Preset Temperatures Research Articles

The constant temperature control system of multi-pass and die-less shear spinning by flame heating

In order to improve the formability of challenging materials, the innovative flame-heating integration into a spinning machine is proposed to apply new processing strategies for flame-assisted die-less shear and multi-pass metal spinning. The device mainly includes measurement system and control system. The calculating function of control system is designed to adjust the forming temperature according to the feedback of measurement system. TC4 and TA2 are used for shear spinning and multi-pass spinning to verify the feasibility and reliability of the system with the forming temperature 450 and 850 °C respectively. The temperature change during the process of spinning is recorded once a second by temperature sensors. Then the absolute values of mean relative deviations under two conditions are less than 5% by comparing measurement temperatures and preset temperatures. Furthermore, the result shows that the forming accuracy by adopting the system under two conditions is acceptable.

Low Environmental Temperature Influences the Fatigue Resistance of Nickel-titanium Files

IntroductionThe purpose of this study was to evaluate the effect of different temperatures (0°C, 10°C, 22°C, 37°C, and 60°C) on the cyclic fatigue life of nickel-titanium (NiTi) files using a new fatigue test model in zirconium oxide. MethodsThree superelastic NiTi files (EndoSequence [Brasseler USA, Savannah, GA], ProFile [Dentsply Tulsa Dental Specialties, Tulsa, OK], and K3 [SybronEndo, Orange, CA]), and 3 heat-treated (K3XF [SybronEndo], Vortex [Dentsply Tulsa Dental Specialties], and HyFlex CM [Coltene-Whaledent, Allstetten, Switzerland]) NiTi files, all size 25/.04, were subjected to cyclic fatigue tests inside a novel, artificial ceramic canal with a curvature of 60° and a 5-mm radius. The model was immersed in water at 5 different preset temperatures. The number of cycles to failure (NCF) was recorded, and the fracture surface of the fragments was examined by a scanning electron microscope. The data were analyzed using 2-way analysis of variance with the significance level at 0.05. ResultsWhen the temperature was reduced from 60°C to 0°C, the NCF significantly increased from over 2 to 10 times for the NiTi file groups (P < .01). K3XF had the highest fatigue resistance of all files at 0°C (P < .05). Vortex files had the highest NCF at 10°C–60°C. The NCF of heat-treated files was significantly higher than superelastic NiTi files at 10°C and 20°C (P < .05). There was no significant difference in the NCF of HyFlex CM at 0°C and 22°C. There was little difference in the fractographic appearance among different temperatures, except that the fraction area occupied by the dimple region of some instruments at 0°C was slightly smaller than at 60°C. ConclusionsCooling down to low temperatures may be an interesting strategy to improve the fatigue resistance of rotary NiTi files.

More realistic warming by including plant feedbacks: A new field-tested control method for infrared heating

Infrared heating is a technique that allows warming experiments to be conducted in open-air conditions. Several improvements have been made since the method was introduced two decades ago, but none of these succeeded in reconciling controllability with an adequate consideration of vegetation responses that can counteract or reinforce warming. In an earlier conceptual study, we proposed a new infrared heater control method based on energy balance calculations that offers both custom-adjustable target temperatures and unconstrained vegetation responses. Here, we refine that concept, and test the control method under field conditions.Although quantitatively assessing the performance of the new control system is not straightforward as no pre-set canopy temperatures are used (because the vegetation is allowed to influence these), the test results suggest that our system functioned as envisaged. We adopted a scenario of 2°C air warming and gradual drying. Warming of the canopy was +1.4°C in a first phase with plentiful water, but increased to +3.5°C at the end of the test when the soil water content approached the wilting point. In other words, the amount of water lost via evapotranspiration was higher when the vegetation could afford to transpire freely (high soil water availability), counteracting the warming, but lower when water became scarce, reinforcing the warming. Such a response would also occur naturally, while these vegetation-mediated differences would be erased by the classical, fixed ΔT control.The successful test under field conditions demonstrates that this alternative infrared heater control method is ready to be applied in both new and existing set-ups. The advantages over traditional control methods would especially benefit studies that combine warming with precipitation manipulation by explicitly taking the interdependence between the water and the energy balance into account.

