Choice Of Coolant Research Articles

Прогнозирование смазочных свойств СОЖ по их плотности и смачивающему действию

Introduction. The processes occurring in the cutting zone contribute to the rapid wear of the cutting tool and a decrease in the quality of the workpiece. It is possible to reduce the impact of negative factors during metal cutting through a rational choice of coolant. The aim of the work is to develop a methodology for the accelerated assessment of the coolant lubricating properties. Methods. Experimental studies of the lubricating effect of seven different grades of coolant, during friction of a T15K6 (15% TiC–79% WC–6% Co) hard alloy pad and a rotating roller made of carbon structural Steel 45 (0.45% C) are presented. As a parameter of coolant efficiency in terms of lubricating effect, paper proposes an efficiency coefficient Kc, which is equal to the ratio between the friction coefficient that occurs when using coolant and the friction coefficient during friction without coolant. The lower the coefficient Kc, the more effective this coolant is in terms of lubricating effect. Results. Empirical dependences of the coefficient Kc on the coolant density ρ and the limiting wetting angle Θ (Kc = f(ρ;Θ)) are established. Since the low significance of the parameter ρ is established, the formula for the dependence of the Kc only on the limiting wetting angle Θ (Kc = f(Θ)) is established in the work. It is established that the dependence formula (Kc = f(Θ) provides the highest accuracy of calculations. Discussion. After evaluating the research results presented in this paper, the following conclusions are made: 1) the paper establishes the influence of the coolant density and the limiting wetting angle on the coolant efficiency coefficient for the lubricating effect determined for the friction between a roller made of Steel 45 and a pad made of T15K6 alloy: Kc = f(ρ;Θ) and Kc = f(Θ); 2) the greatest accuracy of calculations from 2.75 to 15% is provided by the formula for the dependence Kc = f(Θ); 3) the dependence Kc = f(Θ)is proposed to be used for the method for the accelerated assessment of the coolant lubricating properties during friction of a pad made of T15K6 alloy and a rotating roller made of Steel 45. The proposed method consists in measuring the limiting wetting angle of a coolant drop on the surface of the workpiece and calculating the derived empirical dependence of the coolant efficiency coefficient on the lubricating effect.

On developing a practical safety culture for the advanced reactor workforce: Experiences of working with sodium

The Versatile Test Reactor is meant to fill a need in the advanced nuclear reactor development community. Accelerated nuclear testing of fuels and materials is needed to allow designs to proceed. To accomplish this, a fast neutron spectrum is needed. To have a fast neutron spectrum, the reactor coolant needs to not only have excellent heat transfer properties to sufficiently cool the reactor core, but also not significantly slow neutrons down following their birth in the fission process. Sodium is an excellent coolant choice that can fulfill these needs and many others. Sodium is the sixth most abundant element in the Earth’s crust and can be acquired easily through simple chemical separation methods. Sodium, however, reacts when in contact with water and air, but with proper precautions, these scenarios can be avoided. Nuclear reactors that utilize molten sodium as a primary heat transfer medium [a.k.a. sodium-cooled fast-neutron reactors, or SFRs, Figure 1 (1)] provide unique challenges in their daily operation, and therefore require focused training for researchers, scientists, staff, and employees alike to understand these unique challenges. Therefore, a comprehensive understanding of sodium properties is needed by all personnel involved in the design, construction, operation, experiment planning and execution of SFRs. Additionally, several commercial advanced reactor designs are under development which will use sodium for the reactor coolant. These advanced reactor designs include the Natrium reactor from TerraPower and GE-Hitachi (2), the ARC-100 reactor from Advanced Reactor Concepts (3), and the Aurora reactor from Oklo (4).

Determination of the influence of the composition of lubrication coolants on the properties and surface structure

The problem of reducing the wear of the cutting tool in the process of metal cutting are presented. The features of the use of lubricating and cooling fl uids as one of the most common method of increasing the effi ciency of machining are considered. The results of a study of the tribological characteristics of the lubricant cooling liquids (coolant) when tested according to the scheme "roller-shoe" are presented. Not only comparative tests of different types of coolant were carried out, but also to obtain experimental dependencies of the coeffi cient of friction on the strength of mutual pressing of samples for different concentrations were obtained. Recommendations on the choice of coolant to improve the efficiency of the metal machining process are given.

