Nitrogen Coolant Research Articles

Recent Trends in Nitrogen Cooling Modelling of Extrusion Dies

Nitrogen cooling has been identified as a powerful industrial solution for the hot extrusion process to remove heat in the die and in the profile. The complexity involved in the design of cooling channels depends on many factors, including the cooling path, its position with respect to the hottest zones as well as the nitrogen phase change that strongly affects the heat removal capacity. However, the industrial approach is still stuck in the empirical and based-experience practices that too often strongly limit the possibilities of obtaining a performing cooling solution. In this context, this work intends to summarize and discuss the advanced recent trends in the design of cooling channels for extrusion dies proposed by the authors based on the numerical approaches, with the final aim to propose possible solutions to fill the current gaps of the suboptimal industrial approaches.

Optimizing the drilling process parameters of AZ91 based hybrid composites using TOPSIS and grey relational analysis

AZ91 is a popular magnesium alloy that contains aluminum (Al), zinc (Zn), and small amounts of other elements that offers a good balance of mechanical properties and corrosion resistance, making it suitable for various applications such as automotive, aerospace, sports, and biomedical. The current research works focused on optimizing drilling process parameters such as cutting speed, feed rate, a set of standard tools, and biofriendly coolants against the surface roughness and axial thrust force for AZ91/ nano hBN/ micron TiB2 hybrid composites. Taguchi L18 orthogonal array was used to design the drilling experiments. The axial thrust force and surface roughness of the drilled hole were observed as response of the experiments. Based on the results from TOPSIS and GRA, the optimal conditions were determined to be a spindle speed of 65 m/min, feed rate of 1 mm/rev, using a High-Speed Steel (HSS) tool, and Liquid Nitrogen (LN) coolant for 1 wt% of nano hBN in the hybrid composite. These parameters resulted in the lowest axial thrust force and surface roughness, highlighting their effectiveness in optimizing the drilling performance of AZ91/TiB2/hBN composites.

A Liquid Nitrogen Cooling Circulation Unit: Its Design and a Performance Study

A Liquid Nitrogen Cooling Circulation Unit: Its Design and a Performance Study

Risk Assessment and Analysis of Rock Burst under High-Temperature Liquid Nitrogen Cooling

Rock burst, an important kind of geological disaster, often occurs in underground construction. Rock burst risk assessment, as an important part of engineering risk assessment, cannot be ignored. Liquid nitrogen fracturing is a new technology used in the geological, oil, and gas industries to enhance productivity. It involves injecting liquid nitrogen into reservoir rocks to induce fractures and increase permeability, effectively reducing rock burst occurrences and facilitating the flow of oil or gas toward the wellbore. The research on rock burst risk assessment technology is the basis of reducing rock burst geological disasters, which has important theoretical and practical significance. This article examines the temperature treatment of two types of rocks at 25 °C, 100 °C, 200 °C, 300 °C, and 400 °C, followed by immersion in a liquid nitrogen tank. The temperature difference between the liquid nitrogen and the rocks may trigger rock bursting. The research focused on analyzing various characteristics of rock samples when exposed to liquid nitrogen. This included studying the stress–strain curve, elastic modulus, strength, cross-section analysis, wave velocity, and other relevant aspects. Under the influence of high temperature and a liquid nitrogen jet, the wave velocity of rocks often changes. The structural characteristics and possible hidden dangers of rocks can be understood more comprehensively through section scanning analysis. The stress–strain curve describes the deformation and failure behavior of rocks under different stress levels, which can help to evaluate their stability and structural performance. The investigation specifically focused on the behavior of rocks subjected to high temperatures and liquid nitrogen. By analyzing the stress–strain curves, researchers were able to identify the precursors and deformation processes that occur before significant deformation or failure. These findings have implications for the mechanical properties and stability of the rocks.

