Multilayer Thermal Insulation Research Articles

Optimization of MTI structure based on material characteristics under extreme aerodynamic heating environment

Thermal insulation structure is a key factor to protect a high-speed aircraft to work safely and complete various tasks. The multilayer thermal insulation (MTI) structure has attracted much attention because of its light weight and good thermal insulation effect. The performance of an MTI structure is not only related to its physical sizes, but also closely related to the material optimization and temperature influences. A transient nonlinear thermal transfer model of the MTI structure is established, and a numerical solution strategy of the nonlinear thermal transfer model is proposed. Considering material selection, introducing the temperature influence of materials, and taking the geometric dimensions and equivalent mechanical properties of the MTI structures as constraints, an optimization frame of the MTI structures is established. Then two intelligent methods are adopted to solve the problem. Using the aerodynamic heating environment of X-43 flight trajectory, the results of a typical high-speed aircraft show that the proposed optimization framework can reduce the structural mass density from 13.95 kg‧m−2 to 9.10 kg‧m−2 by about 34.8 %. The temperature effect analysis shows that the temperature variation has an important influence on the optimization results. If the temperature effect on material properties is not considered, the optimized design scheme may not meet the temperature design constraints (The maximum temperature of the inner surface is 410 K, far exceeding the maximum allowable temperature of 320 K) which further leads to structural failures. Finally, the reliability and rationality of the optimization scheme are verified by a finite element model (FEM). The equivalent modulus of the optimized MTI structure is 146 GPa and the mass area density of the MTI structure is 7.7 kg‧m−2. The optimization design method of an MTI structure proposed in the current paper provides a technical support and lays a foundation for the overall design of a high-speed aircraft.

Optimizing the Thickness of Multilayer Thermal Insulation on Different Pipelines for Minimizing Overall Cost-Associated Heat Loss

Optimizing the multilayer thermal insulation of pipelines transporting liquids and gases at higher than ambient temperatures is crucial for heat energy conservation and cost optimization. This study utilizes a multi-objective genetic algorithm to optimize the multilayer thermal insulation thickness around a pipe carrying fluid to minimize heat loss and associated costs. The model adopted mathematical associations between design variables and the overall installation cost of layers over a pipe from the available literature. The proposed model considered one or more insulation layers of rock wool and calcium silicate to oil pipelines containing steam, furfural, reduced crude or 300-distillate oil. All calculations considered fixed-charge rates as a fraction of 1 or 0.15. The results were compared with standard values and those predicted by other researchers in the literature. For the steam line, the standard insulation thickness was 50 mm, jumping to 327 mm for rock wool and 232 mm for calcium silicate. However, it decreased to 38 mm for double-layer calcium silicate and 138 mm for double-layer rock wool. For furfural, the insulation thickness was 40 mm, which rose to 159 mm for rock wool and 112 mm for calcium silicate. In general, for all four cases, the results show that using normal insulation thickness is inadequate and not economical. For example, for 300-distillate oil, the present practice puts the cost function at 54 USD/m, which drops to 20 USD/m for rock wool and 24 USD/m each for single-layer silicate and double-layer insulation. This amounts to almost 60% cost savings. Similar trends are observed for the other three cases. This model can provide up to 60% savings in cost and a 92% reduction in heat loss at optimum insulation thickness compared to other models.

Application and thermal field analysis of multilayer thermal insulation in in-situ forming process of thermoplastic composites

The carbon fiber reinforced polyetheretherketone (CF/PEEK) composite material can achieve high efficiency and integrated assembly molding through in-situ consolidation, suitable for the preparation of high-speed motor rotor sleeves. However, the high forming temperature of CF/PEEK may cause demagnetization of the magnet once the temperature exceeds the curie temperature of the magnet. To address the insulation issues during the sleeve forming process, this study proposes using metal-containing multilayer thermal insulations (MTI) to prepare the insulation layer, which takes advantage of the heat transfer within the metal layer to achieve thickness-wise insulation. A finite element heat field model is established to analyze the effect of material thermal properties, layer structure, and thermal field conditions on the thermal insulation effect. The response surface methodology analysis shows that metal materials with high thermal conductivity and high volume-specific heat have better insulation performance. The highest temperature of the bottom surface of the copper-containing MTI is only 64% of that of the glass fiber reinforced polypropylene (GF/PP) layer MTI. Analysis of the layer structure shows that the closer the metal layer is to the heat source, the better the insulation effect. The sensitivity analysis of the thermal field conditions shows that the thermal conductivity of the inner layer has a greater impact on the insulation effect. Subsequently, the MTI containing copper was optimized in response to the specific insulation requirements of the motor rotor sleeve, providing a reference for the application of in-situ consolidated integrated assembly molding in thermoplastic composites.

