Air Interlayer Research Articles

Thermal performance analysis and optimization of air-supported membrane building envelope based on numerical simulation

Air-supported membrane (ASM) envelopes offer an effective solution for creating large interior spaces for buildings with lower energy consumption and carbon emissions. However, there is little research on the thermal performance of ASM envelopes, particularly regarding the natural convection within the air interlayer and its impact on thermal resistance. To address this gap, this study developed a numerical model of ASM envelopes and validated it through experiments. Subsequently, a numerical investigation was conducted to analyze natural convection and thermal resistance while considering factors such as indoor-outdoor temperature difference, membrane emissivity and air interlayer thickness. Results indicated that with the emissivity increased from 0.2 to 1, the thermal resistance of the air interlayer and the envelope decreased by 32.35% and 9.13%, respectively. Besides, the thickness of air interlayer also had evident effect on thermal resistance. When it increased from 5 mm to 35 mm, the thermal resistance of the air interlayer and the envelope increased by 156.19% and 14.74%, and further results in the heat transfer decreased by 13.85%. However, the convective heat transfer would remain constant when the thickness exceeded 35 mm. This study provided valuable reference for optimizing the design of ASM envelopes and accurately calculating their thermal resistance.

Study of heat transfer in heated garments based on the JOS-3 model

Abstract Body temperature prediction and control are important in cold environments or extreme temperatures. In this paper, a multi-segmented heated garment model based on J0S-3 thermoregulation is proposed, and the effects of multi-layer garments and air interlayers on human heat transfer are explored, as well as the role of heating pads in the heat transfer path. By comparison, the simulation results of the present study were found to align with the temperature change curves observed in available experimental data. Moreover, the root mean square of the overall core temperature and the root mean square of the skin temperature were both below 0.08°C and 0.36°C, respectively, which provided good prediction results. This study helps people to adapt to the environment with variable temperatures and has a great potential for development in body temperature prediction technology and application.

Optimization and Renovation Design of Indoor Thermal Environment in Traditional Houses in Northeast Sichuan (China)—A Case Study of a Three-Section Courtyard House

The three-section courtyard is the most representative traditional residence in the traditional villages in northeast Sichuan. As a unique cultural landscape, it carries the local historical style and cultural connotation. However, the high temperature weather in summer leads to a poor thermal environment in traditional residential buildings, which cannot meet the needs of building users for human thermal comfort, and the wall is the most critical factor affecting the indoor thermal environment. Therefore, to optimise the indoor thermal environment of traditional residential buildings, this study designed four groups of wall renovation schemes according to the original traditional residential buildings and modern technology, and simulated and verified the feasibility of the building renovation schemes by using Design Builder. Then, the four groups of wall renovation schemes were compared and tested based on the Design Builder. Comparative results of the thermal-performance evaluation index revealed that compared with Case 1 and Case 2, the building refrigeration energy consumption of Case 3 in the hottest week was the least, only 427.7 kW·h, which indicates that the external wall renovation scheme using aerated concrete blocks had the best thermal insulation and energy-saving effects. The cooling energy consumption of Case 4 in the hottest week was 422 kW·h, which was 4.3 kW·h less than that of Case 3, indicating that the wall renovation scheme with an air inter-layer had better thermal insulation and energy-saving effects. The refrigeration energy consumption of Case 7 in the hottest week was only 409.8 kW·h, which was 4.19% lower than Case 3 (without insulation material), indicating that the scheme of selecting central insulation and extruded polystyrene board (XPS) had better thermal insulation and energy-saving effects in practical projects. In summary, the above transformation scheme not only improves the indoor thermal environment of traditional residential buildings, but also provides guidance for architectural designers on green, energy-saving and sustainable design.

Development of models and analysis of temperature fields of new energy-saving enclosing structures with an air layer

The author of the article propose new models of energy-saving envelope structures with air interlayers. To calculate the temperature fields in the enclosing structures they used the finite element modeling method in ANSYS environment. The authors analyzed the temperature fields at different variants of the outdoor temperature index. To calculate the temperature field in the envelope was used finite element model of the envelope, in which the influence of the ventilated air layer is replaced by the Convection type boundary condition with the temperature value. The result of the study is the analysis of temperature fields of new models of enclosures in different variants. So when analyzing the values of thermal resistance of traditional (scheme-1) and developed envelope structures (schemes 2-4) it was found that the thermal resistance of scheme-2 relative to the traditional scheme-1 value of thermal resistance at minimum temperature is 6.2 % higher. The authors also calculated by analogy the thermal resistance index at maximum temperature (4.5 %), at five days (5.8 %) and for the month of April (5.7 %). The analysis showed that scheme-2 is the most efficient of the new envelope schemes considered. In the comparative analysis of schemes - 3,4 with traditional scheme-1, the value of thermal resistance showed a negative effect. The authors determined that the temperature field is insignificantly different when using horizontal and vertical closed channels. The developed new energy-saving designs of external enclosure with air layer can be used in the design and construction of buildings, as well as in the teaching of relevant disciplines in universities.