Microstructure Imaging and Characterization of Rocks Subjected to Liquid Nitrogen Cooling

Liquid nitrogen (LN2) fracturing is a potential stimulation method in unconventional hydrocarbon recovery, showing its merits in being water free, creating low formation damage and being environmentally friendly. The microstructure evolution of rocks subjected to LN2 cooling is a fundamental concern for the engineering application of LN2 fracturing. In this paper, pore-scale imaging and characterization were performed on two rocks, i.e., tight sandstone and coal specimens subjected to LN2 cooling using computed tomography scanning. The digital core technique was employed to reconstruct the microstructures of rocks and give a quantitative analysis of the pore structure evolution of both dry and water-saturated rocks. The results indicate that LN2 cooling has a great effect on the pores’ morphology and their spatial distribution, leading to a great improvement in pore diameter and aspect ratio. When compared to the sandstone, coal is more sensitive to LN2 cooling and thermal stresses, having a more noticeable growth in pore–throat size. The porosity growth of coal is 291% higher than that of sandstone. There is a growing trend in the irregularity and complexity of pore structures. After LN2 cooling, the fractal dimensions of the pores of sandstone and coal grow by 11.7% and 0.87%, respectively, and the proportion of pores with a shape factor > 100 increases. More bundle-like and strip-shape pores with multiple branches are generated, which causes a significant growth in the throat size and the proportion of connected pores with a coordination number ≥ 1, enhancing the complexity and connectivity of pore structures dramatically. Additionally, pore water plays an important role in aggravating rock damage during LN2 cooling, enhancing the pore space and connectivity. The porosities of the saturated sandstone and coal samples grow by 22.6% and 490.4%, respectively, after LN2 cooling, which are 5.6% and 186.6% higher than dry samples. The generation of macropores ≥ 70 μm is the primary contributor to porosity growth during LN2 cooling, although such pores account for only a small proportion of the total. These findings contribute to our understanding of the microscopic mechanism of LN2 cooling on rock damage and may provide some guidance for the engineering application of LN2 fracturing.

Mass-Heat Coupling in Film Cooling Experiments—The Influence of Temperature and Turbulence on the Dufour Effect

Abstract The use of foreign gases in laboratory film cooling experiments is attractive since variable density ratios can be achieved with coolant-to-freestream temperature ratios near unity, often reducing the cost and difficulty of the experimental campaign. In adiabatic effectiveness experiments employing pressure sensitive paint along with the mass transfer analogy to heat transfer, isothermal surfaces are often an experimental requirement. Furthermore, low-temperature laboratory experiments using thermal techniques often employ relatively close matches between the coolant and freestream temperatures. Using foreign gases, however, introduces off-diagonal couplings of heat and mass transport, which can produce unexpected results in film cooling experiments. In particular, the Dufour effect—also called the diffusion-thermo effect—which is the transfer of thermal energy by mass transfer processes, can manifest in surface temperatures that break the traditional bounds of thermal adiabatic effectiveness experiments: outside the upper and lower bounds of the coolant and freestream temperature. Beyond the expected confusion for the researcher, this effect can also be detrimental to those that assume that matching the coolant and freestream temperatures are the necessary and sufficient conditions to ensure isothermal surface conditions in traditional pressure sensitive paint experiments. In this work, the influence of cooling gas selection, experimental temperature, and experimental freestream turbulence conditions are explored on a simulated leading edge with compound injection from a cylindrical cooling hole. Air, argon, carbon dioxide, helium, and nitrogen coolants were analyzed due to their use in prior film cooling studies. The Dufour effect was found to be significant when using helium as the coolant, though temperature separation was also observed in argon and carbon dioxide cases. Additionally, elevated experiment temperatures generally increased temperature separation. Finally, high freestream turbulence intensity was found to reduce, but not eliminate, the Dufour effect in helium experiments.

