Local Temperature Drop Research Articles

Development and validation of a fully coupled thermo-mechanical model for in-situ micro-rolling in laser-directed energy deposition: Single-track multi-layer case

Directed Energy Deposition (DED) has recently been hybridised with in-situ rolling, providing elevated temperature deformations and enhancing build quality. Analysing the thermo-mechanical aspects of deformations with sufficient fidelity can not be achieved experimentally. So, a fully coupled thermo-mechanical model for a multi-layer case using the finite element method has been developed to capture the thermal and mechanical facets of the deposition and rolling processes. Modelling features a hybrid active and quiet element activation strategy that mitigates convergence issues from activating a newly deposited layer over previously rolled ones. The model's predictions have been validated with reasonable accuracy against temperature history and rolling load measurements in an experimental case study using IN718. These predictions provide insights into the in-situ rolling effects with their quantification, including the impact on the thermal and stress-strain fields and histories. For instance, the temperature at the rolling location and the local temperature drop increase with the number of layers. The thermal stress induced by deposition overshadows the influence of in-situ rolling. The rolling deformation penetrates till the third preceding layer, and deposition leads to above the recrystallisation temperature reheating till the fourth layer. These predictions can be used for parametric optimisation with metallurgical criteria.

Droplet impact and Leidenfrost dynamics on a heated post

This study experimentally explores fluid breakup and Leidenfrost dynamics for droplets impacting a heated millimetric post. Using high-speed optical and infrared imaging, we investigate the droplet lifetime, breakup and boiling modes, as well as the cooling performance of different substrates. The post substrate leads to a shorter droplet lifetime and a 20 °C higher Leidenfrost temperature compared to a flat substrate, attributed to mixed boiling modes along the height of the post and additional pinning. For temperatures below the Leidenfrost point, in the nucleate boiling regime, the post substrate also provides a larger maximum temperature drop than its flat counterpart. The enhanced cooling capacity can be attributed to better droplet pinning and an enlarged droplet-substrate contact area. The post's superior cooling performance becomes especially clear for impact on an inclined surface, where the post successfully prevents the rolling and bouncing of the droplet, providing a 51% to 180% increase in the maximum local temperature drop. Interestingly, at temperatures slightly above the Leidenfrost point and for a relatively narrow range of Weber numbers, droplets on the post substrate rebound rather than break up due to a complex interplay of inertial, capillary, and bubble (thin film) dynamics. Overall, the findings show that a large-scale structure increases the Leidenfrost temperature and enhances droplet breakup and interfacial heat transfer efficiency during non-isothermal droplet impact.

The extinct shark, Ptychodus (Elasmobranchii, Ptychodontidae) in the Upper Cretaceous of central-western Russia—The road to easternmost peri-Tethyan seas

ABSTRACT Isolated teeth belonging to the genus Ptychodus Agassiz, 1834 (Chondrichthyes; Elasmobranchii) from the Upper Cretaceous of the Ryazan and Moscow Oblast regions (European Russia) are described and discussed in detail herein. The taxonomic composition of the Ptychodus assemblage from the Ryazan region is very diverse including the first records of the cuspidate species P. altior and P. anonymus, which thus is largely consistent with those from other contemporaneous European localities. Ptychodus ubiquitously inhabited epicontinental seas of Europe during most of the Cretaceous with the most diverse assemblages coming from southern England, northern Italy, Belgium, and European Russia. Additionally, the material documented here from the Cenomanian of Varavinsky ravine area (Moscow Oblast) represents the northernmost occurrence of Ptychodus hitherto reported from Europe. It is evident that the Late Cretaceous shallow seas of the Russian platform represented a crucial pathway for the dispersal of Ptychodus from the European peri-Tethys to the eastern margins of the Neo-Tethyan Ocean. The Albian–Campanian records of Ptychodus from Europe indicate that its dominance in the peri-Tethys persisted for most of its evolutionary history. A local temperature drop across most of the European shallow seas probably contributed to the narrowing of its geographic range in the peri-Tethyan seas towards the end of the Mesozoic Era. The fossil remains of Ptychodus documented herein are accordingly of utmost importance for better understanding the taxonomic composition of Russian fossil ichthyofaunas and also inform about the dispersal of Ptychodus towards western and eastern peri-Tethyan seas during the Late Cretaceous.

