Heat Insulation Effect Research Articles

Transparent Photochromic Coatings for Smart Windows and Information Storage

AbstractOrganic–inorganic composite photochromic coatings receive significant attention in energy utilization and conservation due to their easy application and rapid photoresponse. However, their high sensitivity to moisture limits practical applications. This study fabricates organic–inorganic composite functional coatings using a simple one‐pot method, producing materials with excellent photoresponsive, water resistance, and thermal insulation. Unmodified phosphotungstic acid serves as the inorganic photochromic filler, while methacrylate derivatives act as the polymer matrix, resulting in coatings with high initial transparency (over 85%). After 5 min of UV exposure, the samples shift to nearly non‐transmittable states in the visible range and maintain color depth through 14 coloring‐erasing cycles. Unlike polyvinylpyrrolidone substrates, which absorb moisture and soften quickly, this coating has a static water contact angle of up to 91.7°, showing excellent water resistance. Additionally, the composite material provides effective heat insulation in simulated chamber experiments, lowering the temperature by 15 °C compared to untreated chambers. In summary, this composite coating, with its excellent thermal insulation, rapid light responsiveness, stable cycling performance, and outstanding waterproof capabilities, proves highly suitable for applications such as smart windows, information storage, and building energy efficiency.

A gradient flame retardant strategy to improve the overall performance of polylactic acid/fiber composites

AbstractTo enhance the flame retardant property of fiber‐reinforced polymer composites without adding more flame retardants, we prepared film stacking composites by maintaining a total flame retardant content of 20% and applying a gradient flame retardant strategy. The gradient composites have been designated as 3113FRPLA/F and 1331FRPLA/F, respectively. 3113FRPLA/F is characterized by an augmented concentration of fire‐resistant additives in the surface layer, while 1331FRPLA/F features a reduced content. 20%FRPLA/F is prepared with a homogeneously distributed flame retardant composition. Results derived from LOI test and cone calorimeter test unequivocally demonstrate that 3113FRPLA/F outperforms both 1331FRPLA/F and 20%FRPLA/F in improving flame retardancy. The LOI value of 3113FRPLA/F is 36.1%, exceeding that of 20%FRPLA/F and there is also a reduction in the pk‐HRR compared with 20%FRPLA/F. It is of interest to note that 3113FRPLA/F exhibits the most effective heat insulation properties while 20%FRPLA/F has the worst, which is reflected by the infrared thermal imaging results. It bears mention that the impact strength and tensile strength of 3113FRPLA/F surpasses that of 20%FRPLA/F. In summary, 3113FRPLA/F, characterized by its increased surface concentration of flame retardants, demonstrates the most superior overall performance.Highlights The characteristics of PLA/fiber composites using a gradient strategy were compared. The LOI value of 3113FRPLA/F is 36.1%, exceeding that of 20%FRPLA/F. 3113FRPLA/F has the best heat insulation effect while 20%FRPLA/F has the worst. The impact strength and tensile strength of 3113FRPLA/F surpasses 20%FRPLA/F. Improving the surface flame retardant concentration increases the overall property.

Preparation of P/N/Si‐containing covalent organic framework‐based flame retardants and their application in epoxy resins

AbstractBalancing the enhancement of flame retardancy of epoxy resin while maintaining its mechanical capacities intact poses a significant challenge in the realm of flame‐retardant epoxy resins. To reach the above objectives, a COF‐based synergistic flame retardant with phosphorus, nitrogen, and silicon (PA‐COF@MT) was synthesized using phytic acid (PA), montmorillonite (MT), and covalent organic framework (COF). When PA‐COF@MT was added at 4 wt%, EP/PA‐COF@MT exhibited a reduction of 42.1% in peak heat release rate (PHRR), 45.84% in total heat release (THR), and 59.8% in total smoke production (TSP) compared with the pure EP. LOI increased by 30.5% and UL‐94 tested to V‐0 grade. flame‐retardant index (FRI) value of 3.03, achieving a “good” rating. Fire growth indices and mean effective combustion heat were increased while mechanical properties also improved. These findings suggest that the flame retarding mechanism of PA‐COF@MT is mainly through vapor phase and condensed phase actions. The combined effects of phosphorus, nitrogen, and silicon make the surface of carbon residue solid and dense, resulting in excellent heat insulation and smoke suppression effects. In simple terms, this study provides new insights into COF‐based flame retardants. Combining low‐cost and simple preparation methods, PA‐COF@MT has broad application prospects in flame‐retardant epoxy resin systems.

