End Temperature Research Articles

Investigation of elevated temperature microstructural stability and tribological behavior of MoxNbTiZr refractory high-entropy alloy coatings optimized by Mo-doping

Refractory high-entropy alloys (RHEAs) possess substantial potential for applications in high-temperature environments. In this work, the structural and high-temperature properties of MoxNbTiZr RHEA coatings are optimized by Mo-doping. The results show that Mo-doping promotes the HCP phase precipitation and proliferation of nanotwins, strengthening the microhardness but weakening the fracture toughness of the coatings. Mo-doping raises the phase transition onset temperature and end temperature by reducing the bulk diffusion rate of MoxNbTiZr RHEAs. The BCC phase of Mo1.0NbTiZr HEA coating can be stabilized to at least 1300 ℃. Mo-doping in a particular range is favourable to accelerate the sintering and curing rate of the tribo-layer. The MoxNbTiZr RHEA coatings demonstrate outstanding high-temperature tribological performance before Mo content exceeds 0.6 at%.

Exploration and optimization on thermoelectric conversion of waste heat of blast furnace slag

The iron and steel industry involves processes that generate abundant waste heat resources. The energy utilization rate can be improved by using thermoelectric conversion technology to directly convert waste heat into electric energy through the Seebeck effect. In this study, a special waste heat recovery device, designed according to the production environment characteristics of blast furnace (BF) slag, is proposed. The heat transfer process between the BF slag and thermoelectric generator (TEG) is analyzed, and the heat source temperature field model is constructed. Based on the temperature distribution, the size of the TEG is determined. The heat transfer behavior of the thermoelectric module (TEM) is optimized using a non-contact heat collection mode and a water-cooling device, which improves the temperature gradient. A thermal conductive silicone grease is introduced as the thermal conductive layer to achieve uniform distribution of the hot end temperature and improve the heat transfer capacity of the collector plate. After design optimization, the temperature gradient of the TEM increased by 15.3 °C and 38 % on average. The experimental results show that a single TEM can generate about 3.084 J of electric energy. Using 70 kg of BF slag with an initial temperature of 600 °C, the TEG per unit installed area can generate about 1.23 kJ of electric energy in 1 h. This study provides an important foundation for research in thermoelectric conversion, utilization of BF slag waste heat and sustainable development of the iron and steel industry.

Numerical simulation and experimental validation of the heat transfer characteristics in a circuit gas gap heat switch for the dilution refrigerator

The gas gap heat switch (GGHS) used for controlling heat transfer between different stages can be an important component for the precooling process of some dilution refrigerators. In this paper, a novel circuit GGHS is a rotationally symmetric heat switch assembly with annular fin arrangements to strengthen the heat-transferring effect. A numerical model considering 4He actual gas properties is proposed to investigate the heat transfer characteristics in the circuit GGHS, in which the effects of charge pressure, cold end temperature, thickness and length of walls on the mean thermal conductance (MTC) are studied. Simulation results show that the MTC increases with the growing cold end temperature, wall thickness, and length, respectively. Given the pressure of 10 kPa, cold end temperature of 4.2 K, wall thickness of 0.97 mm, and wall height of 66 mm, the theoretical MTC is 0.828 W/K. Experimental results indicate that the proposed simulation model is reasonable. Furthermore, the increment of the MTC decreases with the growing temperature. The GGHS used in experiments had a cold end temperature of 4 K, wall thickness of 0.65 mm, and wall height of 33 mm; the measured MTC was 0.219 W/K. Only when the temperature is above 10 K does the charge pressure have a pronounced effect on the MTC. This study provides helpful theoretical guidance for the design and optimization of the circuit GGHS.

