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In order to find the anti-freezing durability differences between concrete in the frequent natural freeze–thaw conditions in the northwest of Sichuan Province, China, and concrete in the rapid freeze–thaw conditions of the standard rapid method, the typical temperature and humidity of the northwest of Sichuan Province were simulated. The results showed that the average number of freeze–thaw cycles in the northwest of this province can reach up to 150 per year. The relative dynamic modulus of C30 ordinary concrete, which is 100% pre-saturated, still remained above 90% after 450 cycles in simulated environments. However, during the rapid freeze–thaw test, even the C30 air-entrained concrete failed after 425 cycles. Compared to the saturation degree of concrete itself, the continuous replenishment of external moisture during freeze–thaw cycles is a key factor affecting the frost resistance of concrete. Rapid freeze–thaw reduces the number of the most probable pore sizes in ordinary concrete, and the pore size distribution curve tends to flatten. The reduction rate of the surface porosity of air-entrained concrete before and after rapid freeze–thaw is only about one third of that of ordinary concrete. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Xinjiang University (Natural Science Edition) is the property of Xinjiang University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Railway Construction Technology is the property of Railway Construction Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Transportation Science & Technolgy is the property of Transportation Science & Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Drilling Fluid & Completion Fluid is the property of Drilling Fluid & Completion Fluid Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Drilling Fluid & Completion Fluid is the property of Drilling Fluid & Completion Fluid Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study aims to explore the temperature field and mechanical characteristics of hydraulic tunnels during operation in an area with large temperature differences throughout a year. By relying on the measured displacement field change results of a water transmission tunnel in Xinjiang, a finite element calculation model applicable to the hydraulic tunnel-surrounding rock under the action of large temperature differences was established. Then, the FEM model was used to analyze the temperature field distribution and stress field variation of hydraulic tunnel-surrounding rock under the effect of large temperature differences. The results showed that, under the action of large temperature differences, the displacement of the cave top was the largest, followed by the cave bottom, and finally the cave waist. The obtained displacement field data using the calculation model in this study were basically consistent with the on-site measured data, and the displacement field change law was the same, indicating that the established finite element calculation model is reliable. When the ambient temperature was below zero, the freezing front gradually expanded to the depth of the surrounding rock along the tunnel radial direction, while the frozen rock at the intersection of the lining and the surrounding rock melted first when the ambient temperature was above zero. The stress in various parts of the surrounding rock of the hydraulic tunnel increased continuously. To be specific, the growth rate of the tensile stress at the cave bottom, the tensile stress at the cave top, and the compressive stress at the cave waist of the tunnel reached 0.052 MPa/year, 0.053 MPa/year, and 0.096 MPa/year, respectively, in the first year, but the increasing rate subsequently tended to slow down continuously. Therefore, in actual projects, attention should be focused on the effect of large temperature differences on the stress growth of tunnel-surrounding rocks at an early stage, especially the growth of compressive stress at the cave waist. Notably, there are a large number of symmetrical and asymmetric phenomena related to engineering in this study. [ABSTRACT FROM AUTHOR]

Silica aerogel is an excellent thermal insulator for high-speed aircraft, but there is little research on it in a high-temperature and complex-pressure environment. This research aims to evaluate the thermal insulation performance of silica aerogel monoliths with different porosities under large temperature differences and pressure gradients. We established an experimental system to measure and analyze the hot surface temperature response by fixing the heat flux and the cold surface temperature at transient pressure conditions. An unsteady-state heat transfer model considering gas flow is developed. The effective thermal conductivity of silica aerogels with 79.55 ~ 90.91% porosity is measured at different temperature differences between cold and hot surfaces (127 ~ 512 K), near-vacuum (<10 Pa), and transient pressure conditions. The results demonstrated that silica aerogel with 90.91% porosity showed the best thermal insulation performance when the temperature differences were over 500 K, while the aerogel with 79.55% porosity became the best when the temperature differences were less than 500 K. In addition, both the temperature and pressure difference affect the thermal insulation performance: the energy transport caused by gas flow affects the dynamic temperature response when gas permeability is of the order of 10−15 m2; the thermal insulation performance is improved by increasing gas permeability and pressure difference when gas flow and heat transfer directions are opposite. [ABSTRACT FROM AUTHOR]

