Special Heat Research Articles

Development of a special thermal-hydraulic component model for the core makeup tank

We have assessed the applicability of the thermal-hydraulic system analysis code, SPACE, to a small modular reactor called SMART. For the assessment, the experimental data from a scale-down integral-test facility, SMART-ITL, were used. It was conformed that the SPACE code unrealistically calculates the safety injection flow rate through the CMT and SIT during a small-break loss-of-coolant experiment. This unrealistic behavior was due to the overprediction of interfacial heat transfer at the steam-water interface in a vertically stratified flow in the tanks. In this study, a special thermal-hydraulic component model has been developed to realistically calculate the interfacial heat transfer when a strong non-equilibrium two-phase flow is formed in the CMT or SIT. Additionally, we developed a special heat structure model, which analytically calculates the heat transfer from the hot steam to the cold tank wall. The combination of two models for the tank are called the special component model. We assessed it using the SMART-ITL passive safety injection system (PSIS) test data. The results showed that the special component model well predicts the transient behaviors of the CMT and SIT.

The effect of temperature on the tribological characteristics of high speed steels under conditions of friction without lubricant on the structural steel 30HGSA

This article focuses on the study of the effect of temperature in the contact zone on the process of dissipative structures formation on the surfaces of specimens made of high speed steels (HSS) grades with different levels of thermal entropy and absolute thermo-EMF under conditions of friction without lubricant on the structural steel 30HGSA. Tribological tests were performed on the tribometer which implemented a scheme of friction “pin on disk” at constant sliding speed and normal load values. The temperature in the friction zone has changed artificially from 100 to 300°C with a special intelligent heating device. It has been established experimentally that in the process of friction of HSS specimens characterized by low values of absolute thermo-EMF the dissipative structures thickness growth rate over time at temperatures of 200-250oC decreases or remains virtually unchanged; friction coefficient decreases with the increase in temperature. For specimens made of steels with high absolute thermo-EMF the rates of dissipative structures thickness growth and their utmost thicknesses increase when the contact zone temperature increases, which is accompanied by an increase in friction coefficients.

Predicting the onset of nucleate boiling heat flux of one-side heated flat heat sink in sub-cooled flow conditions for fusion divertor cooling

For the cooling system of the future, nuclear fusion tokamak, to operate stably and continuously, it is important to identify potential hazards that may occur in the system in advance. Among the various hazards associated with the nuclear fusion tokamak, the onset of nucleate boiling (ONB) is a point at which the heat-transfer mechanism changes dramatically and is a crucial factor that must be addressed. In particular, the equipment inside the tokamak is loaded with a heat flux of several MW m−2 under single-side heating conditions, and it is important to predict the ONB under these special heating conditions. Therefore, in this study, the ONB of a flat heat sink was experimentally investigated under highly subcooled flow conditions. Based on the physical understanding of the thermo-hydraulic aspect of the ONB, the wall temperature gradient change point, which is mainly used in the subcooled flow condition, was selected as the ONB detection criterion. Trends in the ONB heat flux change were analyzed as representative system parameters that can be tuned in the cooling system, such as subcooling, mass flow rate, and pressure. In addition, the ONB correlations developed in the previous studies were evaluated for predicting the performance under one-side high heat load conditions. However, the large difference in the experimental conditions (range of system parameters and heating conditions) and the fact that the influence of system parameters was not reflected in the correlation resulted in high error rates. Therefore, the ONB correlation that can be used in the tokamak heat flux condition was newly developed through a dimensional analysis that can effectively reflect the influences in the correlation through dimensionless numbers. The developed correlation can be of great help in designing a diverter or blanket cooling system and establishing an operational strategy.

Effect of Thermal Stabilization on PAN-Derived Electrospun Carbon Nanofibers for CO2 Capture.

