Large Temperature Difference Research Articles

Investigation on self-healing polyurethane coating doped with lignin composites for protecting cementitious materials

Surface protective coatings are prone to cracking and failure due to the deformation of concrete structure itself and harsh service environment factors such as UV, ion erosion, and large temperature differences during the period of service. It is urgently required to develop new types of self-healing coatings to provide long-lasting protection for concrete structures and extend their service life. In this investigation, a lignin-based self-healing agent was prepared using aniline and lignin as raw materials. Its characterization was analyzed by SEM and FT-IR. By introducing the lignin-based healing agent and dynamic disulfide bonds, a new kind of self-healing polyurethane coating was prepared, and its self-healing ability was qualitatively and quantitatively evaluated, indicating that it had excellent self-healing performance. After self-healing process, the crack could withstand bending force. Moreover, with the increased temperature, the self-healing efficiency of tensile strength gradually increased, reaching a maximum of 86.42% at 60 ℃. Meanwhile, the self-healing efficiency of its elongation at break firstly increased and then gradually decreased, reaching a maximum of 93.77% at 40 ℃. This self-healing polyurethane coating had high hydrophobicity (139.4°) and excellent abrasion resistance. After 40 friction cycles, its hydrophobicity only decreased by 10.9% to 124.2°. In addition, this self-healing protective coating also showed excellent resistance to chloride ions, effectively protecting cementitious materials with the damaged surface. This work provides a new method for long-term protection of concrete structures.

Design of Conformal Cooling System with Lattice-structure of Mold Based on 3D Printing

The conformal cooling water circuit manufactured by using metal 3D printing SLM technology has significant advantages, compared to the straight drilling cooling water circuit, but there is still a problem of large temperature differences in local mold positions. Based on a circular cross-section spiral-shaped waterway, this article proposes a design that replaces a circular cross-section single helix with a runway-shaped double helix structure and sets a lattice structure in areas with large temperature differences. Finally, Moldflow is used to simulate the cooling effects of the two cooling forms. The results show that the lattice structure can significantly improve the phenomenon of uneven cooling, and the surface temperature difference of the mold has been improved by 41%. Compared to the circular section, the runway-shaped section has a better cooling effect, better temperature distribution, and more uniform cooling.

Investigation of compressible flow under low Mach number in an enclosed square cavity with a novel non-Boussinesq algorithm

Natural convection is widely observed in various scales of natural phenomena and industrial applications. The low Mach number (i.e., low-velocity) natural convection, especially under large temperature differences and significant density and pressure fluctuations, is of great research significance in industrial fields such as nuclear engineering. The Boussinesq approximation based on the incompressible Navier–Stokes (NS) equation is not fully descriptive due to the neglect of coupling effects among temperature, density, and pressure. As for numerical algorithms based on the compressible Navier–Stokes equation, they often suffer from high computational costs and convergence difficulties. In this paper, a novel numerical algorithm based on the decoupled and stabilized Lattice Boltzmann multiphase model with a complete physical description and clear conceptual framework is proposed. It couples the equation of state and the temperature equation, considering the full effects of gravity, pressure, and temperature-dependent density on flow disturbances, and it recovers the complete compressible NS equation. Taking the natural convection in an enclosed cavity as an example, the non-dimensional numbers governing the fluid system are identified by Buckingham π theorem; thus, a new thermal expansion number is proposed to connect the pressure effect. The accuracy and reliability of the numerical algorithm are validated by comparing it with standard benchmarks. On this basis, the proposed algorithm enables a unified physical description from low to high Rayleigh numbers and from small to large temperature differences. By analyzing the flow and heat transfer characteristics of natural convection under different Rayleigh numbers, temperature differences, and thermal expansion numbers, this study reveals the coupled physical mechanisms of low Mach number flow from small to large temperature differences, from low to high Rayleigh numbers and under different thermal expansion numbers.