An integrated alkali metal thermoelectric converter with sodium hydroxide thermoelectric water splitter and organic Rankine cycle for efficient power and hydrogen production

This study proposes the integration of the NaOH thermochemical water splitting cycle with both an alkali metal thermoelectric converter and an organic Rankine cycle. The objective of the proposed model is to enhance the overall efficiency by utilizing the waste heat generated by the NaOH thermochemical water splitting process and redirecting the heat from the alkali metal thermoelectric converter using bypass when hydrogen demand is low.Performance parameters such as system efficiency, system power, hydrogen production, AMTEC power production, and ORC power production were examined in the study. The results indicated an increase in power and hydrogen production with higher hot-end temperatures, along with an overall reduction in system efficiency for low values of load resistance. The system achieved a maximum efficiency of 53.37%.The system efficiency reached its peak at an AMTEC hot end temperature of 1173 °C, achieving 53.37 % efficiency at an RL value of 1.01 O. When the system operates at its maximum AMTEC power production, the AMTEC modules supply 12.81 kW, while the ORC generates 5.57 kW, and the hydrogen compressor consumes 0.13 kW. The total electrical power generation is 18.38 kW. The findings also indicate that the utilization of the bypass led to a reduction in hydrogen production while increasing the power output of the organic Rankine cycle.

Analysis of the Hydrogen‐Filling Process of Fixed Station and Skid Station Based on Different Working Conditions

Hydrogen energy is recognized as the most potential renewable energy in the 21st century due to the rising depletion of fossil fuels. Hydrogen refilling stations, as the infrastructure of hydrogen energy, are one of the key components of the entire hydrogen energy industry chain. Analyzing the filling process of hydrogen‐refueling stations (HRS) helps to promote the construction of HRSs. Thus, it promotes the construction of a clean, low‐carbon, safe, and efficient energy system and the high‐quality development of the hydrogen energy industry. In this article, gas cylinders with nominal working pressures of 35 and 70 MPa are filled using three different HRSs, such as single‐stage fixed station, three‐stage fixed station, and skid station. The filling end temperature, filling energy consumption, filling rate, and filling time during the filling process are compared and analyzed. In the results, it is shown that skid station has the advantages of lower filling end temperature and less energy consumption. Thus, in terms of reducing energy loss, the skid‐mounted HRSs can be promoted.

Verification experiment of maximum hydraulic diameter in a novel three-dimensional asymmetric oscillating heat pipe

A novel three-dimensional asymmetric oscillating heat pipe (3DAOHP) with unequal curvature radius of upper and lower bends has been designed. Setting the basic factor of diameter from 1.9 mm to 6.2 mm, a verification experiment on the criterion of conventional maximum hydraulic diameter (MHD) has been conducted. The results show that the 3DAOHP can still perform normally and transfer heat effectively, even if the diameter exceeds the MHD by 98.1 %. And the temperature profiles at each end does not show obvious abnormalities. The thermal performance also does not show any deterioration, which still follows the rule that the larger the diameter, the stronger the heat transfer capability. The thermal resistance of the 6.2 mm 3DAOHP can reach 0.07 °C/W at 1300 W without touching the dry-out limit. Moreover, the frequency and amplitude of hot end temperature fluctuation show suppression as the diameter increases. Therefore, the conventional MHD is not a diameter limitation of oscillating heat pipe (OHP) in enhancing heat transfer. Thus, the availability of OHP in high heat loads can be improved by further increasing the tube diameter. These findings are important for the OHP application in higher heat flux.

Using conditional normalizing flows to generate material placements in an optimized thermal composite

We present an application of conditional normalizing flow neural networks (cFlows) to the problem of generating optimized topologies for burst-duty thermal mitigation, specifically targeting the placement of both linearly-conducting and phase-change materials (PCMs). Topological optimization naturally generates very large amounts of data. This enables us to acquire a high-resolution map of optimization space, accomplish cheap model generation, interpolate between points, and rapidly examine the statistics of the optimized topologies. The modeling is subject to two constraints: system mass (m) and maximum simulation end temperature (Tmax), i.e., our model takes these optimization constraints as inputs to predict the distribution of compatible topologies. The generated topologies are highly performant and realizable as verified by simulation; moreover, using the statistical properties of normalizing flows and an independent check against simulation, we show that the model is indeed sampling from the true distribution of possible qualified configurations.