The effect of coolant on the durability and wear of turning tools

The process of wear of the cutting tool when using different types of cutting fl uids (coolant) is considered, the dependence of the wear of the cutter on the cutting path when using different technological media is determined, the analysis of the experimental results is carried out and recommendations are given for the choice of coolant in the cutting process.

Benefits, Drawbacks, and Future Trends of Brayton Helium Gas Turbine Cycles for Gas-Cooled Fast Reactor and Very-High Temperature Reactor Generation IV Nuclear Power Plants

Abstract Numerous studies are on-going on to understand the performance of generation IV (Gen IV) nuclear power plants (NPPs). The objective is to determine optimum operating conditions for efficiency and economic reasons in line with the goals of Gen IV. For Gen IV concepts such as the gas-cooled fast reactors (GFRs) and very-high temperature reactors (VHTRs), the choice of cycle configuration is influenced by component choices, the component configuration and the choice of coolant. The purpose of this paper to present and review current cycles being considered—the simple cycle recuperated (SCR) and the intercooled cycle recuperated (ICR). For both cycles, helium is considered as the coolant in a closed Brayton gas turbine configuration. Comparisons are made for design point (DP) and off-design point (ODP) analyses to emphasize the pros and cons of each cycle. This paper also discusses potential future trends, include higher reactor core outlet temperatures (COT) in excess of 1000 °C and the simplified cycle configurations.

Development of the mathematical model for calculation of energy efficiency of mobile diesel compressor stations

The experience of development of domestic and foreign specialists in the sphere of energy loss reduction during gas cooling of mobile diesel compressor stations of the oil and gas industry is analyzed. The reason why the productivity of the compressors decreases after short period of operation, while the specific energy consump-tion increases. The disadvantages of existing cooling systems of compressed gas of mobile diesel compressor sta-tions are presented. Requirements for refrigerant coolants for compressor gas cooling systems are formulated. A reasonable choice of Freon R134a as a coolant for cooling of the compressed gas of the compressor stations is made. The structure and principle of operation of the system of high-efficiency reduction of temperature of the perspective system of cooling of compressed gas are presented. The tasks and basic assumptions of mathematical modeling of energy efficient scheme of gas cooling system are formulated. The purpose of this article is to investigate theoreti-cally the choice of coolant for a promising highly efficient system for cooling the compressed gas of mobile diesel compressor stations in the oil and gas industry. Inputs, outputs and general structure of mathematical model of multistage gas cooling of mobile diesel compressor stations are offered. The structure of the system of high-efficiency reduction of temperature of the perspective system of cooling of compressed gas and the principle of action are presented. The description and calculation formulas of the mathematical model of compressed gas cool-ing of mobile diesel compressor stations are given. When choosing a refrigerant with the condition of further use of the obtained energy, the main requirement was taken into account. The total specific energy costs for the opera-tion of the compressor installation according to the existing and perspective schemes and its energy efficiency indicators are determined.

ОБОСНОВАНИЕ ТЕХНИЧЕСКИХ РЕШЕНИЙ РЕАКТОРНОГО КОНТУРА УСТАНОВОК БРС-ГПГ МАЛОЙ И СРЕДНЕЙ МОЩНОСТИ С ТЯЖЕЛЫМ ЖИДКОМЕТАЛЛИЧЕСКИМ ТЕПЛОНОСИТЕЛЕМ

The analysis and new scientific and technical solutions corresponding to the evolutionary development of low and medium power reactor plants with heavy liquid metal coolants are presented. The analysis was carried out on the basis of experience in the creation and operation of reactor installation with lead-bismuth coolant and research, primarily experimental, performed at the Nizhny Novgorod State Technical University (NSTU) in rationale of the small and medium-sized power plants developed at NNSTU reactor installation with horizontal steam generators (BRS-GPG). The paper substantiates the choice of coolant. With the proposed arrangement of the reactor loop, the maximum possible natural circulation is achieved, which significantly increases the safety of reactor installation. The results of studies (simulations) of one of the most potentially dangerous accidents in reactor installation with HLMC - ″large steam generator leak″ can qualitatively reduce the consequences of the accident when using the design of a horizontal steam generator in which the pipe system is placed with minimal burial of pipes under the level of HLMC, which eliminates the flow of water into the reactor core, re-pressurization of the reactor circuit, etc. It is probably advisable to consider the characteristics of the core, analog ary accepted for SVBR or BREST-OD-300. A system is proposed for cooling the reactor and providing the reactor installation shutdown modes, its characteristics are studied and tested at the NSTU stands.

