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The lunar surface and its deep layers contain abundant resources and valuable information resources, the exploration and exploitation of which are important for the sustainable development of the human economy and society. Technological exploration and research in the field of deep space science, especially lunar-based exploration, is a scientific strategy that has been pursued in China and worldwide. Drilling and sampling are key to accurate exploration of the desirable characteristics of deep lunar resources. In this study, an in-situ condition preserved coring (ICP-Coring) and analysis system, which can be used to test drilling tools and develop effective sampling strategies, was designed. The key features of the system include: (1) capability to replicate the extreme temperature fluctuations of the lunar environment (−185 to 200 °C) with intelligent temperature control; (2) ability to maintain a vacuum environment at a scale of 10−3 Pa, both under unloaded conditions within a ϕ580 mm × 1000 mm test chamber, and under loaded conditions using a ϕ400 mm × 800 mm lunar rock simulant; (3) application of axial pressures up to 4 MPa and confining pressures up to 3.5 MPa; (4) sample rotation at any angle with a maximum sampling length of 800 mm; and (5) multiple modes of rotary-percussive drilling, controlled by penetration speed and weight on bit (WOB). Experimental studies on the drilling characteristics in the lunar rock simulant-loaded state under different drill bit-percussive-vacuum environment configurations were conducted. The results show that the outgassing rate of the lunar soil simulant is greater than that of the lunar rock simulant and that a low-temperature environment contributes to a reduced vacuum of the lunar-based simulated environment. The rotary-percussive drilling method effectively shortens the sampling time. With increasing sampling depth, the temperature rise of the drilling tools tends to rapidly increase, followed by slow growth or steady fluctuations. The temperature rise energy accumulation of the drill bits under vacuum is more significant than that under atmospheric pressure, approximately 1.47 times higher. The real-time monitored drilling pressure, penetration speed and rotary torque during drilling serve as parameters for discriminating the drilling status. The results of this research can provide a scientific basis for returning samples from lunar rock in extreme lunar-based environments.

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]

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.

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]

• Temperature step on thermal responses were studied under field conditions. • The results of field study were affected by temperature, air speed, and behavior, and thus differ from the laboratory. • Short-term thermal experience has an effect on human thermal response. • Thermal sensation changes faster than skin temperature when temperature changes from cold to near neutral. Big environmental difference between the artificial indoor environments and the outdoor environments affects human comfort and physiological responses. This study examines the dynamic changes in human psychological and thermal responses to sudden, large temperature differences under three indoor conditions: slightly warm, neutral, and slightly cold. The similarities and differences between field studies and existing laboratory research were also analyzed. The results indicated that the indoor-outdoor temperature differences under slightly cold, neutral, and slightly warm conditions were 24.5 °C, 32.6 °C, and 39 °C. Environmental differences between indoor and outdoor conditions were influenced by various factors, including temperature, air speed and so on. Human thermal responses differed significantly among the three conditions (P < 0.01). Thermal sensation vote (TSV), thermal comfort vote (TCV), and skin temperature showed great changes after the environmental shift. Skin temperature fluctuated more during down-step, while heart rate and heart rate variability (HRV) exhibited greater changes during up-step in this test. In real-world scenarios, human thermal responses were influenced by temperature, air speed, and human behavior, resulting in deviations from laboratory findings. Furthermore, a time-dependent model for skin temperature and TSV was developed, revealing that thermal sensation changes more rapidly than skin temperature during abrupt shifts from cold to near-neutral environments. [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]

