Preheat Time Research Articles

Developing an Optimum Protocol for Thermoluminescence Dosimetry with GR-200 Chips using Taguchi Method.

Thermoluminescence dosimetry (TLD) is a powerful technique with wide applications in personal, environmental and clinical dosimetry. The optimum annealing, storage and reading protocols are very effective in accuracy ofTLD response. The purpose of this study is to obtain an optimum protocol for GR-200; LiF: Mg, Cu, P, by optimizing the effective parameters, to increase the reliability of the TLD response using Taguchi method. Taguchi method has been used in this study for optimization of annealing, storage and reading protocols of the TLDs. A number of 108 GR-200 chips were divided into 27 groups, each containing four chips. The TLDs were exposed to three different doses, and stored, annealed and read out by different procedures as suggested by Taguchi Method. By comparing the signal-to-noise ratios the optimum dosimetry procedure was obtained. According to the results, the optimum values for annealing temperature (°C), Annealing Time (s), Annealing to Exposure time (d), Exposure to Readout time (d), Pre-heat Temperature (°C), Pre-heat Time (s), Heating Rate (°C/s), Maximum Temperature of Readout (°C), readout time (s) and Storage Temperature (°C) are 240, 90, 1, 2, 50, 0, 15, 240, 13 and -20, respectively. Using the optimum protocol, an efficient glow curve with low residual signals can be achieved. Using optimum protocol obtained by Taguchi method, the dosimetry can be effectively performed with great accuracy.

Numerical Simulation of the Effects of Preheating on Electron Beam Additive Manufactured Ti-6Al-4V Build Plate

In an earlier study, a 3-D thermomechanical coupled finite element model was built and experimentally validated to investigate the evolution of the thermal residual stresses and distortions in electron beam additive manufactured Ti-6Al-4V build plates. In this study, an investigation using this robust and accurate model was focused on an efficient preheating method, in which the electron beam quickly scanned across the substrate to preheat the build plate prior to the deposition. Various preheat times, beam powers, scan rates, scanning paths and cooling times (between the end of current preheat scan/deposition layer and the beginning of the next preheat scan/deposition layer) were examined, and the maximum distortion along the centerline of the substrate and the maximum longitudinal residual stress along the normal direction on the middle cross-section of the build plate were quantitatively compared. The results show that increasing preheat times and beam powers could effectively reduce both distortion and residual stress for multiple layers/passes components.

Thermomechanical failure modeling and investigation into lining optimization for a Ruhrstahl Heraeus snorkel

Abstract Snorkels used in Ruhrstahl Heraeus (RH) degassers in the steel industry undergo severe thermomechanical loads due to normal cyclic operations including preheating, submerging, and idle time. A finite element model was developed to simulate the first operational process cycle experienced by a RH snorkel. The presented analysis investigates the thermomechanical failure mechanisms of the magnesia chromite bricks in the wear lining. The Drucker–Prager, Drucker–Prager creep and fictitious crack models were applied to model creep and failure. The wedge-splitting test using an inverse analysis method, and the modified shear and compressive creep tests were utilized to characterize the mechanical properties of the refractories at elevated temperatures. The results show that at the beginning of the submerging process, tensile failure occurs closest to the hot face of the lowest refractory section prior to shear failure or creep. Because of refractory creep, the hot face of the wear lining does not experience shear failure during submerging. Furthermore, shear failure and creep contribute to the process of joint opening at the hot face. The concept of using less brittle material for the wear lining and a relative stiff monolith indicated that the tensile failure occurring from the hot thermal shock can be mitigated.

漏洩水素の高速移動センシングに関する研究

As an alternative fuel to fossil fuels, the usage of hydrogen has been spreading. However, there are always risks of leakage, which may lead to explosion. Each method of conventional hydrogen sensing has its own characteristics such as that fixed-sensing requires time until hydrogen reaches the location of the sensor, or that optical sensing is not necessarily cheap although it is the quickest. In this study, we propose a sensing method by continuous high-speed movement of a hydrogen sensor. After checking its necessary preheat time of the sensor, the performance of the method is examined.