Superhydrophobic zinc oxide/epoxy coating prepared by a one-step approach for corrosion protection of carbon steel

Corrosion in carbon steel (CS) has been an existing issue and it calls attention to the need for improved corrosion protection. At present, superhydrophobic (SHB) coating technology has piqued the interest of researchers as alternative means of mitigating metal corrosion. Herein, a one-step solution deposition process was used to prepare an SHB coating based on nano-zinc oxide/epoxy (ZnO/EP) on CS and its corrosion resistance performance was analyzed by the means of electrochemical analysis and compared with that of the blank CS metal and the regular coatings (plain EP and regular ZnO/EP). Results implied the as-prepared SHB coating shows remarkable improvement in corrosion protection for the substrate. Notably, it exhibited higher in both impedance modulus (|Z|) and coating resistance (Rc) results approaching 1010 Ωcm2, than those of regular coatings by 3 orders of magnitude to that of plain EP (∼107 Ω cm2), and 1 order of magnitude to regular coating (∼109 Ω cm2), indicating its superior corrosion resistance performance. Besides that, the superior inhibitive effect of the SHB ZnO/EP (ZES) is also proven by the potentiodynamic polarization (PDP) results, in which the Icorr value is suppressed down to 2.08 × 10−11 A/cm2, thereby achieving an excellent corrosion rate result of 3.38 × 10−11 mm/year. The exceptional barrier protection is ascribed to the presence of a stabilized air interlayer captured within the coating/electrolyte interface thus effectively blocking the penetration of electrolyte into the coating. This facile yet effective one-step processed SHB coating offers an effective route to improve the corrosion resistance performance of the CS metal and thereafter expand its potential applications.

Thermal performance of concrete masonry units containing insulation and phase change material

The stationary thermal performance requirements of building energy codes are mainly met by compounding insulation materials in building envelope or adding air interlayers. However, with the transformation of building envelope to lightweight and hollow, its thermal capacity value decreases significantly, which causes the indoor thermal environment to fluctuate with the outdoor space. The introduction of phase change materials is a potential solution to improve the transient performance. However, since the thermal properties of phase change materials vary with several environmental factors, it is a complex problem to rationalize the use of phase change materials, including their location in enclosures, the selection of types, quantities, and how to couple with insulation materials, so that the enclosures can achieve high stationary and transient performance simultaneously. In this study, a thermal environment simulator was built for the investigation of a series of triple concrete masonry unit blocks (bricks) equipped with insulation materials or/and phase change materials using dynamic testing method. The experiments were conducted under three typical boundary conditions reflecting different orientations of walls. A complete specification of the thermal performance of the walls with different configurations is summarized. It is found that the performance of insulation materials is stable, while the performance of phase change materials is influenced by the type and quantity of materials, indoor and outdoor temperatures, and the location in envelope. Phase change materials can show much higher thermal performance than insulation materials if under appropriate conditions. A series of construction optimization cases that can significantly improve the thermal performance of envelope are summarized, and general construction principles for envelopes with high thermal performance are given. From the influence laws of thermal performance to the improvement measures and the general rules of envelope configuration, this study provides the theoretical basis, optimization cases, and guidance rules for thermal applications of insulation-phase change building envelopes.

Thermophysical indicators of elaborated sandwich cladding constructions with heat-reflective coverings and air gaps

In this paper, an experimental study of the thermophysical processes occurring in the developed two new structures of external fencing with the use of heat-reflecting screens in comparison with the traditional one is carried out. The results of the study showed that the use of air interlayers and heat-reflecting screens in the design leads to a significant increase in the value of heat transfer resistance by 3.4% in cases with horizontal channels and by 17.7% in the presence of a conventional interlayer with heat-reflecting screens. At the same time, during the experimental studies, it was also found that, unlike the traditional design of the external fence, both models of wall fencing with air layers and heat-reflecting screens developed showed a positive effect in terms of the heat flow value by 52.5% and 51.8%, respectively. Thus, the study experimentally confirmed the effectiveness of the developed new structures of external fencing, and the results of the study can be used in the design and construction of buildings in order to reduce heat consumption and energy saving.