Dual thermostating in flow analysis

An advanced strategy involving concentric tubes is proposed for fast and controlled heating (or cooling) of the reaction medium in flow analysis. Different temperatures are set by sequentially circulating two thermostated water streams through the outer larged bore (2.0mm i.d.) silicone tube, which acted as a water-jacket of the inner (0.8mm i.d.) PTFE tube, and directing the sample zone to flow through it. Each end of the outer tube is connected to a three-way valve that selects the stream to flow inside it. For 25–85cm tube lengths and a 12.0mLmin−1 flow rate, the time interval required for temperature attainment, and the uniformity of temperature along the tube were evaluated. For the 85-cm tube, low differences in temperatures along the coil (1.1–8.7°C) and between programmed and attained values (2.3–13.4°C) were noted within a wide range of pre-set temperatures (15–75°C). The feasibility of the innovation in flow analysis was demonstrated in a model system relying on the iodide-nitrite reaction. The strategy allows fast (15–120s) thermostating of the reaction medium in a versatile and simple way, and is especially attractive when two controlled temperatures are set during the analytical course. Potentialities and limitations of the innovation are discussed.

Drying based on temperature-detection-assisted control in microwave-assisted pulse-spouted vacuum drying.

An online temperature-detection-assisted control system of microwave-assisted pulse-spouted vacuum drying was newly developed. By using this system, temperature control can be automatically and continuously adjusted based on the detection of drying temperature and preset temperature. Various strategies for constant temperature control, linear temperature control and three-step temperature control were applied to drying carrot cubes. Drying kinetics and the quality of various temperature-controlled strategies online are evaluated for the new drying technology as well as its suitability as an alternative drying method. Drying time in 70 °C mode 1 had the shortest drying time and lowest energy consumption in all modes. A suitable colour, highest re-hydration ratio and fracture-hardness, and longest drying time occurred in 30-40-50 °C mode 3. The number of hot spots was reduced in 40-50-60 °C mode 3. Acceptable carrot snacks were obtained in 50-60-70 °C mode 3 and 70 °C mode 2. All temperature curves showed that the actual temperatures followed the preset temperatures appropriately. With this system, a linear temperature-controlled strategy and a three-step temperature-controlled strategy can improve product quality and heating non-uniformity compared to constant temperature control, but need greater energy consumption and longer drying time. A temperature-detection-assisted control system was developed for providing various drying strategies as a suitable alternative in making a snack product. © 2016 Society of Chemical Industry.

Key thermodynamic characteristics of nucleation on charged and neutral cores of molecular sizes in terms of the gradient density functional theory

The gradient density functional theory and the Carnahan–Starling model formulated for describing the contribution of hard spheres have been used to calculate the profiles of condensate density in small critical droplets formed via homogeneous nucleation, as well as in stable and critical droplets formed via heterogeneous nucleation on solid charged and neutral condensation cores of molecular sizes. The calculations performed for water and argon at different values of condensate chemical potential have yielded the heights of the activation barriers for homoand heterogeneous nucleation as functions of vapor supersaturation at preset system temperatures. The interaction of condensate molecules with a solid core has been described by the resultant potential of molecular attractive forces. In the case of a charged core, the long-range Coulomb potential of electric forces has additionally been taken into account. Dielectric permittivities have been calculated as known functions of the local density of the fluid and temperature. The radius of the equimolecular droplet surface has been chosen as a variable describing the droplet size. Dependences of the chemical potential of condensate molecules in a droplet on its size have been plotted for water and argon with allowance for the action of capillary, electrostatic, and molecular forces. It has been shown that the role of the molecular force potential in heterogeneous nucleation increases with the size of condensation cores.

UV degradation of clay‐reinforced polypropylene nanocomposites

The aim of this work is to experimentally characterize the UV‐degradation process at both the surface and at different layers across the thickness of injection‐molded polypropylene (PP) matrix containing different amounts of nanosized montmorillonite (MMT) clay particles. These nanocomposite materials have been exposed to UV irradiations (λ = 320 nm) at different preset temperatures (25, 45, and 65°C) in the presence of oxygen and during different exposure times. The extent of such process at these layers was determined using both the FTIR spectroscopy and the wide‐angle X‐ray diffraction analyses. The micromechanical properties across the thickness have been characterized using the nanoindentation technique. The obtained results have indicated that the UV‐degradation process for the nanocomposite materials is much more intense than the one observed for the neat PP. Moreover, it has been noted that such degradation process is not uniform across the thickness of the exposed materials. Results obtained from the X‐ray analysis have shown an increase of the crystallinity of the polymer molecules at only the external surface of the exposed materials. This was confirmed using the nanoindentation test as an increase of the Young's modulus at this layer was noted. POLYM. ENG. SCI., 56:469–478, 2016. © 2016 Society of Plastics Engineers