Three-dimensional model of DEMO-FNS facility considering neutronics and radiation shield problems

Recent neutronics studies of blankets for tokamak-based demonstration fusion neutron source (DEMO-FNS) showed a crucial influence of coolant composition on the transmutation rate of transuranic elements and tritium breeding in the system. The coolant choice varies with the neutron spectrum and shielding properties of the blanket. This paper presents a three-dimensional model developed for the Monte Carlo calculations of DEMO-FNS neutronics. The model was used for estimating the capability of the radiation shield to protect the superconducting electromagnetic system (EMS) from neutrons and gamma radiation for two types of coolants, namely water and supercritical carbon dioxide. The neutron balance, neutron energy spectra, and energy release of the neutrons and gamma radiation were evaluated in the shield, case, and superconductor at the inner and outer contours of the EMS. In comparison with the closed shielding option, the radiation heating power at the case and superconductor of the outer contour located between the injection port (IP) and the blanket maintenance port was 10 times higher than that in the area facing the injector. Thus, further improvement of the local shield design near the IP is needed.

Thermal-hydraulic analysis of the First Wall of a CO2 cooled pebble bed breeding blanket for the EU-DEMO

The Demonstration Fusion Reactor in Europe (EU-DEMO) is considered to be the last step before building a commercial fusion power plant. Up to now, He has been chosen as gas coolant for three of the four candidate breeding blankets proposed for the EU-DEMO, being the Helium Cooled Pebble Bed (HCPB) among them. The choice of He coolant is supported, among other features, by its superior heat transfer capabilities, its transparency to neutrons and chemical inertness. However, the use of this coolant in DEMO poses some feasibility questions, like the large coolant inventory, resulting in possible safety issues, as well as the large circulating power. On the other side, CO2 has been the fluid coolant choice in the nuclear fission industry for gas-cooled reactors since the 1950s. The key advantage of this gas is its larger density, which results in more compact components, lower coolant inventories, lower circulating powers and thus better plant thermal efficiency. This, coupled also with a relatively high molecular stability at moderate temperatures (up to 600 °C), its larger availability and lower price make CO2 an attractive coolant for a pebble bed breeding blanket, as an alternative to He.As a Plasma Facing Component, the First wall (FW) is one of the components under the most challenging environment. Currently, the FW region at the upper port inboard location is expected to suffer the most critical heat flux loads. Indeed, a peak charged particle heat flux 0.99 MW/m2 together with a radiation heat flux of 0.18 MW/m2 is foreseen at this location. This paper reports the thermal-hydraulic analyses carried out to find the practical heat flux limits by using CO2 as coolant. The analyses have been performed by using the commercial computational fluid dynamics (CFD) code ANSYS CFX. Different augmented technical wall roughness areas have been considered, for a best heat transfer-to-pressure drop ratio. Sensitivity analyses have been performed as well for higher peak particle heat fluxes, evidencing that a CO2-cooled FW can dissipate peak heat fluxes up to 1.8 MW/m2 keeping the circulator power in a reasonable range.

Comparative analysis of the efficiency of a CO2-cooled and a He-cooled pebble bed breeding blanket for the EU DEMO fusion reactor