• The performance fluctuation of HPD system was given quantitatively. • A new SHPD system for large temperature difference conditions was proposed. • COP of SHPD mode is 1.8 times higher than that of HPD mode under the same conditions. In this study, a heat pump drying (HPD) system platform complemented by solar hot water was designed and established. The objective was to address the declines in the heating performance of air source HPD at high altitudes (more than 3000 m), cold conditions (annual average temperature at 5 °C), and with large temperature differences between day and night (more than 20 °C), i.e. under harsh conditions. A theoretical model was derived to determine the system parameters and to support the experimental analysis. Under no-load conditions, four cases with ambient temperature were tested and compared to explore the relationships between the system parameters and performance, as well as the effectiveness of the supplementary solar hot water. The heating performances under HPD and solar-assisted HPD (SHPD) modes were compared and analysed under load conditions (930 kg Mu Xiang). The results indicate that a decrease in the ambient temperature and increase in the temperature in the drying room causes attenuations of the compressor mass flow rate, evaporator cooling power, condenser heating power, and system coefficient of performance (COP). In addition, solar water heating can significantly improve the heating performance of the HPD system. Under no-load conditions, the average heating power of the HPD-mode system is 19.27 kW, and the average COP is 2.76. The average heating power of the SHPD mode system is 23.34 kW, and the average COP of the system reaches 3.24, an increase of 17.4%. Under load conditions, the average heating capacity power of the HPD mode is 9.64 kW; the COP is only 1.34, and fluctuates significantly with the decrease in ambient temperature. The average heating capacity power of the SHPD mode is 17.62 kW and the COP is 2.42, i.e. 1.8 times of that of the HPD mode. By raising the drying room temperature to the same set temperature, the SHPD mode time is shortened by 70%. [ABSTRACT FROM AUTHOR]

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]

Semi-rigid base asphalt pavements in Xinjiang suffer from various defects, particularly reflection cracks caused by extreme environmental conditions and dynamic vehicle loads. Adopting a flexible asphalt pavement is effective in inhibiting reflection cracks. In this study, asphalt pavement structures with three typical flexible bases were selected for numerical simulation under the coupled fields of a dynamic load and the actual environmental conditions in Xinjiang (high-, low-, and large-temperature-difference areas) using ANSYS. Heat transfer systems and heat radiation conditions were established based on an investigation of the temperature variations in typical high- and low-temperature areas. Simulations were conducted to establish the temperature field within the internal structure. A half-sine wave model was used to simulate the dynamic vehicle load, and a coupled field was established. The tensile strain, tensile stress, shear stress of the asphalt layer, shear stress of the graded gravel layer, vertical compressive strain at the top of the subgrade, and surface deflection were adopted to analyze the mechanical response under the coupled fields. According to the simulation results, the variations in tensile strain, shear stress of the asphalt layer, and shear stress of the graded gravel layer were 8.45 %-26.52 %, 38.38 %-52.96 %, and 12.66 %-20.65 %, respectively, in high-temperature areas. Increasing the asphalt layer thickness can significantly reduce the amplitude of the variation and peak value of the mechanical index of the pavement structure. At high temperature differences of 30 °C, 40 °C, and 50 °C, the maximum peak values of the asphalt layer tensile stress were 4–8 MPa. A summer climate can increase the shear stress in the asphalt layer by more than 30 %. These results support the application of flexible bases in asphalt pavements in complex external environments. • Coupling fields of temperature and dynamic load was established. • Actual environmental conditions was considered during numerical simulation. • Recommends of design for flexible base pavement structure in special environment in Xinjiang. [ABSTRACT FROM AUTHOR]

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]

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.

The unique environment of Qinghai, which includes low temperatures and large temperature differences, has posed serious challenges to quality control for concrete. The geological features of the hinterland of the inland plateau include large temperature differences between day and night, frequent snow storms, thin air, anoxic dryness, and large areas of permafrost. Through investigations of concrete quality problems in bridges in Tongtianhe, Huang-Qinggou and other areas in the plateau hinterland, this article studies the influences of factors such as raw material selection, blending ratio optimization, and shrinkage and creep control on controlling the construction quality, enhancing the structural performance, and improving the construction techniques, adaptability, and feasibility of the concrete. [ABSTRACT FROM AUTHOR]

• The first prototype of the second type absorption heat exchanger was completed. • The second type absorption heat exchanger process was realized through experiments. • A simulation model for the second type absorption heat exchanger is established. • Tested the performance of the prototype under different working conditions. • The temperature efficiency of the prototype has been tested between 1.25 and 1.34. Absorption heat exchanger(AHE), as a kind of heat transformation device, is widely used in long-distance heat transportation system, waste heat recovery and other heat exchange processes s with large flow ratio on both sides. A second type of absorption heat exchanger was first designed, manufactured, and tested to get the performance in this research. The falling-film prototype absorption heat exchanger is consisting of a multi-section absorption heat transformer and a plate heat exchanger, using LiBr-H2O as working fluid. Under different working conditions, the tested results showed that the outlet temperature of the heat sink water was 916 K higher than the inlet temperature of the water on the heat source side. The coefficient of performance (COP) of the absorption heat transformer (AHT) was between 0.33 and 0.42. The temperature efficiency of the absorption heat exchanger was 1.24–1.35. Finally, the simulation model used to design the prototype machine was verified by the test results. [ABSTRACT FROM AUTHOR]