Correction of flow stress and determination of constitutive constants for hot working of API X100 pipeline steel

Uniaxial compression tests of X100 pipeline steel were conducted to investigate its hot working behavior. Cylindrical specimens were compressed over a wide strain rate range of 0.001–50 s−1 and a temperature range of 850–1100 °C. Due to the heat generated from deformation and friction, the measured temperatures of compressed specimens at higher strain rates (≥1 s−1) deviated from the preset temperatures. Therefore, their measured stresses were corrected to obtain the true stresses at the pre-set temperatures before they were used for calculating constitutive equations. The Arrhenius-type constitutive equation was selected to describe the hot working behavior on the basis of corrected stresses. Strain-dependent constitutive constants were determined. The constitutive equation and corrected stress-strain data were both verified by using the results of additional tests at a strain rate of 20 s−1.

Impact of rotating permanent magnets on gallium melting in an orthogonal container

Abstract Gallium melting in an orthogonal container under the impact of a magnetic field was studied. The main goal of the work was the numerical modeling and study of solid–liquid interface behavior and exploration of the possibility to control its dynamics using a magnetic system. The container comprised heated and cooled side faces with preset temperatures. The fluidized part of the metal was exposed to a rotating magnetic field generated by a system of rotating permanent magnets. A three-dimensional (3D) numerical model based on COMSOL Multiphysics software that accounted for thermal variations in the metal properties and the presence of a mushy zone was devised. Simulation reliability was verified by comparison with experimental data obtained using ultrasonic Doppler velocimetry.

Umedecimento do substrato e temperatura na germinação e vigor de sementes de melão

This study was conducted to evaluate different volumes of distilled water and substrate temperatures on germination and vigor of melon, cucumber variety. The experiment was conducted at the Laboratory of Seed Analysis Unimontes in the period february to april 2012. Sowing was done on paper rolls like “germitest” moistened with volumes (mL) of distilled water equivalent to 1.0; 1.5; 2.0; 2.5 and 3.0 times the weight of dry substrate without further addition of water, with three sheets per roll. The rolls were kept in germination preset constant temperatures of 25 to 30°C and 20-30°C alternate. The experimental design was completely randomized in a factorial 5 x 3 (distilled water volume an temperatures), with four replicates of 50 seeds. We evaluated the germination percentage, germination velocity index, root length and shoot, fresh and dry weight of seedlings. Given the results, it is concluded that combinations of substrate distilled water volume and temperature of exposure that provide better answers on germination and vigor of melon seeds, cucumber variety, are 1.0 times the weight of dry substrate at a temperature of 30oC and 3.0 times the dry weight of the substrate 25 and 20-30°C. Among the studied temperatures, the temperature of 30°C promotes better responses in all variables, is recommended as an additional temperature to evaluate the physiological quality of melon seeds.

Effect of pre-irradiation annealing treatments on the response of high-temperature glow peaks of LiF:Mg,Ti

A need to study the effect of pre-irradiation annealing on LiF:Mg,Ti was recognized to enhance the intensity of its high-temperature thermoluminescence (HTTL), and the ratio of HTTL and dosimetric glow peaks (DP). Slow cooling following thermal annealing enhanced the intensity of HTTL and reduced the DP. Following 400 °C – 1 h annealing (established for this type of phosphor and used widely), additional pre-irradiation annealing treatments and oven-cooling (by switching off the power to the oven) were investigated in steps of 20 °C in the range of pre-set temperatures from 400 °C to 100 °C. The oven-cooling from pre-set temperature of ∼170 °C enhanced the HTTL and the HTTL/DP ratio by up to 1.66 and 4.88 times, respectively, as compared to that for the fast cooling from 400 °C but reduced the DP by 2.9 times. The slow cooling from pre-set temperatures in the range of 180 °C–160 °C appears crucial for the intensities of DP and HTTL, and thereby for the applicability of LiF:Mg,Ti in mixed-field dosimetry of low and high LET radiation.