Design of Aerospace Vehicles’ Thermal Protection Based on Heat-Insulating Materials with Optimal Structure

Highly porous open-cell carbon materials have great potential for use as high-temperature thermal insulation for space vehicles due to a unique combination of properties: low density, high rigidity, sufficient compressive strength, and low thermal conductivity. The physical properties of these materials essentially depend on their microstructure. This implies the possibility of constructing a new advanced technique for the optimal design of multilayer thermal protection systems for aerospace vehicles, taking into account the dependence of materials’ thermal properties on microstructure. The formulation of the optimization problem traditional to thermal design implies the determination of the layer thicknesses that provide a minimum specific mass of the thermal protection, subject to the specified constraints on the maximum temperatures in the layers. The novelty of this work lies in the fact that, along with the thickness of the layers, the design parameters include the cell diameter and porosity, which characterize the structure of highly porous cellular materials. The innovative part of the presented paper lies in the determination of cell diameter and the porosity of open-cell carbon foam together with the thickness of the layers for multilayer thermal insulation, ensuring the required operational temperature on the boundaries of the layers and a minimum of the total mass of the system. This article reveals new possibilities for using the numerical optimization method to determine the geometric parameters of the thermal protection system and the morphology of the materials used. A new methodology for designing heat-loaded structures based on the simultaneous selection of macro- and micro-parameters of the system is proposed. The basic principles of constructing an algorithm for designing a multilayer thermal protection system are outlined, taking into account the possibility of choosing the parameters of the highly porous materials’ structure. The reliability of the developed optimization method was verified by comparing the results of mathematical modeling with experimental data obtained for highly porous cellular materials with known microstructure parameters.

Analysis of the effect of layer perforation pattern on the rate of gas leakage from multilayer thermal insulation during satellite launch

Analysis of the effect of layer perforation pattern on the rate of gas leakage from multilayer thermal insulation during satellite launch

The Problem of Utilization of Liquefied Natural Gas Vapor at Large-scale LNG Plants

The liquefied natural gas (LNG) is stored under low overpressure in a saturated state in large-capacity tanks with multilayer thermal insulation. Owing to the input of heat from the environment through thermal insulation, LNG is continuously evaporated. Since natural gas is a multicomponent mixture, LNG vapors are enriched with its low-boiling components, then the supply of heat from the environment reduces the amount of liquid in the reservoir and changes its chemical composition. Similar phenomena occur during LNG transportation. The present paper deals with the problem of LNG vapor utilization during its storage and transportation. Information is presented on the causes of the LNG vapor formation (boil-off gas) and methods for its disposal during storage and transportation to consumers. A numerical experiment was performed based on the data of LNG storage in large-capacity storage facilities at the Yamal LNG plant. The technique consists of the estimation of material flows toward the system of accumulation and extradition of LNG. The results show that the vapor flow generated from the inflow of new LNG portions into the storage significantly exceeds that generated from the heat supply from the environment.

Mathematical modeling of the mass transfer of the drying process of a multilayer thermal insulation coating

Polymer thermal insulation materials are widely used in modern industry and technological production of energy carriers. Thermal insulation with polymer coatings is one of the main ways to protect thermal equipment from temperature effects, corrosion, cavitation, erosion, and other influences, reducing the consumption of expensive materials. However, although polymeric materials can significantly reduce the cost of heat losses, their use is kept at a relatively low level. This is due to the low level of culture in the construction industry and the desire to save on projects, even at the expense of quality. The important issue of forming a reliable system “polymer sheet – adhesive film – environment” is given minimal attention, which, as a result, greatly affects the performance and efficiency of the operation of power facilities. In this paper, we studied the problem of mathematical modeling of the mass transfer of the process of drying a multilayer thermal insulation coating on a polymer basis. The proposed method for calculating the concentration and temperature fields allows for optimizing the drying process and improving the quality and reliability of the technological process.

