Temperature Control Measures Research Articles

A Study on Adiabatic Temperature Rise Test and Temperature Stress Simulation of Rock-Fill Concrete

In the present study, we investigate the effect of the adiabatic temperature rise property of rock-fill concrete (RFC) on the temperature stress and crack resistance of RFC gravity dams. We conducted tests on the adiabatic temperature rise of RFC with a rock-fill ratio of 42%, 49%, and 55%, respectively. Based on the regression analysis of the test data, a calculation model of the adiabatic temperature rise, considering the rock-fill ratio, is developed, and the finite element analysis software ANSYS is employed to simulate the whole process of the temperature and temperature stress fields of a RFC gravity dam. The main findings of the study are as follows: (1) Both the adiabatic temperature rise rate and the final adiabatic temperature rise of RFC are negatively correlated with the rock-fill ratio. (2) The calculation model of the adiabatic temperature rise of RFC is characterized by its high accuracy, which can help predict the adiabatic temperature rise of RFC with different rock-fill ratios. (3) Without any temperature control measures, the maximum temperature stress of RFC generated by the temperature rise of hydration heat in the RFC gravity dam is 0.93 MPa, which meets the standard of temperature stress control. The results of the present study indicate that dam construction with RFC can simplify the measures of temperature control and crack prevention, improve the construction efficiency, and reduce the cost of dam construction.

Optimization and Evaluation of Naturally Ventilated BIPV Façade Design

To improve the photovoltaic (PV) power generation, the temperature control measures and optimization of BIPV systems are critical, particularly in tropical weather. There are two categories of cooling mechanisms, i.e. passive and active cooling. In the present study, a simplified numerical model is set up to evaluate the effect of passive cooling of BIPV façades with various configurations, including the PV periphery openings (i.e. area ratio), behind air cavity depth, wind velocity and attack angle (0 to 90 degrees) on the cell temperature of BIPV module. A parametric study is performed. Three-dimensional computational fluid dynamics (CFD) simulation is applied to predict the cell temperatures under various BIPV façade configurations and environmental conditions. The results of the CFD model show that in the case where the areas of the top and bottom openings are equal, there is limited air ventilation at the behind air cavity. However, the BIPV surface temperature has a significant drop when the inlet opening at the bottom is enlarged, compared with that of the same area of inlet and outlet. Changing the wind attack angle from 0º to 60º has limited effect on the BIPV cell temperature, which results in a variation of less than 5 ºC. However, a dramatic temperature drop of around 15ºC is observed when the attack angle is larger than 60º. The influence of air cavity depth is studied with the fixed top and bottom opening size ratio. By varying the air cavity depth from 30 to 200 mm, a lower PV cell temperature can be achieved.

Thermal stability of ordered multi-particle layers of long-chain phosphonate-modified nanodiamond with superior heat-resistance

The maintenance properties of the layered regularity in organized films of heat-resistant, organo-modified nanodiamond upon heating were investigated. In long-chain phosphonic acid-modified nanodiamond, desorption of the modified-molecular chain due to temperature elevation was suppressed until 350 °C. This innovative improvement is compared to the desorption behavior at 155 °C of chains of stearic acid-modified nanodiamond. When two-dimensional films with layered organization were formed, clear layered periods were observed, and it was simultaneously confirmed that unmodified-chain impurities could not be removed. Temperature-controlled X-ray diffraction and IR measurements showed that impurities could be fired and removed. Due to the annealing effect during heating above 100 °C, the layered order was enhanced owing to rearrangement of the organo-nanodiamonds. The layered regularity of the organo-particle layers during heating was maintained up to 175 °C, far exceeding the value of 50 °C of the organized film of stearic acid-modified nanodiamond. This technique is expected to be developed for single-layer coating on the outermost layer of a surface with a nanodiamond, which has excellent antibacterial properties and high refractive index and thermal conductivity.