Design of Runner and Gating Systems for the Investment Casting of 431 Stainless Steel Netting Hook through Numerical Simulation

In the production of netting hook, which requires wear resistance and long service life enabling the fishing net production with high efficiency, there has been some studies to achieve its forming method for high durability and designated smooth surface. The process of investment casting or known as “lost wax casting” is one of casting methods to fabricate metal part with a complex shape. Flow behavior of stainless steel grade 431 at the temperature higher than 1600°C is a critical factor in casting mold design of the lost wax process. In the study, CAST-DESINERTMsimulating software was used to analyze flow of liquid metal to clarify the solidification of SS431 which caused defects in the product. Non-preferred heat transfer phenomena and using of the unsuitable mold design normally lead to defects in casting such as misruns, cold shuts, shrinkage, pin holes and porosity. Parameters in casting such as pouring temperature, preheating temperature, preheat time, pouring rate and cooling rate were given by the current production condition. The experimental design technique for simulation analysis of casting and gating system has been designed to be consistent and appropriate to the casting part. The cross-sectional design of the runner was two types of hexagonal and circular cross-section runner. The angle of gating system was kept constant at 90 degrees to the runner. As a results of the simulations, shrinkage porosity, filling time as well as solidification time were used to evaluate the cross-sectional design of runners. It was found that a circular cross-section runner led to the shorter filling time than a hexagonal one. Furthermore, there was no remarkable difference of shrinkage porosity in all simulated conditions. However, in terms of filling time, the results depended on the combination of runner design and gating system.

Physicochemical characterization of wet microalgal cells disrupted with instant catapult steam explosion for lipid extraction

Instant catapult steam explosion (ICSE) was employed to disrupt wet microalgal cells for efficient lipid extraction. Physicochemical properties of exploded cells were investigated through SEM, TEM, FTIR, and TGA. The exploded cells increased in fractal dimension (1.53–1.65) when preheat time was prolonged from 0min to 5min and in surface pore area when steam pressure was increased. Meanwhile, the exploded cells decreased in mean size (1.69–1.44μm) when the filling ratio of wet microalgal biomass in the preheat chamber decreased (75–12.5%). Flash evaporation and volume expansion exploded the cell walls and released the cytoplasm of the microalgal cells. These phenomena decreased the carbohydrate content and increased the lipid content in the exploded biomass. However, ICSE treatment did not change the lipid compositions in the microalgal cells. Using isopropanol as a cosolvent significantly increased the yield of lipids extracted with hexane from the exploded wet microalgal biomass.

Joinability of different thermoplastic polymers with aluminium AA6082 sheets by mechanical clinching

The joinability of different rigid thermoplastic polymers with aluminium AA6082-T6 alloy sheets by mechanical clinching is investigated. The polymers were heated using a convective source prior of clinching. Experimental tests were conducted by varying die geometry and pre-heating time. The joinability window for different thermoplastic polymers including polystyrene (PS), polycarbonate (PC) and poly(methyl methacrylate) (PMMA) was determined. The mechanical behaviours of clinched connections were assessed by means of single lap shear tests. To understand the effect of process parameters on the mechanical behaviours of clinched joints, dimensional analysis was also carried out. It was turned out that mechanical clinching could be successfully employed for joining thermoplastic polymer sheets with aluminium sheets being characterized by a very short processing time and producing high strength joints as compared to competitive technologies. The formability of the aluminium alloy and the toughness of the polymer component are crucial for the success of the process. However, even materials with reduced formability were joined by modifying conveniently the pre-heating time and die geometry.