Study on the thermal characteristics and heat-insulation ability of gel-stabilized foam used for preventing the spontaneous combustion of coal

Gel-stabilized foam serves a critical role in preventing spontaneous combustion of coal by impeding heat transfer from the coal-fire area to adjacent safe areas. To elucidate the thermal characteristics of gel-stabilized foam, the microstructure and heat-transfer characteristics were investigated. The results revealed that gel-stabilized foam was an accumulation system of many stable and closed bubbles, and there was a layer of gel structure on the bubble surface. This gel layer endows the bubbles with exceptional heat-insulation capability by effectively encapsulating air. To further analyze the relationship of heat-transfer characteristics and foam structure parameters, a theoretical thermal-conductivity model was established to revel the thermal characteristics of gel-stabilized foam. Moreover, the experimental tests were conducted to verify the accuracy of theoretical model, and found that the fitting errors were around 8 %, affirming the model's suitability for gel-stabilized foam. Notably, the theoretical model demonstrated that foam's thermal-conductivity was only monotonically related to foam expansion ratios in theory. In addition, the heat-insulation experiments indicated that the heat-transfer rate of foam depended not only on the thermal-conductivity but also on the foam's stability, both of which were affected by the expansion ratio. Hence, the effective heat-insulation time (EHT) was proposed to assess gel-stabilized foam's heat-insulation characteristics. The heat-insulation ability tests results showed that EHT values initially increased and then decreased with rising foam expansion ratios, primarily influenced by the volume of air encapsulated within the foam. Particularly noteworthy were the test results indicating that gel-stabilized foam with an expansion ratio of 10 times and a stacking thickness of at least 15 cm exhibited excellent heat-insulation capability against heat transfer from the spontaneous combustion zones. The research may provide a theoretical foundation and offer guidance for the prospective utilization of gel-stabilized foam in coal mines.

Asphalt pavement heat insulation bonding layer materials: Composition optimization and engineering application

To alleviate the influence of extreme temperature on the service quality and life of asphalt pavement, the heat insulation effect of the pavement bonding layer was endowed, and the composition of the heat insulation bonding layer materials were optimized. The microstructure of heat insulation bonding layer material was revealed, and its optimal spraying amounts was determined. On this basis, the engineering application and service performance monitoring of heat insulation bonding layer materials were carried out. The results show that the curing rate of the heat insulation bonding layer is significantly higher than that of the ordinary emulsified asphalt (OEA) bonding layer. Hollow glass bead (HGB), floating bead (FB), and expanded perlite (EP) bonding layer materials exhibit excellent mechanical strength, and the interlayer bonding strength can reach 0.41 MPa, 0.49 MPa, and 0.49 MPa, respectively. The recommended dosage of HGB, FB, and EP is 15%, 20%, and 20%, respectively, and the spraying amounts of heat insulation bonding layer material is 1.2 kg/m2. The maximum temperature of the test section in July can be reduced by 2.2 °C–3.6 °C, the maximum annual and daily temperature differences can be reduced by 6.2 °C and 2.3°C–4.9 °C, and the rate of temperature changes can be reduced by 37.5%–63.64%.

