Extreme Thermal Loads Research Articles

Extreme thermal load generation method for high-temperature structures in atmospheric environment

For addressing the severe aerodynamic thermal load simulation challenge of hypersonic aircraft in ground tests, an extreme thermal load generation method based graphite for high-temperature structures in atmospheric environment is proposed. Firstly, a thermal stress relief design method of graphite heating elements has been developed to ensure the integrity of graphite heating elements during high-power heating. Secondly, a method of creating closed transparent environment for graphite heating elements has been developed, with double-layer gas film cooling, which avoids severe oxidation of graphite heating elements in contact with oxygen at high temperatures and achieves the application of large heat flux loads in the atmospheric environment. Finally, a modular graphite ultra-high temperature heating device was developed based on the above method, and heating capacity tests were conducted on C/SiC test pieces in atmospheric environment. The research shows that the modular graphite ultra-high temperature heating device has the ultra-high temperature heating ability in atmospheric environments, with maximum radiation heat flux of 1.38 MW/m2, hot surface temperature of around 1 800 ℃, and the temperature rise rate can reach 40.3 ℃/s, providing technical conditions for the thermal test of hypersonic aircraft structure.

Tailored directional porosity in ceramic matrix composites (CMCs) for hypersonic applications

AbstractIn the field of hypersonic systems and their missions, the occurring flows impose extreme mechanical and thermal loads on the materials used. At the German Aerospace Center (DLR), extensive research is conducted in this area, ranging from design and specification to the development of suitable materials concluding with the proof of concept under realistic conditions in wind tunnels. In recent years, ceramic matrix composites (CMCs) have been investigated for specific aspects of hypersonics. These materials exhibit consistent mechanical behavior over a wide temperature range (up to 1600 °C), coupled with high damage tolerance and thermal shock resistance, distinguishing them from metals and superalloys. Particularly, special porous C/C–SiC ceramics (carbon-fiber-reinforced carbon with silicon carbide) enable innovative material applications for components in transpiration cooling, fuel injection, or boundary-layer transition control. The work presented focuses on the next generation of porous C/C–SiC ceramics currently in development. By deliberately modifying the textile preform, the resulting microstructure and pore morphology are influenced, allowing for control over both the total volume and the orientation of the pores. Relevant parameters influencing porosity have been determined based on the results, and an initial characterization has been conducted. It has been demonstrated that there is a preferred direction of porosity within the sample thickness (Z-axis), and in terms of hypersonic-relevant properties, an absorption coefficient of 0.58 for an acoustic wave at 500 kHz (static pressure of 15 kPa), as well as a length-specific flow resistance of 3.4 MPa s/m2 and an overall porosity of 12.25% were determined. Building upon these promising initial findings, the goal is to further expand the understanding of the parameters influencing porosity and to generate a tailored material for different application scenarios by correlating them with hypersonic properties.

Investigation of surface integrity in grinding of nickel based superalloy under different cooling conditions

Investigation of surface integrity in grinding of nickel based superalloy under different cooling conditions

The effect of projected air temperatures on concrete box girders thermal gradients and effective temperatures in Canada

The effect of projected air temperatures on concrete box girders thermal gradients and effective temperatures in Canada

Precise temperature control of electronic devices under ultra-high thermal shock via thermoelectric transient pulse cooling

Precise temperature control of electronic devices under ultra-high thermal shock via thermoelectric transient pulse cooling

Technologies of Coatings and Surface Hardening: Industrial Applications

The most advanced and recently developed coating and surface-hardening technologies make it possible to obtain almost the full range of physical–mechanical and crystal–chemical properties of the metalworking tool surface and electronic component surface for a wide range of applications to enlarge product operational life for working under the most extreme mechanical and thermal loads [...]