Technical and economic analysis of a pebble bed modular reactor with nitrogen coolant

High-temperature nuclear reactors (HTR) could benefit from using the gas turbine in tandem with a steam turbine; this is the principle of combined cycles using natural gas. HTRs have the characteristic that the turbine works in high-temperature conditions. The flue gas could feed a steam generator to produce additional electricity improving system efficiency. The current study assesses the likeliness of having a combined cycle from a Pebble Bed Modular Reactor using nitrogen as a coolant. The balance of the plant and the corresponding configuration to meet this goal are given; the results show an efficiency of 53.56% of electrical generation compared to 42% reported by the HTR-PM. The share cost for turbine plant equipment represents 8.9%–14.0% of the total cost of the power plant. Three scenarios are contemplated to assess the economic impact of the additional generation where an increase in the overnight cost is considered, 9.99%, 12.41%, and 15.73% because of the additional cost of the steam turbine and associated equipment. Assuming a 4500 US$/kW cost for installed capacity for the HTR-PM reactor, for a 10% discount rate, the electricity total levelized cost is 95.56 US$/MWh. For the proposed combined cycle using nitrogen as a coolant, the electricity total levelized cost is 89.78 US$/MWh, assuming a 10% discount rate when the higher overnight cost is taken into account (5208 US$/kW). Using nitrogen under this alternative will produce an additional electricity production of 425,742 MWh annually. It leads to an electricity cost reduction of 5.78 US$/MWh even in the higher cost for the nitrogen combined cycle here considered, and a 10% discount rate compared with the HTR-PM steam cycle reported data, showing the technical and economic feasibility of using nitrogen as a coolant gas.

Effect of Liquid Nitrogen Cooling and Heating on Mechanical Properties and Acoustic Emission Characteristics of Coal

The instability of rock fractures has been extensively studied in domestic and international research. This paper investigates two coal types from the Jiaozuo area, which were subjected to liquid nitrogen cyclic treatment using Brazil’s indirect tensile testing (BITT). The study analyzes the characteristics of acoustic emission (AE) and crack formation during the coal cracking process and evaluates the impact of freeze-thaw treatment with liquid nitrogen cycles on the mechanical properties of coals. The results demonstrate that liquid nitrogen has a significant impact on the formation and development of coal fractures under the Brazil splitting test conditions. As the number of cyclic treatments increases, the maximum load-bearing capacity of coal decreases, indicating a gradual reduction in the effective stress on coal samples. Furthermore, the acoustic emission activity intensity of coal mass during phased loading increases as the number of freeze-thaw cycles of liquid nitrogen increases. Finally, during phased loading of coal specimens, the primary factor is the germination, extension, and failure of tensile cracks, while the secondary factor is the development, extension, and failure of shear cracks. Overall, this study provides valuable insights into the behavior of coals under freeze-thaw cycles of liquid nitrogen treatment and highlights the importance of understanding the characteristics of coal fracture instability.

Mechanical Properties of High-Temperature Granite under Liquid Nitrogen Cooling

The cooling characteristics of liquid nitrogen can effectively weaken the mechanical properties of dry hot rock reservoirs, improve the porosity and permeability of dry hot rock, and thus improve the development and utilization of geothermal resources. In order to explore the weakening effect of liquid nitrogen cooling characteristics on high-temperature reservoir rocks, uniaxial compression tests, Brazil splitting tests, and three-point bending tests were conducted on high-temperature granite, and synchronous acoustic emission tests were conducted to monitor the damage evolution of rocks. It is found that under the action of liquid nitrogen, the elastic modulus, peak strength, fracture toughness, and other mechanical properties of granite decrease to varying degrees. At different initial temperatures, the damage degree of liquid nitrogen to granite is different. The higher the initial temperature of granite, the greater the damage effect of liquid nitrogen on granite. The low-temperature characteristics of liquid nitrogen not only have the effect of cracking damage on granite but also have the effect of thermal stress on granite. If the temperature difference between the two is large, the heat released in the combination process will be higher. The greater the temperature difference, the greater the damage to granite. Under the action of liquid nitrogen, the acoustic emission characteristics of granite also show different evolution laws, and the ringing count of rock increases significantly, which indicates that liquid nitrogen aggravates the internal damage of granite, making the rock more fractured during fracturing. The research results can provide some scientific guidance for the development and utilization of geothermal energy.

