Insulated Sections Research Articles

Discrete element modelling of thermal penetration test with heating and cooling

A three-dimensional discrete element method (DEM) is employed to simulate thermal penetration tests with heating and cooling. This study investigates the mechanical behavior of soil particles during penetration, and examines the effects of temperature boundary condition, overburden load, and heating duration on the heat transfer mechanisms of the probe-soil system. Simulation results of penetration indicate that larger overburden load causes an increase in tip resistance (qc), sleeve friction (fs), and the isotropy of particles, whereas less influence is found on the distributions of penetration-induced displacement. Despite of the negligible effects of various temperature boundary conditions, the thermal responses of DEM model show that both the peak temperature of the probe heating module and the cooling rate of soil increase with the overburden load, while the probe insulation section shows a decreasing trend. The heat concentrates around the vicinity of the cone tip and probe shaft, and the high temperature area gradually expands with longer heating duration. Additionally, thermo-coupling analysis illustrates that the heat transfer process has a milder effect on the mechanical properties of granular soils. The numerical results are then validated against laboratory model chamber tests under comparable conditions, showing acceptable agreements.

Valorization of Wheat Crop Waste in Araucanía, Chile: Development of Prototype of Thermal Insulation Material for Blowing Technique and Geographical Analysis

Houses in the operational stage consume around 40% of the world’s energy, and most of it is consumed by air conditioning. This generates several problems, especially in cities, where biomass combustion is the most widely used form of heating. For this reason, environmental regulation works in parallel with energy efficiency, where efficient and low-impact thermal insulating materials are key to reduce the energy demand and fuel consumption to generate comfort in dwellings. This work considers the valorization of wheat straw from the Araucanía region of Chile, to develop a prototype for a thermal insulating material applied through the blowing technique. The results show the insulation potential of the fiber, which, in post-chopping conditions and at an average density of 80 [kg/m3], has thermal conductivity of 0.034 [W/mK]. This value is much better than that of glass wool and other inorganic materials sold in the Chilean market. In addition, the developed material can be incorporated into partitions using the blowing technique, improving the execution time for the thermal insulation section. Finally, it is indicated that a good option to install a processing plant is in the central valley of the region, specifically in the communes of Victoria and Perquenco.

Investigations on thermoelectric characteristic of heat pipe thermoelectric generator waste heat utilization device in nuclear power system

This paper proposes a waste heat utilization method for new type reactor by Heat Pipe - Thermoelectric Generator (HP-TEG) to utilize the waste heat of lower divertor in fusion device and stirling generator in heat pipe space reactor. The feasibility of the HPTEG waste heat utilization device is verified by its principle prototype. Firstly, the numerical simulations of the single heat pipe and principle prototype were carried out to provide a numerical optimization scheme for the design of the principle prototype. The simulation results show that the heat transfer efficiency of the copper–water heat pipe is about 93%, while the overall heat transfer efficiency of the principle prototype is about 85%. Based on the simulation results, the thermal stress concentration areas were found, mainly concentrated in the thermal insulation short of the heat pipe. During the construction of the principle prototype, stainless steel sleeves were installed outside the insulation section of the heat pipe to limit the thermal expansion caused by the thermal stress concentration. Besides the principle prototype of HPTEG assembled in new type reactor was built, and its thermoelectric characteristics were studied, the results verified the feasibility of using waste heat. The test results show that the principle prototype starts smoothly, and the heat pipe has suitable isothermal properties (△T < 15 ℃). Due to the heat pipe's high heat transfer efficiency, the heat pipe obtained from the experiment is 91%–96%. The principle prototype has good heat transfer efficiency, which is 81.94%–93.25%. The maximum total electric power output of TEG is 16.37 W, in which the corresponding current is 0.52A, and the power generation efficiency is up to 1.49%. This paper verifies the feasibility of HPTEG to utilize the waste heat of lower divertor in fusion device and stirling generator in heat pipe space reactor, which provides a reference for the utilization of reactor residual heat.