Heat and mass transfer analysis and optimization of passive interfacial solar still

Due to the fast thermal response and high solar energy efficiency, the passive interfacial solar still has become a reliable scheme for distributed water supply. In this paper, the thermodynamic performance of the interfacial solar still under different structures and operating conditions is studied experimentally, which provides an optimization direction for strengthening the distillation process. Firstly, based on the different Ra numbers, the calculation correlations for diffusion and convective mass transfer in the air interlayer were established to accurately predict the thermodynamic model of the interfacial distillation process. Then, the temperature distribution of the condenser and the growth process of condensate droplets were analyzed with the constant evaporation temperature. Simultaneously, the influence of different condensing structures and external variables on the heat transfer performance was compared. The results show that the interfacial still could obtain maximum evaporation heat under the vertical operation condition. When the evaporation temperature is 70 °C, the temperature difference between the wick evaporator and condenser can be increased by 49.5 %, after coupling a finned condenser with the aspect ratio of 7.2. In addition, a narrower interlayer spacing and a larger evaporation temperature could bring a higher equivalent heat transfer rate and evaporation efficiency. In a sunny weather, the interfacial solar still coupled with an extended condenser can reach a 4.81 kg/m2/day water yield and a 0.486 daily gained output ratio under 1 cm interlayer spacing.

Onset of Penetrative Convection in a Multilayered Heat-generating Porous System with Thin Air Interlayers

Onset of Penetrative Convection in a Multilayered Heat-generating Porous System with Thin Air Interlayers

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.

Coupled heat and moisture transfer in walls featuring moisture-buffering materials and ventilating layers: An Experimental study

The moisture performance of building envelopes largely depends on the building materials, construction techniques, and exposure loads from the indoor and outdoor regions. A ventilated air interlayer placed in a wall can help dehumidify the wall and indoor air. This paper presents an experimental study of the heat, air, and moisture variations within the envelope wall of a chamber featuring different air interlayer settings under real outdoor air conditions during the summer of 2020 in Shanghai, China. Self-developed humidity-controlling building materials were applied to the inner building envelope. Temperature, humidity, wind velocity, and heat-flow sensors were placed at different positions in the middle of the wall. These parameters were measured and recorded in real-time under three working conditions: humidification, dehumidification, and ventilation. The experimental results show that under the ventilation working conditions, moisture content of 0.52 kg can be removed after a 2-h air layer ventilation, which can benefit the design strategy for the humidification and ventilation of dehumidification walls.

NEW APPROACHES TO THERMAL CALCULATIONS OF VENTILATED CLOTHING

It is shown that the existing mathematical models of heat transfer do not fully take into account the real shape and dimensions of the air layers of ventilated clothing. A numerical modelling method is proposed that takes into account the influence of the morphology of the human body and the physical and mechanical properties of textile materials on the size and shape of the air gap. Peculiarities of convective processes in the air interlayers of ventilated clothing at the ambient temperature of +27 °C are revealed by the calcula-tions. The zones of intensification and deceleration of the air flow under the clothes were revealed. It is shown that the results of calculations are consistent with the results of experimental studies.

A New Model for Analysis of the Shielding Effectiveness of Multilayer Infinite Metal Meshes in a Wide Frequency Range

A new analytical model for the calculation of the shielding effectiveness of multilayer infinite metal meshes is proposed. This model is based on the previously developed one for single- and double-layer metal shielding grids. It enables accurate and fast calculations of the shielding effectiveness of multilayer metal meshes with different air interlayers in a wide frequency range. The proposed model considers the ratio of the wire diameter to the aperture size and the layer interspacing. The model is validated by comparison of the results of calculations with the HFSS simulation results. The model validity in a wide frequency range as well as its calculation speed far bigger than that for HFSS is demonstrated. The results of calculations show that the shielding effectiveness of metal meshes can be effectively improved by increasing the distance between the mesh layers and the ratio of the wire diameter to the aperture size.