The EU DEMO is considered to be the last step before building a commercial fusion power plant. Up to now the Helium Cooled Pebble Bed (HCPB) Breeding Blanket (BB) is one of the four BB concepts being investigated in the EU for their possible implementation in the EU DEMO.While He is the reference gas cooling for the BBs in DEMO, CO2 has been the coolant choice in the nuclear fission industry for gas-cooled reactors during the past 60 years. In the recent years, it is also gaining interest as a secondary coolant for the Balance of Plant (BoP) to replace the traditional vapor (Rankine) cycle. Despite the lower heat capacity and thermal conductivity of CO2 with respect to He, the larger density of the former can lead to an advantageous performance on heat dissipation rate per unit of pumping power. This feature, coupled with its relative transparency to neutrons, the molecular stability at the operating temperatures of the BB and the industrial scale ready turbomachinery makes CO2 an attractive alternative to He.The aim of this paper is to make a parametric study of the gross and net efficiencies and the design of a simplified BoP of a DEMO power plant based on a CO2-cooled compared to the reference EU DEMO HCPB BB, as a function of the BB outlet temperature and turbine inlet pressure. From this study it is concluded that the vacuum vessel and the divertor heat sources are benefitial in order to improve the net plant efficiency for both coolants. Also, it has been observed that the plant net efficiency is better for the case of a PHTS with CO2 as heat transfer fluid under the assumption that both BBs share the same geometry. In the case that the BBs do not share the same geometry, the study concludes that a PHTS with CO2 leaves a pressure drop margin of about 1.5 before reaching the same net efficiency as a HCPB BoP DEMO plant.

Scaling of thermal stratification or mixing in outlet plena of SFRs

Sodium-cooled fast reactors (SFRs) have a tendency for thermal stratification in the hot or outlet plena especially during shut-down and loss of forced convection transients. The formation of thermally stratified zones in the outlet plena can: lead to thermal fatigue in adjoining solid structures; and impact passive heat removal capabilities. There are limited number of experimentally validated models in literature for thermal stratification or mixing in liquid metal pools. A high fidelity scaled-down experimental facility is required to address these needs and capture the physical phenomenon close to what is expected in a real system. The design of experimental facility and instrumentation becomes complicated with use of liquid sodium, so a surrogate fluid can simplify the design and operation considerably, providing flexibility to obtain high quality measurements. Similarity analysis based scaling methodology is used to design a scaled-down model of outlet plenum with liquid gallium (Pr∼ 0.025) as a surrogate for liquid sodium (Pr∼0.005). However, reduction in size and different choice of coolant must be handled carefully to maintain relevance and reliability of the experimental facility. The possible differences in thermal stratification or mixing physics in the scaled-down model and the prototype SFR are evaluated by quantifying eddy thermal diffusivity and mixing efficiency. Empirical models are used to correlate these quantities as a function of Richardson number and turbulent Reynolds number, and verified using computational fluid dynamics simulations. The verified empirical model is used to construct mixing efficiency for the prototypical conditions and the scaled-down model conditions. For low flow rates in both geometries, the results show thermal profiles dominated by molecular thermal diffusivity resulting into a fully stratified interface. The full flow cases for both geometries show energetic mixing, characteristic of eddy thermal diffusivity dominated, mixed temperature profiles. These results provide evidence of accurate scaling analysis by capturing the thermal stratification or mixing physics representing the dominant physical modes of those of the prototype SFR.

Manufacture and Initial Thermo-Fluid Measurements on a Heat Sink Module for Potential Applications in a DEMO

The necessity to handle heat loads in the MW/m2 range has become increasingly prevalent in a number of industries. Termed high-heat flux cooling, some of the most challenging conditions in this field occur at the first wall and divertor regions of a fusion tokamak. Steady-state heat fluxes here may reach values in excess of 10 MW/m2 in some areas for a first stage DEMO. The situation is exasperated further by the environment within the machine, which severely alters material properties with time. Even coolant choice itself can have an impact beyond thermal considerations through tritium inventory and neutron activation. Successfully addressing these issues is of critical importance to the development of commercial fusion power. A number of heat sink modules utilising jet impingement in a flat plate geometry were manufactured using diffusion bonding. Each sample produced was subject to leak and hydrostatic pressure measurements, together with further non-destructive analyses. Thermo-fluid measurements were performed on the components in a purpose built facility employing water as the coolant at pressures of up to 200 bar. To replicate the thermal boundary conditions a resistive thin-film heater technique was utilised. This allowed heat fluxes in the MW/m2 range to be applied to the modules. The results indicate that the concept may be a viable alternative heat sink candidate for first wall or divertor applications in a DEMO, but that further research is required to optimise certain aspects of the design.

