (boride, nitride, oxide) complex which is indicative of a surface with superior dry lubricating properties. This surface is a result of synergetic interaction between h-BN and Fe particles. The iron particles which are scattered in the Cu matrix composite act as low friction regions on the brake pad surface that interrupt the high friction regions on the Cu matrix, thus reducing the local and bulk temperature rise. The two-layer composite brake-pad showed performance intermediate to the two single-layer brake pads. No advantage due to higher thermal conductivities in Fe deficient composite was observed as the two composite layers, showed similar Fe contents in their matrix phases.

Experimental exploration for the performance improvement of a thrust ball bearing using circumferential micro-grooved races

This paper presents the findings of an experimental study performed for exploring and improving the tribodynamic performance behaviours of a thrust ball bearing employing circumferential micro-grooves on the stationary upper race. Investigations were conducted using oil and grease lubricants and operating the bearings at light loads (in the vicinity of requisite minimum loads characterised by pH = 0.4 and 0.6 GPa) and speeds varying in the range of 1.8–4.0 m s−1 at the ambient condition. The effects of micro-grooved stationary races on frictional torque, temperature rise and vibrations of the bearings were measured and have been discussed herein. The surface topographies of races and balls of used test bearings were examined after finishing the experiments for extracting the surface topographies based technical information. Significant reductions in the magnitudes of frictional torque (14%–21%), bulk temperature rise of race (14%–26%), vibrations (7%–34%) were found with micro-grooved bearings (pair of conventional moving lower races and micro-grooved upper stationary races) in comparison to the conventional bearings (pair of conventional races). Moreover, the oil lubricated micro-grooved bearings yielded substantial improvement in the tribo-dynamics as compared to grease lubricated case irrespective of the operating parameters i.e. loads and speeds.

Understanding the behaviour of workpieces' bulk temperature during laser-assisted turning of Ti6Al4V alloy and heating of Al-SiC metal-matrix composite rods

Although laser-assisted turning (LAT) has been studied for decades, little is known on the effect of bulk temperature rise and residual temperature in the workpiece. Here we report an investigation on a comparison of bulk temperature characteristics in LAT of Ti6Al4V alloy and laser heating of Al/SiC metal matrix composite (MMC) as the two materials have significant differences in thermal conductivities. The research shows that at a low cutting speed with a low laser power density, and a larger laser beam spot, commonly used in previous LAT processing of Ti6Al4V alloy and Al/SiC MMC processes, it may cause too much heat accumulation inside the bulk material, particularly for the material with higher thermal conductivity. A new processing strategy for LAT is proposed based on this study, which combines high cutting speed, high laser power density, and a smaller laser beam spot size to avoid heat accumulation in the workpiece bulk and energy wastage during LAT of materials with high thermal conductivities. Besides, it is found that the cutting tool temperature at 0.3 mm cutting depth is higher than that at 0.5 mm cutting depth during LAT of Ti6Al4V, which is opposite to that in conventional machining.

Analysis of flow and heat transfer through a partially blocked fuel subassembly of fast breeder reactor

The influence of local porous flow blockage in the active region of a prototype fuel subassembly having 217 helical wire wrapped pins and five helical pitch length of a sodium cooled fast reactor has been investigated. A non-Darcy porous flow model has been adopted for the investigation. The prediction capability of the model has been validated against the published sodium experiments on a 19-pin electrically heated bundle. The blockage parameters, viz., radius, axial height, porosity and debris size have been systematically varied over a range of practical interest. The critical blockage height that leads to risk of local sodium boiling within blockage (i.e. clad temperature approaching sodium boiling point) has been determined as a function of other parameters. The parametric zone which is safe has been identified from the study. Radial extent of blockage and blockage porosity are found to be the most important parameters that influence the thermal hydraulic characteristics. In the wake region behind the blockage, flow gets established within a short length. However thermal mixing is incomplete. The local porous blockage does not significantly alter the total pressure drop in the bundle region, suggesting bulk temperature rise of sodium in the subassembly will be very marginal, though there can be a risk of local sodium boiling and associated clad failure.