Effect of modified humic acid binder on pelletisation of specularite concentrates

A modified humic acid (MHA) binder was tested as a substitute for bentonite to prepare qualified specularite pellets. The results show that there is stronger chemisorption between organic functional groups in MHA binder molecular and specularite particles, improving the green pellet strength. MHA binder has obvious effect on the strength and microstructure of preheated pellets due to the thermal decomposition of organic matters in MHA binder. Appropriately increasing preheating temperature or time can eliminate the adverse impact of organic matters on the preheated pellet strength. Compared with the bentonite pellets, the roasted pellets with MHA binder have a more compact microstructure, and the recrystallization of the Fe2O3 crystal grains is better. Consequently, under optimal conditions, 0.75% (mass fraction) MHA binder pellets have equal or better pellet strengths and contain 1.06% more total iron than 2 % bentonite pellets. The testing results indicate that MHA binder is a promising and effective alternative to bentonite for the specularite pellets.

Mechanical behaviour of friction stir spot welds of polycarbonate sheets

The present investigation is aimed at analyzing the influence of the processing speeds and processing times on mechanical behaviour of friction stir spot welding (FSSW) joints produced on polycarbonate sheets. The analysis involved the variation of rotational speed, tool plunge rate, pre-heating time, dwell time and waiting time. Mechanical characterization of joints was carried out by means of single lap shear test. Experimental tests were conducted according to two full factorial designs. First, an exploratory 25 full factorial plan was carried out to determine the most influencing factors determining the mechanical behaviour of FSSW joints. Then, a 33 optimization plan was performed by varying the most relevant process parameters among three levels. Therefore, analytical models were developed to predict the mechanical behaviour of welds (maximum shear strength, stiffness and absorbed energy) produced under different processing conditions. In addition, an artificial neural network (ANN) model was developed to improve the matching between experimental measurements and model predictions. On the basis of the achieved results, a framework for improving the mechanical performances of thermoplastic joints was established. According to the achieved results, tool plunge rate, dwell time and waiting time are the most influencing parameters for the joint strength and weld extension. On the other hand, pre-heating time and tool rotational speed have lower influence on the mechanical behaviour of FSSW joints.

Magnetic-field-assisted synthesis of magnetite nanoparticles via thermal decomposition and their hyperthermia properties

In this work, an external magnetic field was utilized during the thermal decomposition process to manipulate the shapes, surfaces and magnetic properties of Fe3O4 nanoparticles. The applied magnetic field of 500 Oe induced the formation of uniform Fe3O4 nanocubes of 250 nm, in sharp contrast to the nanocuboctahedra formed when no magnetic field was applied. The size of the Fe3O4 nanoparticles was also effectively controlled by adjusting the pre-heating time of the reaction precursor. It is noticed that the magnetic field promotes the transformation of Fe3O4 nanocuboctahedra to nanocubes and has no effect on nanooctahedra. Furthermore, first-principles calculation was employed to understand the interaction between the magnetic field and the synthesized nanoparticles by studying the surface magnetic anisotropy of Fe3O4 (001) and (111) surfaces. Moreover, the Fe3O4 nanocubes and nanocuboctahedra were coated with chitosan and were well dispersed in water for hyperthermia measurement. The intrinsic loss power (ILP) of the Fe3O4 nanocubes (1.71 nH m2 kg−1) was 56% higher than that of the nanocuboctahedra (1.09 nH m2 kg−1) inferring a surface magnetic effect on hyperthermia performance.

Effects of preheating and cooling durations on roll-to-roll hot embossing.

In this study, we examined the sensitivity of embossed pattern depth to preheat supply and cooling and investigated how the pattern type and density affect the embossed depth. The main factors that affect embossed pattern qualities of roll-to-roll hot embossing, such as roller temperature, roller speed, and applied force, were determined using the response surface methodology. Eight conditions were then added to determine the time-dependent effects of heat transfer with custom-designed preheating and cooling systems. An extended preheat time for the polymethylmethacrylate substrate contributed to the significant change in the embossed depth, whereas the substrate-cooling did not exhibit a clear increasing or decreasing trend. Larger embossed depths were achieved in the horizontal patterns with lower density than in the vertical patterns, and the lower pattern densities showed greater embossed depths in most embossing conditions. We expect that this result will help to understand the effects of the pre- and posttreatment of roll-to-roll hot embossing by employing time duration factors of heat transfer, depending on the mold pattern type and density.