Assessment of corrosion phenomena in liquid lithium at T < 873 K. A Li(d,n) neutron source as case study

The corrosion induced by alkali metals in steels has been the subject of long decades of intense studies under both nuclear fission and fusion research programs. Li or its eutectic Pb-17Li is the liquid metal coolant choice for fusion blankets due to the tritium breeder capability of Li. Non-metal impurities enhance corrosion, but only N becomes potentially a problem given its high solubility in liquid Li and the depletion of Cr through ternary nitrides Li-Cr-N. The low solubility of C and O allow its cold trapping to values <10wppm, however N can only be hot trapped demanding temperatures typically of 873K. The inherent difficulties of experimentation on physicochemical kinetics related with alkali metals lead to a confusing divergence of results available in the literature; however, the understanding of the corrosion phenomena of RAFM steels exposed to flowing Li up to 873K is mature. Next decade, 14MeV neutrons will be available for fusion materials testing through Li(d,n) nuclear reactions. In such a facility, a concave RAFM steel backplate will be channelling 523K flowing Li in the region where the 40MeV deuteron beam will be impacting. If RAFM steels are considered, two main concurrent mechanisms will take place: a) mass transport of alloying elementsalong the loop and b) depletion of Cr through formation of Li9CrN5. Fortunately, the mass transport phenomena of Cr within the ΔT=350K in the loop is limited due to the poor solubility of Cr in liquid Li (0.21wppm at 873K). In turn, at 523K Li the activity of N to form the ternary compound is negligible. However, the high solubility of Ni in Li (2144wppm at 873K), suggests the presence of mass transport phenomena of Ni from the stainless steel piping; unfortunately, the physicochemical kinetics are not fully understood. Lifus 6, in operation in Brasimone (ENEA) since the end 2015, will close in a definitive manner remaining open questions.

Design of a Measurement Setup and First Experiments on the Influence of CO2-cooling on the Thermal Displacements on a Machine Tool

The paper investigates the thermal influences of CO2- and oil-cooling on the precision of a machine tool. If CO2 is used for process cooling instead of oil, a different temperature distribution in the machine is observed. Different temperature distributions lead to different tool center point (TCP)-displacements. To measure TCP-displacements under real process conditions with CO2 and oil, a special measurement setup is designed, built and applied. A representative process for the machine is chosen to compare the different process coolings. The results show that the choice of coolant has a crucial influence on the TCP-displacements. It is shown that the thermally induced displacements can be reduced by 15 μm in y-direction, but increase about 4 μm in x-direction, when the coolant is changed from oil to CO2.

COMPARISON OF COOLING SCHEMES FOR HIGH HEAT FLUX COMPONENTS COOLING IN FUSION REACTORS

Some components of the fusion reactor receives high heat fluxes either during the startup and shutdown or during the operation of the machine. This paper analyzes different ways of enhancing heat transfer using helium and water for cooling of these high heat flux components and then conclusions are drawn to decide the best choice of coolant, for usage in near and long term applications.

Comparative Assessment of Material Performance in DEMO Fusion Reactors

A key goal for fusion materials modelling research is the development of predictive simulation models and capabilities to assess material performance under the neutron irradiation conditions expected in near-plasma regions of fusion reactor tokamaks. This paper presents computational results from the modelling of neutron fields in the latest concepts for the next-step demonstration fusion reactor, DEMO. In particular, the variation in neutron exposure as a function of coolant choice and tritium-breeding blanket concept are described, and the calculated neutron spectra are then applied to predict damage rates, helium production rates, and helium-induced grain-boundary embrittlement lifetimes—updating previous estimates derived using an earlier DEMO model.

Converting energy from fusion into useful forms

If fusion power reactors are to be feasible, it will still be necessary to convert the energy of the nuclear reaction into usable form. The heat produced will be removed from the reactor core by a primary coolant, which might be water, helium, molten lithium-lead, molten lithium-containing salt, or CO2. The heat could then be transferred to a conventional Rankine cycle or Brayton (gas turbine) cycle. Alternatively, it could be used for thermochemical processes such as producing hydrogen or other transport fuels. Fusion presents new problems because of the high energy neutrons released. These affect the selection of materials and the operating temperature, ultimately determining the choice of coolant and working cycle. The limited temperature ranges allowed by present day irradiated structural materials, combined with the large internal power demand of the plant, will limit the overall thermal efficiency. The operating conditions of the fusion power source, the materials, coolant, and energy conversion system will all need to be closely integrated.