Developing Relationship Between Ambient Temperature and Main Tuning Slide Length of a B-Flat Trumpet

Trumpet players rehearse and perform indoors and outdoors. However, large temperature differences in various settings significantly affect pitch. This project investigates how temperature affects the main tuning slide length of a standard B-flat trumpet to produce accurate harmonic pitches, based on the equal tempered chromatic scale. Six experimental trials were conducted, in which temperature sensors and measuring tapes were attached to respective locations on the trumpet. The project report provides a model with a table of values, of the ambient temperatures and corresponding tuning slide lengths for the trumpet player to reference. They can make accurate adjustments to play in tune and enhance intonation, when located in different environments with varying ambient temperatures.

Temperature self-controlled concrete: Electro-thermal performance and active temperature control strategy

The unique electro-thermal property of temperature self-controlled concrete (TSC) offers significant potential for actively controlling the surface temperature of concrete structures and eliminating cracks induced by large temperature differences. However, devising an active temperature control strategy for TSC is challenging due to the non-uniformity and time-dependent nature of the heat generation process. To address this issue, this paper investigates the electro-thermal performance and active temperature control strategy of TSC. Firstly, a three-factors orthogonal experiment is conducted to optimize the mix proportions based on mechanical properties and electrical resistivity. Subsequently, electro-thermal experiments are performed on the optimized TSC using different power supply strategies under fixed and fluctuating temperature conditions. Furthermore, theoretical formulations for temperature rise and an energy consumption evaluation method are developed to quantify the heating process of TSC. The results demonstrate that the optimized TSC mixture achieves a stable electrical resistivity of 8.2 Ω⋅m at 28 days, with only a 20% increase after 360 days. Moreover, employing a low heating power facilitates a more uniform temperature distribution and reduces the impact of changes in electro-thermal parameters on system safety. Considering safety and stability, strategies to enhance energy utilization and optimize the design and operation of the TSC heating system are proposed. These findings provide valuable guidance for determining appropriate power, current, and voltage for heating systems, as well as recommendations for the safe operation of TSC.

Simulation and enhancement of axial temperature distribution in a reactor filled with in-situ electrically heated structured catalyst

The hydrogen production technology based on the in-situ electrically heated structured catalyst (EHSC) has the advantages of compact structure, fast response, and less CO2 emissions. However, there is still a lack of research on the temperature distribution of the reactor filled with EHSC. Based on the problem, a CFD model was established, and the temperature distribution was revealed. To further reduce the large temperature difference in axial direction, the effects of the gradient-pitch design and segmented-voltage-control design for the EHSC on the temperature distribution and methanol conversion were studied numerically. The results showed that segmented-voltage-control design can significantly reduce the maximum axial temperature difference, due to the fact that the reaction heat and corresponding Joule heat supplied at each axial section were flexibly well matched. When reaction temperature was 275 °C, the maximum temperature difference decreased from 84.7 °C to 31.1 °C. Moreover, when GHSV was 13000 ml/(g h), methanol conversion was improved by up to 10.9%. The segmented voltage control method for the EHSC provides an opportunity to design an isothermal endothermic reactor under any reaction conditions in the case of further optimization of segmented-voltage-control design.

Natural convection effects in insulation layers of spherical cryogenic storage tanks

Natural convection effects in the insulation layers of spherical storage tanks are studied for different cryogenic fluids and tank sizes or curvatures. The non-vacuum-based insulation layers of these tanks are made of gas-filled porous materials such as perlite or glass bubbles. The large temperature difference that can exist between the inner cold wall and outer hot wall may create convective patterns with a multi-cellular flow within the insulation-filled annulus and lead to a higher boil-off rate and cryo-pumping effects. A main objective in the design of these systems is the elimination of the convective patterns by a proper choice of insulation properties. This work examines the impact of the insulation permeability or the Rayleigh number (Ra) on the type of convective flows for liquified natural gas (LNG) and liquid hydrogen (LH2) spherical storage tanks. Bifurcation diagrams of possible solutions are generated by numerical solutions of the governing equations at different Ra numbers. It is found that as Ra increases, new convective cells emerge near the south pole of the insulation layer due to unstable density stratification and lead to the distortion of isotherms, bringing the cold boundary towards the external hot boundary. When the temperature difference is large as in the case of LNG and LH2 tanks, there exist regions of multiple solutions in which multi-cell convective solutions may co-exist with a crescent-shaped weakly convective solution. In order to eliminate the possibility of multi-cell convection, inversion of the cold boundary, and reduce the boil-off rate, the Ra value of the insulation system should be below the limit point of the convective branch.