• A two-stage vertical absorption heat exchanger is designed for district heating system. • The performance of this system is tested in real project. • The system has higher heat exchange effectiveness and better operating performance. • A simulation model for two-stage absorption heat exchanger is established. • The simulation model is verified by the test data, which can be utilized for design. The absorption heat exchanger (AHE) is designed to decrease the temperature of outlet primary water. A two-stage vertical absorption heat exchanger for district heating system is designed and tested in this research. The system consists of two stages absorption heat pump with different vapor pressure in generator and evaporator, while the two stages are only connected with primary and secondary water. The system is designed to a vertical structure in order to reduce the covered area, which consists of condenser, generator, evaporator and absorber from top to bottom. A simulation model is put up and verified to predict the performance of the system. The performance of this system with 6000 kW heating capacity is tested in Taiyuan with the load rate ranges from 4.7% to 50.0%. The outlet water temperature of primary network is below 20 °C in the past heating seasons, which is 15–25 K lower than inlet water temperature of secondary network. The tested temperature efficiency is 1.250–1.420, while the tested temperature efficiency of single-stage system is 1.140–1.200. The two-stage vertical AHE system has higher temperature efficiency and better performance compared with traditional AHE according to field test. [ABSTRACT FROM AUTHOR]

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.

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]

Highlights • Discrete unified gas kinetic scheme for multiscale heat transfer with arbitrary temperature difference is developed. • The Newtonian method is used to handle the nonlinear relation between the equilibrium state and the temperature. • The present scheme can predict the multiscale heat transfer problems accurately and its time step is not restricted by the relaxation time. • The effects of large temperature difference are numerically investigated in different length and temperature ranges. Abstract In this paper, a finite-volume discrete unified gas kinetic scheme (DUGKS) based on the non-gray phonon transport model is developed for multiscale heat transfer problem with arbitrary temperature difference. Under large temperature difference, the phonon Boltzmann transport equation (BTE) is essentially multiscale, not only in the frequency space, but also in the spatial space. In order to realize the efficient coupling of the multiscale phonon transport, the phonon scattering and advection are coupled together in the present scheme on the reconstruction of the distribution function at the cell interface. The Newtonian method is adopted to solve the nonlinear scattering term for the update of the temperature at both the cell center and interface. In addition, the energy at the cell center is updated by a macroscopic equation instead of taking the moment of the distribution function, which enhances the numerical conservation. Numerical results prove that the present scheme can describe the multiscale heat transfer phenomena accurately with arbitrary temperature difference in a wide range. In the diffusive regime, even if the time step is larger than the relaxation time, the present scheme can capture the transient thermal transport process accurately. Compared to that under small temperature differences, as the temperature difference increases, the variation of the temperature distribution behaves quite differently and the average temperature in the domain increases in the ballistic regime but decreases in the diffusive regime. [ABSTRACT FROM AUTHOR]

In high altitude and large temperature difference areas, concrete construction faces the problem and challenge of insufficient frost durability. This paper investigates the macro-micro properties evolution of graphene oxide concrete (GOC) under large temperature difference freeze-thaw action and confirms the good frost resistance of concrete endowed with graphene oxide. The macro test results showed that graphene oxide effectively increased concrete's strength and relative dynamic modulus of elasticity at the initial and final stages of freezing and thawing, reduced the mass loss of concrete, and delayed the apparent damage process of concrete. Microscopic tests revealed that graphene oxide refined the pore size distribution of concrete, increased the number and percentage of gel pores in it, induced the growth of hydration products into petal-like and polyhedral crystalline clusters, better filled the pores inside the concrete, and inhibited crack expansion. The promotion effect of graphene oxide on the macro-micro properties of concrete was proportional to its content, but it was limited when the content reached 0.05%. A freeze-thaw damage model and a residual strength prediction model of concrete were developed using freeze-thaw test data and the Weibull distribution function to simulate and predict the deterioration process of concrete macroscopic properties. The findings of the study can be used to guide the design, construction, and operation of similar concrete structures in alpine regions. • Graphene oxide has a positive effect on the frost resistance of concrete under large temperature difference freeze-thaw cycles. • The mechanism of graphene oxide promoting the frost resistance of concrete is discussed. • A model suitable for predicting freeze-thaw damage of graphene oxide concrete is established. [ABSTRACT FROM AUTHOR]