A study on the potential of carbon-based nanomaterials for enhancement of evaporation and water production

In the present study, the performance of water based-nanofluids containing four different types of carbon nanostructures for solar vapor generation has experimentally been investigated. The considered nanofluids are multi-walled carbon nanotube, single-walled carbon nanotube, graphene nanoplate and graphene oxide. Nanofluids with three nanoparticle mass concentrations of 0.001%, 0.002%, and 0.004% were prepared and their evaporation characteristics were investigated for solar radiation intensities in the range of 1.5 and 3.5 Suns. The results indicated that the multi-walled carbon nanotube nanofluid with a mass concentration of 0.004% provides the highest evaporation rate with the maximum total efficiency of 94% at 3.5 Suns. The total efficiencies for nanofluids containing the single-walled carbon nanotube, graphene nanoplate and graphene oxide at similar conditions and that of pure water, respectively, are about 91%, 90%, 81% and, 54%. Furthermore, it is observed that for the mass concentration of 0.004%, the evaporation rate with respect to water increases to about 72%, 63%, 58% and 36%, respectively, for the multi-walled carbon nanotube, the single-walled carbon nanotube, graphene nanoplate and graphene oxide nanofluids. As far as the sensible heat is concerned, graphene oxide shows the most considerable sensible heating efficiency at the mass concentration of 0.004% with the maximum fluid bulk temperature rise of 20.5 °C, which is 40% higher than that of water. Finally, it was found that increasing the radiation intensity from 1.5 to 3.5 Suns improves the evaporation rate; however, the sensible heat efficiency is more influenced such that the evaporation efficiency declines. The quality of the produced water from a seawater sample is also examined and it was shown that it is well below the limitations of the drinking water standards.

Combining Bulk Temperature and Nanoheating Enables Advanced Magnetic Fluid Hyperthermia Efficacy on Pancreatic Tumor Cells

Many efforts are made worldwide to establish magnetic fluid hyperthermia (MFH) as a treatment for organ-confined tumors. However, translation to clinical application hardly succeeds as it still lacks of understanding the mechanisms determining MFH cytotoxic effects. Here, we investigate the intracellular MFH efficacy with respect to different parameters and assess the intracellular cytotoxic effects in detail. For this, MiaPaCa-2 human pancreatic tumor cells and L929 murine fibroblasts were loaded with iron-oxide magnetic nanoparticles (MNP) and exposed to MFH for either 30 min or 90 min. The resulting cytotoxic effects were assessed via clonogenic assay. Our results demonstrate that cell damage depends not only on the obvious parameters bulk temperature and duration of treatment, but most importantly on cell type and thermal energy deposited per cell during MFH treatment. Tumor cell death of 95% was achieved by depositing an intracellular total thermal energy with about 50% margin to damage of healthy cells. This is attributed to combined intracellular nanoheating and extracellular bulk heating. Tumor cell damage of up to 86% was observed for MFH treatment without perceptible bulk temperature rise. Effective heating decreased by up to 65% after MNP were internalized inside cells.

Nitrogen oxide emissions from rich premixed reacting jets in a vitiated crossflow

This paper describes NOx measurements from reacting jets in crossflow (RJICF). This work is motivated by interest in axial staging of combustion as a means of reducing NOx emissions at high flame temperatures (>1900 K), where thermal NOx production rates are high. In this approach, the majority of the fuel is burned in a conventional lean-premixed flame, but additional fuel is injected from the combustor walls into the vitiated flow further downstream. The NOx emissions of RJICF are influenced by the secondary fuel jet stoichiometry, jet/crossflow mixing before combustion, as well as secondary combustion product mixing with the bulk product stream. In turn, jet/crossflow mixing is controlled by the hydrodynamic stability of the jet, as well as degree of flame lifting. A key challenge in understanding fundamental factors influencing NOx is decoupling the effect of bulk temperature rise due to the RJICF (∆T), JICF momentum flux ratio (J), and JICF stoichiometry (ϕJet), as they cannot be varied independently. As such, significant effort was made in developing a test matrix to differentiate their effects. Measurements reported here were obtained from rich premixed methane/air jets injected into a varying temperature (1650 K–1800 K) vitiated crossflow, for bulk temperature rises from 20 K–290 K, J values from 1.3–4.4, and ϕJet values from 1–9. These measurements show that NOx emissions monotonically increase with ∆T, as noted in prior studies, but the data reported here are able to differentiate the effects of ∆T and other parameters. In fact, for a given ΔT value, NOx values can vary by 2X depending upon other parameters. For example, the lifting of the flame (LO), which varies with ϕJet and J has significant effects on NOx emissions. These data suggest that the key fundamental JICF parameters influencing NOx emissions are ∆T, ϕJet, J, and LO.