Induced Currents in the Lining and Steel Shell of Submerged Arc Furnaces

Numerical models in 2D and 3D are used to study induced currents in the lining and steel shell of large three-phase submerged arc furnaces. The alternating currents supplied through the electrodes cause a significant amount of induced power in the furnace lining and shell. The induced currents flow in three large loops with an accumulation of current near the top of the steel shell between the electrodes. The net result is a thermal loss with heat dissipated at the surface. Furthermore, such accumulation may cause potentially damaging hot spots in the steel. If this persists over a long time, the shell may thin and deteriorate and, in worst-case scenarios, the shell may be cracked or punctured. The influence of an electrically conducting lining and the effect of subdividing the shell in insulated sections have been studied. It is shown that an electrically conducting lining will have a significant shielding effect on the steel shell. The induced currents are considerably reduced in the steel, and “pushed into” the lining. The size of current loops in the shell can be restricted by subdividing the steel into sections with insulation between each section. Such modification is detrimental. Strong opposing currents will be formed on each side of the insulating gaps, leading to higher current concentrations and increasing the risk of hot spots on the steel shell. In addition, the heat loss due to induced currents in the steel will be enhanced.Graphical

A Cable Condition Monitoring Strategy for Safe and Reliable Plant Operation

Electrical cables provide essential functions, such as delivery of power or instrumentation signals for monitoring systems. Most cables installed in industrial applications are constructed with organic polymer insulations that can become brittle, crack, or degrade over time from exposure to harsh environmental conditions, such as elevated temperatures, moisture, vibration, mechanical shock, and radiation. This paper describes an overall strategy for assessing the health and managing the aging of cables during the operating life of an industrial facility. This strategy involves performing condition assessments and monitoring of electrical cables using both in situ and laboratory testing techniques. It includes in situ testing to identify anomalies in the circuits, such as degraded terminations, splices, connections, and degraded sections of cable insulation, as well as as-found evaluations to determine the current condition of installed cables. These cable condition evaluations provide important information about the current state of the cable circuits. Moreover, the test results can be used to trend/monitor age-related degradation and estimate the remaining useful life of installed cables.

Heat extraction from hot dry rock by super-long gravity heat pipe: Effect of key parameters

Extracting hot dry rock energy by super-long gravity heat pipe in a single-well is a novel technical scheme proposed recently. The potential superiority of this scheme is related to its environmental friendliness, economic and technologic feasibility, but the key parameters affecting its performance are not well understood. To this purpose, a detailed sensitivity analysis using a dedicated numerical simulation model is conducted for a 4000 m long gravity heat pipe with water as the working fluid. The analysis considers a wide range of working conditions with the aim of better understanding the effects of operating and structural design variables. It is found that the thermal performance is strongly enhanced with the increasing heat pipe diameter (100 mm–500 mm), which is attributed not only to the increase of heat transfer surface but also to the decrease of fluid flow resistance inside the heat pipe. Lowering the condensation temperature improves the thermal performance of heat pipe, whereas the effect gradually reduces and becomes insignificant when the condensation temperature is less than ∼50 °C. Thermal insulation shows the best positive effect when the insulation section reaches the position where the heat pipe temperature is just equal to the formation temperature. The low thermal conductivity of hot dry rock is confirmed to be a key bottleneck restraining the performance of the heat pipe system. The heat extraction rate can be greatly improved if the local equivalent thermal conductivity is enhanced in the region of 5 m in radius around the heat pipe. The acquired knowledge allows to develop a design strategy for practical super-long heat pipe systems taking into consideration the operating parameters and local geothermal conditions.