Plate-fin heat exchangers (PFHEs) are widely utilized in aviation precoolers, emphasizing not only heat transfer performance but also the outlet temperature distribution, with flow maldistribution impacting both parameters. This study developed a numerical model of crossflow PFHE and a two-dimensional flow distribution model under the condition of flow maldistribution. Experimental validation shows a standard deviation of 6.9%. This investigation delves into the effects of flow distribution offset (ξ) and non-uniformity (ε) on heat transfer performance and outlet temperature distribution. With large temperature differences, variations in fluid properties due to temperature lead to changes in the surface heat transfer coefficient (SHTC). The combined effects of SHTC and temperature difference determine the heat transfer performance. The results indicate optimal heat transfer performance and outlet cross-sectional temperature distribution at ξ = − 0.67 and 1, respectively. For a given ξ , increased non-uniformity deteriorates heat transfer efficiency and outlet cross-sectional temperature distribution. At ε =0.66, relative to the uniform flow, the heat transfer performance and standard deviation of outlet temperature distribution decrease by 10.3% and 45.1%, respectively. [ABSTRACT FROM AUTHOR]

Abstract In order to achieve large temperature difference chilled water storage, A novel type of bag-shaped interlayer device is presented. 16 hours' static temperature rise was tested to verify that the insulation performance of the interlayer can meet the engineering requirements. During the charging/discharging cycle, it was observed that both the outlet water temperature stability and the half-cycle figure of merit（FOM 1/2 ） in the discharging cycle are much better than that of the charging cycle under the large temperature difference of 2-16°C, while the experimental results are opposite in the temperature of 4-12℃. Furthermore, the large temperature difference favors FOM 1/2. [ABSTRACT FROM AUTHOR]

Abstract Gas-kinetic schemes (GKS) have been developed as a kinetic Finite-Volume approach to computational fluid dynamics. The GKS a priori allows to obtain approximate solutions of the fully compressible Navier-Stokes equations. In our contribution we show simulation results of compressible natural convection at large temperature differences and low Mach numbers beyond the applicable range of the Boussinesq approximation. The simulations were performed on non-uniform quadrilateral and unstructured triangular grids. The dependence of the critical Rayleigh number on the temperature difference for compressible Rayleigh-Bénard convection, predicted by theory, is accurately reproduced. Moreover, heat transfer in a buoyancy driven square cavity with differentially heated sides at large Rayleigh numbers and large temperature differences is investigated. Temperature and velocity profiles as well as Nusselt numbers show good agreement with benchmark results in literature. After validating the scheme for thermal compressible convection, we investigate unsteady natural convection at a Rayleigh number of R a = 5 ⋅ 10 9 and at a large temperature difference of T h / T c = 4. We find that compressibility has a leading influence on the stability of the boundary layers, such that the flow at the heated wall becomes unstable, whereas the flow at the cooled wall remains stable. This phenomenon has not yet received much attention. [ABSTRACT FROM AUTHOR]