Temperature Control Measures and Temperature Stress of Mass Concrete during Construction Period in High-Altitude Regions

The focus on the development of China’s vast hydropower resources has shifted to Tibet and other plateau regions. These areas are high-altitude regions whose basic climatic characteristics are as follows: dry climate, significant differences in daily temperature, and strong solar radiation. If a dam is built under such special climate conditions, specific and strict temperature control and crack prevention measures should be taken. Therefore, this study explores the temperature control standards, as well as temperature control and crack prevention measures, for concrete in high-altitude regions using three-dimensional finite element methods and based on the concrete gravity dam in Tibet in combination with the characteristics of material properties that are disadvantageous to temperature control and crack prevention. The temperature drop process can be optimized in time, and the temperature drop rate can be controlled to prevent excessive scale and temperature drop rates. Moreover, the temperature gradient can be spatially optimized, and thus, the differences in foundation temperatures, upper- and lower-layer temperatures, and internal and external temperatures can also be reduced. The research shows that the recommended temperature control and crack prevention measures can effectively reduce temperature stress. This study has a significant value as a reference for similar projects in high-altitude regions.

Temperature control and thermal-induced stress field analysis of GongGuoQiao RCC dam

Temperature control is vital to avoid thermal stress cracking in large volume concrete structures. This paper presents numerical modeling results of the temperature field and the thermal-induced stress in the Gongguoqiao roller-compacted-concrete (RCC) dam. The overflow dam section of the Gongguoqiao RCC gravity dam was numerically simulated by the finite element method, in which the boundary conditions and computing assumptions were described according to the in situ conditions. The control criteria of temperature and induced stable stress were determined for the RCC dam in discussion based on the design code for concrete gravity dam. Numerical simulation of the temperature filed and thermal-induced stress field was then carried out during the full-life stages including the construction and the service period of the RCC dam. The numerical results were used as reference to guide the construction and engineering measures to fulfill the requirements of the dam temperature control criteria. Two working conditions, i.e., without and with water-cooling, were analyzed and compared in detail to demonstrate the simulation of the temperature field and the thermal-induced stress field of the Gongguoqiao RCC dam. Temperature control measurements were finally proposed for the discussed RCC dam to assure its safety.

Temperature Control and Numerical Analysis for Mass Concrete Pile Cap of Hai-huang Bridge

In order to study the heat of hydration in massive concrete, this paper takes Hai-huang bridge for engineering background and uses the finite element analysis software of FEA to analyze the heat of hydration effect of the cushion cap. Comparing the measured data with the theory data, the results showed that the concrete crack was controlled effectively and ensure the construction quality by adopted reasonable temperature control measures. The results of the research prove that the measured data was consistent with calculation data, and it proves the accuracy of the finite element analysis. Finally, the study provides certain reference and guiding significance for similar project.

Study on Temperature and Stress of Hydration Heat of Mass Concrete in Arch Bridge Bearing Platform

Through the simulation of finite element construction, the temperature and stress of hydration heat in mass concrete construction of arch bridge bearing platform were analyzed, and the necessity of setting condenser tube for temperature control was put forward. Based on the monitoring of the site construction of the mass concrete, the temperature and stress of the concrete under the corresponding temperature were obtained when concrete pouring into the mold, and were compared with the theoretical calculation data. Results showed the expected effect was achieved. Practice shows that the temperature control measures for the bridge are effective, and no concrete cracks were found in the mass concrete of the bearing platform. This has a certain reference and guidance for the construction of mass concrete of platform for the similar bridges.

A Case Study On Zoning And Construction Of Roller-Compacted-Concrete Gravity Dams

In order to make full use of the concrete strength, reduce the amount of cementitious materials and simplify the temperature control measures, a roller compacted concrete (RCC) dam needs to be zoned reasonably in consideration of locations and working conditions. Taking the RCC gravity dam of Wuxikou hydropower project in Jiangxi province, this article specifies the zonation design, the problems encountered during construction stage and the corresponding measures. The results indicate that the zonation and the construction schemes of the RCC gravity dam can greatly reduce the amount of cementitious materials, improve the level of mechanization in construction, and thus accelerate the construction progress, reduce the project cost. It not only ensures the quality and safety of the project, but also achieves obvious economic benefits. It can be an important reference for zonation design and construction of similar projects.