Electric Field Distribution and AC Breakdown Characteristics of Polluted Novel Lightning Protection Insulator under Icing Conditions

As a result of lightning strikes, pollution, and ice, overhead distribution wires might be short-circuited and trip. As a result, researchers have developed a new lightning protection composite insulator. There is still a need to test its pollution and icing performance. Based on the finite element and field test method, this paper studies the electric field distribution and AC (Alternating Current) breakdown characteristics of polluted novel lightning protection insulators under icing conditions. Firstly, the finite element calculated results show that this novel insulator’s electric field distribution is different from that of a conventional insulator. The locations with sizeable electric fields are located in the insulation section, and the electric field in the arrester section is tiny. In addition, when the insulator surface is covered with ice, there is an increase in the electric field along the surface and pin electrodes. Compared with the dry conditions, when there is an ice layer and icicle, electric field peaks increase by 48.85% and 46.08%, respectively. Secondly, the test results show that there are three types of arc paths in different pollution levels. The arc paths are related to ESDD (equivalent salt deposit density) under icing conditions. Uf shows a downward trend with increased pollution levels, and the maximum flashover voltage is 2.70 times more than the minimum. Finally, four fitting methods are proposed in this paper. After comparing the goodness of fit of different functions, the quadratic function and negative power function with the constant term are recommended as empirical formulas for calculating flashover voltage of novel insulators under icing conditions in different pollution levels. The research results of this paper have a specific guiding role for the selection of the external insulation of transmission lines and structural optimization of novel insulators.

철도 급전 부하 공유장치에 대한 연구

This paper is a study on an Energy Sharing and Management system (ESM) that shares loads between substations of a railway system to reduce peak power, improve voltage drop, and maximize regenerative power use. ESM is installed on the sectioning post between two railway substations to prevent inrush current and surge from the insulation section, extending the life of power equipment and improving voltage fluctuations in railway power supply systems. In addition, as the load is divided between substations, the maximum power and power loss are reduced, and the use of regenerative power is maximized, resulting in a great electric energy saving effect. The ESM is applied separately from the breaker for extended power supply, and in the event of a failure, the ESM is automatically disconnected from the system. It is necessary to research, develope an ESM with such advantages and apply it to the railway system as a trial to verify its effectiveness.

Performance Evaluation of Different Insulating Materials using Field Temperature and Moisture Data

Including insulation layers in pavement structures has become a common strategy to minimize frost penetration in cold regions. This study investigated the performance of two different insulation materials, extruded polystyrene board and bottom ash, in a test road in Edmonton, Alberta, Canada, eight years after construction. The two insulation materials were used in a fully instrumented test road, including three insulated sections 20 m in length. The insulated sections are as follows: the first section has 1 m of bottom ash (B. Ash), the second section has a 10 cm polystyrene layer (Poly-10), and the third section has a 5 cm polystyrene layer (Poly-5). Both B. Ash and polystyrene layers were placed on top of the subgrade layer, at a depth of 70 cm from the surface. A conventional section next to these three sections was used as the control section. Volumetric water content data and temperature variation were used to analyze the influence of the insulation materials on the subgrade. It was concluded that both B. Ash and Poly-10 layers protected the subgrade from freezing. The Poly-10 section showed the lowest rate of change in subgrade temperature during the monitoring period. B. Ash and Poly-10 reduced the frost depth by 23% and 70% compared with the control section, respectively. It was concluded that Poly-10 protected the subgrade soil from freezing and excessive moisture more effectively than B. Ash; however, the temperature in the layer above the insulation layers (pavement base layer) was significantly lower during winter for the Poly-10 section.

AC Breakdown Characteristics of Polluted 10-kV Post Insulator With Concentric Externally Gapped Line Arrester