Determination of core thermal resistance errors of reflective multifoil insulation products measured in a hot box depending on evaluation accuracy of its low emissivity surfaces

The multilayer reflective insulation is relatively new product on a construction market, used as efficient insulation and continuously improved. The thermal resistance of this product has to be determined according to the standard EN 16012+A1 [1], which not defines product's sample installation procedure into a hot box and indicates only rough requirement for emissivity values of surfaces of a tested sample and of adhesive tape for fixing the thermocouples must be similar, but it does not specify allowed differences and its effect on the accuracy of the measurement result. These standard's shortcomings do not ensure reliable and comparable results of the thermal resistance of multilayer thermal insulation. Therefore, a study was conducted and the method for installation and fixing of these products into hot box using frame was created. The influence of the frame on the measured thermal resistance was evaluated as a linear thermal bridge. The research of the influence of the difference between emissivity values of the sample and adhesive tape surfaces on the measured thermal resistance was performed using a calibration standard with known R-value. The research results showed that the linear thermal bridge value of frame was increasing with the increment of emissivity value of adhesive tape. Significant difference between sample and adhesive tape emissivity values can create more than 20% relative difference between both measured and calculated R-values from the known real R-value of the calibration standard. In order to avoid more than 3% relative errors, the limits of difference between emissivity values were set.

Impact of natural and artificial ageing on the properties of multilayer external wall thermal insulation systems

Multilayer external wall thermal insulation systems are widely used in new constructions and for the retrofitting of building façades. Despite the increasing use as constructive solution, significant anomalies have been frequently identified on these systems only few years after their application, raising questions on their long-term durability. This paper focuses on the effects of one-year natural ageing and artificial ageing through hygrothermal cycles (heat/rain and heat/cold) on the water performance (capillary water absorption and drying kinetics), bio-susceptibility (mould development) and surface properties (colour, gloss, and roughness) of four multilayer external wall thermal insulation systems (three ETICS and a thermal rendering system). Results showed a significant loss of surface hydrophobicity after ageing. Considering the 24 h water absorption results, an increase up to 73% and 432% was obtained for the naturally and artificially aged systems, respectively, and when compared to the reference unaged systems. The drying kinetics was affected by ageing, with increases of the drying resistance ranging between 47% and 122% after artificial ageing. Traces of mould growth were observed on the artificially aged systems; however, no growth was detected on either the unaged or the one-year naturally aged systems. Substantial colour change for all systems after ageing was observed, confirming aesthetic alteration. Results contribute towards the development of implemented artificial ageing protocols, as well as for the delivery of multilayer thermal systems with enhanced performance and durability.

НОВЫЙ ВЗГЛЯД НА ПРИМЕНЕНИЕ СТЕКЛОТКАНИ В СТРОИТЕЛЬСТВЕ ПРОМЫШЛЕННЫХ ДЫМОВЫХ ТРУБ

The change in the operational characteristics of reinforced concrete chimneys with a monolithic lining when changing the traditional construction technology is considered. The difference between the traditional and proposed technology is the replacement of the separating element of the concrete lining and the supporting concrete of the chimney trunk. Traditionally, when installing industrial pipes with a monolithic lining, both with the use of sliding formwork and lifting-adjustable, with almost simultaneous laying of two types of concrete, a steel mesh is used as a separating layer. It is proposed to replace the steel mesh with fiberglass with a heat-insulating coating. Thermal insulation of the "Bronya" type is considered as a multilayer thermal insulation coating. The work presents a comparative analysis of changes in the distribution of temperature fields along the chimney wall during the introduction of this technology on the example of the chimney of the Krasnoyarsk CHPP-1 h=275 m. It is proved that the replacement of steel mesh with fiberglass with a heat-insulating coating improves the physical and chemical characteristics of the structure and provides a more efficient thermal operation of the chimney. The use of this technology will also improve the organization of construction production, reduce construction time and costs, reduce the material consumption of chimney structures and the complication of work on its construction, reduce the possibility of defects and destruction. Therefore, the introduction of the proposed technology will increase the reliability and lifespan of the structures of industrial reinforced concrete chimneys with a monolithic lining

Methodological bases of optimization of thermal insulation structures of glass furnaces

In the construction of modern bathrooms of flaming glass furnaces, glass resistant refractory materials of high quality and a variety of thermal insulation materials are used, which are compounded into multi-layer thermal insulation panels, reducing heat losses. However, increasing the temperature of wall bars when applying thermal insulation sharply reduces their service life due to high-temperature physical and chemical corrosion. Such a contradiction and a wide range of insulation products, as well as various modes of glass melting and intensity of forced cooling of the outer lateral surface of the furnace requires the choice of an optimal set of thermal insulation materials under the chosen conditions of furnace operation to ensure maximum operating life of the unit with maximum efficiency.