Numerical Study on a Liquid Cooling Plate with a Double-Layer Minichannel for a Lithium Battery Module.

The liquid cooling system of lithium battery modules (LBM) directly affects the safety, efficiency, and operational cost of lithium-ion batteries. To meet the requirements raised by a factory for the lithium battery module (LBM), a liquid cooling plate with a two-layer minichannel heat sink has been proposed to maintain temperature uniformity in the module and ensure it stays within the temperature limit. This innovative design features a single inlet and a single outlet. To evaluate the performance of the liquid cooling system, we considered various discharge rates while taking into account the structure, flow rate, and temperature of the coolant. Our findings indicate that at a mass outflow rate of 20 g/s, a better cooling effect and lower power consumption can be achieved. An inlet temperature of 20 °C, close to the initial temperature of the battery string, may be the most appropriate because a higher temperature of the coolant will cause a higher temperature of LBM, so far as to exceed the safe threshold value. In the case of larger rate discharge, the design of a double-layer MCHS at the bottom and an auxiliary one at the side can effectively reduce the maximum temperature LBM (within 28 °C) and maintain the temperature difference in the single cell at approximately 4 °C. In the case of non-constant discharges, the temperature difference between cells increases with the maximum temperature. When the discharge rate is reduced, the large temperature difference helps the temperature to drop rapidly. This can provide guidance for the design of cooling systems for the LBM.

Temperature gradient of ballastless track in large daily temperature difference region and its influence on dynamic responses of vehicle-track-bridge system

Due to the large daily temperature difference on the ultra-high altitude plateau of China, the actual vertical temperature gradient (TG) of ballastless track may exceed the design value in the Code. The temperature monitoring platform of the double-block ballastless track was established to obtain the temperature distribution characteristics of track. The finite element model of the temperature field of the track is developed to study the warping deformation of track, and then the influence of TG on the dynamic responses of the vehicle-track-bridge system (VTBS) are investigated. The results show that the maximum positive temperature gradient (PTG) and negative temperature gradient (NTG) of the track bed slab are 88.875 ℃/m and − 47.159 ℃/m, respectively, and the latter exceeds the design value in the Code. The dynamic responses are positively correlated with the TG, and the influence of the NTG is more significant. The dynamic response of the rail is most sensitive to the TG.

Modelling, validation and analysis of preheating strategy of fuel cell vehicle during Subzero cold start

The rapid cold start capability of fuel cell vehicles in low-temperature environments is one of the key factors restricting their commercialization. Reasonable and effective strategies are crucial to improving the low-temperature cold start capability of fuel cell vehicles. In this paper, a cold start model of fuel cell system is established, and the model is verified based on the cold start experiment of a hybrid fuel cell vehicle. The necessity of the coolant preheating strategy in the cold start is analyzed, and the important role of the coolant preheating strategy in helping the fuel cell system to start quickly at -10°C and below is demonstrated. Furthermore, the effects of air inlet temperature, air inlet flow rate, and external heater power on the cold start performance are investigated. The results show that when the air inlet temperature rises from -13°C to 65°C, the start time is shortened from 279 s to 234 s (reduced by 16.13 %). And at low air inlet temperatures, the lower flow rate of air can significantly reduce the temperature difference and maintain uniformity of temperature inside the stack, while at a higher temperature, the higher air flow rate causes the temperature of the cell stack to rise rapidly. For heating power, the start time is shortened from 421 s to 126 s (reduced by 70.07 %) when the heating power is increased from 3 kW to 11 kW. However, it will cause a larger temperature difference between the inlet and outlet of the coolant, which is not conducive to the uniform distribution of the temperature inside the stack. Thus, the start time can be shortened by increasing the air inlet temperature, air inlet flow rate, and heating power with the consideration of the temperature difference that the stack can withstand. The model developed by this study provides an effective way to analyze the fuel cell system during cold start, which is useful for the development of control strategies in the future.