Feedback Design of Temperature Control Measures for Concrete Dams based on Real-Time Temperature Monitoring and Construction Process Simulation

Crack prevention is a significant issue in the construction process of concrete dams. The vast majority of concrete cracks are related to temperature variations, and hence, temperature control is a primary method used to prevent cracks. This paper presents a new integrated concept, named Feedback Design (FD) of temperature control measures, which incorporates real-time temperature monitoring, temperature field simulation and construction process simulation in a large system to optimize a temperature control scheme for concrete dams. We used a fiber-optic Distributed Temperature Sensing (DTS) system to monitor the temperature variation process of typical dam monoliths in real time. By incorporating a genetic algorithm, neural network algorithm, and finite element theory, we proposed an intelligent inversion method to obtain thermal parameters of concrete dams based on the temperature monitoring data. Meanwhile, we built a simulation model of a concrete dam’s construction process based on a cycling network technique to obtain accurate construction environmental parameters. Finally, we simulated the temperature field of a typical dam monolith based on initial temperature control measures, inversion thermal parameters, and accurate construction environmental parameters. Temperature variance lines of typical points in the model obtained from the finite element method (FEM) accord well with the measured values obtained from the DTS system. We applied the FD approach to the Xiluodu arch dam located in southwest China to forecast the temperature fields and optimize the temperature control scheme of the dam blocks planned for pouring. The FD approach has been proven reliable and efficacious.

Low Dose Photoelectron Spectroscopy at BESSY II: Electronic structure of matter in its native state

The implementation of a high-transmission, angular-resolved time-of-flight electron spectrometer with a 1.25MHz pulse selector at the PM4 soft X-ray dipole beamline of the synchrotron BESSY II creates unique capabilities to inquire electronic structure via photoelectron spectroscopy with a minimum of radiation dose. Solid-state samples can be prepared and characterized with standard UHV techniques and rapidly transferred from various preparation chambers to a 4-axis temperature-controlled measurement stage. A synchronized MHz laser system enables excited-state characterization and dynamical studies starting from the picosecond timescale. This article introduces the principal characteristics of the PM4 beamline and LowDosePES end-station. Recent results from graphene, an organic hole transport material for solar cells and the transition metal dichalcogenide MoS2 are presented to demonstrate the instrument performances.

Porous silicon pillar and bilayer structure as a nucleation center for the formation of aligned vanadium pentoxide nanorods

Porous silicon single layer (PSM), bilayer (PSB) and pillar (PSP) structures have been evaluated as nucleation centers for vanadium pentoxide (V2O5) crystals. Deposition of vanadium precursor over different substrates (drop casting technique), followed by annealing treatment under Ar-H2 (5% H2) atmosphere, induced crystallization of vanadium oxide. With respect to c-Si/SiO2 substrate, V2O5 nanorods with relatively large aspect ratio were formed over and within PSP structures. On the other hand, pores in PSM and PSB were found to be filled with relatively smaller crystals. Additionally, PSB provided a nucleation substrate capable to align the nanocrystals in a preferential orientation, while V2O5 crystals grown on PSP were found to be randomly aligned around the nanoporous pillar microstructure. Nanorods and nanocrystals were identified as V2O5 by temperature-controlled XRD measurements and evidence of their crystalline nature was observed via transmission electron microscopy. A careful analysis of electronic microscopy images allows the identification of the facets composing the ends of the crystals and its corresponding surface free energy has been evaluated employing the Wulff theorem. Such high surface area composite structures have potential applications as cathode material in Lithium-ion batteries.

OPTIMIZATION OF THE TEMPERATURE CONTROL SCHEME FOR ROLLER COMPACTED CONCRETE DAMS BASED ON FINITE ELEMENT AND SENSITIVITY ANALYSIS METHODS