ЕКСПЕРИМЕНТАЛЬНЕ ДОСЛІДЖЕННЯ ПАРАМЕТРІВ НАДХОЛОНОЇ СИСТЕМИ НАДДУВАННЯ БАКА ПАЛЬНОГО РУШІЙНОЇ УСТАНОВКИ

The study is focused on modern rocket engine fuel tank pressurization systems. These systems use the after burn oxidative generator gas principle. The rocket engine can throttle. The pressurization system type was changed during ‘Zenith’ and ‘Energy’ design based on meticulous mathematical modeling results. The transition from the traditional hot helium pressurization system to a newer one was performed. The new methodology got a ‘super-cold’ naming. The feature is helium input with cryogenic-temperature (90-50K) into fuel tanks. All the source data is available at the design stage for super-cold pressurization systems, unlike hot/traditional ones. The new system turns out to be 30% lighter. The super-cold system parameters improvement via experimental data analysis is set as a goal of this study. The experimental results are compared with mathematically modeled. The tank gas pressure sufficient convergence is shown. Some gas temperature differences are explained by gas temperature layering. The in-flight temperature decrease over fuel temperature did not exceed 70K. The temperature difference was decreasing as engine work was finishing. The input fuel temperature drop on the pump was not detected. The fuel upper bottom local temperature drop did not exceed 7 degrees based on two measurements. The difference between modeled and actual cylinder output helium temperature (up to 20K by the end of engine operation) was shown. The hypothesis explaining the fact is established. The modeling methodology assumes the equivalent tank diameter to be one equal to its volume. This leads to reducing the calculated (actual) heat exchange surface. The analyzed experimental data powers further super-cold pressurization system design improvement.

Increasing the energy flexibility of existing district heating networks through flow rate variations

The possibility of recovering waste and renewable heat in urban areas has made district heating networks one of the key infrastructures for decarbonising the heating sector in Europe. The ability to shift the heat production over time is an important asset to improve the competitiveness of both new and existing networks. To this purpose, the present study evaluates the flexibility potential provided by the water volume enclosed in the network pipelines using the district heating network of Verona (Italy) as a case study.Given the users heat demand in two representative weeks, computer simulations were carried out to calculate the network's thermal response to circulating flow rate variations. The latter were designed to cause an early or late shift in the daily peak thermal load. The local temperature drop at the users substations compared to the current situation was used as a relative discomfort indicator. The simulations were carried out using the model NeMo, which has been attached as supplementary material to this publication. The simulation results show that the network pre-charge strategy achieves significant benefits in terms of both peak shaving and load shifting with a limited impact on discomfort for the users. Furthermore, the paper shows that the available storage capacity of the network is significantly influenced by the duration of the flow adjustment, by the average velocity of the heat carrier fluid and by the daily heat demand pattern. Finally, it is shown that the energy flexibility of the network also depends on its topology. In this regard, the article provides preliminary indications on the number and position of the bypass pipes needed to implement the proposed flow rate variations.In conclusion, the article shows that the thermal inertia of the heat carrier fluid is an interesting source of flexibility for existing networks, and the results highlight its potential and limitations.

On the temperature influence on cavitation erosion in micro-channels

The effect of fuel temperature on the erosion intensity in micro-channels for different fuels like calibration fluid ISO 4113 and dodecane is investigated. A high-pressure closed loop test bench for fuels under elevated temperatures up to 160 °C is used to erode micro-channels made of Al 99.0 at a maximum pressure of 500 bar. The evaluation of the erosion intensity reveals a temperature of maximum erosion for each fuel. The temperature of maximum erosion correlates with the temperature dependence of the maximum collapse pressure obtained by the Rayleigh-Plesset equation. Infrared thermography shows a local temperature drop in the cavitation region of the channels. 2D CFD simulations with a thermodynamic cavitation model supplement the measurement results by an assessment of the temporal evolution of the temperature field. Similar to the measurements, the CFD results yield a local cooling by the thermodynamic effect and thus support the measurement results. At high fluid temperatures one crucial link between the progressing local temperature drop and the erosion reduction is pointed out: the change of the detached cloud size distribution with temperature.