Treatment of Out-of-Context Buildings During the Restoration of Historical Territories Using Green Structures

There are historical places with out-of-context buildings, often of low quality. To restore the places, destruction requires heavy machines and may cause strong vibrations and excess load on the historical pavement intensifying destruction and ageing. Giving the appearance of historical objects requires expensive decoration. Hiding by living plants is the most perspective way with positive side effects: thermal insulation, passive air-conditioning, solar radiation control, urban heat island prevention, air cleaning and sanitation, carbon sequestration, noise absorption, better rainwater management, increasing biodiversity, etc. The approach is shown in an example of a bank at the historical centre of Byczyna, Poland. As the building is too large, using a context collage is proposed to show the results. The fears of damage to the structures by fungi and attraction of biting insects are debunked using three ways – analysis of the facing state under the greening, estimation of the critical air state around the greening, and by field studies of the relative humidity under the greening. CFD simulation shows a significant heat insulation effect of the greening in the heating period. The problem of penetration of moustaches into the facing can be solved by winding the ampeleous plants on a wooden lathing or a grid.

Recent Mass Balance Anomalies on the Djankuat Glacier, Northern Caucasus

A 54-year-long series of continuous instrumental measurements of mass balance and its main components has already been accumulated at the Djankuat Glacier, which is representative of the Caucasus and the most studied glacier in Russia. The anomalies of these indicators in 2017/2018–2020/2021 were evaluated against an analysis of meteorological reasons that predetermined them. Each of the four balance years under consideration represents a particular anomaly of varying severity. As for conditions of mass income, three years saw accumulation higher than average, and in one year (2018/2019) it approached the norm. As for summer ablation conditions, similarly, in one season (2019) the melting differed from the average only slightly, but in the other three it was much higher. Consequently, in one year (2020/2021) the state of the glacier was close to normal, in another (2017/2018) the budget situation was much more favorable for Djankuat, and in the other two the final losses significantly exceeded the average annual mass loss rate. At the same time, in 2019/2020, an absolute record of ablation since the beginning of monitoring in 1967/1968 was recorded (4360 mm w.e.). Nevertheless, although negative mass balance values continue to be recorded annually, signs of an inevitable slowdown in the rate of glacier degradation in the Caucasus have appeared in the last 4-year-long period: the continued growth of winter snow accumulation overlaps the ongoing intensification of summer melting. The growth of debris cover in terms of area and thickness also affects this mass loss slowdown to some extent. This inhibits ablation, exerting a heat-insulating effect. Because of this, the congruence of mass balance parameters vs. altitude curves is distorted. Also, a tendency toward increasing annual glacier mass turnover was revealed for the last half-century. This fact gradually increases the energy of glaciation and indirectly indicates a weakening of continentality in the climate of the Caucasian highlands.

Fabrication of thermal insulation sodium alginate/SiO2 composite aerogel with superior radiative cooling function for firefighting clothing

Purpose This study aims to evaluate the thermal performance of sodium alginate (SA) aerogel attached to nano SiO2 and its radiative cooling effect on firefighting clothing without environmental pollution. Design/methodology/approach SA/SiO2 aerogel with refractory heat insulation and enhanced radiative cooling performance was fabricated by freeze-drying method, which can be used in firefighting clothing. The microstructure, chemical composition, thermal stability, and thermal emissivity were analyzed using Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analyzer and infrared emissivity measurement instrument. The radiative cooling effect of aerogel was studied using thermal infrared imager and thermocouple. Findings When the addition of SiO2 is 25% of SA, the prepared aerogel has excellent heat insulation and a high radiative cooling effect. Under a clear sky, the temperature of SA/SiO2 aerogel is 9.4°C lower than that of pure SA aerogel and 22.1°C lower than that of the simulated environment. In addition, aerogel has more exceptional heat insulation effect than other common fabrics in the heat insulation performance test. Research limitations/implications SA/SiO2 aerogel has passive radiative cooling function, which can efficaciously economize global energy, and it is paramount to environment-friendly cooling. Practical implications This method could pave the way for high-performance cooling materials designed for firefighting clothing to keep maintain the wearing comfort of firefighters. Originality/value SA/SiO2 aerogel used in firefighting clothing can release heat to the low-temperature outer space in the form of thermal radiation to achieve its own cooling purpose, without additional energy supply. Graphical abstract

The preparation and fire extinguishing mechanism research of a novel high-efficiency KHCO3 @HM dry powder