Thermoelectric cooler with embedded teardrop-shaped milli-channel heat sink for electronics cooling

Thermoelectric coolers (TECs) offer a site-specific, on-demand, and solid-state thermal management solution for on-chip electronics cooling. To maximize their cooling performance, it is essential to integrate an effective heat exchanger, such as microchannels, on the TEC’s hot side. However, traditional microchannel heat sinks pose challenges, including the necessity for high-cost equipment and the manifestation of deleterious parasitic contact thermal resistance with the TEC. Recent studies have demonstrated the superior performance of teardrop-shaped microchannels compared to their conventional counterparts, yet their effectiveness at the milli-scale remains unexplored. In this work, through systematic numerical simulations across nine milli-channels with distinct variable cross-sections, we propose a teardrop-shaped milli-channel heat sink designed for fabrication through cost-effective mechanical machining. The optimized teardrop-shaped milli-channel exhibits a superior overall thermo-hydraulic performance evaluation factor (PEC) of approximately 1.8 with respect to its rectangular cross-sectional counterpart. Furthermore, we seamlessly embed the designed milli-channel heat sink into the substrate of the TEC to mitigate the parasitic contact thermal resistance. Measurements on the TEC embedded with the teardrop-shaped milli-channel heat sink show that the cold end temperature reaches a minimum value of −18.6 °C at an optimal input electrical current of 3.5 A and an inlet coolant flow velocity of 0.2 m/s. This temperature represents an improvement of approximately 3.5 °C and 4.4 °C compared to the TEC with an attached teardrop-shaped milli-channel and a conventional water block heat sink, respectively, under identical operating conditions. Additionally, a prototype TEC cooling system with the embedded teardrop-shaped milli-channel for high-power field-effect transistor (FET) cooling is demonstrated. Operating at an input electrical current of 3.5 A and an inlet flow velocity of 0.6 m/s, our proposed TEC cooling system achieves a steady-state working temperature of 51.3 °C for the FET at a high heat flux of 75 kW/m2, outperforming the TEC with an attached teardrop-shaped milli-channel and a conventional water block heat sink by approximately 1.4 °C and 2 °C, respectively.

ŞEKER ŞURUBUYLA TAĞŞİŞ EDİLEN PEKMEZ ÖRNEKLERİNİN TERMAL ÖZELLİKLERİ İÇİN GELİŞTİRİLMİŞ BİR DIFFERENTIAL SCANNING CALORIMETRY ÇALIŞMA

This research was carried out to determine the pH, titratable acidity, ash, specific gravity, color (L*, a*, b*), water activity, electrical conductivity, glass transition temperature (Tg) and melting characteristics of grape and mulberry pekmez samples adulterated with different levels (10%, 30%, 50%) of high fructose corn syrup (HFCS). Ash, titratable acidity and electrical conductivity values have decreased significantly (P<0.05) with the level of adulteration and determined that these properties can be used as a criterion in the determination of adulteration. Two glass transition temperatures occurring between -25.64℃ to -32.58℃ (Tg1) and 23.29℃ to 31.22℃ (Tg2) were detected in all pekmez samples. The single glass transition temperature was determined in the pekmez samples diluted with water, and both the glass transition temperatures and the onset, peak, end temperatures and enthalpy values of the melting peaks increased significantly with the increase in the amount of adulteration (P<0.05).

Substitution effects on Y-type hexaferrites’ magnetic characteristics

The effect is discussed of the partial replacement of the Me2+ in the Y-type hexaferrite crystal structure with non-magnetic (Mg2+) and magnetic (Ni2+) cations on the observed magnetic characteristics of Ba0.5Sr1.5Me2Fe12O22. Y-type hexaferrite powder material was prepared by citric acid sol-gel self-ignition and sintering at 1170 °C in air to reach Ba0.5Sr1.5MgxNiyFe12O22. To determine the magnetic phase transitions, the ZFC/FC magnetisation was followed in magnetic fields of 50 Oe and 100 Oe between 4.2 K and 300 K; this was complemented with hysteresis loops recorded at the end temperatures. The results show that combining the magnetic Ni2+ with the nonmagnetic Mg2+ in Ba0.5Sr1.5 Me2Fe12O22 can be effective in controlling the magnetic interactions to regulate the temperature of the magnetic transition from helical to ferrimagnetic arrangement above room temperature.