The Choice of Coolants in Accelerate Driven System

The accelerate driven system has an important role in sub-critical reactor. With the good physical property of high specific heat, low vapor pressure, low thermal decomposition rate and so on, the glycerol, hydrogenated terphenyls and water of low pressure are widely used in the accelerate driven sub-critical reactor as the secondary coolant. Compare the three coolant by the aspect of heat economy and engineering safety, we conclude that, compared with the glycerol and the hydrogenated terphenyls, water of low pressure has the best heat economy, at the same time it has the lowest pressure drop and the highest coefficient of heat transfer in the heat exchange tube. Therefore, choose water in low pressure as the secondary coolant in sub-critical reactor can decrease the heat exchange area to a large extent, together with the advantage of economy and safe.

Blade cooling optimisation in humid-air and steam-injected gas turbines

Humidified gas turbine cycles such as the humidified air turbine (HAT) and the steam-injected gas turbine (STIG) present exciting new prospects for industrial gas turbine technology, potentially offering greatly increased work outputs and cycle efficiencies at moderate costs. The availability of humidified air or steam in such cycles also presents new opportunities in blade and disk cooling architecture. Here, the blade cooling optimisation of a HAT cycle and a STIG cycle is considered, first by optimising the choice of coolant bleeds for a reference cycle, then by a full parametric optimisation of the cycle to consider a range of optimised designs. It was found that the coolant demand reductions which can be achieved in the HAT cycle using humidified or post-aftercooled coolant are compromised by the increase in the required compression work. Furthermore, full parametric optimisation showed that higher water flow-rates were required to prevent boiling within the system. This corresponded to higher work outputs, but lower cycle efficiencies. When optimising the choice of coolant bleeds in the STIG cycle, it was found that bleeding steam for cooling purposes reduced the steam available for power augmentation and thus compromised work output, but that this could largely be overcome by reducing the steam superheat to give useful cycle efficiency gains.

Three-dimensional analyses of candidate blanket designs for the compact tokamak reactor concept

Three-dimensional nucleonic analyses have been performed for five candidate blanket systems proposed for a compact tokamak fusion reactor. These analyses were carried out using the Monte Carlo code MCNP and the nuclear data ENDF/B-IV. It has been found that the ternary ceramic breeder LiAlO 2 does not meet the required tritium breeding goal (TBR=1.1) even when the best nonfissionable neutron multiplier and different design configurations were utilized. Liquid metal breeders have better nucleonic performance than the solid breeders. Liquid lithium is superior to Li 17Pb 83 in terms of nucleonic performance especially when no breeding in the inboard is utilized and when peneteration systems are considered. Complete elimination of inboard breeding and accounting for penetration systems resulted in breeding losses of 23.0%, 25.3%, 23.5% and 32.9% in blankets of Li 2O/H 2O/SS316L, Li 2O/He/SS316L, Li/Li/V15Cr5Ti and Li 17Pb 83/Li 17Pb 83/HT-9 respectively. A careful choice of limiter structure and coolant leads to less breeding loss. The effect of the RF-system on the TBR was small for all the blanket systems considered. When Li 17Pb 83 is used as a static breeder to minimize its circulation, and thus making MHD losses negligible, a separate coolant such as water, helium or sodium should be used. It has been found that when high 6Li-enrichment is used the effect of the coolant choice on the TBR and energy multiplication factor, EMF, is negligible. The TBR of the Li 2O blanket cooled with water and without inboard breeding can be enhanced to 1.28 which is large enough to compensate for the losses associated with penetration systems. The atomic displacement rate in the first wall of the Li 17Pb 83 blanket system is the largest followed by that of the Li-blanket, with rates in the solid breeder blankets about 10% lower than that of Li 17Pb 83. The helium production rate in the first wall of a LiAlO 2 blanket system is the largest and it is high in the structure of the front breeder zones of solid breeder blankets. The hydrogen production rate in the first wall and front breeder structures is also high for solid breeder systems.