A method to minimise the fading effects of LiF:Mg,Ti (TLD-600 and TLD-700) using a pre-heat technique

Passive integrating dosemeters [thermoluminescent dosimeter (TLD) and optically stimulated luminescence (OSL)] are the only legally permitted individual dosemeters for occupational external radiation exposure monitoring in Korea. Also its maximum issuing cycle does not exceed 3 months, and the Korean regulations require personal dosemeters for official assessment of external radiation exposure to be issued by an approved or rather an accredited dosimetry service according to ISO/IEC 17025. KHNP (Korea Hydro & Nuclear Power, LTD), a unique operating company of nuclear power plants (NPPs) in Korea, currently has a plan to extend a TLD issuing cycle from 1 to 3 months under the authors' fading error criteria, ±10%. The authors have performed a feasibility study that minimises post-irradiation fading effects within their maximum reading cycle employing pre-heating technique. They repeatedly performed irradiation/reading a bare TLD chip to determine optimum pre-heating conditions by analysing each glow curve. The optimum reading conditions within the maximum reading cycle of 3 months were decided: a pre-heating temperature of 165°C, a pre-heating time of 9 s, a heating rate of 25°C s(-1), a reading temperature of 300°C and an acquisition time of 10 s. The fading result of TLD-600 and TLD-700 carried by newly developed time temperature profile (TTP) showed a much smaller fading effect than that of current TTP. The result showed that the fading error due to a developed TTP resulted in a ∼5% signal loss, whereas a current TTP caused a ∼15% loss. The authors also carried out a legal performance test on newly developed TTP to confirm its possibility as an official dosemeter. The legal performance tests that applied the developed TTP satisfied the criteria for all the test categories.

Improved Interfacial Bonding in Magnesium/Aluminum Overcasting Systems by Aluminum Surface Treatments

“Overcasting” technique is used to produce bimetallic magnesium/aluminum (Mg/Al) structures where lightweight Mg can be cast onto solid Al substrates. An inherent difficulty in creating strong Mg/Al interfacial bonding is the natural oxide film on the solid Al surfaces, which reduces the wettability between molten Mg and Al substrates during the casting process. In the paper, an “electropolishing + anodizing” surface treatment has been developed to disrupt the oxide film on a dilute Al-0.08 wt pct Ga alloy, improving the metallurgical bonding between molten Mg and Al substrates in the bimetallic experiments carried out in a high-vacuum test apparatus. The test results provided valuable information of the interfacial phenomena of the Mg/Al bimetallic samples. The results show significantly improved metallurgical bonding in the bimetallic samples with “electropolishing + anodizing” surface treatment and Ga alloying. It is recommended to adjust the pre-heating temperature and time of the Al substrates and the Mg melt temperature to control the interfacial reactions for optimum interfacial properties in the actual overcasting processes.

Producing synthetic lightweight aggregates by treating waste TFT-LCD glass powder and reservoir sediments