Lightning strikes and pollution could cause short circuits and tripping of the overhead distribution lines. To alleviate this, a 10-kV post insulator with concentric externally gapped line arrester (EGLA) has been proposed and its performance is studied in service. However, its pollution performance has to be established. This paper studies the AC pollution breakdown characteristics of the EGLA and broaden current knowledge of pollution flashover. Compared with the flashover of the normal insulator, three kinds of specificity of the EGLA were found. Firstly, the pollution flashover process can be divided into three categories. Secondly, the wet flashover voltage, <i>U_f&#x005F;wet</i>, of the novel insulator is higher than the dry flashover voltage, <i>U_f&#x005F;dry</i>. Thirdly, the piecewise fitting methods with <i>a</i>&#x00A0;&#x00D7;&#x00A0;ESDD^^&#x2212;<i>^b</i>&#x00A0;&#x002B;&#x00A0;<i>d</i> and <i>a</i>&#x00A0;&#x00D7;&#x00A0;ESDD^^&#x2212;<i>^b</i>&#x00A0;&#x002B;&#x00A0;<i>c</i>&#x00A0;&#x00D7;&#x00A0;ESDD^^&#x2212;<i>^d</i> are more suitable for fitting the empirical formula of flashover voltage. Furthermore, to explain specificity, the electric potential and electric field distribution are calculated based on the finite element method. Calculated results indicate that when the EGLA is covered with a 0.5mm water film, the maximum electric field intensity decreased from 2.17&#x00A0;kV&#x002F;cm to 1.99&#x00A0;kV&#x002F;cm. Also, <i>U</i><i>_{&#x005F;arrester} </i>(the withstand voltage of the insulation section) was obtained from the tests and it presents a discontinuous and random increasing trend until flashover occurs, which is considered to be one of the important reasons for the specificity. Besides, based on the Obenaus&#x2019; model and Hampton&#x0027;s criterion, we further analyzed the arc development process by a simplified plate model.

Numerical Investigation on Effect of Thermal Expansion Joint in a Tube Holder Insulating Section in Shell and Tube Heat Exchanger

As shell and tube heat exchangers become more widely used, their challenges are becoming more and more important. In some of these heat exchangers, an insulating section is used to reduce thermal stresses on the tube holder section. In this study, the effect of the presence and absence of expansion joints in this insulation section has been investigated. For this purpose, the desired section with and without expansion joint has been analyzed using the finite element method (FEM) in ANSYS software. Based on the results, it was found that the thermal expansion joint reduces thermal deformation and significantly reduces the rate of stresses in the mentioned section, which increases the life of the tube holder section. Also, the presence of expansion joints reduces the applied pressure to the insulation tape around the tube holder section, which increases the life of the insulation tape around the insulation section.

Simulation optimization research of anti-freezing heat pipe for preheating fresh air in wellbore

In order to solve the icing phenomenon of mine wind gap, a physical model of L-type gravity heat pipe was designed in combination with calculation of shaft operating condition, which based on the new idea that geothermal energy of thermostatic formation is used as driving heat source of heat pipe for shaft antifreeze. The numerical simulation showed that the condensation end temperature of the heat pipe could reach 275K. The heat pipe optimization simulation was carried out for the length of the condensation and insulation section of the heat pipe. When the condensing section is 5 m, the effect is the best. The results showed that the temperature at the condenser end of the heat pipe was increased by 275.6K after optimization. The optimized scheme for extracting heat energy from thermostat by heat pipe has a good effect.

Analisis Beban Kerja Karyawan PT XYZ Indonesia pada Bagian Insulation Menggunakan Metode Full Time Equivalent

PT XYZ Indonesia is a company engaged in manufacturing by producing power transformers located in west java. In the implementation of the production process of PT XYZ Indonesia, there are sometimes problems. The problem that occurs in PT XYZ Indonesia is the production process time in the insulation section exceeds the specified target time, because the operator’s work activities are less productive, it is necessary to calculate workload in order to know the workload obtained by the operator. The purpose of this study is to level the operator workload and determine the number of workers to be optimal. Researchers used the full time equivalent method to revise the problem, by measuring the operator’s work time so that it knows the value of the workload obtained. After calculating using this method, the actual conditions at PT XYZ Indonesia have 16 operators in the insulation section, with an average value of the workload obtained is 0.34 while the recommendation of the researchers is 9 work operators in the insulation section with an average value the workload obtained is 1.06, so that it is easy to supervise the operator due to a reduction or diversion of 7 operators.