MP06: Predictors of hypothermia upon emergency department arrival in severe trauma patients transported to hospital via emergency medical services

Introduction: Hypothermia in severe trauma patients can increase mortality by 25%. Active re-warming decreases mortality and is recommended in trauma management guidelines. Despite this, many emergency medical services (EMS) vehicles do not carry equipment for active re-warming. This study sought to determine the local rate of hypothermia in major trauma patients on trauma centre arrival (TCA), and to establish which patients are at highest risk by identifying factors present in the pre-hospital setting associated with hypothermia in a humid continental climate. Methods: This single-centre retrospective chart review included adults (age 18) in the local trauma registry (trauma team activation or injury severity score >12) from January 2009-June 2016. Patients were excluded if: temperature on TCA unknown or 38°C, not transported by EMS, or if there was >24 hrs from injury to TCA. The primary outcome was the rate of hypothermia (<35°C) in major trauma patients transported by EMS on arrival at the local trauma centre. Secondary outcomes included hospital length of stay and survival to discharge. Logistic regression was used to identify predictors of hypothermia on TCA; it included the following factors: age, sex, weight, number of comorbidities, injury severity, injury mechanism, EMS modality, direct transport from scene or referred from peripheral hospital, time on scene, transport time, local temperature, and pre-hospital heart rate, systolic blood pressure (SBP), intubation, and volume of crystalloid. Results: A total of 3070 adult traumas were included, 159 of which were hypothermic on TCA a rate of 5%. Multivariate analysis identified seven risk factors for hypothermia: intubation pre-hospital (OR 8.10, p<0.001), blunt trauma (OR 3.37, p=0.044 vs. penetrating, and OR 7.35, p=0.023 vs. other), direct transport (OR 1.94, p=0.005), number of comorbidities (OR 1.14, p=0.036), injury severity (OR 1.03, p<0.001), 1°C local temperature drop (OR 1.03, p<0.001), and 1mmHg SBP drop (OR 1.01, p<0.001). Ninety-four percent of normothermic patients and 69.2% of hypothermic patients survived to discharge. Average length of stay was 7.98 and 15.23 days respectively. Conclusion: Avoidance of hypothermia is imperative to the management of major trauma patients. Those at highest risk in a humid continental climate are severely injured blunt trauma patients with multiple co-morbidities, a low pre-hospital SBP and EMS intubation. Future studies should focus on the benefits of pre-hospital rewarming in these high-risk patients.

Control of minimum film-boiling quench temperature of small spheres with micro-structured surface

The control of minimum film-boiling quench temperature, TMFB is investigated in water quenching experiments with several micro-structured surfaces on small spheres (diameters 10 and 15 mm) under saturation temperature Tsat and 1 atm. The results show increase in TMFB and is related to the temperature drop across the micro-structures, and affected by its effective thermal conductivity 〈k〉, height L, and base diameter D, based on the fin theory. The local temperature drop of surface microstructure depends on the hybrid Biot number,Bih=hL2/(〈k〉D), where h is the heat transfer coefficient. The liquid–solid contact depends on this microstructure-tip temperature, and a model for TMFB with synthetic surface micro-structure is proposed and compared with the experimental results. The theoretical limit of maximum TMFB (under saturated water at 1 atm) for surface micro-structured small sphere is reached when Bih is beyond 102.