Carbon capture is amongst the key emerging technologies for the mitigation of greenhouse gases (GHG) pollution. Several materials as adsorbents for CO2 and other gases are being developed, which often involve using complex and expensive fabrication techniques. In this work, we suggest a sound, easy and cheap route for the production of nitrogen-doped carbon materials for CO2 capture by pyrolysis of electrospun poly(acrylonitrile) (PAN) fibers. PAN fibers are generally processed following specific heat treatments involving up to three steps (to get complete graphitization), one of these being stabilization, during which PAN fibers are oxidized and stretched in the 200–300 °C temperature range. The effect of stabilization temperature on the chemical structure of the carbon nanofibers is investigated herein to ascertain the possible implication of incomplete conversion/condensation of nitrile groups to form pyridine moieties on the CO2 adsorption capacity. The materials were tested in the pure CO2 atmosphere at 20 °C achieving 18.3% of maximum weight increase (equivalent to an uptake of 4.16 mmol g−1), proving the effectiveness of a high stabilization temperature as route for the improvement of CO2 uptake.

Experimental and computational thermal analysis of partial-body cryotherapy

During the partial body cryotherapy, human surface is cooled with gas for several minutes. For this, special heat and mass exchanger is used – a cryocabin. From a thermal engineering viewpoint, to improve this empirical treatment, detailed data are needed on the temperature and velocity of the cooling gas, as well as on the biological tissues cooling. For this, current study proposes an improved human, partial body cryotherapy simulation models and study of the partial body cryotherapy heat transfer problem in a single system “equipment-gas-biotissue” using experiment and computer simulation. For the first time the cryoexposure duration up to 420 s was analyzed. The data on the actual cooling gas temperature and velocity distributions, skin and internal biotissue temperature, bioheat flux for the considered typical gas supply mode is obtained. The impact of body mass index, external thermal resistance (body hair) and internal structure of a body parts on cooling dynamics is analyzed. This information is expected to be useful for understanding the effect-exposure correlation of the cryotherapy and in the design of the cryotherapy equipment.

Influence of temperature on secretion and functionality of lupin seed γ-conglutin.

Basic 7S globulins, a group of proteins commonly found in legumes, undergo the intriguing phenomenon of release from the seeds into hot water. γ-Conglutin is a representative of this group of proteins found in lupin seeds. The physiological significance and the molecular mechanism of the selective release of γ-conglutin from lupin seeds remain unknown. Therefore, the presented study aimed to determine changes in the functionality of this protein in response to the high temperature occurring during lupin seed incubation. It was confirmed that the main protein fraction released from the seeds during high-temperature incubation was γ-conglutin. The incubation condition favours the occurrence of this protein in a monomeric form, and the temperature used corresponds to its midpoint unfolding temperature. Subsequent analysis carried out on the γ-conglutin monomer revealed changes in its functionality after heat shock. The thermally treated protein shows a considerable increase in its interaction strength with flavonoids. Moreover, the inhibitory activity against glycoside hydrolases was enhanced when γ-conglutin monomer was exposed to specific temperatures. The results of the present study provide a potential explanation of the physiological relevance of γ-conglutin and shed new light on a possible mechanism of its activation upon specific heat treatment. This knowledge will help characterise homologous proteins, which are commonly found in other legumes and undergo a similar heat-induced secretion phenomenon. © 2021 Society of Chemical Industry.

Peculiarities of Structure and Physical-Mechanical Properties of High-Strength Cr-Mo Pipe Steel Applicative Mainly in a Sour Environment

This paper demonstrates the results of the study of microstructure and physical-mechanical properties of the high-strength economically alloyed Fe-Cr-Mo steel, developed by RosNITI JSC for the production of the oil country tubular goods (OCTG) (casing and tubing). The main requirement for this steel is to provide simultaneous increased strength and resistance to sulfide stress cracking (SSC). It was shown that this problem could be solved by special heat treatment. As a result, the structure of this steel consists of a secondary sorbite with a lower dislocation density. Hardening is provided by dispersion-strengthened V, Nb carbides.