Hydromagnesite (HM) is a widely distributed primary natural carbonate mineral. To expand the application range of hydromagnesite and tap its fire-extinguishing potential, a new type of high-efficiency KHCO3 @HM dry powder was prepared by coating potassium bicarbonate on the surface of hydromagnesite with a dip coating method. KHCO3 @HM dry powder obtained a chemical inhibition effect through this method, and the fire extinguishing efficiency has been further improved. A series of tests were carried out to confirm the excellent physical and chemical inhibition effect of KHCO3 @HM dry powder. Specific surface area tests showed that the specific surface area of KHCO3 @HM dry powder (31.405 m2/g) was higher than NH4H2PO4 dry powder (12.766 m2/g). Flowability tests showed that KHCO3 @HM dry powder (0.04 g/s) achieved the same flowability as NH4H2PO4 dry powder (0.04 g/s). Local oil basin fire experiments showed that the average fire extinguishing time of KHCO3 @HM dry powder was shorter with less powder consumption. Under 0.2 MPa driving pressure, the fire extinguishing time of KHCO3 @HM dry powder was 2.2 s faster than NH4H2PO4 dry powder, and the dry powder consumption was 3.71 g less than NH4H2PO4 dry powder. The cooling effect of KHCO3 @HM dry powder (208 ℃) in 10 s was better than NH4H2PO4 dry powder (157 ℃), and KHCO3 @HM dry powder (399 ppm) showed a better smoke suppression effect than NH4H2PO4 dry powder (545 ppm). The pyrolysis of KHCO3 @HM dry powder reduced the fire temperature, diluted the oxygen concentration, and captured free radicals. The final pyrolysis products formed a thick oxide film to provide good heat insulation and asphyxiation effects. The excellent cooling, dilution, asphyxiation, and chemical inhibition mechanisms of KHCO3 @HM dry powder were demonstrated, and finally achieved a comprehensive performance comparable to NH4H2PO4 dry powder.

Investigation on the effectiveness of transpiration cooling under the influence of shock wave

As an advanced active cooling method, transpiration cooling can be used for thermal protection of high-temperature wall. The change of cooling effect caused by the incident shock wave on the transpiration cooling boundary layer is sufficient to affect the safe flight of the aircraft. In this paper, the interaction mechanism between shock wave and transpiration cooling is studied based on the thermal equilibrium model. The effects of shock wave incident angle, coolant injection ratio, Mach number of high enthalpy airflow and coolant type on thermal protection effect were studied respectively. Shock wave incidence in the boundary layer of transpiration cooling can cause the change of coolant flow and heat sink distribution in porous media, and cause the fluctuation of fluid parameters in the boundary layer. The temperature inhomogeneity on the porous wall and the inhomogeneity of the total enthalpy difference are markedly affected by the shock wave intensity. The heat insulation effect of the coolant on the solid surface limits the improvement effect of the increase of the injection ratio on the effective heat absorption power. Hydrogen as a coolant can form a better cooling effect and has less resistance to the mainstream.

Anomalous thermal structures of subduction zones revealed by thermal properties of clinochlore at high temperature and pressure

Clinochlore is a major hydrous mineral in subduction zones, and its thermophysical properties at high temperature and pressure are critical to the thermal structures of subduction zones. Here, we used the pulse heating method to measure thermal diffusivity and thermal conductivity of clinochlore at 0.5−4.0 GPa and 298−1373 K. Our results indicate that upon heating, thermal diffusivity and thermal conductivity decrease from ∼9.6 × 10−7 m2 s−1 to 4.3 × 10−7 m2 s−1 and from ∼3.5 W m−1 K−1 to 1.9 W m−1 K−1, respectively, before dehydration, but this trend is reversed after dehydration. In general, the pressure derivatives for the thermal transport properties also decrease with temperature before dehydration. Lattice heat transfer is the dominant mechanism before dehydration, but fluid is involved after dehydration. Using our experimental data, we simulated the temperature distribution of subducting slabs containing clinochlore at volume fractions of 0%, 10%, 20%, 50%, and 100%. Our simulations showed that the heat insulation effect caused by the presence of clinochlore could result in an increase in temperature by 30−60 K for the upper part of the subducting slab.