Electrical Discharge Machining of Al2O3 Using Copper Tape and TiO2 Powder-Mixed Water Medium

Aluminum-based ceramics are used in industry to produce cutting tools that resist extreme mechanical and thermal load conditions during the machining of Ni-based and high-entropy alloys. There is wide field of application also in the aerospace industry. Microtexturing of cutting ceramics reduces contact loads and wear of cutting tools. However, most of the published works are related to the electrical discharge machining of alumina in hydrocarbons, which creates risks for the personnel and equipment due to the formation of chemically unstable dielectric carbides (methanide Al3C4 and acetylenide Al2(C2)3). An alternative approach for wire electrical discharge machining Al2O3 in the water-based dielectric medium using copper tape of 40 µm thickness and TiO2 powder suspension was proposed for the first time. The performance was evaluated by calculating the material removal rate for various combinations of pulse frequency and TiO2 powder concentration. The obtained kerf of 54.16 ± 0.05 µm in depth demonstrated an increasing efficiency of more than 1.5 times with the closest analogs for the workpiece thickness up to 5 mm in height. The comparison of the performance (0.0083–0.0084 mm3/s) with the closest analogs shows that the results may correlate with the electrical properties of the assisting materials.

Electrical Discharge Machining of Alumina Using Ni-Cr Coating and SnO Powder-Mixed Dielectric Medium

Aluminum-based ceramics exhibit excellent wear resistance and hot hardness that are suitable for various responsible applications allowing products to work under extreme mechanical and thermal loads (up to 1000 °C). The problem of high-precision forming complex-shaped parts is a known engineering challenge due to the insulating properties of aluminum-containing ceramics and the formation of chemically active carbides in a hydrocarbon medium. The alternative approach for electrical discharge machining non-conductive sintered Al2O3 in the water-based medium using nickel-chrome plasma-vapor-deposed coating of 12 mm, SnO powder suspension (particle diameter of ⌀10 µm, concentration of 150 g/L), and brass wire-tool is proposed. The productivity was evaluated by calculating the material removal rate and discharge gap for various combinations of pulse frequency and duration. The maximal material removal rate of 0.0014 mm3/s was achieved for a pulse frequency of 30 kHz and pulse duration of 1.7–2.5 μs. The recommended value of the interelectrode gap is 48.0 ± 4.9 µm. The possibility of electrical discharge machining aluminum-containing insulating ceramics without using hydrocarbons, carbon and copper-group assisting measures was proposed and shown for the first time. The chemical content of the debris in the interelectrode gap between components of the materials was thermochemically analyzed.

Effect of mass injection on secondary instability of hypersonic boundary layer over a blunt cone

In low environmental disturbances, secondary mechanisms play a crucial role in flow instability and transition. Over the years, researchers have shown the existence of secondary waves prior to nonlinear breakdown and turbulence. In high-speed flows, the vehicles are subjected to extreme thermal loads, and usually, an ablative heat shield is used for protection. The ablative materials eject gaseous products upon heating, significantly affecting flow stability. Mass injection through the surface in the boundary layer loosely replicates the ablation process. Its effect on stability and transition has been explored earlier using experiments, numerical simulation, and Linear Stability Theory (LST). However, the effect of the surface injection on secondary instability, the most viable path to transition, remains uncertain. The present work studies the secondary instability of a hypersonic boundary over a 7° half-angle blunt cone in the presence of mass injection through the surface of the boundary layer. Mean flow over the cone is solved using a high-order shock fitting direct numerical simulation code. Primary instability is studied using the LST, and secondary instability is studied using the secondary instability theory based on the Floquet model. Computations are carried out for different injection rates, and it is found that instability increases with mass injection rate. The mass injection has increased the primary and secondary growth rates. Fundamental modes are more dominant than subharmonic and detuned modes at higher primary wave amplitudes. The mass injection has increased the primary and secondary N-factor, and transitioning behavior is observed at the maximum injection rate.