Numerical Simulation of Turbulent Mixing of LBE between Sub-Channels of Wire-Wrapped Fuel Assembly

The lead-bismuth eutectic (LBE) is a candidate coolant for the fourth generation liquid metal reactors. In view of its special thermophysical properties, its flow and heat transfer process in the fuel assembly sub-channels need to be studied. For this purpose, the authors conduct numerical simulation and analysis of the turbulent flow of the LBE in the wire-wrapped fuel assembly, and compare the numerical simulation results of the wall temperature of fuel rods with the experimental data for response. The simulation results agree well with the experimental data, indicating that the mathematical model and numerical results are highly reliable and accurate. The authors also characterize the turbulent mixing of LBE between different sub-channels at different values of the ratio of spacing between fuel rods to the fuel rod diameter (S/D), using the turbulent mixing coefficient β. The characterization results show that the fluctuation of β between different sub-channels varies and that the β value is negatively correlated with the S/D. Based on different calculation results of the S/D and Renolyd number, the correlation formula for the β between different sub-channels is obtained by fit. It provides a turbulent mixing model for the development of a sub-channel analysis code of fuel assembly consisting of wire-wrapped fuel rods arranged in triangular form.

Microstructure and elevated-temperature mechanical properties of dispersoid-strengthened Al-Mg-Si-Mn alloys produced by twin roll casting

The microstructure and elevated-temperature mechanical properties of dispersoid-strengthened Al-Mg-Si-Mn alloys produced by twin roll casting (TRC) and conventional mold casting (MC) were studied. A specific heat treatment at 430 ​°C for 6 ​h was applied, followed by rolling. Tensile tests were carried out at 300 ​°C. The results show that in the as-cast microstructures, equiaxed grains formed in the MC sample while elongated grains with substructures formed in the TRC sample. The eutectics in the TRC sample were much finer than those in the MC sample. Upon heat treatment, large numbers of α-Al(Fe, Mn)Si dispersoids precipitated, and the TRC sample had a greater number density of dispersoids than those in the MC sample. During the tensile test after rolling, the TRC samples exhibited higher strength than the MC samples, which resulted from the combination of the strengthening effect of the stronger dispersoids and the greater substructure hardening effect in the TRC sample; the TRC sample exhibited better ductility due to its finer initial eutectic than that in the MC sample, which depressed the stress concentration and delayed the occurrence of microcracks and fracture in the TRC sample.

Semi-analytical thermo-mechanical model for the shield tunnel segmental joint subjected to elevated temperatures

The segmental joint is the most critical component for determining the mechanical response of concrete segmental linings in a shield-tunnel structure. Existing segmental joint models have been developed mainly for the analysis of segmental lining design, but in the event of a fire, the conditions that a tunnel joint may experience could well exceed the normal design range. Consequently, the validity of the existing segmental joint models becomes questionable. In this paper, an improved semi-analytical thermo-mechanical model is derived based on the general plane joint model to consider the thermal effect induced by elevated temperatures. As a benchmark for the development of the model, a laboratory experiment was conducted on concrete lining segmental joints under elevated temperatures. The general heat transfer and special heat flow invading through the joint were deduced by theorical and numerical methods. A finite element (FE) model is developed and calibrated against experimental model tests, whilst the FE model is employed to generate the required parametric data, from which a fitting function is created. A temperature adjustment coefficient is introduced to improve the calculation of the joint section temperature field. The influence of elevated temperature and axial force on the bending moment of a segmental joint is also incorporated according to the stress state of the joint section. The validation of the proposed semi-analytical thermo-mechanical model is demonstrated through comparisons with the results of fire tests. Finally, the influences of the heating curves, bolt location, and axial load on the rotation stiffness of the joint are investigated using the proposed model.