Low-emissivity interior wall strategy for suppressing overcooling in radiatively cooled buildings in cold environments

Buildings with radiative cooling can significantly reduce energy consumption for cooling, but the overcooling phenomenon also occurs in cold seasons, which causes negative effects in buildings. Herein, a strategy of using low-emissivity interior surfaces to reduce the heat loss from humans to cold walls is proposed to suppress the negative overcooling effect of radiative cooling. Comparative experiments are conducted based on two small-scale boxes with internal heat sources and low/high emissivity interior surfaces. Results show that the heater temperature in the box with the low-emissivity interior surface is higher than that with the high-emissivity surface, with maximum and average temperature differences of 2.3 °C and 1.8 °C, which indicates that the radiative heat insulation effect is achieved for humans by the low-emissivity interior surface. Moreover, large-scale building modeling is performed, which not only confirms the existence of the overcooling phenomenon but also shows over 30% of heat loss can be avoided for internal heat sources by applying low-emissivity interior surfaces under overcooling conditions. Importantly, we found that interior surfaces with low emissivity under cold seasons and high emissivity under hot seasons can fully explore the potential of passive radiative cooling for buildings, which can guide the next-generation material design for energy-saving buildings.

Bioinspired Self-Standing, Self-Floating 3D Solar Evaporators Breaking the Trade-Off between Salt Cycle and Heat Localization for Continuous Seawater Desalination.

Facing the global water shortage challenge, solar-driven desalination is considered a sustainable technology to obtain freshwater from seawater. However, the trade-off between the salt cycle and heat localization of existing solar evaporators (SE) hinders its further practical applications. Here, inspired by water hyacinth, a self-standing and self-floating 3D SE with adiabatic foam particles and aligned water channels is built through a continuous directional freeze-casting technique. With the help of the heat insulation effect of foam particles and the efficient water transport of aligned water channels, this new SE can cut off the heat transfer from the top photothermal area to the bulk water without affecting the water supply, breaking the long-standing trade-off between salt cycle and heat localization of traditional SEs. Additionally, its self-standing and self-floating features can reduce human maintenance. Its large exposure height can increase evaporation area and collect environmental energy, breaking the long-standing limitation of solar-to-vapor efficiency of conventional SEs. With the novel structure employed, an evaporation flux of 2.25kgm-2 h-1 , and apparent solar-to-vapor efficiency of 136.7% are achieved under 1sun illumination. This work demonstrates a new evaporator structure, and also provides a key insight into the structural design of next-generation salt-tolerant and high-efficiency SEs.

Analyses of non-aqueous reactive polymer insulation layer in high geothermal tunnel

The scenario of geothermal tunnel is commonly observed around the world, and increases with the new constructions in the long and deep tunnels, for example in China. Tunnel insulation is generally divided into active and passive insulation. In passive insulation, it is an effective way to set low thermal conductivity materials as the thermal insulation layer as the choice of insulation material mainly depends on the thermal conductivity. Polymer is a kind of material with good geothermal performance, but there are relatively few studies. In this context, the transient plane source (TPS) method was used to measure the thermal conductivity of the developed polymer. Then, the temperature field of the high geothermal tunnel insulated by the non-aqueous reactive polymer layer was simulated. With the parametric analysis results, the suggestions for the tunnel layers were proposed accordingly. It revealed that the thermal conductivity of polymer first increases and then decreases with temperature. There are two rising sections (-40–10 °C and 20–90 °C), one flat section (10–20 °C) and one descending section (>90 °C). It is observed the thermal conductivity of polymer increases with increase of the density of insulation layer and the density, and the thermal conductivity decreases when exposed to high temperatures. The temperature of the surrounding rocks increases with increase of the thermal conductivity and the thickness of polymer. Finally, a more economical thickness (5 cm) was proposed. Based on the parametric study, a thermal insulation layer with thermal conductivity less than 0.045 W/(m K), thickness of 5 cm and a density less than 0.12 g/cm 3 is suggested for practice. • The non-aqueous reactive polymer can be applied in high geothermal tunnel with good insulation performance. • The parameters (i.e., thermal conductivity, thickness and density) on the tunnel temperature field have been analyzed. • Reasonable parameters for polymer insulation layer in practice were suggested for tunnel engineering. • When the thermal conductivity is lower than 0.045 W/(m·K), the heat insulation effect is the most significant. • When thickness is about 5 cm, the polymer layer shows best heat insulation performance.