Is frictional heating needed to cause dramatic weakening of nanoparticle gouge during seismic slip? Insights from friction experiments with variable thermal evolutions

AbstractTo examine whether faults can be lubricated by preexisting and newly formed nanoparticles, we perform high‐velocity friction experiments on periclase (MgO) nanoparticles and on bare surfaces of Carrara marble cylinders/slices, respectively. Variable temperature conditions were simulated by using host blocks of different thermal conductivities. When temperature rises are relatively low, we observe high friction in nano‐MgO tests and unexpected slip strengthening following initial weakening in marble slice tests, suggesting that the dominant weakening mechanisms are of thermal origin. Solely the rolling of nanoparticles without significant temperature rise is insufficient to cause dynamic fault weakening. For nano‐MgO experiments, comprehensive investigations suggest that flash heating is the most likely weakening mechanism. In marble experiments, flash heating controls the unique evolutions of friction, and the competition between bulk temperature rise and wear‐induced changes of asperity contact numbers seems to strongly affect the efficiency of flash heating.

Unified approach for conjugate heat-transfer analysis of high speed air flow through a water-cooled nozzle

ABSTRACTThis article presents a unified approach to solve steady-state conjugate heat-transfer problem including simultaneously gas, liquid and solid regions in just one 3D domain, distinguished by their particular properties. This approach reduces approximation errors and the time to solve the problem, which characterise iterative methods based on separated domains. The formulation employs RANS equations, realisablek-ε turbulence model and near-wall treatment model. A commercial CFD code solves the pressure-based segregated algorithm combined with spatial discretisation of second order upwind. The problem consists of a convergent-divergent metallic nozzle that contains cooling channels divided in two segments along the wall. The nozzle wall insulates the high-speed hot air flow, dealt as perfect gas, from the two low-speed cold water flows, dealt as compressed liquid, both influenced by transport properties dependent of the local temperature. The verification process uses three meshes with increasing resolutions to demonstrate the independence of the results. The validation process compares the simulation results with experimental data obtained in high-enthalpy wind tunnel, demonstrating good compliance between them. Results for the bulk temperature rise of the water in the second cooling segment of the nozzle showed good agreement with available experimental data. Numerical simulations also provided wall temperature and heat flux for the gas and liquid sides. Besides, distribution of temperature, pressure, density and Mach number were plotted along the nozzle centerline showing a little disturbance downstream the throat. This phenomenon has been better visualised by means of 2D maps of those variables. The analysis of results indicates that the unified approach herein presented can make easier the task of simulating the conjugate convection-conduction heat-transfer in a class of problems related to regeneratively cooled thrust chambers.

Examination of Electrical Conduction of Carbonyl Iron Powder Compacts

In this study, we report the electrical conduction of carbonyl iron powder compacts when a constant voltage/current source is supplied, especially under a typical voltage 9.7V of electric current activated sintering (ECAS). The potential driving forces for resistance drop during stressing, including bulk temperature-dependent and -independent, were discussed. By using a proposed competition mechanism and percolation theory, it can successfully describe electrical behavior in metal powder compacts. The results indicate bulk temperature rise resulting from Joule heating is the main cause for the formation and growth of metallic contact at particle interfaces during ECAS. [doi:10.2320/matertrans.M2014311]

Model for the prediction of bulk temperature changes and pressure losses in rubber compounds flowing through conical dies: An engineering approach

The bulk temperature is a very important parameter for the processing of rubber compounds. Currently, standard injection molding simulation is taking into account just shear heating, while elongational heating is neglected by most available software tools. A new viscous model for the prediction of temperature changes in rubber compounds flowing through conical dies and runner segments was deduced where elongational heating is considered as well. Shear viscosity was directly measured on a Capillary Rheometer and elongational viscosity was calculated from the inlet-pressure drops using a new approach. To verify the theoretical calculations experiments on a rubber injection molding machine were carried out by means of a specially designed mold. Varying injection speed and the die angle bulk temperature measurements in the purged material were performed. The measured bulk temperature rise showed a dependence on the flow rate and the cone angle with the flow rate being dominant. The results of the temperature measurements showed good correlation with the model results with an average error being <5%. POLYM. ENG. SCI., 55:701–709, 2015. © 2014 Society of Plastics Engineers

Chemical stability of molten 2,4,6-trinitrotoluene at high pressure

2,4,6-trinitrotoluene (TNT) is a molecular explosive that exhibits chemical stability in the molten phase at ambient pressure. A combination of visual, spectroscopic, and structural (x-ray diffraction) methods coupled to high pressure, resistively heated diamond anvil cells was used to determine the melt and decomposition boundaries to &amp;gt;15 GPa. The chemical stability of molten TNT was found to be limited, existing in a small domain of pressure-temperature conditions below 2 GPa. Decomposition dominates the phase diagram at high temperatures beyond 6 GPa. From the calculated bulk temperature rise, we conclude that it is unlikely that TNT melts on its principal Hugoniot.