Angle of inclination and radiation intensity variation effects on the flat plate solar collector’s performance using graphene oxide (GO)-water nanofluid

Flat Plate Solar Collector is a special heat exchanger instrument that transforms solar radiation energy into heat energy. Various attempts have been completed to improve the flat plate solar collector’s performance. One of them is by developing advanced heat transfer fluid with better thermophysical properties than base fluid. Further, the flat plate solar collector’s inclination angle and radiation intensity were investigated to identify the most optimal solar radiation angle of incidence. This study discusses the use of a 0.006% graphene oxide-water nanoparticle toward the nanofluid’s thermophysical properties, sufficient radiation intensity of flat plate solar collector performance, as well as the inclination angle of flat plate solar collector toward the collector’s performance. The used radiation intensity variations were 415 W/m2, 515 W/m2 and 615 W/m2. Meanwhile, the radiation used in this study was from a sun simulator 750 W/m2. In each radiation intensity variation, the inclination angle test of 30°, 45°, and 60° for the flat plate solar collector were carried out. This study was expected to discover the best performance of graphene oxide-water nanofluid usage, collector’s inclination angle variation, and radiation intensity variation.

E/Z isomerization of astaxanthin and its monoesters in vitro under the exposure to light or heat and in overilluminated Haematococcus pluvialis cells

Thermo- and photoisomerization of astaxanthin was investigated in a model system (solutions in methanol and chloroform), and the dynamics of astaxanthin isomers and esters content was analyzed in Haematococcus pluvialis green algal cells exposed to factors inducing astaxanthin accumulation. In both systems, the astaxanthin isomerization process seems to be defined by a) the action of light (or heat), and b) the dielectric constant of the surrounding medium. Upon heating, the accumulation of Z-isomers occurred in a model system during the entire incubation period. For the first 5 h of illumination, both Z-isomers accumulated in the solutions up to 5%, and then their content decreased. The accumulated amount of the Z-isomers in the cells of H. pluvialis was found to reach 42% of the total content of astaxanthin initially, and then it decreased during the experiment. The results lead to a conclusion that both cultivation of H. pluvialis culture in specific conditions and heat treatment of the resulting extracts from it might be efficient for obtaining large amounts of economically useful astaxanthin Z-isomer.

A mathematical model for vaporization of explosive thin film in active detection techniques

When detecting explosive traces by optical remote methods based on recording the vapors, it is essential to know the applicability limits of these techniques. The amount of a vaporized explosive depends on the vaporization kinetics, which, in turn, relies on the physicochemical properties of the explosive, film weight and thickness, ambient air temperature, and film temperature. In active detection techniques, the explosive film temperature on the surface of objects may be higher than the air temperature due to special heating devices. In this case, the questions on how the quantity of matter available for detection is about to change and how much energy has to be consumed to heat up the film can be answered by mathematical modeling. The mathematic model is based on the Hertz–Knudsen–Langmuir equation that describes the vaporization rate of matter with mass transfer between the surface and surrounding air, which is taken into account. In an elaboration of the mathematical model, we introduced previously the temperature difference between the film and ambient air, which is now taken into consideration. The basic parameters influencing the film vaporization rate, and their variation range, were identified. The kinetic parameters of vaporization of thin films of some explosives with a quantity of matter typical of a fingerprint were estimated. The weight of matter in air during vaporization of explosive thin films in a wide range of parameters under study was calculated. Conclusions were made of the applicability limits of the developed standoff detection methods for trace explosives.

Experimental investigation on the flow-induced vibration of spatial bended section of heat exchanger tubes

Flow induced vibrations in heat exchanger tubes have led to numerous accidents and economic losses in the past decades. The vibration characteristics of traditional heat tubes have been studied comprehensively through experiment, numerical simulations and theoretical analysis. Special tubes with spatial bended forms possess the great performance in nuclear engineering. The present work is motivated to understand the unclear flow-induced vibration features of these original heat exchanger tubes. An experimental system including of the tested objects are designed in water environment. The vibration responses and frequencies of spatial bended section of the heat exchanger tubes are tested and analysed. The results show that the spatial-bended tubes are safe enough to suffer the water flow within the velocity of 1m/s. The considerable vibration responses are in the bended areas with square configure, which should be specifically designed. The present work can be a guide for the special heat exchangers in nuclear engineering.

Experimental energy improvement of a special design heat exchanger-based hybrid solar collector for a photovoltaic module square surface.