Achieving an effective combination of various temperature control measures is critical for temperature control and crack prevention of concrete dams. This paper presents a procedure for optimizing the temperature control scheme of roller compacted concrete (RCC) dams that couples the finite element method (FEM) with a sensitivity analysis method. In this study, seven temperature control schemes are defined according to variations in three temperature control measures: concrete placement temperature, water-pipe cooling time, and thermal insulation layer thickness. FEM is employed to simulate the equivalent temperature field and temperature stress field obtained under each of the seven designed temperature control schemes for a typical overflow dam monolith based on the actual characteristics of a RCC dam located in southwestern China. A sensitivity analysis is subsequently conducted to investigate the degree of influence each of the three temperature control measures has on the temperature field and temperature tensile stress field of the dam. Results show that the placement temperature has a substantial influence on the maximum temperature and tensile stress of the dam, and that the placement temperature cannot exceed 15 °C. The water-pipe cooling time and thermal insulation layer thickness have little influence on the maximum temperature, but both demonstrate a substantial influence on the maximum tensile stress of the dam. The thermal insulation thickness is significant for reducing the probability of cracking as a result of high thermal stress, and the maximum tensile stress can be controlled under the specification limit with a thermal insulation layer thickness of 10 cm. Finally, an optimized temperature control scheme for crack prevention is obtained based on the analysis results.

Temperature-controlled portable Raman spectroscopy of photothermally sensitive pigments

In this work, an innovative NIR Raman device (excitation wavelength at 1064nm) was developed in order to avoid thermal stress and consequent chemical alterations of the materials analyzed. In particular, we devised and tested for the first time a sensored Raman probe allowing for temperature-controlled measurements based on a thermoelectric sensor providing the feedback signal for suitably modulating the output power of the laser source and then limiting undesired heating effects within the irradiated volume. The experimentation was carried out on cinnabar, lead white and indigo pigments frequently used during the past centuries, which presents pronounced photothermal instability. The results achieved in a set of instrumental and analytical tests using different measurement control parameters allowed demonstrating the effectiveness and reliability of the present approach for preventing thermal alterations effects during Raman spectroscopy and speeding the measurements, as well as for monitoring spectral variations associated with the crystals anharmonicity over large temperature ranges. These features along with the portability of the novel device can make in situ Raman characterisation of valuable painted surfaces including photosensitive materials very safe and efficient.

Influence of maximum aggregate sizes on the performance of RCC

The maximum aggregate size exhibits a substantial influence on many important characteristics of hydraulic concrete. This paper is dedicated to study the effects of coarse aggregate size by a series of experiments on full and triple graded Roller Compacted Concrete (RCC) mixtures, as well as experiments of full grade and wet screening on mechanics, deformation, thermotics and durability. The results show that full graded RCC with a water-binder ratio of 0.45–0.50 is acceptable for water consumption of 70kg/m3, a sand ratio of 30% and a stone combination of 20:30:30:20. The full-graded large samples had compressive strength of 10% higher than that of wet-screened small samples, with however a considerable drop in tensile strength. The large aggregate had a more obvious function of restriction and restraint to the deformation of concrete, while full-graded RCC had better volume stability. The full-graded concrete samples preceded RCC small samples in terms of frost resistance. The impact mechanism of the coarse aggregate’s maximum size mainly lied in the transformation of interface structure, and was also related to the characteristics of RCC. The full-graded RCC could further reduce the consumption of plastic materials, lower the temperature rise of hydration heat, simplify temperature control measures, reduce cracks and improve the characteristics of concrete, which is promising in both technical and economic perspectives.

Adaptability of cut rose (Rosa hybrida L.) varieties for shade and high temperature conditions in tropical greenhouses

Rose (Rosa hybrida L.) is one of the most popular cut flower species grown under protected culture in the world. However, in Sri Lanka, the commercial cultivation is limited to upcountry region due to low temperature. Even though many rose varieties are grown in relatively warm regions, their growth rates and productivity vary due to the lack of adaptability to temperature stress. Therefore, this research was conducted to identify adaptable varieties for moderately high temperature and partial shade in a replicated greenhouse research in Mid Country Wet Zone (MCWZ) and Intermediate Zone (MCIZ) of Sri Lanka. Rose varieties Black Magic and White Success were identified to be more adoptable to warm and humid greenhouse conditions in the MCWZ and MCIZ during Yala season with respect to plant growth and flower yield. However, White Success was comparatively lower in marketable flower percentage and flower quality, compared to Black Magic. Cut flower varieties, Grand Gala and Peach Pope showed longer shelf-life compared to Black Magic and White Success. The types of shades, Aluminet (25 %) and black shade net (50 %), reduced the mean daytime temperature difference to 2.1±0.13 between greenhouse air and outside air. The rose varieties Black Magic, Grand Gala and White Success could successfully be grown to obtain a good quality flower yield under the shade of Aluminet (25 % shade) in the greenhouse. The recognized the adaptability of the selected rose varieties to tropical greenhouse conditions, and the potential use of Aluminet (25 % shade) as a temperature control measure in rose-producing greenhouses.