502 関節シミュレータを用いた人工股関節の摩耗試験におけるバルク温度上昇の影響

502 関節シミュレータを用いた人工股関節の摩耗試験におけるバルク温度上昇の影響

The efficiency of a hypoid axle—a thermally coupled lubrication model

The final drive unit in road vehicles, such as medium and heavy trucks, and four-wheel-drive and rear-wheel-drive passenger cars, usually consists of a hypoid or spiral bevel geared transmission and differential, housed in a self-contained, dip-lubricated axle. Such units are subjected to very variable duty—including extreme combinations of speed, gradient, applied torque and external temperature—and are typically cooled by natural and forced convection on the exterior surface. On the other hand, there are appreciable internal power losses due to gear friction and churning and to bearing and seal losses. These losses are highly dependent upon the lubrication regime of the internal components and hence to the thermal behaviour of the entire axle.In the present paper, we describe a thermally coupled model of axle lubrication. The torque and speed demand is first found from a specified duty (“drive cycle”) which includes terrain as well as speed-versus-time and external temperature data. The evolution of sump oil and component temperatures is followed, and increments of energy loss evaluated in each time-step. Elastohydrodynamic film thickness is determined for the hypoid gear set, using a development of Buckingham's method, and friction losses calculated using a simple oil rheological model based on tribometer (MTM) testing. Churning, seal and bearing (speed-dependent) losses are found using empirical algorithms. Energy losses over complete drive cycles for different lubricants are derived, enabling the relative fuel economy for different oils to be evaluated.Results show that (i) the bulk temperature rise of the axle is highly dependent on the specified vehicle duty and (ii) the efficiency can be strongly influenced by choices available to the lubricant formulator. Taken together, these findings suggest that specialist axle lubricant formulations for particular vehicle types and applications will be attractive as a route to optimum fuel economy.

Nanoscale heating of laser irradiated single gold nanoparticles in liquid

Biological applications where nanoparticles are used in a cell environment with laser irradiation are rapidly emerging. Investigation of the localized heating effect due to the laser irradiation on the particle is required to preclude unintended thermal effects. While bulk temperature rise can be determined using macroscale measurement methods, observation of the actual temperature within the nanoscale domain around the particle is difficult and here we propose a method to measure the local temperature around a single gold nanoparticle in liquid, using white light scattering spectroscopy. Using 40-nm-diameter gold nanoparticles coated with thermo-responsive polymer, we monitored the localized heating effect through the plasmon peak shift. The shift occurs due to the temperature-dependent refractive index change in surrounding polymer medium. The results indicate that the particle experiences a temperature rise of around 10 degrees Celsius when irradiated with tightly focused irradiation of ~1 mW at 532 nm.

Magnetic resonance microwave absorption imaging: Feasibility of signal detection

Magnetic resonance (MR) technique was used to detect small displacements induced by localized absorption of pulsed 434 MHz microwave power as a potential method for tumor detection. Phase contrast subtraction was used to separate the phase change due to motion from thermoelastic expansion from other contributions to phase variation such as the bulk temperature rise of the medium and phase offsets from the MR scanner itself. A simple set of experiments was performed where the motion was constrained to be one dimensional which provided controls on the data acquisition and motion extraction procedures. Specifically, the MR-detected motion signal was isolated by altering the direction of the microwave-induced motion and sampling the response with motion encoding gradients in all three directions when the microwave power was turned on and turned off. Successful signal detection, as evidenced by the recording of a systematic alternating (zigzag) phase pattern, occurred only when the motion encoding was in parallel with either the vertical or horizontal direction of the microwave-induced motion on both 10 and 4 mm spatial scales. These results demonstrate, for the first time, that motion associated with thermoelastic expansion from the absorption of pulsed microwave power can be detected with MR.