To study the effect of pore structure changes on the fatigue life of concrete in areas with large temperature differences, a concrete fatigue test program was designed after a temperature cycle of −50 to 70°C. Results show that temperature differences considerably influence pores with a size ranging from 0.1 to 27.98 nm. Furthermore, the fatigue life of concrete gradually decreases with the increase in the pore structure parameters of 0.1 to 27.98 nm. This result indicates that the effect of temperature difference on the fatigue life of concrete in areas with large temperature differences must not be ignored. The combined effect of temperature differences and load increases the coarsening rate of the pore structure, and the load remarkably affects pores with a size ranging from 524.26 to 10,000 nm. To characterize the pore structure of concrete under temperature cycling and fatigue load, two pore structure characteristic parameters, namely, comprehensive change rate of pore size (Sz) and pore structure complexity coefficient (Cz), are proposed. These parameters, together with the total porosity (Ptotal), form a three‐dimensional pore structure characteristic parameter and establish the relationship expression between the three‐dimensional pore structure parameters and the fatigue life of concrete (N); thus, they provide basis for the prediction of the fatigue life of concrete on the basis of pore structure. [ABSTRACT FROM AUTHOR]

Silica aerogel composite is an excellent thermal insulator for spacecraft under high-temperature and complex air environments. This study intends to evaluate SiC-doped silica aerogel's thermal insulation performance under large temperature and air pressure differences. In this paper, the hot surface's temperature response of SiC-doped silica aerogel with different content was studied at significant temperature differences (ΔT) when pressure changes instantaneously. Their thermal insulation performance was evaluated by analyzing the influence of pressure gradients on the unsteady-state heat transfer. When the cold surface's temperature of the specimen keeps constant at 15 °C and ΔT = 171~912 K, the results demonstrate that the correlative thermal conductivities of silica aerogel with 1% and 5.84% SiC are 0.02223~0.04077 W·m−1·K−1 at P ≈ 10 Pa and 0.03165~0.04665 W·m−1·K−1 at P = 1 atm, respectively. The aerogel composite with 0% SiC showed the best thermal insulation performance at ΔT < 200 K and P ≈ 10 Pa, while the aerogel with 5.84% SiC became the best at ΔT > 700 K and P = 1 atm. In addition, the transient pressure decreases will significantly impair the heat transfer of the gas inside the aerogel, thereby weakening the gaseous thermal conductivity and improving the thermal insulation performance. [ABSTRACT FROM AUTHOR]

Copyright of Railway Standard Design is the property of Railway Standard Design Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The large temperature difference condition in Northwest China threatens a myriad of concrete structures during construction, with the daily temperature varying by around 40 °C. To investigate the macro-mechanical properties and microstructural characteristics of concrete containing different amounts of mineral admixtures under such harsh conditions, this investigation used an environmental chamber to simulate a saline soil erosion environment with a large temperature difference. Four types of concrete containing different proportions of fly ash and slag were prepared and exposed in the environmental chamber with a daily temperature change of −5~40 °C to investigate their compressive strength, flexural strength, and fracture properties. Moreover, the X-ray diffraction (XRD) characteristics, microscopic morphological characteristics, pore structure characteristics, and post-erosion chloride ion distribution characteristics were also observed and recorded. Results showed that the mineral admixture could improve the early strength development of the concrete and effectively improve the fracture performance of the concrete. The average compressive strength growth rate of concrete from day 3 to day 14 was 83.25% higher than that of ordinary concrete (OC) when 15% fly ash and 15% slag were added. In addition, the fracture energy of the concrete was maximized when 15% fly ash and 20% slag were added, which was 50.67% higher than that of OC; furthermore, the internal compactness and pore structure were optimized, and the resistance to saline soil erosion was strong. This provides a basis for the practical application of compounded mineral admixture-modified concrete in an arid environment with a large temperature difference and saline soil erosion. [ABSTRACT FROM AUTHOR]