CFD simulation study of flow equalisation plate model in single-phase immersion liquid cooling for servers

Immersion liquid cooling is progressively being adopted for server cooling applications within data centers. Uneven coolant distribution in liquid-cooled cabinets may cause large temperature difference between servers under some extreme conditions, prompted this study on a flow equalization plate structure. Firstly, the servers, the cabinet and the flow equalisation plate were modelled using Ansys Icepak software, and then the effects of holes radii, inlet layout configurations, and the number of holes on the flow distribution of the FC-40 coolant and the temperature control across servers was investigated. The results indicate that the smaller radii is beneficial in balancing the flowrate within the holes of the flow equalization plate by increasing the flow resistance, yielding a maximum temperature difference and a maximum temperature standard deviation of 2.1 °C and 0.8 °C at r = 7.5 mm. However, excessively small radii can lead to higher internal pressures and flow resistance. With larger hole radii, temperature control is significantly influenced by the inlet flowrate. As the flowrate increases, ΔT and Tsd also increase, reaching up to 3.8 °C and 1.3 °C at r = 12.5 mm, respectively. Larger hole radii result in smaller coolant flowrate, leading to lower convective heat transfer coefficient and higher server temperature. Locating inlets on one side creates large low-velocity vortex areas, disrupting server cooling, while center placement enhances thermal performance. When the number of holes is 18, the hole spacing increases, which leads to an increase in the flowrate in the holes and an increase in the convective heat transfer coefficient, which improves the thermal performance factor ε to 1.04.

Study on low temperature crack resistance of warm-mixed recycled SBS modified asphalt mixtures

In view of the cold winter in northern China and the large temperature difference between day and night, the asphalt pavement has been in low temperature service for a long time, in addition to experiencing the aging effect of water and salt erosion, jointly leading to a particularly serious pavement cracking phenomenon. Therefore, a quantity of Reclaimed Asphalt Pavement (RAP) is produced for the repair and renovation of old roads. Faced with the problems of inadequate reuse rate of RAP and high energy consumption of thermal regeneration, it is of great practical significance to explore the technology of warm mix regeneration. In order to study the adaptability of recycled SBS modified asphalt mixtures to low temperature after complex environmental erosion (long-term aging, water freeze-thaw cycle, and salt freeze-thaw cycle), two mixing methods, including hot mixing and warm mixing, were selected, and a Semi-Circular Bending Test was performed. SCB and Digital Image Correlation (DIC) techniques were used to evaluate the low temperature properties of recycled asphalt mixtures by fracture toughness, fracture energy and horizontal strain density damage. Combined with an Atomic Force Microscope (AFM) test, the microscopic analysis of recycled asphalt was carried out to verify the mechanism of low temperature cracking. The results showed that the low temperature cracking resistance of the reclaimed asphalt mixtures with warm mix was slightly worse than that with hot mix. The overall low temperature cracking resistance of the reclaimed SBS modified asphalt mixtures decreased with the increase in RAP content. The low temperature performance of the warm-mixed reclaimed asphalt mixtures deteriorated greatly when the RAP content was 80 %. The influencing factors of environmental conditions on the low temperature cracking resistance of the warm-mixed recycled SBS modified asphalt mixtures were listed as below: long-term aging > salt freeze-thaw cycle > water freeze-thaw cycle. The influence of salt on the stress field of crack tip and the microstructure of recycled asphalt after freeze-thaw was greater than that of water erosion. The changes of the microscopic adhesion were in good agreement with the macroscopic test results, which could be employed as the index evaluating the low temperature crack resistance of the warm-mixed SBS modified asphalt mixtures. The addition of warm mixing agent would play a positive role in the low temperature crack resistance of recycled asphalt mixtures with a RAP content of less than 60 % to a certain extent, so warm-mixed recycled asphalt mixtures were more suitable for the application in northern areas.