Feasibility of Locating Leakages in Sewage Pressure Pipes Using the Distributed Temperature Sensing Technology

The cost effective maintenance of underwater pressure pipes for sewage disposal in Austria requires the detection and localization of leakages. Extrusion of wastewater in lakes can heavily influence the water and bathing quality of surrounding waters. The Distributed Temperature Sensing (DTS) technology is a widely used technique for oil and gas pipeline leakage detection. While in pipeline leakage detection, fiber optic cables are installed permanently at the outside or within the protective sheathing of the pipe; this paper aims at testing the feasibility of detecting leakages with temporary introduced fiber optic cable inside the pipe. The detection and localization were tested in a laboratory experiment. The intrusion of water from leakages into the pipe, producing a local temperature drop, served as indicator for leakages. Measurements were taken under varying measurement conditions, including the number of leakages as well as the positioning of the fiber optic cable. Experiments showed that leakages could be detected accurately with the proposed methodology, when measuring resolution, temperature gradient and measurement time were properly selected. Despite the successful application of DTS for leakage detection in this lab environment, challenges in real system applications may arise from temperature gradients within the pipe system over longer distances and the placement of the cable into the real pipe system.

Ultrafine-Grain and Isotropic Cu/SAC305/Cu Solder Interconnects Fabricated by High-Intensity Ultrasound-Assisted Solidification

With the miniaturization of portable electronic devices, the size of solder joint interconnects is decreasing to micrometer levels. These joints possess only several or even one or two grains, resulting in anisotropy and failure issues. Direct ultrasound-assisted solidification of Cu/SAC305/Cu interconnects for grain refinement and fabrication of isotropic solder joints is presented herein. These joints consist of many β-Sn grains. The average cross-sectional area of the Sn-rich phase is significantly reduced by up to 99% when compared with conventional as-reflowed samples. The ultrasonic power density exhibits a threshold value for affecting the microstructures. Below 200 W cm−2, the β-Sn grains were refined and had circular shape. The Ag3Sn phase grew in a manner similar to branched coral to sizes reaching 30 μm, or as rods aggregated together with Cu6Sn5 tube fragments. Above 200 W cm−2, the microstructures were coarsened and Ag3Sn had plate-like shape. The thickness of Cu6Sn5 intermetallic layers at the Cu/solder interfaces was reduced by more than 26%. The relationships among the ultrasonic power, nucleation rate, local temperature drop, and pressure were identified. At the highest power density of 267 W cm−2, the nucleation rate was about 4.05 × 1014 m−3 s−1, the local temperature drop was 248 K, and the local pressure was on the order of several GPa.

Local Heat Flux Investigation During Pool Boiling Single Bubble Cycles Under Reduced Gravity

In the present work the bubble diameter, heater surface temperature distribution, and local heat flux during different stages of single bubble cycles during pool boiling of PF-5060 at a pressure of p = 600 mbar have been investigated in several stable low g levels during the 1st Joint European Partial-g Parabolic Flight (JEPPF) Campaign. In previous parabolic flight campaigns, microgravity conditions were achieved by following a parabolic trajectory with the specially equipped A-300-Zero-G Aircraft. In this recent JEPPF campaign, the parabolic trajectories were slightly shifted, to establish—apart from microgravity conditions—also stable gravity levels of 0.16 g (lunar gravity) and 0.38 g (Martian gravity). High-resolution measurements of the heater surface temperature were performed using high-speed infrared thermography. An infrared (IR)-transparent sputtered heater design was employed in order to allow temperature measurements by IR thermography at a distance of approximately 800 nm to the heater/fluid interface. From the acquired temperature data, the local heat flux distribution was calculated numerically. Bubble shape and interaction were recorded with a high-speed black-and-white camera. In contrast to previous investigations, the stable low gravity levels enabled performance of measurements during single bubble (ebullition) cycles without the influence of residual flows induced by boiling under a different gravity level, as is the case in the beginning of a regular microgravity parabola. The accuracy of the measurement technique could be drastically enhanced compared to earlier publications. A local temperature drop and corresponding heat flux peak have been observed close to the three-phase contact line.