A heat exchanger based on the piezoelectric pump for CPU cooling

To satisfy the cooling demands required by the highly integrated electronic devices, a heat exchanger integrated with a ball valve piezoelectric pump and a multi-stage Y-shaped micro-channel heat sink was proposed and demonstrated. The effects among the flow rate, back pressure of the piezoelectric pump, and the driving frequency of the heat exchanger were investigated to assess the driving performance. Subsequently, the piezoelectric heat exchanger was used to cool the CPU of commercial computers, and the performance of the heat exchanger was discussed under different thermal power consumption. The results showed that the temperature of the CPU under extreme thermal load was controlled by the heat exchanger within 55 ℃. The relationship between heat resistance and convection heat transfer coefficient was also analyzed. When the CPU was operating at 30 W, the heat sink owned the smallest thermal resistance and the largest heat transfer coefficient. From the conclusion of the comparative tests, the heat exchange speed and heat exchange effect of the piezoelectric heat exchanger were obviously better than the original air cooling system of the computer. The proposed heat exchanger may contribute in the field of the heat exchange of electronic devices in near future due to its certain performances. • A novel piezoelectric heat exchanger with high reliability and fast response time is proposed for CPU cooling. • The selective laser melting (SLM) technology is utilized to fabricate the micro-channel heat sink. • By experiment, the heat dissipation of the piezoelectric heat exchanger was obviously better than the air-cooled system.

Influence of Mechanical, Thermal, Oxidative and Catalytic Processes on Thickener Structure and Thus on the Service Life of Rolling Bearings

Constant further developments in application technology with the aim of higher economic efficiency and power density place ever greater demands on mechanical components and construction elements and thus on the lubricating greases used. This is particularly true in the area of roller bearings, in which lubricating greases are sometimes used with high mechanical stress and in wide temperature ranges. A current example is the rolling bearings in the assemblies of hybrid vehicles, which are subjected to extreme thermal and mechanical loads due to engine downsizing, high speeds and the radiant heat from the combustion engine. Investigations at the Competence Center of Tribology Mannheim (KTM) show that the grease service life for roller bearing lubrication, even at high temperatures, does not only depend on classic oil aging. In numerous roller bearing tests and by means of rheological measurements, it could be shown that the loss of the lubricating effect is a consequence of the change in the thickener structure. Mechanical, thermal, oxidative and catalytic processes play a decisive role here. In this article, a scientific method is presented for the first time as to how these individual influencing factors can be examined and evaluated independent from one another. For this purpose, the first results of an ongoing DGMK project are presented and evaluated.

Helium-induced swelling and mechanical property degradation in ultrafine-grained W and W-Cu nanocomposites for fusion applications

Besides high dose radiation and extreme thermal loads, a major concern for materials deployed in novel nuclear fusion reactors is the formation and growth of helium bubbles. This work investigates the swelling and mechanical property degradation after helium implantation of ultrafine-grained W and nanocrystalline W-Cu, possible candidates for divertor and heat-sink materials in fusion reactors, respectively. It is found that ultrafine-grained W and single crystalline W experience similar volumetric swelling after helium implantation but show different blistering behavior. The W-Cu nanocomposite, however, shows a reduced swelling compared to a coarse-grained composite due to the effective annihilation of radiation-induced vacancies through interfaces. Furthermore, the helium-filled cavity structures lead to considerable softening of the composite.

Analysis of the Influence of Surface Modifications on the Fatigue Behavior of Hot Work Tool Steel Components.

Hot work tool steels (HWS) are widely used for high performance components as dies and molds in hot forging processes, where extreme process-related mechanical and thermal loads limit tool life. With the functionalizing and modification of tool surfaces with tailored surfaces, a promising approach is given to provide material flow control resulting in the efficient die filling of cavities while reducing the process forces. In terms of fatigue properties, the influence of surface modifications on surface integrity is insufficiently studied. Therefore, the potential of the machining processes of high-feed milling, micromilling and grinding with regard to the implications on the fatigue strength of components made of HWS (AISI H11) hardened to 50 ± 1 HRC was investigated. For this purpose, the machined surfaces were characterized in terms of surface topography and residual stress state to determine the surface integrity. In order to analyze the resulting fatigue behavior as a result of the machining processes, a rotating bending test was performed. The fracture surfaces were investigated using fractographic analysis to define the initiation area and to identify the source of failure. The investigations showed a significant influence of the machining-induced surface integrity and, in particular, the induced residual stress state on the fatigue properties of components made of HWS.