Solar cells convert a part of the solar irradiance into electrical energy, and the remaining produces heat, which can be converted as a thermal energy accumulated in the module. This conversion depends on the solar cells temperature. Since conversion efficiency is very low, 5-20%, this investigation proposes an optimal combination of a photovoltaic module with a specially designed heat exchanger in order to improve the conversion energy efficiency. So, an experimental prototype of a photovoltaic thermal collector, with a special heat exchanger design for a PV module square surface is built and tested outdoor. The system is constituted of a PV module with square surface and a heat exchanger with a copper tube, in a spiral form. In order to assess the effect of the exchanger design on hybrid system performance, a comparison with a traditional photovoltaic module is done. During the experimental tests, various parameters were measured, such as solar irradiance, ambient temperature, coolant inlet/outlet temperature and surface temperature of the device. Based on the obtained results, it has been found that the use of the new PVT decreases the PV cells temperature in the order of 20°C. A consequence of that shows that the electrical power increases, by 6 W; moreover, the electrical energy efficiency goes from 7.93 to 9.65%, while the thermal energy efficiency of the PVT reaches 74.3%. The overall energy efficiency for the same system achieved was 84 %. Therefore, the energy loss is minimized, reaching 16%.

Tailoring of the Microstructure of Laser Powder Bed Fused Inconel 718 Using Solution Annealing and Aging Treatments

Inconel 718 (IN718) is a nickel-based superalloy with high weldability and is thus ideal for being processed via laser powder bed fusion (LPBF). Unlike traditional casting, LPBF IN718 develops a complex microstructure due to the rapid solidification that characterizes this manufacturing process. As a result, LPBF microstructures are different from those expected in equilibrium conditions, and for this reason, specific heat treatments should be designed. This paper, using differential scanning calorimetry (DSC), thermal mechanical analysis (TMA), and a field emission scanning electron microscope (FESEM), aims to develop a complete heat treatment that maximizes the material strength, thereby enhancing its microstructure. The paper shows that high-temperature annealing followed by two aging steps is the most suitable way to achieve the abovementioned task. More specifically, a complete dissolution of the δ phase via solution annealing at 1080 °C is the key factor in gaining an even and intense precipitation of γ′ and γ″ during the subsequent aging treatments. The microstructural analyses showed the elimination of needle-like δ particles and detrimental Laves phases. At the same time, intense precipitation of spherical and of discoidal reinforcing particles was achieved by performing the aging treatments at 720 and 630 °C, respectively.

Study on phase transformation of CMnSi steel when heat treatment

After manufacturing, if the CMnSi steel was heat treatment, it would create the multi-phase microstructure consists of highly ductility ferrite matrix, martensite, bainite and amounts of austenite. Thereby, the strength and ductility of the steel were improved. In the process of improving the quality of steel, there will be two processes: the plastic deformation process and the heat treatment process. In this paper, we present the study on the microstructure and mechanical properties of CMnSi steel which was heated. The heat treatment process of CMnSi steel is a special heat treatment process including the process of heating the steel to austenite temperature at 900 °C then keeping the heat to ensure uniformity of steel. This steel was cooled quickly from austenite temperature to phase transformation temperature which had bainite transformation equal to about 400 °C (this temperature is determined by CCT diagram). The results of microstructure analysis show that by the heat treatment process, the microstructure of steel is included three main phases: ferrite, bainite, and residual austenite. The results of mechanical tests show that after the heat treatment, the strength limit of steel is 1141 MPa, the elastic limit is 943 MPa and the elongation is 36%.

Repair of a Cracked Historic Maryan Bell by Gas Welding.