Study of hot tensile deformation behavior and microstructure characteristics of Zn-22Al microtubes using direct resistance heating-assisted tensile tests

To explore the deformation behavior of Zn-22Al alloy microtubes during hot forming processes with rapid heating, direct resistance heating (RH)-assisted tensile tests using microtubes are introduced based on their quick and easy temperature control. Notably, the large temperature difference of the sample during the RH-assisted tensile tests affected the accuracy of the tensile test results. To perform the RH-assisted tensile tests of the microtubes correctly, the specimens were designed with optimized structures of effective and total lengths of 30 and 60 mm, respectively. Better ductility was observed in the microtube drawn at 200 °C owing to the highly activated grain boundary sliding (GBS) caused by its uniform finer grain structure, greater high-angle grain boundary (HAGB) densities in the close-to-fracture area, and intergranular ductile fracture mode. The primary deformation mechanism of the microtube during hot forming was built based on hot tensile behavior, microstructure, and fracture surface analysis. It was also demonstrated that there is an intrinsic relationship between the temperature distribution, change in the microstructure of different parts, and multiple necking phenomena of the microtube formation process.

Study on Anti-Weathering Protection of Excavated Ancient Stone Arch Bridge with Nano-Composites

After archaeological excavation, the underground ancient bridge has changed from a relatively stable underground environment to a modern environment with a large temperature difference between day and night, long sunshine, changeable climate, rain erosion and serious air pollution. In addition to the need to control the external environment, it is necessary to actively carry out research on anti-weathering materials for stone cultural relics. In this study, five common weathering materials were selected, and three of them were hybridized with nano-silica to obtain nano-composites. Through a series of property tests and anti-weathering ability tests, the comprehensive anti-weathering effect of brick samples coated with anti-weathering protective materials was evaluated. The results showed that the composite of nano-silica-methyltrimethoxysilane hydrolysate showed the best comprehensive anti-weathering ability, which provides a certain reference value for the protection of similar masonry cultural relics.

Amine-functionalized MIL-101(Cr) fibers for direct air capture at cold temperatures using rapid temperature vacuum swing adsorption

Given that most of the world shows annual temperatures lower than 25 °C and some regions exhibit a large diurnal temperature difference in a single day, it is desirable to explore the CO2 sorption behavior of materials not only at ambient (25 °C) but also at cooler, “sub-ambient” conditions (defined here as < 25 °C). These cold temperatures may offer advantages for DAC such as higher gas adsorption capacities and lower absolute humidity, reducing concomitant water adsorption. Here, amine-functionalized MIL-101(Cr) fibers are evaluated at cold temperatures using rapid temperature vacuum swing adsorption (RTVSA). MIL-101(Cr)/cellulose acetate fibers loaded with macromolecular amines are evaluated as practical gas–solid contactors. As spun MIL-101(Cr) fibers show desirable properties for use as structured contactors such as high permeance and low pressure drop. Breakthrough and RTVSA experiments are conducted in the presence of humidity at sub-ambient temperatures to understand the CO2 adsorption and desorption behavior of the sorbent/contactor under conditions approaching practical operation. With optimized amine loading, the PEI-MIL-101(Cr) fibers give CO2 capacities comparable to the powder form of the sorbent, as well as sharp breakthrough curves at fast flow rates (1.4 m/s superficial velocity) suggesting the system is not limited by additional mass transfer resistances under the tested conditions. RTVSA shows fast desorption kinetics (14.4 mmol of CO2/g of fiber/h) at moderate desorption conditions, at 0.1 bar vacuum with temperatures below 80 °C. The entire cycle during RTVSA finishes in ∼ 25 min with ∼ 76 mol% CO2 purity as the product in this initial, modestly optimized study.