An Error Correction Method Based on CBR for End Temperature Prediction of Molten Steel in Ladle Furnace

An Error Correction Method Based on CBR for End Temperature Prediction of Molten Steel in Ladle Furnace

A day-night solar thermoelectric generator enabled by phase change material and forced water cooling

Solar thermoelectric generators (STEGs), which are capable of directly converting solar energy to electricity, are essential to many potential applications in addition to photovoltaics. It is of great importance to advance the design of STEGs to significantly boost the output performance by combining solar selective absorbers, cooling technologies and phase change materials. In this work, a novel day-night STEG integrated with transparent phase change materials of methyl palmitate and forced water cooling (PCM-STEG-WC) is proposed. The fabricated solar selective absorber exhibits a high solar absorption of 96.05 %, leading to its surface temperature up to 100 °C under 1-sun illumination (1 kW m−2), while the surface temperature of conventional thermoelectric module is only about 44.4 °C. Consequently, the temperature difference between hot and cold ends can be significantly increased to 5.6 °C from 2 °C, about 2.8 times higher than the conventional thermoelectric module. Moreover, this unconcentrated PCM-STEG-WC can realize a power level of 6.42 mW associated with output voltage of 307.3 mV at a solar density of 1 kW m−2, which is about 9 times higher than that of conventional thermoelectric module (35.5 mV). Additionally, the hot end temperature of PCM-STEG-WC only decays by 17 % in 100 s without solar radiation. To demonstrate the effectiveness of the PCM-STEG-WC in power generation at night, a single red LED is completely powered. Finally, this study may provide a promising strategy to develop high-performance STEGs for remote applications.

Generation of Current in Thermoelectric Generator by Absorption of Heat Using ANSYS Thermal

Thermoelectric power generation is a renewable energy conversion process that directly converts heat to electricity. This research proposes a novel fluid-thermal-electric multi-physics numerical model for predicting the performance of a thermoelectric-producing system. On the ANSYS platform, numerical simulations are done along with the exhaust temperature and mass flow rate. The range of hot end temperatures is from 100 to 450 degrees Celsius. Similarly, the cold end temperature can reach a maximum of 25 degrees Celsius and a minimum of 10 degrees Celsius. When the temperature at the generator's hot end rises, it means the temperature at the generator's cold end must fall. It means both have an inverse relation to each other. The maximum heat absorbed at the hot junction is 32.762 W and the minimum heat absorbed at the hot junction is 4.6305 W. Hence the maximum and minimum current values produced in this paper by the thermoelectric generator are 72.156 A & 10.816 A respectively. The hot side heat exchanger's position of the thermoelectric modules has a significant impact on output. Combining the benefits of many models are advised to construct an inclusive thermoelectric generator system for use in real-world applications.

Structural-phase transformations of 12% chromium ferritic-martensitic steel EP-823

The features of phase transformations of 12 % chromium ferritic-martensitic steel EP-823 under heating and cooling conditions in the temperature range from 30 to 1100 ℃ were studied by the methods of high-temperature X-ray diffraction analysis (XRD) in situ and differential scanning calorimetry (DSC). According to XRD in situ data, upon heating, the temperatures of the beginning and end of the (α → γ) transformation of ferrite (martensite – austenite) are Ac1 ≈ 880 °C, Ac3 ≈ 1000 °C, respectively. Upon cooling, a diffusion (γ → α) transformation occurs with critical points – Аr1 ≈ 860°С (beginning temperature) and Аr3 ≈ 840 °С (end temperature). According to DSC data, during heating, the critical points of the (α → γ) transformation are Ac1 ≈ 840 °C and Ac3 ≈ 900 °C. During cooling, a martensitic (γ → α) transformation is realized with critical points of the beginning of Ms = 344 ℃ and the end of Mf = 212 ℃ of this transformation. The XRD in situ analysis revealed no precipitation of carbide phases under heating and cooling conditions of steel EP-823. Position of the critical points of phase transformations depends on the research method (XRD in situ or DSC), which is determined by the difference in effective (taking into account the time for shooting in the XRD method) heating-cooling rate. The effect of elemental composition on the position of critical points of phase transformations and the formation of structural-phase states of ferritic-martensitic steels is discussed. It is shown that the increased content of ferrite-stabilizing elements (Cr, Mo, Nb) in composition of EP-823 steel, compared with other steels of the same class, expands the region of existence of the ferrite phase, which can contribute to an increase in the temperature of Ac1 .