Mechanical Properties and Damage Evolution of Heated Granite Subjected to Liquid Nitrogen Cooling

To investigate the effect of liquid nitrogen on the granite failure process, the deterioration effect of liquid nitrogen on heated granite was investigated from experimental and theoretical perspectives. The mechanical properties of heated granite (25, 100, 200, 300, and 400 °C) after different cooling treatments (air cooling and liquid nitrogen cooling) were investigated by uniaxial compression tests. The damage evolution analysis was performed by a statistical damage constitutive model and the dissipation energy ratio was newly defined. The results show that there is an increase in the uniaxial compressive strength of heated granite before 200 °C, which is due to the competitive relationship between the thermal cracking and crack closure. Liquid nitrogen cooling can deteriorate the mechanical properties of heated granite in terms of strength and deformability. At 400 °C, the reduction rates of compressive strength and stiffness between air cooling and liquid nitrogen cooling reached 32.36% and 47.72%, respectively. Liquid nitrogen cooling induces greater initial thermal damage and, consequently, leads to a greater degree of total damage before the peak stress and makes rock easier to be damaged. At 400 °C, the total damage at the peak stress increased from 0.179 to 0.587 after the liquid nitrogen cooling. The difficulty of damage can be quantified by the dissipation energy ratio. In addition, the deterioration of liquid nitrogen on granite is positively related to temperature. This study confirmed the deterioration effect of liquid nitrogen and promoting effect of temperature, providing a theoretical approach to the degradation mechanism of liquid nitrogen.

Transient analysis of a direct cycle nuclear heated gas turbine plant with nitrogen coolant

This paper investigates the thermodynamic cycle compatibility of combining a modified commercial gas turbine with a prismatic High Temperature Gas Reactor (HTGR) with a nitrogen coolant. In-addition the paper investigates the transient response of the combined reactor and turbine combination against operational power transients for a variety of control methodologies. The analysis methodology utilises turbine gas dynamics, lumped thermal mass and a point reactor kinetic model built within the Matlab and Simulink modelling environment. Design point data from commercial gas turbine data sheets provide the key turbine gas dynamic parameters enabling transient performance estimates of output power coolant mass flow and heat transfer properties of the direct cycle reactor plant. The methods permit simple assessment of a variety of currently available gas turbine products for use within a nitrogen cooled direct cycle prismatic HTGR. The combination of a Siemens SGT 600 gas turbine with a ∼ 45MWth prismatic HTGR is illustrated and considered to have potential as an overall plant combination. The transient analysis explored a novel control approach where characteristics of both inventory and turbine bypass control features were combined, delivering both fast and proportional power control within a single control system, whilst maintaining high part load system efficiency. Furthermore, when combined with passive reactivity control based on the core negative temperature coefficient, the control method was shown to reduce overall core thermal transients experienced during power level changes. The proposed design illustrates the potential for minimising development risk associated with the direct cycle HTGR through direct use of current commercial gas turbine products, whilst using negative temperature coefficients for reactivity control and maintaining a simple turbine control system design.

Assessment of the Optimization Strategy for Nitrogen Cooling Channel Design in Extrusion Dies

Aluminum extrusion is an efficient industrial process. However, one of the main problems is related to the temperatures developed during the process that can detrimentally affect the achievable productivity, profile quality and/or die life. Cooling of the die with liquid nitrogen represents an efficient solution to overcome this limit but a further issue arises lying in the number of process and design variables that need to be managed in order to set-up of an efficient system. In this context, a 3D FE model of the extrusion process, coupled with a 1D model of the cooling channel, previously proposed by the authors, has been integrated in an optimization platform in order to iteratively and automatically adjusts the channel geometry and the process variables gaining to a final optimal solution in terms of thermal balance, cooling efficiency and nitrogen consumption. The original channel design used during the extrusion of industrial hollow AA6060 profile guaranteed an efficient but unbalanced cooling with a maximum temperature deviation of 60 °C registered by the thermocouple positioned around the bearings. The optimized designs showed temperature deviations below the 16 °C as well as the reduction of 50% in terms of nitrogen consuming.