In this article, the range of works connected with the repair of a historical Maryan bell from 1639 are presented. The first attempts to repair damaged bells occurred in the 1930s in Poland. However, this process was stopped because of extensive technological difficulties. Welding and soldering-welding were the basic methods. There is one difference between these two methods—connecting surfaces are melted during the welding process but only heated until the melting temperature of the material added to the connection (that is the solder) during the soldering-welding process. It was important to heat the bell to the proper temperature during welding. Uneven heating causes the enlargement of existing cracks or the appearance of new ones, or even the complete destruction of the bell. Nowadays, a method of even heating using a special heating mat has been devised. Thanks to this method it is possible to control the heating and cooling process. The most important task during the whole operation of bell welding was obtaining the original sound. During this research, the chemical composition was examined to prepare a welding rod with a suitable chemical composition. After the repair process, an analysis of the sound of the bell was conducted. It was shown that the repair of bells is possible when correct thermal parameters are used. The most highly recommended technique for repairing bells is gas welding.

Multiple, comparative heat treatment and aging schedules for controlling the microstructures and mechanical properties of laser powder bed fusion fabricated AlSi10Mg alloy

Abstract In this investigation, the optimization of mechanical properties with thermal post-processing treatments was analyzed across a wide range of variants. A major aspect of additive manufacturing is the correlation between heat treatments and the effects on the mechanical properties and microstructure of the printed materials. Therefore, the present paper describes a comprehensive overview of post-process heat treatments for Laser Powder Bed Fusion fabricated AlSi10Mg alloy consisting of stress relief anneals at 190 C and 285 C for 2 h, hot isostatic pressing at 515 C for 3 h, hot isostatic pressing + T6 treatment for 6 h, and final aging of each of these conditions at 177 C for up to 1000 h. This has resulted in 40 experimental variants: 20 in the vertical and 20 in the horizontal tensile direction. After tensile testing, the resulting mechanical properties (ultimate tensile strength, yield strength, and elongation) and stress–strain curves are analyzed for comparison between all variants. Ultra-fine cellular, micro dendritic structures (0.6–1.2 μm) along with melt-band structures dominated the asbuilt and stress relief anneal conditions. In contrast, hot isostatic pressing and hot isostatic pressing + T6 conditions were dominated by ~10 μm, equiaxed, recrystallized grain structures and pseudo-eutectic silicon particles with varying sizes and size distributions. Microhardness and fractography results also corresponded to their specific heat treatment and microstructure. The comparison and correlation of the heat treatments are presented to help advance the selection of design strategies for high performance applications.

Features of annealing of alloy steels with mixed structure

It is necessary to obtain initial rolled product with a structure which has high ductility and low hardness for further mechanical processing of alloyed rolled metal products into the ready product. In this case the enterprises carry out a special softening heat treatment to increase the ductility of the metal. The treatment represents the annealing at subcritical temperatures (А1 — 25…40 °С) with long holding. During annealing the structural transformations are running and the formed structure has a granular morphology. To obtain spheroidizing in the steels with a mixed structure (contains at the same time pearlite, bainite or martensite) usually requires a lot of time and energy, because the structural transformations during heat treatment are running with different intensities in different phases. Established by study, that in the steels with a mixed structure during annealing the structural transformations begin from the thermodynamically less stable structures. So, to reduce the mode of the softening heat treatment (annealing) of the investigated steels it is rationally to change the cooling conditions after rolling and to provide the increased quantity of bainite and martensite. For medium-carbon steels alloyed by chromium, molybdenum and vanadium and also for low-carbon steel alloyed by manganese and silicon, an increase of the cooling rate after hot rolling by ~1.5 times allows to obtain more sensitive structure to annealing. So, the structure consists at least 80 % of the bainite, ~15 % of the ferrite and 5 % of the pearlite for chromium-molybdenum steel. The base of the structure contains bainite (~90 %), martensite (~5 %) and ferrite (up to 5 %) for chromium-molybdenum-vanadium steel. For low-carbon silicon-manganese steel an increase of the cooling rate leads to the formation of the structure which contains at least 35 % of the bainite-martensite, ~60 % of the ferrite and 5 % of the pearlite. The structural transformations proceed at the low temperatures and require a shorter duration of the holding in the obtained structures during further annealing. Receiving such structure after rolling, allows to speed up intermediate softening heat treatment, thereby reducing energy costs, and provides high ductility of steel before mechanical processing.