The use of lightweight aggregate (LWA) instead of ordinary aggregate may make lightweight aggregate concrete, which possesses many advantages such as lightweight, lower thermal conductivity, and better fire and seismic resistance. Recently the developments of LWA have been focused on using industrial wastes as raw materials to reduce the use of limited natural resources. In view of this, the intent of this study was to apply Taguchi optimization technique in determining process condition for producing synthetic LWA by incorporating waste thin film transition liquid crystal displays (TFT-LCD) glass powder with reservoir sediments. In the study the waste TFT-LCD glass cullet was used as an additive. It was incorporated with reservoir sediments to produce LWA. Taguchi method with an orthogonal array L16(45) and five controllable 4-level factors (i.e., cullet content, preheat temperature, preheat time, sintering temperature, and sintering time) was adopted. Then, in order to optimize the selected parameters, the analysis of variance method was used to explore the effects of the experimental factors on the performances (particle density, water absorption, bloating ratio, and loss of ignition) of the produced LWA. The results showed that it is possible to produce high performance LWA by incorporating waste TFT-LCD glass cullet with reservoir sediments. Moreover, Taguchi method is a promising approach for optimizing process condition of synthetic LWA using recycled glass cullet and reservoir sediments and it significantly reduces the number of tests.

Quality of shelf-stable low-acid vegetables processed using pressure–ohmic–thermal sterilization

Pressure ohmic thermal sterilization (POTS) involves ohmic heating of foods by applying an electric field under elevated pressure. Experiments were conducted using a custom made POTS apparatus using carrot as the model food. The samples were processed at a target temperature of 105 °C at 600 MPa and treated for 0, 1, 3, and 5 min by regulating the electric field (30 V/cm). POTS treated carrot sample quality attributes were compared against those processed using ohmic heating (0.12 MPa, 30 V/cm, 105 °C) and pressure-assisted thermal processing (PATP; 600 MPa, 0 V/cm, 105 °C). Within the experimental conditions of the study, the thermal come-up time of the POTS, Ohmic and PATP were 1.45 min, 3.58 min and 6.84 min respectively. PATP come-up time also included the pre-heating time (≈6 min). Results indicate the POTS samples had the least textural damage due to minimal thermal exposure. POTS samples had higher crunchiness index (CI) of 0.76 compared to PATP (CI = 0.57) and ohmic heated (CI = 0.62) carrots. All the technologies investigated had minimal impact on product color. This study demonstrates the potential to produce high quality shelf stable low-acid vegetable products using POTS.

Effect of Carrier Gas Flow Rate in Thermal Desorption Process of PCBs Contaminated Soil

A real PCBs contaminated soil was heated at 500°C using pure nitrogen as carrier gas under different flow rate to investigate the influence of carrier gas flow rate on the thermal desorption process. After 1 hour thermal treatment, the residual PCBs in soil decreased and the removal efficiency (RE) of PCBs is up to 95.1%. The distributions of PCBs in soil under different flow rate were identical. The World Health Organization toxic equivalency quantity (WHO TEQ) of PCBs in soil got its lowest value at 400Nml/min. Tetra-and higher chlorinated PCBs desorbed to carrier gas increased with increased flow rate, while the total amount of PCBs, Tri-and lower chlorinated PCBs first increased then decreased. The distributions of PCBs in carrier gas became more closely to the raw soil with increased flow rate. The TEQ of PCBs in carrier gas increased with increased flow rate. Increased flow rate enhanced the mass transfer of PCBs in the soil but shortened the preheating time of carrier gas and the retention time of carries gas, weakening the mass transfer and degradation process in gas phase. The RE of WHO TEQ of PCDDs in treated soil decreased from 86.7% to 83.2% with increased flow rate while the RE of WHO TEQ of PCDFs decreased from 85.4% to 70.0%. After thermal treatment process, the total amount of PCDD/Fs TEQ in soil and carrier gas increase from 43.8% to 18.6% times of that in raw soil. Considering removal efficiency of PCBs and PCDD/Fs and generation of PCDD/Fs in soil and gas phase, an optimized flow rate should be set at about 400Nml/min.