Study of the coolant type influence on the thermal and hydraulic characteristics of cooling channels for high-temperature turbine blades in an oxy-fuel energy system

Electricity consumption by people is increasing every year, followed by an increase in harmful emissions of carbon dioxide into the atmosphere during its generation. A promising solution to the problem of global pollution can be an oxy-fuel technology for energy production. It has been proven that the Allam cycle at an initial temperature of 1100 C is the most efficient oxy-fuel cycle. With a further increase in the initial temperature, the efficiency of this cycle decreases due to an increase in the relative coolant flow rate. This paper discusses the effect of the changeover from carbon dioxide to nitrogen coolant on thermal and hydraulic characteristics of cooling channels for the first-stage blade of a carbon dioxide turbine. We have found that, upon changeover from carbon dioxide to nitrogen cooling, the heat transfer coefficient decreases for a channel with pin intensifiers 1.3 to 1.65 times, for a channel with pin-and-dimple intensifiers, 1.65 to 1.77 times. We have also found that, upon changeover from pin intensifiers to pin-dimple ones, the heat transfer coefficient is increased for a cooling system using carbon dioxide coolant 2.2 to 2.5 times, whereas when using nitrogen coolant, the heat transfer coefficient remains unchanged. It has been also found that, to maintain a constant heat transfer coefficient upon changeover from carbon dioxide to nitrogen coolant, we should provide a 23.6% higher nitrogen flow rates compared to dioxide.

Influence of Liquid Nitrogen Cooling State on Mechanical Properties and Fracture Characteristics of Coal

Influence of Liquid Nitrogen Cooling State on Mechanical Properties and Fracture Characteristics of Coal

Role of Liquid Nitrogen Cooling State in Physical and Tensile Properties of Sandstone

Role of Liquid Nitrogen Cooling State in Physical and Tensile Properties of Sandstone

Transient Analysis of a Direct Cycle Nuclear Heated Gas Turbine Plant with Nitrogen Coolant

Transient Analysis of a Direct Cycle Nuclear Heated Gas Turbine Plant with Nitrogen Coolant

Influence of Various Control Factors on Fracture Toughness and Fracture Energy of Sandstone Subjected to Liquid Nitrogen Cooling

Liquid nitrogen (LN2) cryogenic fracturing can significantly enhance the permeability of tight-sandstone gas reservoirs. In order to evaluate the control factors influencing the changes in the crack toughness and fracture energy of the sandstone in LN2 cryogenic fracturing, the influences of the LN2 cooling state, freeze–thaw cycle (FTC) times, moisture content of the sandstone, and notch inclination angle were studied using combined three-point bending experiments. At the same time, the internal structural damage and induced fracture morphology are employed to analyze the failure mechanism. The results show that the LN2 freeze–thaw treatment can decrease the crack toughness and fracture energy of the sandstone, while these values increase for the LN2 freezing treatment. The water saturation condition can enhance the LN2 cooling effect, but it has a larger influence on LN2 freezing. With the increase of the notch angle, both the crack toughness and the energy release rate (ERR) of the saturated sandstone significantly reduce, but the applied energy only has a slight increase. The crack toughness, ERR, and applied energy of the saturated sandstone gradually decrease with the increase in the LN2 FTC, and their values after 30 LN2 FTC times decrease by 52.67, 76.04, and 41.15%, respectively. The strength feature and fracture energy of the sandstone heavily depend on the internal microstructure and crack propagation mechanism of the sandstone.