Multiwalled Carbon Nanotube Nanofluids Used for Heat Dissipation in Hybrid Green Energy Systems

This study was conducted to characterize carbon nanotube (CNT)/water nanofluids (CNWNFs) and to apply the nanofluids in a heat‐dissipation system of dual green energy sources. CNTs were mixed with water in weight fractions of 0.125%, 0.25%, and 0.5% to produce nanofluids. The thermal conductivity, density, viscosity, and specific heat of the nanofluids were measured. An experimental platform consisting of a simulated dual energy source and a microchip controller was established to evaluate the heat‐dissipation performance. Two indices, the heat dissipation enhancement ratio and specific heat dissipation enhancement ratio (SHDER), were defined and calculated. The CNWNFs with a CNT concentration of 0.125 wt.% were used because they exhibited the highest SHDER. The steady‐state performance was evaluated at 2 flow rates, 11 hybrid flow ratios, and 3 heating ratios for a total power of 1000 W. The transient behavior of the energy sources at preset optimal temperatures was examined, and the CNWNFs exhibited average increases in stability and heat dissipation efficiency of 36.2% and 5%, respectively, compared with water. This nanofluid heat‐dissipation system is expected to be integrated with real dual energy sources in the near future.

Mathematical modelling and simulation of the thermal performance of a solar heated indoor swimming pool

Buildings with indoor swimming pools have a large energy footprint. The source of major energy loss is the swimming pool hall where air humidity is increased by evaporation from the pool water surface. This increases energy consumption for heating and ventilation of the pool hall, fresh water supply loss and heat demand for pool water heating. In this paper, a mathematical model of the swimming pool was made to assess energy demands of an indoor swimming pool building. The mathematical model of the swimming pool is used with the created multi-zone building model in TRNSYS software to determine pool hall energy demand and pool losses. Energy loss for pool water and pool hall heating and ventilation are analyzed for different target pool water and air temperatures. The simulation showed that pool water heating accounts for around 22%, whereas heating and ventilation of the pool hall for around 60% of the total pool hall heat demand. With a change of preset controller air and water temperatures in simulations, evaporation loss was in the range 46-54% of the total pool losses. A solar thermal sanitary hot water system was modelled and simulated to analyze it's potential for energy savings of the presented demand side model. The simulation showed that up to 87% of water heating demands could be met by the solar thermal system, while avoiding stagnation.

Thermal behaviour of new crystalline semitransparent solar cell structure

This paper presents the structure of a novel semitransparent solar cell and its thermal behaviour, which cell can be used for building integrated applications. The crystalline self-made test cells can be manufactured using basic semiconductor technological steps, arbitrary pattern of holes can be etched. We report on two alternative methods for thermal behaviour characterisation of the novel semitransparent solar cell compared to non-transparent solar cells. The first method is thermal dependence and High Temperature Store (HTS)—condition A testing and the second is application of conventional thermal imaging in combination with electrical current heating of the solar cell. I–V characteristic measurements at preset temperatures demonstrate that the new semitransparent sample despite the throughout holes can be as effective as the without hole solar cell. IR imaging results reveal the localised resistive heating zones or shunting in the test cells. This research examines the influence of the through-holes on the thermal properties of solar cells.

Solid-state bonding between Al and Cu by vacuum hot pressing

Diffusion bonding between aluminum and copper was performed by vacuum hot pressing at temperatures between 623 and 923 K through two thermal processes: hot compression under the deformation rate of 0.2 mm/min for 10 min at pre-set temperatures, and additional pressing at 0.2 mm/min for 20 min during furnace cooling. After analyzing interface, the feasible diffusion bonding temperature was suggested as 823 K. The three major intermetallic layers generated during diffusion bonding process were identified as Al2Cu, AlCu+Al3Cu4 and Al4Cu9. Furthermore, local hardness values of Al2Cu, AlCu+Al3Cu4 and Al4Cu9 layers average at (4.97 ± 0.05), (6.33 ± 0.00) and (6.06 ± 0.18) GPa, respectively.

Partial Oxidation of Methane in Porous Reactor: Part I. Unidirectional Flow

Partial oxidation of methane in a unidirectional flow porous reactor is studied numerically. A number of partial oxidation mechanisms affecting H2 and CO yields are comparatively analyzed using kinetic modeling for a range of rich and ultrarich equivalence ratios, residence times, and preset reactor temperatures. Temperature profiles, hydrogen yields, and methane conversion ratios are predicted for various equivalence ratios using two-temperature filtration combustion model with selected detailed chemical mechanism. The simulation results show that the hydrogen yield has two obvious sections: the ignition section and stream reforming section. The hydrogen yield increases with temperature and equivalence ratio increase. The two-temperature model results show a good qualitative agreement with the experimental results especially for the maximum solid temperature and hydrogen production. The wave starts to propagate downstream at φ > 1.5. The maximum solid temperature decreases from 1760 K to 1665 K as the eq...