The failure arc paths of the novel device combining an arrester and an insulator under different pollution levels

Lightning strokes on transmission lines could trigger insulation failure if no protective measures are taken. Typically, a lightning arrester is used for this purpose. In order to combine the insulator and the lightning arrester as a single entity, a novel lightning protection composite insulator, combining an arrester and an insulator was developed for 10 kV distribution lines. Studied in this paper are the various arc paths of the novel insulator. The arc path tests under both AC and impulse voltage were conducted. The findings indicate that low, medium, high, very high, and extremely heavy pollutions caused different types of arcings under AC voltage. In addition, arc paths were affected by both the pollution level and the magnitude of impulse voltage. Based on the arc paths recorded by a high-speed camera, the flashover modes can be divided into three categories (flashover of the air gap, flashover of silicone rubber sheds in insulation section, and flashover of the whole insulator). More specifically, we defined and analyzed 14 types of arc paths in detail, and the critical pollution level (0.1 mg/cm2) of normal operation were obtained. Further, the statistical probability of each arc under impulse voltage was calculated. Due to the complexity of the arc paths under the switching impulse voltage, a 90% probability distribution figure of arc paths with different Us (switching impulse voltage) and ESDD (equivalent salt deposit density) was presented according to the test results. At last, we discuss the impulse voltage waveform corresponding to the typical arc path and describe the research prospect. The research results in this paper present the failure modes of the novel lightning protection insulator, and the results can be used for designing insulators for various pollution levels.

Development of antithunder composite insulator for distribution line

In this article, the antithunder composite insulator combining a surge arrester and insulator is developed. The insulation design and configuration principle of the composite insulator are analyzed through experiments and simulation. The studies of insulation performance have shown that the external breakdown air distance is 60 mm, and the length of the polymeric support insulator is 70 mm. Considering the more serious pollution (0.3 mg/cm2), the creepage distance of the insulation section must be larger than 250 mm. Test data of the antithunder composite insulator meet the standard requirements. The analysis of mechanical performance of the antithunder composite insulator is carried out, which shows that the overall mechanical strength needs to be greater than 2.38 kN. A three‐dimensional (3D) element finite model is built to simulate the behavior of the antithunder composite insulator in the distribution line. The simulation results indicate that the stress on the varistor and the core rod decreases with the increase of the size of the core rod. A core rod of 20 mm or more can meet the operation requirements. The simulation indicates that the stress of the varistor determines the force limit of the antithunder composite insulator. Therefore, attention should be paid to the performance stability of the varistor of the antithunder insulator under force. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley &amp; Sons, Inc.

Numerical modeling of a coaxial borehole heat exchanger to exploit geothermal energy from abandoned petroleum wells in Hinton, Alberta

Deep petroleum wells are often associated with high bottom-hole temperatures and can provide a cost-effective way to produce geothermal energy. The goal of this study is to develop a reliable simulation model to demonstrate the feasibility of extracting geothermal energy with deep coaxial borehole heat exchangers in abandoned petroleum wells in the Western Canadian Sedimentary Basin. Our simulation model was constructed with COMSOL Multiphysics and verified with analytical results. The temperature dependence of the working fluid’s (water) and the reservoir rocks’ thermodynamic properties were found to significantly affect the long-term performance of the heat exchanger. The production temperature and the geothermal well power stabilize at ∼29 °C and 0.38 MW, respectively, during long-term running of the model. The performance of the heat exchanger can be controlled by varying the injection flow rate, the injection temperature, and the thermal conductivity of the insulating pipe. Heat exchanger performance is only marginally affected by a thermally insulated section at the top of the well casing. We conclude that abandoned petroleum wells in the Western Canadian Sedimentary Basin have a great potential for geothermal exploitation using coaxial borehole heat exchangers.

Mathematical model-based design of an industrial box furnace

A zero dimensional thermodynamic model (0D-model) is used to represent the conservation equations of energy in an industrial box furnace for designing purposes. Thus, this paper proposes a 0D model-based design approach for industrial box furnaces which results very processing time efficient, minimizing the design analysis time period that can exist when two-dimensional (2D) or Computational Fluid Dynamics (CFD) modeling is used. 2D or CFD models can be highly accurate but with also high computational load; the time spent in an industrial design from the concept to the prototype can take several months where the bottleneck is the simulation phase. The modeling results in the proposed approach consists on analyzing the fuel energy power requirement required to achieve a desired temperature profile, given the most important design parameters such as physical furnace dimensions, composition material in the insulation section, thermal load properties, fuel/air ratio conditions, etc. In this case, the proposed approach for a 0D-model based furnace design has been validated with different operation set-ups and compared with simulation data provided by a complex 2D model as well as with experimental data from an industrial box furnace. Quantitatively, the modeling result was up to 96.77% of fit with respect to the simulator behavior, taking less than 5% of processing time considered by the complex 2D model.