Effect of Preheating and Post-Curing Time on the Mechanical Properties of Epoxy Resin

The purpose of this study is to compare the mechanical properties in the form of ultimate tensile strength, ultimate tensile strain and Young's modulus of an epoxy resin at different curing cycles. The work carried out consisted of investigating the effect of preheating time and then the effect of post-curing time at the same temperature. Five repeats of static tensile tests were then carried out using universal test machine. Results indicated that compared to a shorter epoxy resin preheat duration of 15 min at 80°C, a longer duration of 30 min at 80°C of preheating degrades the material ultimate tensile strength and ultimate tensile strain leading to a suffer material. However, compared to no further post-curing of the epoxy resin, a two-hour post-cure duration at 80°C slightly increased the ultimate tensile strength and significantly decreased the ultimate tensile strain making the material even suffer than in the case of preheating. The implication is that in-house cure cycle tests should be carried out to characterize the resin instead of exclusively relying on resin manufacturer proposed cure cycles.

Modeling a solar-powered double bed novel composite adsorbent (silica activated carbon/CaCl2)-water adsorption chiller

During the past few decades, the growing demand for air conditioning has caused a significant increase in demand for primary energy resources. Adsorption cooling system is one of the technologies which could be powered by renewable energy. This study aims to improve the performance of a solar-powered adsorption chiller by applying a novel composite adsorbent, a mixture of activated carbon, silica gel and calcium chloride. Modeling is established to investigate the cooling performance of a composite adsorbent based adsorption chiller driven by flat-type solar collectors with three different configurations of glaze: (1) single glazed cover; (2) double glazed cover and (3) transparent insulation material (TIM) cover. The simulation results show that the coefficient of performance (COP) and the specific cooling power (SCP) of the adsorption chiller depend hugely on the solar collector temperature. It is found that a double glazed cover shows the best cooling performance and 30 m2 is the most optimized solar collector area. Two to three hours of pre-heating time is required to initiate the desorption process of the adsorber in a day of operation. This newly developed silica activated carbon/CaCl2 composite material as adsorbent used in the adsorption chiller could achieve a high mean COPsc of 0.48. Its satisfactory performance suggests that this novel composite material has a potential to be used in the adsorption chiller system even if it is powered by unstable solar energy.

Effect of Process Variables on Transformation-Texture Development in Ti-6Al-4V Sheet Following Beta Heat Treatment

The effect of preheat time, prestrain, cooling rate, and concurrent deformation during cooling on the preferential selection of hcp alpha variants during the decomposition of the high-temperature, bcc beta phase in two-phase titanium alloys was established using Ti-6Al-4V sheet material. For this purpose, sheet tension samples were pre-soaked in the beta phase field for 0 or 10 minutes (to vary the beta grain size), subjected to a prestrain of 0 or 0.1, and cooled at a rate of 11 or 155 K/min (11 or 155 °C/min) under conditions comprising free ends, fixed ends, or concurrent deformation at a strain rate between ~10−5 and 3 × 10−4 s−1. Electron-backscatter diffraction was used to determine the orientations of the alpha variants so formed, from which the underlying high-temperature, beta-grain microstructure and orientations were reconstructed. These measurements revealed that the parent beta texture changed due to grain growth during preheating. A comparison of the alpha- and beta-phase textures indicated that preferential variant selection was most noticeable under conditions involving a slow cooling rate especially when prestrain or concurrent straining was imposed.

Producing Lightweight Aggregates by Incorporating Waste LCD Glass with Reservoir Sediments

This paper reports the application of Taguchi optimization technique in determining process condition for synthetic lightweight aggregates by incorporating waste liquid crystal displays (LCD) glass with reservoir sediments. In the study the waste LCD glass cullet was used as an additive. It was incorporated with reservoir sediments to produce lightweight aggregates. Taguchi method with an L16(45) orthogonal array and five controllable 4-level factors (i.e., cullet content, preheat temperature, preheat time, sintering temperature, and sintering time) was adopted. Then, in order to optimize the selected parameters, the analysis of variance method was used to explore the effects of the experimental factors on the performances (particle density and water absorption) of the produced lightweight aggregates. The results showed that it is possible to produce high performance lightweight aggregates by incorporating waste LCD glass cullet with reservoir sediments.