The onset of penetrative convection in a three-layered porous–air–porous system with internal heat source

The study is devoted to a linear stability problem for a system of two horizontal porous sublayers separated by an air interlayer under the influence of the gravity field. The porous sublayers are capable of generating heat with a constant volumetric strength of heat source proportional to the solid volume fraction. Equal temperatures are maintained at the external boundaries of the three-layered system. The onset value for internal convection is numerically determined in the limiting case of a thin air sublayer. The critical wave number is also found, upon reaching which the equilibrium stability is lost in the system, and convective patterns begin to arise. The influence on the convective stability of the ratio of the permeabilities of the layers, the relative thickness of the lower porous sublayer, and the parameter of the air interlayer is analyzed. This parameter is the ratio of the air sublayer thickness raised to the third power to the Darcy number. New results are obtained that take into account the localization of the convective flow. It is shown that the permeability ratio can both destabilize and stabilize the motionless state. An increase in the interlayer parameter unambiguously reduces the convection onset value. A map for the local and large-scale convective regimes has been constructed in the coordinates of permeability ratio versus the air interlayer parameter. A demarcation line of the transition from one regime to another on the map corresponds to the parameters at which the critical internal Rayleigh–Darcy numbers for the two minima of the bimodal neutral curve have equal values. One of the minima belongs to the region of small wave numbers (a long-wave minimum) and defines the onset value for large-scale convection, and the other one is in the region of large wave numbers (a short-wave minimum) and indicates the onset value for local convection. It is shown that with an increase in the air interlayer parameter, the ratio of permeability required for a transition from large-scale to local convective regimes decreases.

Parametric Analysis of a Novel Photovoltaic/Thermal System Using Amorphous Silicon Cells and Micro-Channel Loop Heat Pipes

Photovoltaic/thermal (PV/T) systems are taking up an increasing market share owing to a high overall solar energy efficiency. An innovative PV/T system that combines amorphous silicon cells and micro-channel loop heat pipes is proposed in this paper. It can overcome problems of large thermal stress at fluctuating temperature and frosting in winter which exist in conventional PV/Ts using crystalline silicon cells and copper tube heat exchangers. A distributed parameter model is built and experimental validation on heat transfer and electricity generation is conducted. The parametric influences of thickness of air interlayer, cover factor, number of MCHPs, area of condenser are investigated. The results indicate that the overall energy efficiency increases from 22.30% to 47.61% as the thickness of air interlayer rises from 0 to 15 mm. A number of MCHPs of 8–14 and length of condenser of 4–6 m are recommended for the sake of cost-effectiveness, and the corresponding thermal and electrical efficiencies are about 47% and 6%. The proposed PV/T system can efficiently harness solar heat with a minor impact on electricity output and has significant potential in the medium temperature applications.

Study on heat transfer characteristics of hollow composite thermal barrier structure at high temperature

Air interlayers are often used as a part of thermal insulation structure and form a system with solid materials to reduce heat transfer. However, the heat transfer process in the composite structure is affected by many factors at high temperatures. In this paper, a series of heat preservation systems with air gap and solid structure were proposed. Based on the research background of heat preservation in the riser of ingot casting, the heat transfer process in the composite structure was systematically studied by means of numerical simulation and experiment. The heat transfer laws under different geometric structures, thermophysical properties of materials, and surface emissivity were obtained, which could provide theoretical basis for the design of heat preservation structures at high temperatures.

Retrospective analysis of a multi-stage experiment on developing high-performance insulation panels to sustain jet impingement at high temperatures

Over the years, numerous insulation panels have been developed to reduce heat transfer and meet the growing requirements imposed by industries. For a panel, the topology of the core can be delicately designed while novel and advanced materials are put into use. However, in the shipbuilding industry, the development of high-performance insulation panels using low-cost or cost-effective materials is still in great demand. A four-stage experimental study was conducted to develop high-temperature-proof panels without major thermal bridges caused by fastening methods for ships. A specimen chamber matching setup was used to test 36 panels based on nine designs with three commonly found core materials, i.e., polycrystalline filaments (PF), silica aerogel (SA), and aluminum silicate, under an impinging jet at temperatures ranging from 500 to 585 °C for 30 min. Besides analyzing overall heat transfer coefficient (U), heat flux (q), and Fourier number (Fo) for all panels, a method was proposed to estimate thermal diffusivity at testing temperatures (α) based on the Levenberg–Marquardt algorithm and an analytical model of heat conduction. Major conclusions include the following: First, thermal properties varied among the eligible panels: U: 0.4–1.43 W·m−2·°C−1; q: 100–318 W/m2; α: 6.0 × 10–8–1.3 × 10–6 m2/s; and Fo: 0.07–0.35. Second, because the improvement of thermal performance by adding an air interlayer was not significant, traditional panel designs with internal insulation were preferable. Third, by balancing thermal performance and economic and practical considerations, panels with SA or PF core and fastened by in-core battens were recommended for large-scale industrial applications, and it would be more cost-effective to use PF core.