Structural, Thermo‐Functional, and Rheological Properties of Dielectric Modified Underutilized Jicama (Pachyrhizus, spp.) Starch

AbstractIn this study, underutilized jicama starch (JS) is treated in dielectric‐heating at different power (300, 450, 600 W) and time (1, 3, 5 min), and the change in structural, thermo‐functional, and rheological properties is observed. The dielectric modification increases the water absorption (0.81–2.88 g g−1), whereas the oil absorption capacity (1.02–0.83 g g−1) and bulk density (0.52–0.39 g mL−1) are reduced as compared to native starch. Lightness (95.46–96.26) of JS non‐significantly varies with dielectric‐heating, whereas a significant effect is observed in redness (0.01–0.06) and yellowness (3.74–4.24). The apparent viscosity of all treated samples shows shear thinning behavior. All the pasting properties other than the setback and pasting temperature of dielectric treated samples are significantly (p < 0.05) decreased at higher power than control. The onset (46.50–81.67 °C), peak (64–99.23 °C), and end temperature (68.27–100.77 °C) of gelatinization transition increased, which shows better thermal stability as compared to control. The strong‐peak for the control and treated sample is observed at around 1000 cm−1 wavenumber in the Fourier transform infrared spectroscopy. The structural changes have been observed by X‐ray diffraction analysis (XRD) and scanning electron micrographs (SEM) shows shrinkage and deformation at each power and time.

Steady melting in material extrusion additive manufacturing

PurposeA main cause of defects within material extrusion (MatEx) additive manufacturing is the nonisothermal condition in the hot end, which causes inconsistent extrusion and polymer welding. This paper aims to validate a custom hot end design intended to heat the thermoplastic to form a melt prior to the nozzle and to reduce variability in melt temperature. A full 3D temperature verification methodology for hot ends is also presented.Design/methodology/approachInfrared (IR) thermography of steady-state extrusion for varying volumetric flow rates, hot end temperature setpoints and nozzle orifice diameters provides data for model validation. A finite-element model is used to predict the temperature of the extrudate. Model tuning demonstrates the effects of different model assumptions on the simulated melt temperature.FindingsThe experimental results show that the measured temperature and variance are functions of volumetric flow rate, temperature setpoint and the nozzle orifice diameter. Convection to the surrounding air is a primary heat transfer mechanism. The custom hot end brings the melt to its setpoint temperature prior to entering the nozzle.Originality/valueThis work provides a full set of steady-state IR thermography data for various parameter settings. It also provides insight into the performance of a custom hot end designed to improve the robustness of melting in MatEx. Finally, it proposes a strategy for modeling such systems that incorporates the metal components and the air around the system.

Numerical analysis of a novel coaxial annular tube convective heat switch

Heat switches are commonly used in cryogenic instruments to provide thermal contact or isolation between the hot and cold masses over a temperature range from millikelvin to room temperature. This study presents a new type of convective thermal switch that implements an annular tube design replacing the twin-tube structure. To study the effects of geometry and operating parameters on thermal performance, a computational fluid dynamics (CFD) model is developed. The results show that the designed heat switch provides a thermal conductance of 33.79 mW/K when the end temperatures are 4.2 K and 40 K. In addition, it can automatically change to thermal isolation mode with a residual thermal conductance of 0.19 mW/K. The thermal conductance is increased from 33.79 mW/K to 38.90 mW/K by extending the length of the inner tube. This novel heat switch holds promise for precooling the modern cryogen-free dilution refrigerator (DR) and adiabatic demagnetization refrigerator (ADR).

Preparation and characteristic study of the hydrogel of coal spontaneous combustion environmental protection

In order to solve the problem of spontaneous combustion of coal in mined-out areas, a new type of P/S/T/H environmentally friendly hydrogel was designed by using polyvinyl alcohol, sodium alginate and di(triethanolamine) titanate diisopropyl to form a gel system and adding the environmentally friendly material hybrid shell bio-filler. The formulation of P/S/T/H gel was studied by orthogonal experiment, and the forming time was precisely controlled. The synthesis mechanism and flame-retardant properties of the gels were investigated by various experimental methods. The results show that: There are folds and three-dimensional pore structures inside the P/S/T/H gels, and the two cross-linked networks strengthen the stability of the gels. Compared with WG gel and single cross-linked network gel, P/S/T/H gel has the best water retention, water absorption/salt resistance and flame-retardant effect. The water retention rate of P/S/T/H gel is still as high as 20% after 12 h, the water-absorbing multiplicity is more than 400 after 90 min, and the salt-resistant multiplicity is 54 after 90 min. When P/S/T/H gel is added to the coal samples, the combustion end temperature lags 8.4 °C, the heat release is reduced by 19.9%, the average CO inhibition rate is 45.9%, the maximum heat release rate is reduced by 20.1 KW/m2, the total heat release rate is reduced by 36.6%, and the maximum flue gas inhibition rate is 87.1%. Therefore, the highly efficient and environmentally friendly P/S/T/H gel is expected to play an important role in the work of fire prevention in mined-out areas.