Copyright of Natural Gas Industry is the property of Natural Gas Industry Journal Agency and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Summary: On most dual fuel ships, the waste heat of engine exhaust gas and the cooling capacity of liquefied natural gas (LNG) in the fuel regasification process are not effectively used. In order to recover these redundant energy under the large temperature difference around 600 K, thermoelectric technology provides a feasible solution with the advantages of small size, no noise and high stability. In this article, a waste energy recovery system has been developed for LNG‐diesel dual fuel ships using multistage thermoelectric generators (TEGs) scheme. According to the thermodynamic analysis and the materials selection, the recoverable energy, recovery form and thermoelectric materials used in the large temperature range of the dual fuel ship were determined. A multistage TEGs model considering the temperature distribution, fluid properties, connection methods and contact effects has been developed to predict the thermoelectric performance under the operating condition with large temperature difference. The results show that the maximum conversion efficiency can reach up to 18.54% with appropriate thermoelectric materials in different temperature zones and suitable multistage series‐parallel schemes. Besides, the thermoelectric conversion effect makes the temperature distribution of the cold and hot fluids in the TEG quite different from that in the traditional heat exchangers. The output characteristics of TEGs are directly affected by the flow parameters of the cold and hot fluids and the connection methods of thermoelectric elements. This study provides a brand‐new inspiration for developing the waste energy recovery and corresponding power conversion system on LNG‐diesel dual fuel ships. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Jiangsu University (Natural Science Edition) / Jiangsu Daxue Xuebao (Ziran Kexue Ban) is the property of Editorial Department of Journal of Jiangsu University (Natural Science Edition) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Temperature responses of asphalt pavements are significant, because of their potential influence on pavement structure design and distress prevention, particularly in areas that experience large temperature difference. In this study, a 3D finite element model is developed based on transient heat transfer. The aim is to analyse the temperature responses of the Karamay–Altay Highway in northern Xinjiang, which tends to experience large temperature differences and low temperatures. First, the climatic characteristics and pavement distresses in northern Xinjiang were investigated, and the condition defining a large temperature difference was established. Then, to guide the design of the Karamay–Altay Highway pavement structure, the temperature fields of seven pavement structures were determined. The temperature field of the Str-m structure in the Karamay–Altay area was compared to that in Xi'an. In the Karamay–Altay area, it was observed that Str-4 exhibited the minimum temperature variation at the bottom of the asphalt course and base course. It was clear that the degree of downward temperature transfer was closely related to the structure combination type. The results also suggested that a thicker asphalt layer would effectively reduce temperature effects and diminish distresses resulting from temperature. By comparing of the temperature fields of the Str-m structure in the Karamay–Altay area and in Xi'an, it was observed that pavement temperature fields changed drastically in the case study area, and hence revealed that severe pavement cracks in this area were closely related to abrupt temperature changes, low temperatures and large temperature differences. Hence, it was concluded that in northern Xinjiang, pavement designers should consider the large temperature difference condition very carefully. [ABSTRACT FROM AUTHOR]

Copyright of Oil Drilling & Production Technology / Shiyou Zuancai Gongyi is the property of Shiyou Zuancai Gongyi Bianjibu and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Jiangsu University (Natural Science Edition) / Jiangsu Daxue Xuebao (Ziran Kexue Ban) is the property of Editorial Department of Journal of Jiangsu University (Natural Science Edition) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Oil Drilling & Production Technology / Shiyou Zuancai Gongyi is the property of Shiyou Zuancai Gongyi Bianjibu and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)