The Effect of Deformation Heating on Restoration and Constitutive Equation of a Wrought Equi-Atomic NiTi Alloy

In this study, a set of constitutive equation corrected for deformation heating is proposed for a near equi-atomic NiTi shape memory alloy using isothermal hot compression tests in temperature range of 700 to 1000 °C and strain rate of 0.001 to 1 s−1. In order to determine the temperature rise due to deformation heating, Abaqus simulation was employed and varied thermal properties were considered in the simulation. The results of hot compression tests showed that at low pre-set temperatures and high strain rates the flow curves exhibit a softening, while after correction of deformation heating the softening is vanished. Using the corrected flow curves, the power-law constitutive equation of the alloy was established and the variation of constitutive constants with strain was determined. Moreover, it was found that deformation heating introduces an average relative error of about 9.5% at temperature of 800 °C and strain rate of 0.1 s−1. The very good agreement between the fitted flow stress (by constitutive equation) and the measured ones indicates the accuracy of the constitutive equation in analyzing the hot deformation behavior of equi-atomic NiTi alloy.

Implementation of a heat recovery unit in a proton exchange membrane fuel cell system

A heat recovery unit (HRU) has been developed and implemented in a proton exchange membrane (PEM) fuel cell cogeneration system that generates electricity and hot water efficiently. It consists of a stack coolant circuit, a heat exchanger, and a heat recovery circuit. An intelligent thermal control algorism is proposed as well to manage the cogeneration system. The HRU together with the control scheme has managed the fuel cell cogeneration system properly and efficiently. The stack coolant inlet temperature (SCIT) is well controlled at the preset temperatures (55 °C and 59 °C) under different external loads (0–3 kW). Results also show that the dynamics of the SCIT is closely related to the actions of the secondary fluid pump. Up to 50% fuel energy can be recovered thermally in the present cogeneration system. Examination of the external-load effects reveals that increasing external loads increases the electrical efficiency but decreases the heat recovery efficiency slightly. The maximum efficiency as a combination of heat and power is 82% based on hydrogen's lower heating value.

Kinetic study of high density polyethylene (HDPE) pyrolysis

In this study, 15 mg samples of high density polyethylene (HDPE) were pyrolysed in an isothermal thermogravimetric set-up in a micro-thermobalance reactor with pre-set temperatures. The objective was to study the thermal degradation behaviour of the polymer and determine the kinetic rate constants and overall activation energy ( E o). Yielded pyrolysis products under different temperatures were analyzed and lumped into the following categories: rich gases ( C 1 –C 4), liquids (non-aromatic C 5 –C 10), aromatics (single ring structures), waxes ( C 11) and char. It was observed that the gas yield was increasing with the operating temperature. Data obtained enabled us to propose a novel kinetic modelling approach based on the thermal cracking of the polymer by primary and secondary depolymerisation reactions to form the pyrolysis products. The E o was estimated to be 147.25 kJ mol −1 for the total conversion of HDPE in isothermal pyrolysis.

Biochemical and stress responses of rohu Labeo rohita and mrigal Cirrhinus mrigala in relation to acclimation temperatures

The biochemical and stress responses of two Indian major carps, rohu Labeo rohita and mrigal Cirrhinus mrigala were studied after acclimating them to four preset temperatures (26, 31, 33 and 36 degrees C) for 30 days. The blood glucose and liver glycogen levels showed an inverse trend in both the species and were significantly different in L. rohita at higher temperatures. The decrease in the liver glycogen level of C. mrigala, however, was not significant. Plasma cortisol levels increased significantly whereas the ascorbic acid content in the brain and kidney of both the species decreased significantly with increasing temperatures. Total lipid content in the liver of both the species decreased significantly with increasing acclimation temperatures. The phospholipid concentration decreased in L. rohita with increasing acclimation temperatures, and in C. mrigala the values decreased up to 33 degrees C and increased at 36 degrees C. In C. mrigala, the cholesterol level decreased up to 33 degrees C and then increased at 36 degrees C, but the absolute value was lower in comparison to L. rohita. The cholesterol levels, however, were not significantly different in L. rohita. Triglycerides and free fatty acids concentrations decreased significantly with increasing acclimation temperatures in both the species. The present study indicates species-specific metabolic responses of L. rohita and C. mrigala to thermal acclimation.