Study of the Volume Deformation and Stress Development of Concrete Influenced by the Different Cooling Rate

This paper studied the development of stress and strain influences by different cooling rates based on the concrete thermal stress tests. furthermore, discussed the temperature control measures for early concrete placement.

Measures to Control the Temperature of the Concrete Cracks in Foundation Mass

In the construction process, the concrete has been get fully utilized, there have been a variety of concrete strength grade configuration requirements and the corresponding raw materials. In the pouring process large volume concrete base, since the temperature stress generation will produce concrete temperature cracks, so the concrete pouring, raw material selection, after pouring temperature control measures have higher requirements. Based on a practical project, the construction of the control temperature stress did some exploratory research.

Sensitivity Analysis of Temperature Control Parameters and Study of the Simultaneous Cooling Zone during Dam Construction in High-Altitude Regions

There are unprecedented difficulties in building concrete gravity dams in the high altitude province Tibet with problems induced by lack of experience and technologies and unique weather conditions, as well as the adoption of construction materials that are disadvantageous to temperature control and crack prevention. Based on the understandings of the mentioned problems and leveraging the need of building gravity dam in Tibet, 3D finite element method is used to study the temperature control and crack prevention of the dam during construction. The calculation under recommend temperature control measures and standards shows that the height and number of simultaneous cooling zone have the more obvious influencers on concrete stress; therefore, it is suggested to increase the height of simultaneous cooling zone to decrease the stress caused by temperature gradient of adjoin layers so as to raise the safety level of the whole project. The research methods and ideas used on this project have significant values and can be taken as references in similar projects in high altitude regions.

Research on Crack Prevention of Premixed Concrete of Pump Station Built in Summer

In the summer of southern cities of China, the duration of high temperature becomes longer which requires stricter temperature control and crack prevention measures for mass concrete in construction. By using finite element method for unsteady temperature field and stress field a simulation is made for a pump station built in summer. The cement hydration velocity of this engineering is so high that makes the temperature control very difficulty. Through result analysis of different cases, some optimized measures which include surface preservation and water cooling are proposed. It has an important significance for concrete structure in the same area.

Line shapes, positions and intensities of water transitions near 1.28 μm

We present measurements of approximately 70 isolated, self-broadened, water vapor lines which are assigned to the (1,0,1)–(0,0,0), (0,0,2)–(0,0,0), (1,2,0)–(0,0,0), and (2,0,0)–(0,0,0) vibrational bands and which occur in the transparency window region from 7710cm−1 to 7920cm−1. We acquired absorption spectra on room-temperature, water samples over the pressure range 150–800Pa with the frequency-stabilized cavity ring-down spectroscopy technique. In order to optimize measurement accuracy, we integrated mK-level temperature control and SI-traceable pressure measurements into our cavity ring-down spectroscopy measurements. This technique yielded relative uncertainties of 0.04% and 0.20% in sample density and measured line intensity, respectively. We also referenced our spectrum frequency axes to a Cs clock, which provided vacuum line positions with a combined standard uncertainty of 3MHz. Comparison of our measured intensities, positions and self-broadening parameters with literature values reveals that the present work substantially reduces uncertainty in these line parameters. For the (1,0,1)–(0,0,0) vibrational band, the measured line intensities agree at the 1%-level with published ab initio calculations. Our spectra exhibited signal-to-noise ratios up to ≈20,000:1 to enable stringent tests of theoretical line profiles through multispectrum least-squares data analysis. We show that the partially correlated, quadratic-speed-dependent Nelkin–Ghatak profile gives a quality of fit that is commensurate with the high spectrum signal-to-noise ratio, and unlike most other profiles considered here, reproduces the measured line shapes without systematic residuals over the entire pressure range. Our results confirm that mechanisms of (1) collisional narrowing, (2) speed-dependent effects and (3) partial correlation between velocity-changing and dephasing collisions, contribute to the self-broadened line shape of isolated water vapor transitions.