Theoretical and experimental study of free piston Stirling generator for high cold end temperatures

The cold end temperature of the free piston Stirling generator (FPSG) should be increased to reduce the heat sink radiator area for space application. A comprehensive model coupled with thermodynamics, dynamics, and electromagnetism was built and solved numerically to investigate the intrinsic relationship between cold end temperature and FPSG performance. It shows that, with fixed heating power, as the cold end temperature increases, the magnetic field strength of alternator air gap decreases. The output power and efficiency show a steadily declining trend. A 100W prototype was tested for model verification. The relative error between experiment and model prediction of the amplitude of piston and displacer is 2.48 % and 11.97 % respectively. For phase difference between piston and displacer, thermal efficiency, and working frequency, the relative error is 54.32 %, 27.23 %, and 2.39 % respectively. When the cold end temperature rises from 320.5K to 394K, the output power and efficiency relative error is 26.06 %∼37.85 % and 27.67 %∼34.24 % respectively. The predicted parameter effect trend is well consistent with experiment, showing the important guiding role for generator optimization operating at high temperatures. The exergy analysis shows that increasing cold end temperature causes input exergy decline and aggravates exergy loss, which is main cause of generator performance degradation.

Studies on some engineering properties of dried egg powder reference to its bulk handling

Abstract This study investigated some physicochemical and engineering properties of dried egg powder concerning to its bulk handling with the view to promote its usage. The egg was deshelled to have whole egg, egg white and yolk; oven-dried in convective air at 60 °C (± 1 °C), milled and screened with a sieve size with a mesh size of 500 µm. The physicochemical and engineering properties analyses were carried out using standard procedures. The moisture contents ranged from 2.64 to 2.69%, loose and packed bulk densities ranged between 0.45 g/ml and 0.66g/ml (loose), 0.57 g/ml and 0.71g/ml, (packed). The least gelation concentration (LGC) of egg white and whole egg powder occurred at 10%, and, 12% respectively with egg yolk having poor LGC. The density ratio of egg white, whole egg and egg yolk powder were 92%, 76% and 77%, respectively. Egg white, whole egg and egg yolk powder samples had 7.80, 23.43 and 22.12% porosity, respectively The foaming stability of egg white, whole egg and egg yolk powder are 25.05, 28.41 and 26.01, respectively Similarly, the Carr index and Hausner ratio of dried egg white, whole egg and egg yolk powder are 24.48, 7.29 and 22.80; 1.18, 1.35 and 1.32, respectively indicating the egg powder samples were free-flowing. The emulsifying activity index of egg white, whole egg and dried egg powder are 3.84, 1.78 and 5.96, respectively while emulsifying stability index of the same samples are 503.30, 57.83 and 37.87, respectively. The colour intensity determined for egg white, whole egg and egg yolk powder was 61.75, 41,15 and 52.45, respectively Also, the thermal properties of the samples measured using differential scanning calorimeter ranged between 79.3 ⁰C - 92.8 ⁰C, 106.4 ⁰C - 121.2 ⁰C, 106.2 ⁰C - 122.8 ⁰C, 56.75 J/g - 278.6 J/g, 21.4 ⁰C - 94.743.5 ⁰C, 10.95 J/(gK) - 20.28 J/(gK), 0.50 w/m⁰C - 0.70 5 w/m⁰C, and 0.090 m2/s - 0.094 m2/s for onset temperature, peak temperature, end temperature, enthalpy, temperature range, specific heat capacity, thermal conductivity and thermal diffusivity respectively. The study therefore, provides engineering data about process design, control and bulk handling to extend the usage of dried egg powder samples in food process industries.