A new thermal lattice Boltzmann (LB) method is proposed for the simulation of natural convection with large temperature differences and high Rayleigh number. A regularization procedure is developed on LB equation with a third order expansion of equilibrium distribution functions, in which a temperature term is involved to recover the equation of state for perfect gas. A hybrid approach is presented to couple mass conservation equation, momentum conservation equations and temperature evolution equation. A simple and robust non-conservative form of temperature transport equation is adopted and solved by the finite volume method. A comparison study between classical Double Distribution Function (DDF) model and the hybrid finite volume model with different integration schemes is presented to demonstrate both consistency and accuracy of hybrid models. The proposed model is assessed by simulating several test cases, namely the two-dimensional non-Boussinesq natural convection in a square cavity with large horizontal temperature differences and two unsteady natural convection flows in a tall enclosure at high Rayleigh number. The present method can accurately predict both the steady and unsteady non-Boussinesq convection flows with significant heat transfer. For unsteady natural convection, oscillations with chaotic feature can be well captured in large temperature gradient conditions. [ABSTRACT FROM AUTHOR]

Generally, the temperature of domestic waste water is high above 30℃. However, when dealt with by common sewage-source heat pump system, temperature difference between inlet side and outlet side is small as 5℃. It leads to manifold cycles and energy waste. To acquire a unit of heat pump water heater of sewage dealing with large temperature difference with high energy utilization rate, through which the cold water (about 5℃) can be heated once to hot water (about 45℃) to reach the temperature for daily use and waste water (about 30℃) can be rapidly dropped to cold water (about 6℃) to satisfy the standard of waste water emissions. In this paper, two staged series of heat pump water heater dealing with large temperature difference is proposed. And performance factor of system is analyzed through simulation by MATLAB so as to find the optimum middle operating point. This method ensures pattern operating in large temperature difference but in small flow at both the hot and cold sides. At the same time, it avoids the lasting elevation of condensing temperature and the constant reduction of temperature in evaporation, which helps to facilitate the stability and optimal performance of the operating unit. [ABSTRACT FROM AUTHOR]

• The incorporation of EDTA and CN improves the controllability of the thickening time of cementing slurry. • The combination of EDTA and CN solves the slow strength development under large temperature difference. • EDTA, CN and GH-8L form a chelated network, which promote cement hydration after the high temperature destruction. In wellhole environments with large temperature differences, high-temperature retarders can slow the strength development of the top of a cement slurry column, thus affecting construction progress and safety of cementing projects. Herein, to address the problem of slow strength development of the top of a cement slurry caused by the addition of the high-temperature retarder GH-8L, the synergistic effect of the co-addition of ethylene diamine tetraacetic acid (EDTA) and calcium nitrate (CN) is considered. The experimental results show that the thickening time of the cement slurry system mixed with EDTA and CN exceeds 300 min at 150 °C and 75 MPa and its strength at 48 h is >14 MPa. As demonstrated by the hydration heat tests, EDTA and CN promote the hydration heat release rate of the GH-8L cement slurry at low temperature. The synergistic mechanism of EDTA and CN in the GH-8L doped cement slurry promotes the initial dissolution of cement particles, significantly increases the content of C-S-H and CH in the hydration products, and promotes the formation of needle-like NO 3 –AFt ettringite. The cementing slurry, with the co-addition of EDTA and CN, can not only meet the requirements of thickening time and cementing with a large temperature difference but also compressive strength. [ABSTRACT FROM AUTHOR]

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To solve the problem of cement slurry suspension instability caused by a geothermal gradient in low-pressure and leakage formation, a hydrophobically associating long-chain polymer (PSAN) was designed as a suspension stabilizer by introducing hydrophilic monomer acrylamide (AM), temperature-resistant monomer 2-acrylamide-2-methyl propane sulfonic acid (AMPS), hydrophobic monomer styrene (St) and temperature-sensitive monomer N-vinyl caprolactam (NVCL). The synthesis conditions of PSAN were optimized by orthogonal response surface method. The structure and performance of PSAN were characterized and tested by IR, 1H NMR, GPC, SEM, TG, high-temperature rheology, and fluorescent probes. The research and analysis showed that PSAN had a good temperature response. At 30–65 ℃, the apparent viscosity of PSAN aqueous solution increased with the increase of temperature. At 65 ℃, the hydrophobically associating ability of PSAN was enhanced, and the retention rate of the apparent viscosity of its aqueous solution at 65–110 ℃ was still more than 83%. The good temperature response of PSAN was conducive to the suspension stability of cement slurry under the condition of large temperature differences. When 1% bwoc (percentage of cement mass) was added to the cement slurry, the free liquid of the cement slurry was 0, the water loss was less than 90 mL, and the density difference between the upper and lower sections of the cement stone column was less than 0.01 g/cm3. SEM analysis showed that there was a network structure formed by hydrophobic association between PSAN molecules in cement. In a word, under the condition of 30–110 ℃ (80 ℃ large temperature difference), the suspension stabilizer PSAN can effectively alleviate the floating of light materials and the sinking of heavy materials in cementing slurry through the hydrophobic association between molecules, and ensure the suspension stability of cementing slurry, thus contributing to the safety of cementing construction and improving the quality of cementing. [Display omitted] • The orthogonal response surface method was introduced to optimize the synthesis conditions. • Fluorescent probes explored the thermosensitive association properties. • SEM observed the microscopic reticular stereoscopic structure caused by association. • The suspension stability of cement slurry was evaluated by the Archimedes drainage method. [ABSTRACT FROM AUTHOR]