Study of the functional parameters of main engine turbocharger for a tanker ship

To correctly understand the requirements of a system, we must first study its schematics. In the case of energy systems, they require a detailed diagram of energy performance. Heat losses can be classified into high-temperature losses, medium-temperature and low-temperature losses. On board ships with low-speed propulsion engines, heat recovery systems operate in the range of 100-400 °C. Many residual energy recovery systems from internal combustion engines are under development: for example the MAN WHR development program for Tier III technologies. In this paper, I will treat both theoretical calculation elements and real elements of the operation of the turbocharging system, for the main reference engine. I chose to treat this system because it is a main subassembly for the engine, in terms of operation and thus its efficiency. In the theoretical calculation, I will start from the initial calculation data and I will expose the geometric and functional parameters of the turbocharger. The exhaust gases up to a temperature of 650 °C passes continuously through the turbine and heat its components, without its system of contraction cooling. In particular, the shaft bearing must withstand high operating temperatures without ever breaking the lubrication device. On the compressor side, the air is heated to over 200 °C. High temperatures lead to extreme thermal loads of the material in many locations. Speeds are extremely high: METxxSE turbochargers, as in figure 1, run at speeds between 10000 and 35000 rpm, depending on size. In this respect, the tangential speeds of 560 m / s and even more are reached at the compressor turbine, which rises to 1.7 times the speed of sound or 2000 km / h. The efficiency of the operation of the turbocharger system related to the main propulsion engine depends on the internal processes that take place in its operation, and also on the environmental conditions. In this way, the direction of processing on the installation is dictated by the engine load, taking into account the extreme situations, corresponding to the operation of the ship in special conditions (overload, tropical temperature, arctic temperature etc.).

Improving the Film Cooling Performance of a Turbine Endwall With Multi-Fidelity Modeling Considering Conjugate Heat Transfer

Abstract The gas turbine endwall is bearing extreme thermal loads with the rapid increase of turbine inlet temperature. Therefore, the effective cooling of turbine endwalls is of vital importance for the safe operation of turbines. In the design of endwall cooling layouts, numerical simulations based on conjugate heat transfer (CHT) are drawing more attention as the component temperature can be predicted directly. However, the computation cost of high-fidelity (HF) CHT analysis can be high and even prohibitive especially when there are many cases to evaluate such as in the design optimization of cooling layout. In this study, we established a multi-fidelity (MF) framework in which the data of low-fidelity (LF) CHT analysis were incorporated to help the building of a model that predicts the result of HF simulation. Based upon this framework, MF design optimization of a validated numerical turbine endwall model was carried out. The high- and LF data were obtained from the computation of fine mesh and coarse mesh, respectively. In the optimization, the positions of the film cooling holes were parameterized and controlled by a shape function. With the help of MF modeling and sequentially evaluated designs, the cooling performance of the model endwall was improved efficiently.

Deterministic and stochastic thermomechanical nonlinear dynamic responses of functionally graded sandwich plates

Functionally graded composites are commonly used under extreme mechanical and thermal loads wherein a minimal degree of uncertainty might significantly deviate the structural responses. Meanwhile, there is a lack of studies that consider the effects of inevitable source-uncertainty, especially in the stochastic dynamics of composites. This paper, for the first time, investigates both deterministic and stochastic dynamics of functionally graded sandwich plates with four different layering configurations under thermomechanical loads. Euler-Lagrange equations are derived based on the third-order shear deformation theory and Hamilton principle. Closed-form solutions for fundamental frequencies are obtained by introducing a stress function. Dynamic responses, phase-space plots, backbone curves, and forced response curves are numerically solved and graphically illustrated leading to notable insights into the stability and softening/hardening behaviors of the plate dynamics. A large number of random configurations are generated and analyzed resulting in stochastic dynamic bounds of dynamic responses, backbone curves, and forced response curves. The study shows that the plates have dynamic hardening behaviors, and the existence of thermal loads makes the plate random responses more diverse in stochastic environments. This work provides a good understanding of the deterministic and stochastic dynamics of the composites, which are crucially important for practical engineering applications.