Numerical simulation of temperature field of CRTS III ballastless track with Tarmac in Harbin area

The three-dimensional transient thermal analysis technology of ABAQUS is used to analyze the temperature field and temperature stress characteristics of CRTS Ⅲ ballastless track with thin layer of asphalt concrete under the typical climatic conditions of summer and winter in seasonal freezing area due to the influence of heat transfer such as solar radiation, wind speed and temperature amplitude. The results show that the temperature distribution of track structure is nonlinear along the vertical direction, and there is a lag phenomenon; After adding asphalt concrete layer, the temperature of Subgrade under the layer is reduced, which has a good heat insulation effect; Asphalt concrete layer is more prone to interlayer damage in winter than in summer.

Fire Resistance Test and Numerical Simulation on the Tube Structure of Steel–Concrete–Steel Immersed Tube Tunnel

To provide references for the fire prevention design of steel–concrete–steel immersed tube tunnels, four types of test conditions—no fire protection, fireproof coating insulation, single-layer seam fireproof boards, and double-layer seam fireproof boards—were carried out using partial full-size structural test members. Additionally, the thermal insulation effects of various fireproofing technology solutions were contrasted and analyzed. Combined with the numerical simulation analysis, the temperature distribution law inside the tube structure under various fireproofing measures and the temperature rise law of measuring points at different depths were studied, and the protective effect of the fireproof layers on the tube structure under high fire temperature was demonstrated. The results of the numerical simulation and the experimental data agree well. The results show that adding fireproof layers can significantly lower both the steel shell’s surface temperature and the depth of fire impact. Without fire protection, the surface temperature of the bottom steel shell exceeds 300 °C at 69 s, and the member bursts. The fireproof coatings are cracked and flaking and cannot meet the fire resistance limits. Both single-seam and double-seam schemes of calcium silicate boards can meet the fire resistance limit requirements and the latter has a better heat insulation effect.

Numerical Investigation of the Initial Charging Process of the Liquid Hydrogen Tank for Vehicles

Liquid hydrogen has been studied for use in vehicles. However, during the charging process, liquid hydrogen is lost as gas. Therefore, it is necessary to estimate and reduce this loss and simulate the charging process. In this study, the initial charging process of a vehicle liquid hydrogen tank under room temperature and atmospheric pressure conditions was numerically investigated. A transient thermal-fluid simulation with a phase-change model was performed to analyze variations in the volume, pressure, mass flow rate, and temperature. The results showed that the process could be divided into three stages. In the first stage, liquid hydrogen was actively vaporized at the inner wall surface of the storage tank. The pressure increased rapidly, and liquid droplets were discharged into the vent pipe during the second stage. In the third stage, the mass flow rates of liquid and hydrogen gas at the outlet showed significant fluctuations, owing to complex momentum generated by the evaporation and charging flow. The temperatures of the inner and outer walls, and insulation layer, decreased significantly slower than that of the gas region because of its high heat capacity and insulation effect. The optimal structure should be further studied because the vortex, stagnation, and non-uniform cooling of the wall occurred near the inlet and outlet pipes.

A comparative study of the effect of multidimensional carbon fillers on polystyrene using supercritical carbon dioxide foaming