Experimental Investigation of Nucleate Boiling on a Thermal Capacitive Heater Under Variable Gravity Conditions

In the present work the behavior of single vapor bubbles of FC-72, generated on a thermal capacitive heater element, has been investigated during microgravity. A newly developed heater design allows temperature measurements by highspeed infrared thermography on the backside of the heater surface at a distance of approx. 800 nm from the fluid/heater-interface. The employed heater was manufactured by Physical Vapor Deposition (PVD) of a chromium based layer for better emissivity (Slomski et al., Mater Sci Technol 41:161–165, 2010) and a pure chromium heating layer supplying the energy required for bubble generation and sustainment by electrical heating. The thermal diffusivity of the employed Calcium Flouride (CaF) heater substrate is comparable to the thermal diffusivity of stainless steel, which makes this heater design very close to technical applications. The acquired transient temperature fields of the heater surface allow numerical determination of the local heat flux from the heater surface to the fluid. A local temperature drop and high heat fluxes have been observed in the vicinity of the 3-phase contact line. This effect has already been reported by former publications for thin stainless steel foil heaters (Stephan and Hammer, Int J Heat Mass Transfer 30:119–125, 1994; Wagner et al., Int J Heat Mass Transfer 42:875–883, 2006) and is also confirmed for heaters with significantly higher thermal capacities.

Analysis of NO<sub>x</sub> reduction in diesel engines by air injection using stochastic

Combustion phenomena have been found to be dependent on the turbulence of the air/gas and fuel in the cylinder. By enhancing turbulent mixing of fuel in the combustion chamber it is possible to improve combustion process. Based on the stochastic nature of turbulence ofcombustion processes as occurring in an IDI internal combustion engine, a model was developed based on these principles when compressed air was injected into the engine. The air injection was carried out in order to control the emission of NOx and soot simultaneously. In the presentmodel, the mechanism of NOx formation is modeled using the thermal NOx principles while the soot emission is modeled using the global combustion model, which considered combustion as heat addition. Obtained results show close agreement with the experimental ones. The Zeldovich model used has been found model closely IDI engine processes also for the case of air injection as is case of a normal engine. This is due to the microscopic treatment of the mixing process, which involved over-simplification of HC combustion chemistry. It is shown that although there is no substantial temperature drop when compressed air was injected into the chamber, at microscopic scales, the mixing process that occur lead to local temperature drop. It is these local areas of temperature quenching that enhance the suppression of the formation of NOx. At high loads, however, particulate and HC are increased due to the enrichment of fuel in the local areas where the temperatures have substantially been reduced.

Does the restoration of an inner-city stream in Seoul affect local thermal environment?

Changes in local thermal environment associated with the restoration of an inner-city stream in Seoul, Korea, are investigated using observational data. The stream, called the Cheonggye stream, which had been hidden and covered with cement/asphalt for 46 years, runs 5.8 km eastward through a central region of Seoul. Intensive observations were made in the stream area for a number of summertime periods before, during, and after the stream restoration to detect the effects of the stream on local environment and to quantify them. It is estimated that after the stream restoration the near-surface temperature averaged over the stream area dropped by 0.4 °C, with the largest local temperature drop being 0.9 °C. However, it cannot be stated that this 0.4 °C temperature drop is due entirely to the stream effect only, because synoptic-scale and local-scale weather conditions during the two periods were inevitably not identical. The stream effect on air temperature is also evident in the temperature distribution along a street traversing the stream. In the daytime after the stream restoration, the sensible heat flux was greatly reduced and the ratio of sensible heat flux to net radiative flux dramatically decreased. These first-time results of the restored-stream effects on urban thermal environment could contribute to the scientific basis of urban planning which aims to make a large city comfortable to live in and nature- and environment-friendly.

Experimental study of nucleate boiling heat transfer under low gravity conditions using TLCs for high resolution temperature measurements

Heat transfer in nucleate boiling is strongly influenced by a very small circular area in the vicinity of the three phase contact line where a thin liquid film approaches the heated wall. This area is characterised by high evaporation rates which trigger a local temperature drop in the wall. The wall temperature drop can be computed using an existing nucleate boiling model. To verify the complex model and the underlying assumptions, an experiment was designed with an artificial nucleation site in a thin electrically heated wall featuring a two-dimensional, high resolution temperature measurement technique using unencapsulated thermochromic liquid crystals and a high speed colour camera. The shape of the bubble is observed simultaneously with a second high speed camera. Experiments were conducted in a low gravity environment of a parabolic flight, causing larger bubble departure diameters than in normal gravity environments. Thus, it was possible to measure the evolution of the predicted temperature drop in a transient boiling process.