Application of a new thermal insulation layer to subgrade

The use of thermal insulation has great potential for preventing frost damage to roads in seasonally frozen areas, in fact more so than in permafrost. With the aim of recycling the vast quantities of waste coal fly ash and rubber tyres in north-east China, a new combined thermal insulation layer consisting of extruded polystyrene (XPS) board and modified soil (silty clay modified with fly ash and crumb rubber) is proposed. Field tests on an insulated test section and an uninsulated control section were designed to assess the thermal performance of the sections over the change of time and depth. The thermal characteristics and the effect and mechanism of the layer were investigated. Finite-element analysis was used to evaluate its long-term performance. The results showed that the temperature regime of the subgrade varied regularly. The combined thermal insulation layer effectively protected the road surface from cold and heat erosion, elevating the freezing depth to the upper surface of the combined layer. Furthermore, the thermal insulation effect was greater for the combined layer than the use of XPS only. The finite-element analysis showed that the impact on cold resistance was more evident in the road shoulder and roadway centre than on the slope toe, and the layer will still perform normally after 50 years.

Study on the flashover performance of an anti‐thunder composite insulator under ice accretion conditions for a 10 kV distribution line

In this paper, an anti‐thunder composite insulator combining an arrester and an insulator is developed and applied to 10‐kV distribution line. The anti‐thunder composite insulator is divided into an insulation section and a lightning protection section. The flashover performance of the anti‐thunder composite insulator and an ordinary composite insulator under ice accretion conditions are experimentally analyzed. The relationship between the icing thickness (d) and the flashover voltage is derived under the contaminated condition of 0.25 mg/cm2 salt density. With the increase of d, the effect of icing on the breakdown voltage of the anti‐thunder composite insulator is less than that of an ordinary composite insulator. When d increases from 2 to 12 mm, the breakdown flashover voltage of the anti‐thunder composite insulator and the ordinary composite insulator drops by 40.0 and 61.9%, respectively. Based on the simulation model, the potential and electric field distribution of the anti‐thunder composite insulator are analyzed. Our simulation and experimental results indicate that the proportion of the potential of the insulation section is more than 90% under the rated voltage. Based on the analysis, it is concluded that the anti‐ice flash performance of the insulation section has an important influence on the flashover performance of the anti‐thunder composite insulator and that an appropriate increase of AC reference voltage of the anti‐thunder composite insulator will be an effective method to promote the stability of the internal zinc oxide varistor under ice accretion conditions. © 2018 Institute of Electrical Engineers of Japan. Published by John Wiley &amp; Sons, Inc.

Boundary effects on flow oscillations in transient heat transfer of n-decane at supercritical pressure

A numerical study has been conducted to analyze boundary effects, including different inlet boundary conditions and different inlet section lengths (distances from the inlet boundary to the heated section), on flow dynamics in transient supercritical-pressure heat transfer of n-decane in a circular tube. As the inlet boundary condition changes from a constant flow velocity to a constant stagnation pressure, the pressure oscillation frequency is nearly doubled, and the thermoacoustic wave is in the first longitudinal mode. The frequency of mass flow rate oscillation is essentially the same as that of the pressure wave. Different inlet boundary conditions exert no effect on the pressure wave amplitude but make strong influence on the amplitude of mass flow rate oscillation at the outlet of the heated section. As the inlet insulation section length increases under a constant inlet stagnation pressure, frequencies of both pressure and mass flow rate oscillations proportionally decrease, and the thermoacoustic waves remain in the first longitudinal mode. Different inlet section lengths appear to make only minor effect on the amplitudes of both pressure and mass flow rate oscillations at the outlet of the heated section, and the maximum amplitude in each wave is around 10% of its steady-state value.