Study on Solar Radiation and the Extreme Thermal Effect on Concrete Box Girder Bridges

Thermal effect is an essential factor in the durability and safety of concrete bridges. Therefore, this paper mainly studied the concrete bridge box girder temperature distribution and thermal effect under solar radiation and the thermal load. With a concrete rigid frame bridge as the engineering background, the temperature distribution of the box girder on a clear summer day was observed. Then, according to the solar physics and heat transfer theory, the different surfaces of the box girder cross-section are classified based on the heat transfer conditions, and the variation of solar radiation on different surfaces is investigated. The temperature field of the box girder is simulated by ANSYS. To obtain the extreme thermal condition, the meteorological data of the bridge site from 1990 to 2020 are collected. The data are fitted by generalized extreme value distribution to obtain the extreme temperature and average wind factors in the bridge design lifetime. Combined with the solar radiation, temperature, and wind factors, the extreme thermal condition of the concrete box girder is obtained. Lastly, the thermal effect of the box girder under the extreme condition is analyzed, and the thermal stress is compared with the allowable stress in the design code. The results show that the girder temperature difference is closely related to the solar radiation intensity and heat transfer conditions, and the solar radiation intensity is the more critical factor. The tensile stress caused by the extreme thermal load is more significant than the design strength value in the girder cross-section. The results also provide a method to obtain the extreme thermal condition and evaluate the impact of the thermal effect on concrete box girder bridges.

Numerical and experimental study on high-speed hydrogen–oxygen combustion gas flow and aerodynamic heating characteristics

The need to increase the payload capacity of the rockets motivates the development of high-power rocket engines. For a chemical propulsion system, this results in an increasing thermal load on the structure, especially the combustion chamber and nozzle must be able to withstand the extreme thermal load caused by high-temperature and high-pressure combustion gas. In order to protect the structure from the effect of increasing heat flux, it is necessary to counteract such effect with more advanced thermal management technology. This requires us to accurately predict the aerodynamic heating of the structure by high-temperature and high-speed combustion gas. In this study, a high-temperature combustion gas tunnel developed in the laboratory is used to produce high-speed combustion gas. Combined with the results of numerical calculation, the flow and aerodynamic heating characteristics of air and hydrogen–oxygen combustion gas under the same total temperature and pressure are analyzed and compared. The comparison revealed that the combustion gas flow in the nozzle has higher static temperature, velocity, and smaller Mach number. When the combustion gas flows around the sphere, the shock standoff distance and stagnation pressure are smaller than those of air, and the wall heat flux is much larger than that of air. The active chemical reaction in the combustion gas makes the aerodynamic heating of the structure more severe. Finally, through the analysis of a large amount of data, a semi-empirical formula for the heat flux of the stagnation point heated by a high-speed hydrogen and oxygen equivalent ratio combustion gas is obtained.

Studying in-vessel component materials under heat and plasma loads relevant to fusion installations

The results of studies of materials under extreme thermal and plasma-beam loads, carried out to justify existing technological solutions in the design of thermonuclear reactors, are presented. The study of materials under plasma and beam loads and the intensifying heat transfer of in-vessel cooled components of fusion devices is reported. Tests of limiter and divertor mock-ups irradiated with high heat fluxes in electron beam and plasma facilities are described. Methods for cooling in-vessel components using advanced approaches with dispersed gas-liquid flow for heat removal, including at loads of up to 15 MW/m2 have been developed and tested.

Optimization of the radiotransparent constructions in a mode of extreme heat loads

An experimental method has been developed for optimizing the composition of multilayer radiotransparent structures operating under extreme thermal loads. To optimize the composition of the layers of the radiotransparent radome researchers for the following materials with structures of the glass filler are carried out: glass-fiber laminate (GFR-CM), reinforced quartz material of SiO2–SiO2 class (HTRC-CM), organosilicon rubber with a ground mica filler (TCT). The parameters of the heat loads that cause physicochemical transformations in radiotransparent materials and significantly affect the transmission and reflection coefficients of materials, as well as their complex permittivity, are determined. It is shown that the decrease in the transmission coefficient for the construction made of HTRC-CM material is up to 3–4 dB in the frequency range from 2 to 40 GHz, and for constructions made of GFR-CM+TCT is up to 25 dB, respectively. As a result, the radome made of ceramic matrix composite HTRC-CM has the best radiotransparency characteristics.