Unbound water in mechanochemical reactions of brown coal.

Mechanochemical activation of coal is commonly employed in industry. However, even the simplest solid-phase reactions, such as neutralization of humic acids in brown coal, remain insufficiently studied. The hypothesis regarding the occurrence of mechanochemical neutralization under local hydrothermal conditions for humic acids in brown coal has been tested in this study. 3D modelling of the “block–interlayer” system (where coal particles are separated by air interlayers saturated with water vapor) was used. The 3D model showed that the permittivity is expected to rise from 14 to 16% as the moisture content in the system increases from 12 to 15%. The actual permittivities of coal with different moisture contents have been measured by dielectric spectroscopy. In the real system, the permittivity increases more than threefold as the moisture content rises from 12 to 15%. This increase is much greater than the calculated one, demonstrating that the phase containing unbound water appears in the system at a moisture content of ∼12–13% and may exert various effects on the solid-phase reaction. There is a correlation between the moisture content, permittivity, and predominant mechanisms of the reaction between the organic matter in brown coal and sodium percarbonate (a reagent simultaneously containing the alkaline and peroxidic components). The reactions between brown coal and alkaline reagents proceed under local hydrothermal conditions. Both the alkaline and peroxidic components of sodium percarbonate participate in the solid-phase reaction between brown coal and sodium percarbonate. The emergence of unbound water in coal significantly inhibits the oxidation reaction.

Experimental investigation on thermal insulation performance of air interlayer under an impinging jet at high temperature

Air interlayers are widely used in building envelope to reduce heat transfer between indoor and outdoor environments. However, it is less common to apply to industrial processes in confined spaces, especially when the heating source is at high temperature with high velocity. In this paper, a special structure with air interlayer between two plates for thermal insulation was derived from an industrial manufacturing application. The effects of the interlayer on heat transfer was investigated under an impinging jet at high temperature. An experimental mock-up was designed to produce high temperature (∼ 500 °C) impinging gas jet with relative stable high velocity (∼56 m/s) at the nozzle exit. The impingement surface of the test structure was covered with a 2mm thick stainless-steel plate at a distance of 5mm, which formed a horizontal air insulation layer. Benchmark test was also conducted after the removal of the stainless-steel layer. In each case, a standard procedure within a duration of 30 min was applied to minimize the variations of testing conditions. The temperatures at both inner and outer surfaces of the structure, as well as the temperatures from inside and outside the air interlayer, were measured by thermocouples. In addition, an analytical model to account for the effects of air insulation was proposed to compared with experiments. The results showed that, the air interlayer can reduce the highest temperatures for about 48 °C. The temperature difference at the end of the experiment was about 30 °C. The analytical model was in good agreement with the experimental data and the maximum difference was ∼6.5 °C.

Numerical analysis on the load reduction of a pipe-embedded window with different water temperatures and structures under different climates

Pipe-embedded windows can significantly reduce the cooling/heating load of buildings when integrated with low-grade energy. However, the studies on the load reduction effect under different climates remain insufficient, and the optimal location of double-glazing glass and the width of the air interlayer have not been studied. Thus, in this study, the performance of a pipe-embedded window with different water temperatures under different representative climates and structures is investigated numerically. According to the simulation, a linear relationship is found between the load and the climatic parameters with the specific structure of the pipe-embedded window, and the water temperature has a greater effect on the load than the outdoor air temperature. For three typical weather conditions from cold to hot environments (summer: 26 °C, 200 W/m2; 30 °C, 400 W/m2; 34 °C, 600 W/m2; winter: –25 °C; –10 °C; 5 °C), the limits of water temperature under a 25% load reduction rate are 27.7 °C, 39.8 °C, and 51.8 °C for summer and 8.4 °C, 12.0 °C, and 15.6 °C for winter, respectively. Internal thermal insulation is recommended for a pipe-embedded window, and the air interlayer thickness and pipe location have almost no influence on the performance of the pipe-embedded window.