The effect of thermal stratification on natural convection in a vertical porous insulation layer

We consider the two-dimensional free convection flow in a rectangular porous container where the impermeable bounding walls are held at a temperature which is a linearly decreasing function of height. Attention is focused on the case where the local temperature drop across the container is zero. Two cases are considered, namely, containers of finite aspect ratio and those of asymptotically large aspect ratio. For both cases it is found that modes bifurcate in pairs as the linear stability equations admit an infinite set of double eigenvalues. The weakly nonlinear evolution of the primary pair of eigenmodes is analysed, and it is found that the resulting steady-state flow is nonunique as the realized steady flow is dependent on the precise form of the initial disturbance. For asymptotically tall boxes the weakly nonlinear evolution of the pair of modes is governed by coupled pair of Burger-like equations. These are analyzed both numerically and using asymptotic methods. No evidence of persistently unsteady flow is found. Copyright © 1996 Elsevier Science Ltd.

Evaluation of Thermocouple Fin Effect in Cladding Surface Temperature Measurement during Film Boiling

Thermocouple fin effect on surface temperature measurement of a fuel rod has been studied at elevated wall temperatures under film boiling condition in a reactivity initiated accident (RIA) situation. This paper presents an analytical equation to evaluate temperature drops caused by the thermocouple wires attached to cladding surface. The equation yielded the local temperature drop at measuring point depending on thermocouple diameter, cladding temperature, coolant flow condition and vapor film thickness. The temperature drops by the evaluating equation were shown in cases of free and forced convection conditions. The analytical results were compared with the measured data for various thermocouple sizes, and also with the estimated maximum cladding temperature based on the oxidation layer thickness in the cladding outer surface. It was concluded that the temperature drops at above 1,000°C in cladding temperature were around 120 and 150°C for 0.2 and 0.3 mm diameter Pt-Pt-Rh thermocouples, respectively, under a stagnant coolant condition. The fin effect increases with the decrease of vapor film thickness such as under forced flow cooling or at near the quenching point.

Evaluation of thermocouple fin effect in cladding surface temperature measurement during film boiling.

Thermocouple fin effect on surface temperature measurement of a fuel rod has been studied at elevated wall temperatures under film boiling condition in a reactivity initiated accident (RIA) situation. This paper presents an analytical equation to evaluate temperature drops caused by the thermocouple wires attached to cladding surface. The equation yielded the local temperature drop at measuring point depending on thermocouple diameter, cladding temperature, coolant flow condition and vapor film thickness. The temperature drops by the evaluating equation were shown in cases of free and forced convection conditions. The analytical results were compared with the measured data for various thermocouple sizes, and also with the estimated maximum cladding temperature based on the oxidation layer thickness in the cladding outer surface. It was concluded that the temperature drops at above 1,000°C in cladding temperature were around 120 and 150°C for 0.2 and 0.3 mm diameter Pt-Pt-Rh thermocouples, respectively, under a stagnant coolant condition. The fin effect increases with the decrease of vapor film thickness such as under forced flow cooling or at near the quenching point.

アルミニウム被覆鋼に関する研究（第6報）合金層の形成について

In the present paper, the authors studied the effect of thickness, cold working and preheating of base metal. Two different methods were used to coat the steel sheet of 0.2∼1.2 mm thickness namely; the single bath method and double bath method. The results obtained were as follows: (1) The formation of the alloy layer is affected by thickness of the sheet. It is due particularly to the local temperature drop adjacent to the base metal. (2) Cold working of the base metal has no effect on the alloy formation. The internal strain is removed during the dipping process and an annealed structure is obtained. (3) The alloy layer can be formed thicker by the preheating effect of double bath method but its effect is practically the same if the duration of the preheating treatment varies. The authors have tried to study the experimental results statistically and also the mechanism of alloy layer formation are considered.