Performance improvement of a pulse tube cryocooler with a single compressor through cascade utilization of cold energy

The high-frequency pulse tube cryocooler (HPTC) has been attracting increasing and widespread attention in the field of cryogenic technology because of its compact structure, low vibration, and reliable operation. The gas-coupled HPTC, driven by a single compressor, is currently the simplest and most compact structure. For HPTCs operating below 20 K, in order to obtain the mW cooling capacity, hundreds or even thousands of watts of electrical power are consumed, where radiation heat leakage accounts for a large proportion of their cooling capacity. In this paper, based on SAGE10, a HPTC heat radiation calculation model was first established to study the effects of radiation heat leakage on apparent performance parameters (such as temperature and cooling capacity), and internal parameters (such as enthalpy flow and gas distribution) of the gas-coupled HPTC. An active thermal insulation method of cascade utilization of the cold energy of the system was proposed for the gas-coupled HPTC. Numerical simulations indicate that the reduction of external radiation heat leakage cannot only directly increase the net cooling power, but also decrease the internal gross losses and increase the mass and acoustic power in the lower-temperature section, which further enhances the refrigeration performance. The numerical calculation results were verified by experiments, and the test results showed that the no-load temperature of the developed cryocooler prototype decreased from 15.1 K to 6.4 K, and the relative Carnot efficiency at 15.5 K increased from 0.029% to 0.996% when substituting the proposed active method for the traditional passive method with multi-layer thermal insulation materials.

Improving energy efficiency and reliability of heating networks through the use of multilayer thermal insulation structures

Thermal insulation of pipelines is actively used to reduce heat losses in heat supply systems, as well as to reduce the temperature on the utilities surfaces, for safety during daily operation. This method ensures uninterrupted operation of heating systems in the winter, eliminating the risk of the heat carrier freezing and, consequently, their failure. At the moment, the application of effective thermal insulation of heating network equipment and pipelines is of great importance. The lack of a high-quality heat-insulating coating on the pipeline surface leads to significant losses of fund from various level budgets and a decrease in the quality of the heat carrier, that is, its temperature. Special requirements are imposed on thermal insulation materials, according to current regulatory documents, compliance with which is monitored by specialized organizations. The thermophysical indicators study of modern heat-insulating materials of domestic production and their application impact on the efficiency of the heat supply system is an urgent task aimed at improving energy efficiency and reducing energy consumption by reducing heat losses in heating networks pipelines.

Thermal protective qualities of the combined material with reflective thermal insulation from aluminium foil

The article presents the results of experimental and theoretical studies of the thermal insulation qualities of foamed polyethylene with layers of reflective thermal insulation located in its thickness. Currently, the determination of the heat-protection properties of multilayer materials with reflective thermal insulation is carried out experimentally in laboratory conditions. Theoretical studies of the processes of heat transfer in the bulk of such multilayer materials and developed thermophysical model of the heat transfer process through this combined multilayer thermal insulation allowed to develop an engineering calculation method for determining the thermal resistance of multilayer polyethylene foam with reflective thermal insulation from aluminium foil, taking into account thermal conductivity and radiation. The obtained values of the thermal resistance of multilayer polyethylene of various thicknesses by calculation showed the convergence with experimental values. This indicates that reflective thermal insulation with a low emissivity of the surface, located in the thickness of the foamed polyethylene, increases its thermal performance qualities.