The Dufour Effect in Film Cooling Experiments With Foreign Gases

Abstract In typical film cooling experiments, the adiabatic wall temperature may be determined from surface temperature measurements on a low thermal conductivity model in a low-temperature wind tunnel. In such experiments, it is generally accepted that the adiabatic wall temperature must be bounded between the coolant temperature and the freestream recovery temperature as they represent the lowest and highest temperature introduced into the experiment. Many studies have utilized foreign gas coolants to alter the coolant properties such as density and specific heat to more appropriately simulate engine representative flows. In this paper, we show that the often ignored Dufour effect can alter the thermal physics in such an experiment from those relevant to the engine environment that we generally wish to simulate. The Dufour effect is an off-diagonal coupling of heat and mass transfer that can induce temperature gradients even in what would otherwise be isothermal experiments. These temperature gradients can result in significant errors in the calibration of various experimental techniques, as well as lead to results that at first glance may appear non-physical such as adiabatic effectiveness values not bounded by zero and one. This work explores Dufour effect induced temperature separation on two common cooling flow schemes, a leading edge with compound injection through a cylindrical cooling hole, and a flat plate with axial injection through a 7–7–7-shaped cooling hole. Air, argon, carbon dioxide, helium, and nitrogen coolant were utilized due to their usage in recent film cooling studies.

Influences of Brass Surface Morphology on Leidenfrost Effect during Liquid Nitrogen Cooling

Cooling in liquid nitrogen is a typical service condition of high-temperature superconducting wire, and the variation of boiling stages on the wire protective layers such as the brass layers could be crucial for the quench behavior of superconducting devices. In this study, the influence of brass surface morphology (parameters of surface roughness and fractal dimension) on the Leidenfrost effect (including the wall superheat at critical heat flux and the wall superheat at Leidenfrost point, which are respectively characterized by the temperatures of ΔTCHF and ΔTLP) was studied. The surfaces of brass samples were polished by sandpaper to obtain different morphologies, which were characterized by using white light interferometer images, and the boiling curves were recorded and analyzed by Matlab with lumped parameter method. The experimental results demonstrated that the surface morphology of brass samples could influence the ΔTLP significantly, but had no clear relationship with the ΔTCHF. Moreover, the multi-scaled analysis was carried out to explore the influencing mechanism of surface microstructure, the relationship between ΔTLP and scale was more clear when the scale was small, and the fractal dimension was calculated and discussed together with surface roughness. The findings of this study could be instructive for surface treatment of superconducting wires to suppress quench propagation.

Differences in Petrophysical and Mechanical Properties Between Low- and Middle-Rank Coal Subjected to Liquid Nitrogen Cooling in Coalbed Methane Mining

Abstract Exploring the damage differences between different coal rank coal reservoirs subjected to liquid nitrogen cooling is of great significance to the rational development and efficient utilization of coalbed methane (CBM). For this purpose, the mechanical properties, acoustic emission (AE) characteristics, and energy evolution law of lignite and bituminous coal subjected to cooling treatment were investigated based on Brazilian splitting tests. Then, pore structure changes were analyzed to reveal the differences in microscopic damage between lignite and bituminous coal after a cooling treatment. The results showed that compared with bituminous coal, the pore structure of lignite coal changed more obviously, which manifested as follows: significant increases in porosity, pore diameters, and pore area and a larger transformation from micropores and transition pores to mesopores and macropores. After the cooling treatment, the thermal damage inside lignite and bituminous coal was 0.412 and 0.069, respectively. Thermal damage reduced the cohesive force between mineral particles, leading to the deterioration of the macroscopic physical and mechanical properties. Simultaneously, denser acoustic emission ringing counts and larger accumulated ringing counts were observed after cooling. Moreover, the random distribution of thermal damage enhanced the randomness of the macrocrack propagation direction, resulting in an increase in the crack path tortuosity. With more initial defects inside coal, a more obvious thermal damage degree and wider damage distribution will be induced by cooling treatment, leading to more complicated crack formation paths and a higher fragmentation degree, such as that of lignite coal.