In heat exchanger application, working fluid inside the tubes is subjected to considerable temperature changes. In order to improve heat transfer performance, various strategies are proposed and evaluated; one of them is the application of coiled tubes. Coiled tubes have been used widely in heat exchanger application mainly due to the presence of secondary flow which enhances heat transfer considerably. This study addresses heat transfer performance of three configurations of coiled tubes with square cross-section, i.e. in-plane, helical and conical coiled tubes, subjected to large temperature difference. Their heat transfer performance is numerically evaluated and compared with that of a straight tube with identical cross-section and length. A concept of Figure of Merit (FoM) is introduced and utilized to fairly asses the heat transfer performance of the coiled tube configurations. The results indicate that FoM increase as the wall temperature increase. In addition, combination of temperature-induced buoyancy flow and curvature-induced secondary flow considerably affect the flow behavior and heat transfer performance inside the tubes. [ABSTRACT FROM AUTHOR]

Abstract: Solutions for the fully compressible Navier–Stokes equations are presented for the flow and temperature fields in a cubic cavity with large horizontal temperature differences. The ideal-gas approximation for air is assumed and viscosity is computed using Sutherland''s law. The three-dimensional case forms an extension of previous studies performed on a two-dimensional square cavity. The influence of imposed boundary conditions in the third dimension is investigated as a numerical experiment. Comparison is made between convergence rates in case of periodic and free-slip boundary conditions. Results with no-slip boundary conditions are presented as well. The effect of the Rayleigh number is studied. Results are computed using a finite volume method on a structured, collocated grid. An explicit third-order discretization for the convective part and an implicit central discretization for the acoustic part and for the diffusive part are used. To stabilize the scheme an artificial dissipation term for the pressure and the temperature is introduced. The discrete equations are solved using a time-marching method with restrictions on the timestep corresponding to the explicit parts of the solver. Multigrid is used as acceleration technique. [Copyright &y& Elsevier]

Steady-state two-dimensional solutions to the full compressible Navier–Stokes equations are computed for laminar convective motion of a gas in a square cavity with large horizontal temperature differences. Results for air are presented. The ideal-gas law is used and viscosity is given by Sutherland''s law. An accurate low-Mach number solver is developed. Hereby an explicit third-order discretization for the convective part and a line-implicit central discretization for the acoustic part and for the diffusive part are used. The semi-implicit line method is formulated in multistage form. Multigrid is used as acceleration technique. A convergence behaviour is obtained which is independent of grid size, grid aspect ratio, Mach number and Rayleigh number. Grid converged results are shown for Rayleigh numbers between 102 and 107. [Copyright &y& Elsevier]

Thermal insulation materials are widely used in the fields of thermal protection and the energy conservation at high temperature. Thermal conductivity is one of the most important parameters of characterizing the thermal insulation performance of thermal protection materials. Steady state method such as the guarded hot plate method is normally considered as the most accurate method to measure the thermal conductivity of thermal insulation materials, but the temperature range is limited to below 1000 K. Unsteady state method can be employed at higher temperature but the accuracy is lacking of validation. Consequently, thermal verification experiments are usually conducted by heating the front surface of thermal insulation materials to a very high temperature. However, it is difficult to obtain the temperature-dependent thermal conductivity by using the thermal insulation performance measured with a large temperature difference across the material. In this study, a sandwich structure experimental system is built to carry out the thermal insulation performance tests with a large temperature difference at both steady state and transient state. Both uniform temperature layer method and polynomial fitting method are adopted to extract the temperature-dependent thermal conductivity from the large temperature difference test at steady state. A new transient state identification method is proposed based on the niche genetic algorithm to identify the relation between thermal conductivity and temperature from the transient thermal response. The temperature-dependent thermal conductivity of four thermal protection materials are finally obtained. The identification results prove that the proposed transient identification method is reliable and robust. [ABSTRACT FROM AUTHOR]