A novel instrument for investigating the dynamic microstructure evolution of high temperature service materials up to 1150 °C in scanning electron microscope

High temperature materials usually serve under extreme conditions. In order to ensure the safety and reliability of industrial application, it is very significant to clarify the microstructural evolution and mechanical properties at high temperature. The in situ experiment combining mechanical tensile testing and heating in the scanning electron microscope (SEM) is a feasible method to study the relationship between the microstructure, mechanical properties, and temperature. However, it was challenging to acquire images of high quality when the temperature exceeded 800 °C due to the effect of thermal electrons and the instability of loading conditions at high temperature. In this study, a mini-tensile apparatus was devised and installed in an ordinary SEM, which can achieve a stable loading of 0-2200 N and obtain high quality images in the temperature range of 1150 °C. A highly efficient heat source with multi-layer thermal insulation was designed to prevent the other parts of the apparatus from being affected by high temperature. A symmetrical tensile structure was developed to ensure that the region of interest was always within the field of view of the microscope during testing. Thermal electrons were suppressed to ensure that the sample can be clearly distinguished at 1150 °C. In order to ensure the testing reliability, standard carbon steel was used to calibrate the instrument. Finally, a Ni-based single crystal superalloy, as an example, was tested using this in situ tensile testing system at 1150 °C to verify the main functions and reliability of the apparatus.

Design of thermal protection based on open cell carbon foam structure optimization

Open cell carbon foams with porosity ranging between 82 and 98% can be used as efficient thermal insulation in many high-temperature applications including solar and planetary probes, whose structures and systems are exposed to extreme heat loads. Physical properties of cellular materials are determined not only by thermal and optical properties of solid phase but also significantly by their morphology and fabrication technology. This implies the possibility to create open-cell materials with desirable properties, optimal for specific operating conditions. The paper presents a methodology for optimal design of multilayer thermal protection based on high porosity open cell carbon foam, taking into account the carbon foam morphology. The traditional thermal design problem statement implies the determination of layers thickness for multi-layer thermal insulation, ensuring required operational temperature on the boundaries of layers and minimum of total mass of system. In this work the cell diameter and porosity, that characterize the material’s morphology, are chosen along with thickness of layers in order to obtain an additional weight advantage of thermal insulation. The optimization problem is solved using the algorithm based on the projected Lagrangian method with the quadratic subproblem. To illustrate the implementation of the developed algorithm and the corresponding software, the problem of choosing of the optimal layer thickness for the multilayer heat shield of the solar probe along with the cell diameter and porosity of carbon foam, forming one of the layers, is considered.

Characterisation of a multilayer external wall thermal insulation system. Application in a Mediterranean climate

In recent years, the materials applied to buildings' envelopes have been studied in-depth to improve their thermal insulation properties, enabling significant energy savings. This led to the development of new thermal insulation renders with lower thermal conductivities (λ) (λ < 0.040 W m−1 K−1). However, their mechanical and water resistance performance has also decreased. In this context, this research discusses the performance of a multilayer thermal insulation system with a super-insulating thermal render (λ < 0.030 W m−1 K−1), to be applied on the exterior, subjected to a Mediterranean climate. A set of mechanical, physical, and microstructural tests were conducted. Within the scope of this study, it was possible to improve the render's mechanical performance and water resistance, when protective layers were applied in a multilayer system. When its performance is compared with other multilayer products currently in the market, this new solution presents competitive results, which further encourage the tests in real operative conditions.

Evaluation of Physical Properties for EnergySaving Aluminum Multi-Layer Thermal Insulation Screen

Evaluation of Physical Properties for EnergySaving Aluminum Multi-Layer Thermal Insulation Screen

Gas-filled thermal insulation use in heat supply

The possibility of applying a new type of thermal insulation, which will significantly reduce heat losses during transportation of heat, increase the service life of the pipeline, and reduce the cost of heat insulation work considered. Using multi-layer thermal insulation, which is a system of closed, sealed microvolumes (pores), which are filled with carbon dioxide proposed. As a shell, high-density polyethylene is used. Such a film can be used as a ready-made material for insulation of pipelines. Depending on the temperature of the pipeline, the required number of layers of thermal insulation is applied to the pipeline.

Determination for Thickness of the Multilayer Thermal Insulation Clothing Based on the Inverse Problems

In this paper, the optimal thickness of multilayer special clothing material under the high temperature operation based on the inverse problems is studied. We analyze the parameters of the thickness of thermal insulation clothing material and the surface temperature of the dummy. Using the least-squares fitting, the function with the distribution of the dummy surface temperature is established. Then the heat transfer model and optimization model to obtain the optimal thickness of different clothing layers are built, respectively. Taking the true data as an example, we give the application of thermal insulation clothing in fire area, and the results show that the models are feasible.