Convective heat transportation in exponentially stratified Casson fluid flow over an inclined sheet with viscous dissipation

There are numerous applications related to engineering and industrial manufacturing and processing in which the boundary-driven hydromagnetic flow of non-Newtonian fluids play a vital role. Examples includes glass fiber, electronic devices, paper production, medical equipment, filaments, polymer sheets and medicine. Researchers investigated the heat transportation in fluid flows with linear stratification. However, linear stratification fails when there exists large temperature difference between different bodies. Owing to such facts, here our aim is to explore the features of convective heat model in Casson fluid flow with inclined magnetic field with exponential stratification deformed by linearly stretchable inclined sheet. Characteristics of heat transportations are formulated and investigated through viscous dissipation and heat generation. The reduced non-linear governing expressions are solved analytically by homotopic technique. Analysis of velocity and temperature are comprehensively demonstrated through graphs. Further, rate of heat transfer and drag force are computed graphically via various parameters. It is concluded that inclination and magnetic parameters diminish the flow velocity gradually. Further, temperature field intensifies when Biot number is enlarged while it decays with increasing thermal stratification. It is hoped that the present study will help us to form the homogeneous mixtures of fluids at industrial and biomedical levels especially in food liquids, medical syrups, and medicines.

Effect of flow maldistribution on heat transfer performance and temperature field of plate-fin heat exchangers

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.

A Review on Thermal Modelling of Residual Stresses during Additive Manufacturing

Additive Manufacturing (AM) has received interest since it is simpler to manufacture complicated 3D component without the requirement for casting moulds than convective fabrication. AM has a lot of significance in fields like aerospace, medicine, and more to make parts of any kind of complex shape. Since the finished products are subjected to repeated cycles of heating and cooling, there will always be some residual stresses present in them. During layer-over-layer deposition, the large difference in temperature between the layers causes residual stresses, which hurt the performance of the products. As far as the author’s knowledge, there is no thorough review of the thermal modelling of residual stress in AM. In this review paper, the goal is to first get a good understanding of how residual stresses are developed, and then to look at how different models measure them. So, residual stresses can be seen as a key factor in controlling costs, performance, and quality standards of the finished component. This paper does a thorough review of the field to give engineers and researchers up-to-date information and advice about residual stresses.

A new heat and cold storage system to enhance the thermal autonomy of residential buildings

We integrated 18 kg of PCM in 80 cells of a plate heat exchanger which were placed between a water charge and an air discharge circuit fed by the air renewal. The 0.1 m3 thermal battery can replace radiators to heat and cool, store heat and cold and perform air renewal independently for each room. The narrow PCM cells and the relatively large temperature difference between the PCM with fusion temperature of 25°C and the renewed air allowed to achieve average discharge powers of 300W and 440W for heating and cooling respectively. The integrated total heat and cold storage capacities were found to be 1.5 kWh and 1.8 kWh respectively. By replacing each radiator of a house with such a battery substantial thermal storage can be achieved. The liquid thermal battery, cooled with outdoor air of 17°C, completely solidified in less than 7h. This means that cool summer nights can charge the PCM to cool the room the following day.

Monitoring Soil-Pile Stripping Damage at Different Temperatures via Piezoelectric Ceramic Sensors

Large temperature differences exist between the winter and summer seasons in different regions of China. Such temperature differences, caused by seasonal changes, may affect the life cycles of piles. Under natural conditions, such as long-term operation under the ambient environment and loads, piles and the surrounding soil undergo peel damage. To study such peel damage between the pile and soil at different temperatures, we installed concrete test piles in soil and subjected them to different temperatures. A crack with a width of 2 cm, depth of 10 cm, and damage range of 90° was applied at the side of the piles. Furthermore, a horizontal impact load was applied near the top of the pile and a piezoelectric ceramic sensor was used to obtain the stress wave response signals. The experimental results reveal that with a decrease in the soil temperature, the amplitude and fluctuation range of the signals received by the piezoelectric sensor decreased. According to the experimental results, in the group with the greatest influence of temperature, keeping other conditions unchanged and setting different crack depths, the horizontal impact load can also be introduced to observe the frequency change. It can be observed that the larger the crack depth, the smaller the frequency. Finally, ABAQUS was used for simulations, whose results were found to be consistent with those of the experiments. This paper describes a method for determining the safety of soil and piles with peel damage at different temperatures, and it also provides a validation of the necessity of holding the rest constant.