Drawn on the experience of the heat-flow-meter method, an experimental system is designed, established and validated to investigate the thermal insulation performance of SiC opacifier doped silica aerogel at large temperature difference. The test section of the experimental system is a symmetrical sandwich-structure, while the temperature of the cold surface keeps constant by circulating the water from the thermostat, NESLAB ThermoFlex2500, and the hot surface is electrically heated. Compared with the traditional method of the back-surface temperature response, the cold surface temperature is quantitatively controllable. Based on the present experimental system and method, the thermal insulation performance of insulator can be qualitatively and quantitatively evaluated by analyzing the temperature responses of the hot surface through the whole heat transfer process including the initial steady-state, the unsteady-state, and the final new steady-state. Qualitatively, the higher the temperature of the hot surface is and the faster the temperature rise of the hot surface is, the better the thermal insulation performance of the material has; quantitatively, the effective thermal conductivity of the materials is obtained based on the semi-infinite medium model and Fourier's Law. The present results show that the effective thermal conductivities of silica aerogel doped by 3.5 μm SiC opacifier with different volume fraction of 0%, 1%, and 5.84% are about 0.02559 W m−1 K−1, 0.02844 W m−1 K−1, and 0.03305 W m−1 K−1, respectively, at small temperature difference (<15 K) and low temperature (288–308 K). At large temperature difference (120–812 K) and high temperature (>400 K), the thermal insulation performance of silica aerogel doped by 3.5 μm SiC particle with a volume fraction of 1% is good enough, though 3.5 μm SiC particle with a volume fraction of 5.84% has a marginal improvement in blocking the thermal radiation within silica aerogel. • Design and establish an experimental system with a symmetrical sandwich-structure with the temperature of the cold surface controlled. • Evaluate the insulation performance and measure the effective thermal conductivity of SiC-fiber doped silica aerogel by the temperature response of the hot surface at large temperature differences (up to 1000 K). • Silica aerogel doped by 3.5 um SiC with a volume fraction of 1% is good enough, though 3.5 um SiC with 5.84% has a marginal improvement in blocking the thermal radiation. [ABSTRACT FROM AUTHOR]

Radiant ceiling systems have good comfort levels and energy savings. However, traditional radiant air conditioning systems have many problems, such as condensation forming on the cooling surface, insufficient cooling capacity, and complex structure and control. In this paper, a closed cavity radiation system with a built-in finned heat exchanger is proposed and the heat transfer mechanism, heat transfer performance, and operation characteristics of the system are analysed. The results show that the direct-expansion large-temperature-difference heat transfer method, with refrigerant as the working medium, realises the required cold supply through the low-temperature working medium and the required heat supply through the high-temperature working medium. Heat is transferred to or from the ceiling through a multi-stage strength buffer and direction conversion so that the ceiling respectively forms a hot or cold radiant plate with uniform temperature for indoor heat exchange. The heat transfer efficiency is more than 90%, which greatly improves the cooling or heating potential of the heat exchanger, reduces the required heat exchanger area, and simplifies the installation structure. In this study, the installation area of the finned heat exchanger only accounted for 14% of the ceiling. In practical application, the number of finned heat exchanger plates can be determined according to the cooling and heating load demand, providing a reference for new radiant air conditioning system design. • A closed cavity radiation system with built-in heat exchanger is analysed. • Finned heat exchangers that are not in direct ceiling contact are utilised. • The use of air gaps between the heat exchangers and ceiling reduces condensation. • Improved temperature uniformity of the ceiling is achieved. • It provides a reference for new radiant air conditioning system design. [ABSTRACT FROM AUTHOR]