Due to its low thermal conductivity on average (~0.039 W/(m·K)), supercritical expanded polystyrene (PS) foam could be used as an insulation material in buildings to save energy and minimize the maintenance costs. However, the specific solubilizing and fast diffusing behavior of CO 2 in PS limited the formation of micropores and the further increase of macropores, which resulted in on limited decrease in thermal conductivity. In this study, one-dimensional carbon nanotubes, two-dimensional graphene, and three-dimensional activated carbon were loaded on PS using supercritical CO 2 foaming. The results demonstrated that all these three carbon nanomaterials doped on PS could generate more micropores and macropores during foaming. Moreover, the composite PS foams presented much lower specific thermal conductivity (0.360 cm 3 ·W/(g·m·K)), higher cell density (up to 3.23 × 10 14 cell/cm 3 ), and compressive modulus (up to 1.66 MPa), overwhelming those of pure PS. Particularly, the continuous infrared thermography measurements found that two-dimensional graphene thermally outperformed the others, meaning comparatively better heat insulation effect after foaming. Therefore, multidimensional carbon nanomaterials were promising to minimize the negative environmental impact of PS foaming while comprehensively reinforcing it. • The reinforcements of multidimensional carbon fillers on polystyrene were varied. • Graphene thermally/physically outperformed carbon nanotubes and activated carbon. • Improved coupling of its plasmon with phonon-polariton thermally enhanced graphene. • Carbon nanomaterials are comprehensively better fillers for polystyrene.

Thermal performance analysis of hollow cellular concrete block air convection embankment for cold regions

Crushed-rock air convection embankment (ACE) is an excellent passive cooling technique that uses open-graded crushed rocks as a “thermal semi-conductor” to prevent roadbeds from thawing in summer and enhance the cooling effect in winter in permafrost regions. However, the desired crushed rocks needed for ACE are not readily available in interior Alaska, resulting in extremely high construction costs. Previous studies indicated that using the cost-effective cellular concrete for ACE could effectively enhance the cooling performance of ACE and mitigate moisture warping and temperature curling of the asphalt concrete layer. It is promising to be an alternative to crushed rocks for ACE to mitigate pavement distresses. However, the design of cellular concrete ACE needs to be further studied to maximize performance and facilitate future implementation. Hence, two design configurations of cellular concrete block ACEs were proposed in this study. The thermal performance of pavement structures with these two designs was investigated by comparing them with the other four. A total of six pavement structures were analyzed, including a typical flexible pavement in the Northern Region of Alaska and five pavement structures reinforced with different paving interlayers, i.e., silty sand/gravel, crushed rocks, cast-in-place cellular concrete (full insulation), and two types of precast cellular concrete blocks. The thermal profiles, air pressure gradients, and velocities were numerically analyzed in ANSYS Fluent. The numerical results indicated that the two proposed cellular concrete ACEs exhibited a significant heat insulation effect in summer and a desired cooling effect in winter, which raised the permafrost table significantly. The maximum thaw depth of the two proposed cellular concrete ACEs was only 15% of the thaw depth of traditional silty sand/gravel embankment.

Experimental and numerical study on heat emission characteristics of ventilated air annular in tunneling roadway

With the increase in mining depth, thermal hazard becomes a prominent problem. Reducing heat dissipation of the surrounding rocks on the basis of artificial refrigeration can be an important thermal hazard-control technique. There are several researches on spray and surrounding rock-filling insulations, but only a few researches were conducted on air jacket heat insulation performance. To enrich the research content of air jacket heat insulation, a similar experiment platform was designed. Based on the analysis of the test data, the friction factor for the turbulent flow in the interlayer of air annular is obtained and a modified equation for calculating the friction factor is proposed based on the Blasius equation model. The average Nusselt number of the inner and outer wall surfaces in the annular air of roadway is calculated under turbulent state, and the Gnielinski equation is modified based on the experimental results. Based on the finite volume method, the unsteady mathematical model of the heat dissipation structure of ventilated air annular with surrounding rock was established. A computer program was developed, and the accuracy of the mathematical model was verified using experimental results. The numerical calculation results were used to analyze the variations of heat absorption of airflow in the main roadway and heat exhaust of the ventilated air annular at different wind speeds and annular diameters. The results show that the heat insulation effect of interlayer of ventilated air is the best when the air flow in the annular is at the turning point of laminar flow turbulence. The heat insulation effect of ventilated air interlayer is the best in the early ventilation stage, and the heat insulation rate will decrease with the increase of ventilation time, but the heat insulation rate can reach more than 69.7% in 10 years.